• John
  • Felde
  • University of Maryland
  • USA

Latest Posts

  • USA

  • James
  • Doherty
  • Open University
  • United Kingdom

Latest Posts

  • Andrea
  • Signori
  • Nikhef
  • Netherlands

Latest Posts

  • CERN
  • Geneva
  • Switzerland

Latest Posts

  • Aidan
  • Randle-Conde
  • Université Libre de Bruxelles
  • Belgium

Latest Posts

  • Vancouver, BC
  • Canada

Latest Posts

  • Laura
  • Gladstone
  • MIT
  • USA

Latest Posts

  • Steven
  • Goldfarb
  • University of Michigan

Latest Posts

  • Fermilab
  • Batavia, IL
  • USA

Latest Posts

  • Seth
  • Zenz
  • Imperial College London
  • UK

Latest Posts

  • Nhan
  • Tran
  • Fermilab
  • USA

Latest Posts

  • Alex
  • Millar
  • University of Melbourne
  • Australia

Latest Posts

  • Ken
  • Bloom
  • USA

Latest Posts

Warning: file_put_contents(/srv/bindings/215f6720ac674a2d94a96e55caf4a892/code/wp-content/uploads/cache.dat): failed to open stream: No such file or directory in /home/customer/www/quantumdiaries.org/releases/3/web/wp-content/plugins/quantum_diaries_user_pics_header/quantum_diaries_user_pics_header.php on line 170

Archive for April, 2013

For April first, I wrote that CERN was to give away ten Higgs bosons in a gesture to thank the public for its incredible interest in CERN’s scientific research. About 1500 people eagerly entered the lottery. Most of them wrote very enthusiastic notes, explaining how much they would love one and how much it would mean to them. Many people were not completely fooled but played along just as eagerly.

It was great fun to have a chance to play an April Fools joke that got people all over the world. Entries came from places as diverse as Pakistan, Rwanda, Finland, Canada, Australia, China and Portugal. This shows the incredible interest the Higgs boson has generated on all continents.

I used a random number generator to select the winners who are from Mexico, UK, USA, Belarus (3), Russia (3), Kazakhstan and The Netherlands. Nearly half the entries came from Belarus or Russia, where a popular news agency ran the story. People fell for it even though as everyone knows: “Первого апреля никому не верю!” (On April first, do not trust anyone).

Even some physics students fell for it, so strong was their desire to get their own Higgs boson. Granted, using CERN’s fame is cheating a bit, giving any claim a lot of clout. But many played along: one tried to bribe me with a magnetic monopole, while another promised to feed it only the best particles. Another woman said she already had lots of antimatter and would know how to properly care for a Higgs boson. One physics student said that given the short lifetime of a Higgs boson, he might end up with just two W or Z bosons. One person expressed how great it was for CERN to share. Some asked for a Higgs bosun, bozzon or bison. A guy told me how much this would help him win his girlfriend’s heart as he was about to propose to her. A very disappointed student replied physicists were cruel when he realized it was a joke. But I hope he changed his mind when he found out he was one of the 10 lucky winners.

Custom-made Higgs bosons recently escaped from the Particle Zoo and are on their way to their new home, where all the winners said they would warmly welcome them.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.



This is an age old question, always asked (and always fervently!) of the person with the better vantage point: the older sibling peering into the next room through the keyhole; the watchman scanning the horizon from the ship’s crows nest; and now us, AMS, taking our first glance out over the universe from the space station. What do you see, what do you see?!?!

The answer, as we squint through our sights, trying to make out shapes of unknown and unexpected things, is also age-old: “I’m not sure yet, gimme more time!”

The first AMS-02 results– the positron fraction–were announced this week. Sam Ting, our spokesperson and PI, gave the talk here at CERN as per an agreement with the CERN directorate and, now that the result is public we have all been inundated with that same question. And the answer, of course, is: “We aren’t sure yet… just give us more time!”

So I thought I’d come here and give a few answers to some obvious (or not-so-obvious) questions.

If we can’t tell what we see, why are we publishing?

Well I guess I shouldn’t be so glib: we can tell you exactly what we see and how precisely we see it. We just don’t know exactly what it means yet. It’s the scientific equivalent of saying “I see this hazy thing in the fog…it’s shaped like a person, but I can’t tell for sure if it’s a man or a woman. But I can tell that he or she is wearing a green coat, has short hair, and is 5 and a half feet tall.” As experimentalists, it’s our job to say: “we see this thing, it looks like this”. Then we give that information to theorists, who help explain our observations. This happens back and forth: an experiment has results and publishes them; the theorists look at the results and publish new ideas that might explain the results; the experimentalists then improve their observations to test the new theories and publish their new results; the theorists revise their ideas or come up with new ones to explain the new results… and so on as we refine our understanding of what we see compared to the physical principles we believe to be true.

With AMS-02 we are at the first moment where we are ready to report what we see, and it may or may not point to new physics. So now we publish our results so the theorists can have a look and think about what this might mean. In a few years we hope to publish more results that will probe higher in energy (but it will take awhile to collect enough data to be able to do this reliably), and between now and then the theorists may have new ideas for other things we should look for.

What exactly is it we’re looking for?

Well, the latest round of similar experiments—FERMI and PAMELA—strongly indicated an excess in the number of positrons flying around the universe. This excess might be called “mysterious”, but we do have theories about where it could come from. Many of these theories invoke something with an even more mysterious sounding name: Dark Matter.

