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Aidan Randle-Conde | Université Libre de Bruxelles | Belgium

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LHC Scientists face major setback

Tuesday, April 1st, 2014

1st April 2014. The LHC is currently in shutdown in preparation for the next physics run in 2015. However the record breaking accelerator is danger is falling far behind schedule as the engineers struggle with technical difficulties 100m below ground level.

The LHC tunnels house the 27km long particle accelerator in carefully controlled conditions. When the beams circulate they must be kept colder than anywhere else in the solar system, and with a vacuum more empty the voids of outer space. Any disruption to the cryogenic cooling systems or the vacuum systems can place serious strain on the operations timetable, and engineers have found signs of severe damage.

Scientists patrol the LHC, inspecting the damaged areas.

Scientists patrol the LHC, inspecting the damaged areas.

The first indications of problems were identified coming from Sector 7 between areas F and H. Cryogenics expert, Francis Urquhart said “My team noticed dents in the service pipes about 50cm from the floor. There was also a deposit of white fibrous foreign matter on some of the cable trays.” The pipes were replaced, but the damage returned the following day, and small black aromatic samples were found piled on the floor. These were sent for analysis and after chemical tests confirmed that they contained no liquid Helium, and that radiometry found they posed no ionisation risk, they were finally identified as Ovis aries depositions.

Ovis aries are found throughout the CERN site, so on-site contamination could not be ruled out. It is currently thought that the specimens entered the Super Proton Synchrotron (SPS) accelerator and proceeded from the SPS to the LHC, leaving deposits as they went. The expert in charge, Gabriella Oak, could not be reached for comment, but is said to be left feeling “rather sheepish”.

Elsewhere on the ring there was another breach of the security protocols as several specimens of Bovinae were found in the ring. The Bovinae are common in Switzerland and it due to their size, must have entered via one of the service elevators. All access points and elevators at the LHC are carefully controlled using biometry and retinal scans, making unauthorised entry virtually impossible. Upon being asked whether the Bovinae had been seen scanning their retinae at the security checkpoints, Francis Urquhart replied “You might very well think that. I could not possibly comment.” While evidence of such actions cannot be found CCTV footage, there have been signs of chewed cud found on the floor, and Bovinae deposits, which are significantly larger than the Ovis deposits, owing to the difference in size.

The retinal scans at the LHC are designed exclusively for human use. A search of the biometric record database show at least one individual (R Wiggum) with unusual retinae, affiliated to “Bovine University”.

It is not known exactly how much fauna is currently in the LHC tunnels, although it is thought to be at least 25 different specimens. They can be identified by the bells they carry around their necks, which can sound like klaxons when they charge. Until the fauna have been cleared, essential repair work is extremely difficult. “I was repairing some damage caused by a passing cow” said Stanford PhD student Cecilia, “when I thought I heard the low oxygen klaxon. By the time I realised it was just two sheep I had already put on my safety mask and pulled the alarm to evacuate the tunnels.” She then commented “It took us three hours to get access to the tunnels again, and the noises and lights had caused the animals to panic, creating even more damage to clean up.”

This is not the first time a complex of tunnels has been overrun by farm animals. In the early 90s the London Underground was found to be infested with horses, which turned into a longterm problem and took many years to resolve.

Current estimates on the delay to the schedule range from a few weeks to almost a decade. Head of ATLAS operations, Dr Remy Beauregard Hadley, comments “I can’t believe all this has happened. They talk about Bovinae deposits delaying the turn on, and I think it’s just a load of bullshit!”

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Oh