Dark Matter is so called because we don’t know what it is. Based on our observations of the universe, we are pretty certain that there’s some type of matter out there that we haven’t been able to identify yet, and we think it makes up around 25% of the matter in the universe. (I’ll let you read about this on your own—how stuff works has a pretty good summary )

The trick is that we can’t see it because this Dark Matter doesn’t interact like normal “bright” matter that we see every day (“bright” matter would be like your hand, the desk, the wall, the sun, the stars, etc.–basically anything that glows on its own or anything that you can see by shining light on it). We can’t see the dark matter just by turning on the lights, but we hope that we can see it indirectly—this means that instead of seeing the dark matter itself, we might see its byproducts. It’s like when you go white-water rafting: you can’t see the boulders hidden under the water, but you can avoid danger by watching for the ripples on the surface. Because of the ripples, you know the big boulder’s there, even though you can’t see it. And if you’re a really experienced paddler you might be able to tell me something about the boulder’s shape and size based on the pattern of the ripples. So what AMS-02 does is look for these ripples in the water, and from our collective experience we try to figure out what’s beneath them.

We do this by looking for things that we think should act in a certain way for normal bright matter, and trying to detect something anomalous about the way these things actually behave. In this case, we are looking at the fraction of positrons vs. the total number of positrons + electrons. We think that if dark matter doesn’t exist this fraction should be around 10% and decrease slightly with energy. (For those of you who aren’t familiar with this terminology, energy can essentially be seen as how fast a particle is going. For particles that are all traveling at “normal” speeds, about 10% of them should be positrons. And of the particles moving twice as fast, maybe only 8% should be positrons.) However, according to many theories, if dark matter does exist, it will cause an increase in the number of positrons—which we would see as a bump at a certain energy in the fraction of positrons (where exactly the bump occurs depends on which theory is your favorite). Here are some predictions made two years ago about what AMS “would” be able to see after both 3 years and 20 years of data collection compared to the predictions from a few different Dark Matter models.

So the short answer is, we are looking for a bump in the positron fraction energy spectrum because it’s possible that the bump’s location and shape could indicate the presence of dark matter. Though it might indicate something else entirely…it’s tough to say for sure. Either way, a bump would indicate something different from what is currently expected.

So what do you see, what do you see!?!?

Well, you asked for it: We aren’t sure yet… just give us more time! But, to be serious, what we see is an increase in the positron spectrum at high energies. This plot shows our main result (we’re the red circles):

Our new measurement is similar to experiments past, but extends the energy range of the observations, and measures the positron fraction much more accurately (you can tell this because the little vertical bars which indicate the measurement error are smaller). Notice that most of the experiments agree: first you see a decrease in the fraction (on the left side of the plot), which is what’s expected. When you get to the right side, the fraction begins increasing again. If there was a bump–due to dark matter or something else–then you’d see the fraction start to fall again.  So if there is a bump, it’s right half appears to be somewhere off of the right edge of our plot… but on the other hand, maybe that’s not a bump–maybe the fraction will just keep increasing. To really see what’s going on here, we need to continue to take more data, which will allow us to plot the positron fraction out to higher energies (ie extend the right side of the plot).  To get the full picture, though, we will need to look at many more things–not just the positron fraction.  It will simply take some time before we can give you a good answer.  So far, we have only strong hints of something unexpected happening that is not well understood.

Did you actually get to work on this?

Yes, in fact.  I was really lucky to join AMS at exactly the right time: they let me help with the very first results.  My role was somewhat minor, but it might be interesting to relay how this result was achieved.  You see, most experiments have a cross-check–either another experiment, or two independent analyses.  Well, this experiment doesn’t have a matching experiment to cross-check (like ATLAS and CMS at the LHC) so instead we split our collaboration into two teams: A, and Alpha.  The teams were split by country to be approximately equal in size: A-Team was Italy, Germany, Portugal and Turkey while Alpha was the rest of the world.  Since I work for a young investigator group at Karlsruhe, in Germany, I was on the A-Team (fulfilling a childhood dream).  The teams didn’t communicate with each other at all until collaboration meetings once every month or two, when we would compete to try to show the best new results.  At that point, we’d see the other team’s progress, and then try to catch up or somehow be more clever.  Alpha took the strategy of putting all focus on one analysis, while A-Team separated into groups and did the analysis using five different analyses techniques.  (My analysis was one of these.)  When all of us were finished (after many sleepless nights), we discovered that all of our analyses matched.  This was a huge relief, since when you do something six different ways, you’re never sure you’re going to get six matching results.  This is how we gained the confidence required to publish our findings.

Why aren’t we publishing more points at higher energies?

If you are asking this question, you’re in good company. Almost every question from the physicists in the audience at this week’s announcement was some incarnation of this very question. The answer is that these data points are still a bit foggy. This explanation clearly didn’t satisfy the curiosity of the physicists, who seemed to ask in unison, “But don’t you have some idea? We know you must have data out there at higher energies, why won’t you give us even a preliminary result out there?”

I’ll leave you with Sam Ting’s answer: “It took us 18 years to build this detector. I think in the next 20 years [that it will be running on the space station], no one will be foolish enough to repeat what we’ve done. We want to do it correctly.”


A colleague of mine is an avid fan of the New York Yankees baseball team. At a meeting a few years ago, when the Yankees had finished first in the American league regular season, I pointed out to him that the result was not statistically significant. He did not take kindly to the suggestion. He actually got rather angry! A person, who in his professional life would scorn anyone for publishing a one sigma effect, was crowing about a one sigma effect for his favorite sports team. But then most people do ignore the effect of statistical fluctuations in sports.

In sports, there is a random effect in who wins or loses. The best team does not always win. In baseball where two teams will frequently play each other four games in a row over three or four days, it is relatively uncommon for one team to win all four games. Similarly a team at the top of the standings does not always beat a team lower down.  As they say in sports: on any given day, anything can happen. Indeed it can and frequently does.[1]

Let us return to American baseball. Each team plays 162 games during the regular season. If the results were purely statistical with each team having a 50% chance of winning any given game, then we would expect a normal distribution of the results with a spread of sigma=6.3 games. The actual spread or standard deviation for the last few seasons is closer to 11 games. Thus slightly more than half the spread in games won and lost is due to statistical fluctuations. Moving from the collective spread to the performance of individual teams, if a team wins the regular season by six games or one sigma, as with the Yankees above, there is a one in three chance that it is purely a statistical fluke. For a two-sigma effect, a team would have to win by twelve games or by eighteen games for a three-sigma effect. The latter would give over 99% confidence that the winner won justly, not due to a statistical fluctuation. When was the last time any team won by eighteen games? For particle physics we require an even higher standard–a five sigma effect to claim a discovery. Thus a team would have to lead by 30 games to meet this criterion. Now my colleague from the first paragraph suggested that by including more seasons the results become more significant.  He was right of course. If the Yankees finished ahead by six games for thirty-four seasons in a row that would be five-sigma effect. From this we can also see why sports results are never published in Physical Review with its five-sigma threshold for a discovery–there has yet to be such a discovery. To make things worse for New York Yankees’ fans they have already lost their chance for an undefeated season this year.

In other sports the statistics are even worse. In the National Hockey League (NHL) teams play eighty-two games and the spread in win-loss expected from pure chance is sigma=4.5. The actual distribution for last year was 6.3 sigma. The signal due the difference in the individual teams’ ability is all in the 1.8 sigma difference. Perhaps there is more parity in the NHL than in Major League Baseball. Or perhaps there is not enough statistics to tell. Speaking of not telling. Last year the Vancouver Canucks finished with the best record for the regular season, two games ahead of the New York Rangers and three games ahead of the St. Louis Blues. Only a fool or a Vancouver Canucks fan would think this ordering was significant and not just a statistical fluctuation. In the National Football League last year, 14 of the 32 teams were within two sigma of the top. Again much of the spread was statistical. It was purely a statistical fluke that the New England Patriots did not win the super bowl as they should have.

Playoffs are even worse (this is why the Canucks have never won a Stanley Cup). Consider a best of seven game series. Even if the two teams are equal, we would expect that the series would only go four games one in every eight (two cubed[2]) series.  When a series goes the full seven games one might as well flip a coin. Rare events, like one team winning the first three games and losing the last four, are expect to happen once in every sixty-four series and considering the number of series being played it is not surprising we see them occasionally.

Probably the worst example of playoff madness is the American college basketball tournament called, appropriately enough, March Madness. Starting with 64 teams or 68 depending on how you count, the playoffs proceed through a single elimination tournament. With over 70 games it is not surprising that strange things happen. One of the strangest would be that the best team wins.  To win the title the best team would have to win six straight games. If the best team has on average a 70% chance of winning each game they would only have a 12% chance of winning the tournament. Perhaps it would be better if they just voted on who is best.

But you say they would never decide a national championship based on a vote. Consider American college football. Now that is a multi-million dollar enterprise! Nobel Laureates do not get paid as much as US college football coaches. They do not generate as much money either. So what is more important to American universities–sports or science?

In the past, the US college national football champions were decided by a vote of some combination of sports writers, coaches and computers. Now that combination only decides who will play in the championship game. The national champion is ultimately decided by who wins that one final game. Is that better than the old system? More exciting but as they say: on any given day anything can happen. Besides sports is more about deciding winners and losers rather than who is best.

To receive a notice of future posts follow me on Twitter: @musquod.

[1] With the expected frequency of course.

[2] Not two to the fourth power because one of the two teams has to win the first game and that team has to win the next three games.


Our survey is way more exciting that this!

You read the title correctly! The Snowmass Young Physicists survey is now live and taking data!

You can take the survey by going to this link:


So you might be asking, “Who is this survey for?”. The short answer it is for everyone who is currently in High Energy Physics (HEP), everyone who was in HEP at one time in their career, and for any of the young scientists in training who are considering going into HEP. We want them all! Undergraduates, graduates, post-docs, staff scientists, faculty, researchers and especially any one who received their training in HEP and has decided to go on to jobs outside of HEP.

The survey is structured such that if you are currently involved in HEP you will see a set of questions that asks about your current work life, your career outlook, your physics outlook, and some general information related to the questions being considered during the Snowmass planning process. If you are not currently in HEP you will receive a set of questions asking about your career choices, career outlook, and quality of life.

All of the information is kept anonymous and the compilation of the data will be presented at the Snowmass meeting in July. Our goal is to have greater than 1500 respondents from all the various “frontiers” as defined in the Snowmass process (Energy, Cosmic, Intensity, Outreach, Instrumentation, Computing, Theory) as well as lots of responses from those who have gone on to careers outside of HEP. The survey itself should not take longer than 15 mins in total and there are lots of places where you can feel free to write in responses that we will compile to help formulate the opinions expressed at the Snowmass meeting.

Now for the call for help! The only way this survey will be a success is if we get the word out. So I am asking all the readers here to take a second and advertise for us on social media (Facebook, Twitter, Google+…), to tell your friends, co-workers, and fellow students, and to look for us at many of the upcoming conferences (April APS, Snowmass Planning meetings, etc…). We will have people everywhere handing out business cards and pointing people to the survey in the months running up to July! The link again is http://tinyurl.com/snomassyoung

Finally I cannot close this blog post without giving a long list of names of the people who spent many hours working, discussing, arguing, editing, emailing, and meeting to get the survey done in advance of the summer rush. (If I left your name off the list I am extremely, extremely sorry and I will gladly write an entire blog post dedicated to the work you as penance)

First of all a big thank you to the  Snowmass young conveners:
Roxanne Guenette, Thomass Strauss, Brendan Kiburg, Elizabeth Worcester, Bjoern Penning, Jake Anderson, Andrew Kobach, Randel Cotta, Felix Yu, Hugh Lippincott, and Marcelle Soares-Santos

In addition I need to thank these people for giving so much of their time to help in the process:

Ben Carls, Bryce Littlejohn, Andrzej Szelc, Gavin Davies, Teppei Katori

So, now is the time to go take the survey! http://tinyurl.com/snomassyoung. If you have comments or concerns please email us at [email protected]!


Grey matter confronted to dark matter

Thursday, April 4th, 2013

After 18 years spent building the experiment and nearly two years taking data from the International Space Station, the Alpha Magnetic Spectrometer or AMS-02 collaboration showed its first results on Wednesday to a packed audience at CERN. But Prof. Sam Ting, one of the 1976 Nobel laureates and spokesperson of the experiment, only revealed part of the positron energy spectrum measured so far by AMS-02.

Positrons are the antimatter of electrons. Given we live in a world where matter dominates, it is not easy to explain where this excess of positrons comes from. There are currently two popular hypotheses: either the positrons come from pulsars or they originate from the annihilation of dark matter particles into a pair of electron and positron.  To tell these two hypotheses apart, one needs to see exactly what happens at the high-energy end of the spectrum. But this is where fewer positrons are found, making it extremely difficult to achieve the needed precision. Yesterday, we learned that AMS-02 might indeed be able to reach the needed accuracy.

The fraction of positrons (measured with respect to the sum of electrons and positrons) captured by AMS-02 as a function of their energy is shown in red. The vertical bars indicate the size of the uncertainty. The most important part of this spectrum is the high-energy part (above 100 GeV or 102) where the results of two previous experiments are also shown: Fermi in green and PAMELA in blue. Note that the AMS-02 precision exceeds the one obtained by the other experiments. The spectrum also extends to higher energy. The big question now is to see if the red curve will drop sharply at higher energy or not. More data is needed before the AMS-02 can get a definitive answer.

Only the first part of the story was revealed yesterday. The data shown clearly demonstrated the power of AMS-02. That was the excellent news delivered at the seminar: AMS-02 will be able to measure the energy spectrum accurately enough to eventually be able to tell where the positrons come from.

But the second part of the story, the punch line everyone was waiting for, will only be delivered at a later time. The data at very high energy will reveal if the observed excess in positrons comes from dark matter annihilation or from “simple” pulsars.  How long will it take before the world gets this crucial answer from AMS-02? Prof. Ting would not tell. No matter how long, the whole scientific community will be waiting with great anticipation until the collaboration is confident their measurement is precise enough. And then we will know.

If AMS-02 does manage to show that the positron excess has a dark matter origin, the consequences would be equivalent to discovering a whole new continent. As it stands, we observe that 26.8% of the content of the Universe comes in the form of a completely unknown type of matter called dark matter but have never been able to catch any of it. We only detect its presence through its gravitational effects. If AMS-02 can prove dark matter particles can annihilate and produce pairs of electrons and positrons, it would be a complete revolution.


Here are two plots to show how different the positron fraction spectrum (i.e. the curve showing the fraction of positrons as a function of energy) would differ at high energy (the rightmost part of the plot) if the positrons come from the sum of all pulsars around or if it comes from dark matter annihilation. Note they are not on the same scale and difficult to compare, but they still give some idea. It will be easier once theorists update their plots with the new AMS-02 data points on them and of course, once AMS-02 releases further information at high energy.

This is one theoretical prediction of what the positron fraction spectrum should look like if the positrons come from dark matter particles like neutralinos (represented by the symbol χ). Two curves are shown, depending on the hypothetical mass of the neutralino (mχ) at 400 GeV or 800 GeV. In each case, the maximum energy the positrons can get is roughly equal to the the mass of the neutralino, such that the curve ends close to the neutralino mass. Note the logarithmic scale on both axes.

Here is the expected spectrum if the positrons come from the sum of all pulsars. Three hypotheses were shown but only the middle one seemed to fit the PAMELA experimental results. The important feature is that this curve comes down smoothly, and not sharply at neutralino mass as with the dark matter hypothesis. Again, this curve only represents one theoretical prediction as done by Dan Hooper and his colleagues. The data point in red are from the PAMELA experiment and stop around 100 GeV. The hope is that AMS-02 will be able to provide accurate measurements at higher energies, up to several hundred GeV.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.




Après 18 années passées à bâtir l’expérience et presque deux autres à accumuler des données à bord le la Station Spatiale Internationale, la collaboration du Spectromètre Magnétique Alpha ou AMS-02 a révélé hier au CERN ses tout premiers résultats devant un auditorium plein à craquer. Le Prof. Sam Ting, prix Nobel de 1976 et porte-parole de l’expérience, n’a cependant dévoilé qu’une partie du spectre de l’énergie des positrons mesurés par AMS-02.

Les positrons sont l’antimatière des électrons. Comme on habite dans un monde où la matière domine, il n’est pas facile d’expliquer l’origine de cet excès de positrons venus de l’espace. Il existe deux hypothèses privilégiées : soit ces positrons sont émis par des pulsars, soit ils proviennent de particules de matière sombre qui s’annihilent en produisant un positron et un électron.

Pour distinguer ces deux hypothèses, il faut connaitre très exactement ce qui arrive au spectre de positrons à haute énergie. Mais comme il y en a très peu à haute énergie, il est très difficile d’obtenir un résultat précis. Or voilà la bonne nouvelle annoncée hier par la collaboration AMS : leurs données atteindront le niveau de précision requis.


La fraction de positrons (mesurés par rapport au nombre total d’électrons et de positrons) capturée par AMS-02 en fonction de l’énergie des positrons est indiquée en rouge. Les barres verticales représentent la marge d’incertitude. La partie la plus importante de ce spectre se trouve à haute énergie, au-delà de 100 (ou 102) GeV. Là où les résultats de deux expériences précédentes sont aussi indiqués : en vert, ceux de Fermi et en bleu, ceux de PAMELA. Remarquez que la précision d’AMS-02 dépasse largement celle des expériences précédentes. Le spectre va aussi beaucoup plus haut en énergie. Reste à savoir si cette courbe chutera abruptement à plus haute énergie (signe que les positrons viendraient de matière sombre) ou pas (si les pulsars en sont la source). La collaboration attend d’avoir accumulé plus de données avant de se prononcer.

Seule la première partie de l’histoire a été dévoilée hier. Les données actuelles laissent déjà présager de ce qu’AMS-02 pourra accomplir. C’était la bonne nouvelle communiquée hier: AMS-02 devrait pouvoir mesurer le spectre des positrons à haute énergie avec suffisamment de précision pour trancher sur leur origine.

Mais pour la fin de l’histoire, il faudra encore patienter. Les données à haute énergie révèleront si ces positrons viennent de l’annihilation de particules de matière sombre, ou simplement de vulgaires pulsars. Combien de temps faudra-t-il encore attendre ? Le Prof. Ting n’a pas voulu le préciser. Peu importe, la communauté scientifique patientera en attendant que la collaboration AMS-02 ait suffisamment de données pour obtenir la précision nécessaire.

Si AMS-02 peut prouver que ces positrons viennent de la matière sombre, les conséquences seraient alors aussi époustouflantes que la découverte d’un nouveau continent. A l’heure actuelle, tout ce que l’on sait, c’est que cette matière  sombre correspond à 26.8% du contenu total de l’Univers. On ne la perçoit qu’à travers ses effets gravitationnels. Si AMS-02 réussi à prouver que la matière  sombre peut s’annihiler et produire des paires de positrons et d’électrons, ce serait tout simplement une révolution.

Pauline Gagnon

Pour être averti-e lors de la parution de nouveaux blogs, suivez-moi sur Twitter: @GagnonPauline ou par e-mail en ajoutant votre nom à cette liste de distribution



April 2013 AMS Liveblog

Wednesday, April 3rd, 2013

General information

Today, the Alpha Magnetic Spectrometer (AMS) experiment is going to announce its findings for the first time. The AMS experiment uses a space-based detector, mounted on the International Space Station (ISS), and was delivered on NASA’s shuttle Endeavour, on NASA’s penultimate shuttle mission. To date AMS has observed 25 billion events over the course of the last 18 months. There has been a lot of news coverage and gossip about how this might change our understanding of the universe, and how it might impact on the search for dark matter and dark energy. However until today the results have been a guarded secret for AMS. Sam Ting, who leads the AMS Experiment, will make the presentation in the CERN Main Auditorium at 17:00 CERN time.

AMS-02 on the ISS (Wikipedia)

AMS-02 on the ISS (Wikipedia)

I’ll be live blogging the event, so stay tuned for updates and commentary! This is slightly outside my comfort zone when it comes to the science, so I may not be able to deliver the same level of detail as I did for the Higgs liveblogs. All times are CERN times.

See the indico page of the Seminar for details, and for a live video feed check out the CERN Webcast.

18:25:Congratulations and applause. The seminar is over! Thanks for reading.


Q (Pauline Gagnon): How many events above 350GeV?
A: We should wait for more statistics and better understanding. Note we do not put “Preliminary” on any results.

Q: Is there a step in the spectrum?
A: Good question! Experiments in space are different to those on the ground. This was studied over Christmas, but it’s just fluctuations. “If you don’t have fluctuations something is wrong.”

Q (Bill Murray): What is the efficiency of the final layer of the Silicon tracker?
A: Close to 100%

Q: Some bins not included. Why not?
A: Less sensitive at low energy. We want a simple model for the spectrum.

Q: Are you going to provide absolute flux measurements?
A: Yes, we will provide those. We calibrated the detector very carefully for precise measurements.

Q (John Ellis): Dark matter interpretation constrained by other experiments, eg ground based experiments.
A: Good point, we have a large number of spectra to analyze very carefully.

Q: Why not use a superconducting magnet?
A: NASA could not deliver more Helium, so superconducting is not an option for a long lived experiment.

Q: You have high statistics in the final bin, so why not rebin?
A: That’s an important question! “I’ve been working at CERN for many years and never made a mistake… We will publish this when we are absolutely sure.” (To my mind this sounds like a fine tuning problem- we should not pick which binning gives us the results we want.) “You will have to wait a little bit.”

Q (Pauline Gagnon): How can you tell the difference between the sources of positrons and models?
A: The fraction will fall off very sharply at high energy as a function of the energy.
Q: How much more time do you need to explore that region?
A: It will happen slowly.

The liveblog

18:11: Ting concludes, to applause. Time for questions.
18:10: The excess of positons has been observed for about 20 years and aroused much interest. AMS has probed this spectrum in detail. The source of the excess will be understood soon.
18:09: Conclusion time. More statistics needed for the high energy region. No fine structure is observed. No anisotropy is observed. (anisotropy of less than 0.036 at 95% confidence.)
18:07: Diffuse spectrum fitted and consistent with a single power law source.
18:00: The positron fraction spectrum is shown (Twitpic) Results should be isotropic if it’s a physics effect. The most interesting part is at high energy. No significant anisotropy is observed.
17:57: Time for some very dense tables of numbers and tiny uncertainties. Is this homeopathic physics? Dilute the important numbers with lots of other numbers!
17:53: A detailed discussion of uncertainties. There seems to be no correlation between the number of positrons and the positron fraction. Energy resolution affects resolution and hence bin to bin migration as a function of energy. There are long but small tails in the TRD estimator spectra for electrons and positrons, which must be taken into account. For charge confusion the MC models are used to get the uncertainties, which are varied by 1 sigma.
17:51: Charge confusion must be take into account. The rate is a few percent with a subpercent uncertainty. Sources of uncertainty come from large angle scattering and secondary tracks. Monte Carlo (MC) simulations are used to estimate these contributions and they seem to be well modeled.
17:48: A typical positron event, showing how the various components make the measurements. (Twitpic)
17:46: Ting shows the cover of the upcoming Physical Review Letters, a very prestigious journal, with an AMS event display. Expect a paper on April 5th!
17:45: The positron fraction. Measurements of the number of positrons compared positrons+electrons can be used to constrain physics beyond the Standard Model. In particular it can be sensitive to neutralinos, particles which are present in the Supersymmetric (SUSY) models of particle physics. The models are extensions of the Standard Model. The positron fraction is sensitive to the mass of the neutralino, if it exists.
17:42: Onto the data! There have been 25 billion events, with 6.8 million electron or positron events in the past 18 months. Two independent groups (Group A and Group alpha for fairness) analyze the data. Each group has many subgroups.
17:41: AMS is constantly monitored and reports/meetings take place every day. NASA keep AMS updated with the latest technology. There’s even an AMS flight simulator, which NASA requires AMS to use.
17:40: A less obvious point: AMS have no control over the ISS orientation or position- the position and orientation must be monitored, tolerated and taken into account.
17:38: “Operating a particle physics experiment on the ISS is fundamentally different from operating an experiment in the LHC”. Obvious Ting is obvious! 🙂
17:34: The tracking system must be kept at constant temperature, while the thermal conditions vary by tens of degrees. It has a dedicated cooling system.
17:30: Sophisticated data readout and trigger system with 2 or 4 times redundancy. (You can’t just take a screwdriver out to it if it goes wrong.)
17:27: In addition to all the other constraints, there are also extreme thermal conditions to contend with. The sun is a significant source of thermal radiation. ECAL temperatures vary from -10 to 30 degrees Celcius.
17:25 : Data can be stored for up to two months in case of a communication problem. Working space brings all kinds of constraints, especially for computing.
17:23 : NASA was in close contact to make sure it all went to plan, with tests on the ground. NASA used 2008t of mass to transport 7.5t of AMS mass (plus other deliveries) into space! AMS was installed on May 19th 2011. (I was lucky enough to hear the same story from the point of view of the NASA team, and it was an epic story they told. Apparently AMS was “plug and play”.)
17:21: Calibration is very important, because once AMS is up in space you can’t send a student to go and fix it. (Murmurs of laughter from the audience)
17:19: The detector was tested and calibrated at CERN. (I remember seeing it in the Test Beam Area long before it was launched.)
17:18: Ting shows a slide of the AMS detector, which is smaller than the LHC physicists are used to. “By CERN standards, it’s nothing”. (Twitpic)
17:16: Lots of challenges for electronic when in space. Electronics must be radiation sensitive, and AMS needs electronics that perform better than most commercial space electronics.
17:15: The TRD system measures energy loss (dE/dx) to separate electrons and positrons. A tried and true method in particle physics! The Silicon tracker has nine layers and 200,000 channels, all aligned to within 3 microns. Now that’s precision engineering. The RICH has over 10,000 photosensors to identify nuclei and measuring their energy. This sounds like a state of the art particle detector, but In Space! The ECAL system, with its 50,000 fibers and 600kg of lead can measure up to 1TeV of energy, comparable to the LHC scale.
17:11: Permanent magnet shows <1% deviation in the field since 1997. Impressive. Cosmic rays vetoed with efficiency of 0.99999. 17:10 Studies require rejection of protons versus positrons of 1 million, a huge task! TRD and TOF provides a factor of 10^2, whereas the RICH and ECAL provide the rest of the discrimination. 17:08: AMS consists of a transition radiation detector (TRD), nine layers of silicon tracker, two layers of time of flight (TOF) systems, a magnet (for measuring the charge of the particles), and a ring imaging Cherenkov detector (RICH) and electromagnetic calorimetry system (ECAL). Charges and momenta of particles are measured independently. 17:06: Ting summarizes the contributions from groups in Italy, Germany, Spain, China, Taiwan, Switzerland, France. Nice to see the groups get recognition for their long, hard work. The individual groups are often mentioned only in passing. 17:03: "AMS is the only particle physics experiment on the ISS" which is the size of a football field. The ISS cost "about 10 LHC" units of money! It's a DOE sponsored international collaboration. Ting is doing a good job acknowledging the support of collaborators and the awesomeness of having a space based particle physics experiment. 17:00: "Take your seats please." The crowd goes quiet, as the introduction starts. Sam Ting was awarded the 1976 Nobel Prize for Physics, for the discovery of the J/psi particle. 16:54: Rolf Heuer has arrived. The room is nearly full now! 16:47: Sam Ting is here. He arrived about 10 minutes ago, and spoke to Sau Lan Wu, an old colleague of his. (Twitpic)
16:31: There are a few early bird arrivals. (Twitpic)


On March 27, three young women from CERN participated via a video link in the UN Economic and Social Council “Youth Forum”, delivering a series of recommendations to improve the situation for women in science. During this all-day event held in New York, young people were invited to contribute ideas on how to improve our world, no less.

ECOSOC is still seeking input from young people ahead of its 1 July meeting where governments will meet in Geneva to address the important topics of Science, Technology, Innovation and Culture. They will adopt a Ministerial Declaration for scaling up actions in this field.

At the start of the meeting, the United Nations Secretary General, Mr Ban Ki-moon asked the young audience if the UN was doing enough for youth. A resounding “No” came back from the audience but he got the opposite answer when he said “Could the UN do more for the world’s youth?”

This ECOSOC meeting provided CERN with its first opportunity to engage directly with a UN organization since it was granted Observer status at the United Nations General Assembly last December.

Three graduate students currently based at CERN were speaking during the “Women in Science” session on behalf of a larger group of young women scientists who had gathered to draft a series of recommendations aiming at improving the situation of women in science.

Kate Pachal, a young Canadian woman currently enrolled in a PhD program at Oxford, discussed what could be done to attract more women into science. Her three points were:


  • Fight gender stereotypes at all levels. Improve the representation of women in textbooks, including in the phrasing of problems; Use gender-neutral language when referring to scientists; Increase the visibility of women scientists in the general culture by providing more female contacts for the media.
  • Help young people build a strong “physics identity”: Students who do not feel good at maths or science do not pursue a career in it. Encouragements from peers, teachers and family help young girls believe in their own ability. Classroom activities such as having discussions on cutting-edge physics topics, being encouraged to ask questions or teaching peers all contribute to build a strong  “physics identity”. Having discussions on why fewer women are in science also helps young women see the problem does not come from them but has social roots.
  • Provide role models and mentors for young women. Do it at all stages. Hold career fairs to reinforce girls’ self-esteem and provide a context where they can discuss with other girls facing similar challenges. Provide places where young women can talk with peers and find support.

Sarah seif el Nasr, an Egyptian-Canadian doctoral student at CERN, delivered three recommendations to hire more women in physics and science in general:

  • Implement anonymous job application processes. The applicant’s gender should be hidden during the job application process to avoid gender bias since a study revealed that both men and women discriminate against women. The number of female musicians tripled at five major orchestras once job applicants performed behind a curtain.
  • Implement equitable parental leaves. Both men and women should be given parental leaves and men strongly encouraged to take them. Young women of child-bearing age would then be less likely to be disfavored in hiring if both parents had to share the weight more equally. Shared or split positions would also allow both parents to participate equally in child responsibilities.
  • Add spousal considerations to hiring processes. Institutions should recognize the existence of the dual-career situation and choose to deal with it since half the women with a PhD in physics have a spouse with similar education level (as opposed to only 20% for men). Institutions should take action before beginning a search to provide assistance for spouses and consider split/shared positions. This would help young women find positions without taxing their relationships.


Finally, Barbara Millan Mejias, a Venezuelan graduate student at University of Zurich, explained what can be done to retain women in science:

  • Provide mentors for young women starting their careers. The mentor should be different from their boss or supervisor and have proper institutional support. The mentor could for example make sure the young woman progresses properly, that she is given adequate funding and support, that she gets to attend meetings and give talks at various conferences. The mentor should be able to advise the young women on academic and professional issues.


  • Have broad discussions about gender issues at large scientific meetings. Men are often unaware of the situation faced by women in science and lack opportunities to discuss this situation, even though they are most often open to it. Men often unconsciously discriminate against women. Education would improve the situation.
  • Hold scientific meetings for women where young women could see how valuable women’s work is, find positive reinforcement, get to talk with peers and get support. This would also provide a place for discussions on issues facing young women as well as opportunities to share experiences and support each other.
  • Implement equitable parental leaves. This point is crucial not only at hiring time but also to retain young women in science.

Let’s hope the voice of these young women will be heard and that laboratories like CERN and universities will make all possible efforts to implement these recommendations.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.


Le 27 mars, trois jeunes femmes du CERN ont participé par vidéoconférence au « Forum des Jeunes » du Conseil Economique et Social (ECOSOC) des Nations Unies. Elles y ont présenté une série de recommandations pour améliorer la situation des femmes en sciences. Durant ce forum, des jeunes gens avaient été invité-e-s à contribuer leurs idées pour améliorer le monde, rien de moins!

ECOSOC sollicite les contributions des jeunes jusqu’au 1er juillet, date prévue d’une rencontre des gouvernements mondiaux à Genève pour discuter de sciences, de la technologie, de l’innovation et de la culture. Une déclaration commune sera alors adoptée pour prendre action dans ces domaines.

Au début de la rencontre, le Secrétaire-Général M. Ban Ki-moon a demandé aux participant-e-s si les Nations Unies en faisaient suffisamment pour les jeunes. Un « non » retentissant lui répondit. Par contre, la réponse fut à l’opposé lorsqu’il s’enquit si l’ONU pouvait en faire davantage.

Cette rencontre avec ECOSOC a permis au CERN pour une première fois de collaborer directement avec une organisation de l’ONU depuis l’obtention du statut d’observateur à l’assemblée générale de l’ONU en décembre dernier.

Ces trois étudiantes parlaient durant la session « Femmes en Sciences » au nom d’un groupe de jeunes femmes scientifiques travaillant au CERN qui s’étaient réunies pour élaborer une série de recommandations visant à améliorer la situation des femmes en sciences.

Kate Pachal, une jeune Canadienne étudiant à l’université d’Oxford a résumé en trois points ce qui pourrait être fait pour attirer davantage de jeunes femmes en sciences :

  • Combattre les stéréotypes à tous les niveaux : Accroitre la représentation des femmes dans les manuels scolaires et inclure plus de femmes dans l’énoncé des problèmes. Utiliser un langage non-sexiste en référence aux scientifiques. Augmenter la visibilité des femmes scientifiques dans la culture en général en donnant plus de place aux femmes dans les médias.
  • Aider les jeunes à se bâtir une forte identité de scientifique:s Les étudiant-e-s qui ne se sentent pas compétent-e-s en sciences ne choisiront forcément pas une carrière scientifique. Les encouragements des professeur-e-s, de la famille et des ami-e-s sont donc essentiels pour que les jeunes filles croient en leur propre compétence. En classe, discuter de l’actualité scientifique, encourager les jeunes à poser des questions ou offrir la possibilité de superviser d’autres élèves sont autant d’activités qui peuvent renforcir ce sentiment de compétence. Les discussions sur la sous-représentation des femmes en sciences aident aussi les jeunes filles à comprendre que le problème ne vient pas d’elles mais bien de l’extérieur, qu’il est d’origine sociale.
  • Fournir des modèles féminins et des mentors aux jeunes femmes. Le faire à tous les niveaux. Organiser des foires aux carrières pour renforcir l’estime de soi des jeunes filles et créer des occasions de discussion avec d’autres jeunes filles confrontées aux mêmes questions.

Sarah seif el Nasr, une doctorante du CERN d’origine égypto-canadienne a suggéré quelques pistes pour renforcer l’embauche de femmes en physique et en sciences en général:

  • Instituer un processus d’embauche anonyme. Le genre de l’appliquant-e devrait être masqué durant le processus de sélection jusqu’à l’entretien final afin d’éviter toute rejection biaisée. Une étude a en effet démontré qu’hommes et femmes font tous les deux preuve de discrimination à l’embauche basée sur le genre. Par contre, le nombre de femmes musiciennes de cinq grands orchestres a triplé lorsque les postulant-e-s passaient l’audition derrière un rideau.
  • Mettre en place des congés parentaux équitables. Les hommes comme les femmes devraient bénéficier de congés parentaux identiques et les hommes devraient être fortement encourager à les prendre. Les jeunes femmes en âge de procréer seraient ainsi moins exposées au risque de discrimination à l’embauche si les jeunes pères étaient tout aussi susceptibles de s’absenter pour congé parental.  Des positions partagées permettraient aussi aux jeunes parents des deux genres de partager les responsabilités familiales.
  • Aider les conjoint-e-s à obtenir une position. Les institutions devraient prendre en compte les conjoint-e-s dans le processus d’embauche. La moitié des physiciennes ont des conjoint-e-s de niveau d’éducation semblable contrairement à seulement 20% des physiciens. Les institutions devraient tenir compte des conjoint-e-s avant d’engager le processus de sélection, ce qui permettrait aux femmes de trouver un emploi sans menacer leur vie de couple.

Finalement, Barbara Millan Mejias, une étudiante vénézuélienne de l’université de Zurich a suggéré quelques façons pour retenir davantage de femmes en sciences :

  • Assigner des « mentors »  aux jeunes femmes débutant leur carrière. Les mentors devraient être différent-e-s des superviseur-e-s  et être soutenu-e-s par l’institution. Ces mentors s’assureraient que les jeunes femmes progressent adéquatement, qu’elles reçoivent le soutien financier et matériel dont elles ont besoin, qu’elles participent à des conférences et ont l’occasion de présenter leurs résultats. Les mentors devraient pouvoir aviser les jeunes scientifiques tant au niveau professionnel qu’académique.
  • Organiser des discussions sur les questions de genre durant les grandes conférences scientifiques. Les hommes manquent souvent d’information sur les difficultés particulières auxquelles les femmes sont confrontées en science et ont peu l’occasion d’en discuter même lorsqu’ils sont ouverts à ces questions. Les hommes sont parfois inconsciemment discriminatoires envers les femmes, ce qui pourrait être éviter avec un minimum d’éducation.
  • Organiser des conférences spécifiquement pour les femmes où les jeunes femmes pourraient prendre conscience des contributions importantes faites par les femmes et s’en trouver renforcées. Ceci donnerait aussi l’occasion aux femmes de rencontrer leurs semblables, de trouver du soutien au besoin et de discuter ensemble des difficultés auxquelles elles sont confrontées.
  • Mise en place de congés parentaux équitables. Ce point est essentiel non seulement à l’embauche mais aussi pour retenir plus de jeunes femmes en sciences.

Toutes ces propositions pourraient être mise en place non seulement au CERN et autres grands centres de recherches, mais aussi dans les universités. Espérons que la voix de ces jeunes femmes sera entendue.

Pauline Gagnon

Pour être averti-e lors de la parution de nouveaux blogs, suivez-moi sur Twitter: @GagnonPauline ou par e-mail en ajoutant votre nom à cette liste de distribution


Win your own Higgs boson

Monday, April 1st, 2013

In an unprecedented gesture in the history of particle physics, Sergio Bertolucci, Director of Research, announced this morning that CERN is going to do something unusual: give away fundamental particles.

“Given the interest manifested over the past years by the general public for the Higgs boson search, we felt that we had to give some back as a token of appreciation”, said Dr Bertolucci. “As CERN, we have always believed in sharing the results of our research, and the time has come to make that tangible. This is our way of saying thanks for the incredible level of enthusiasm that has greeted this discovery”. The new particle’s discovery was announced at a special seminar on 4 July last year.

Both the ATLAS and CMS experiments have generously accepted to donate some of their precious Higgs bosons. Particles such as Higgs bosons are created from the energy released in proton-proton collisions in the Large Hadron Collider (LHC). However, Higgs bosons are extremely rare, being created only once out of one million million such collisions.

“We hope the lucky few who will receive a Higgs boson will cherish them as much as we do”, said Dr Bertolucci.

Each boson will come with a complete set of instructions on how to properly care for it. To enter this lottery, please send an e-mail to [email protected]. A Higgs boson will be sent to the ten lucky winners chosen randomly from all requests received within 24 hours of publishing this post.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.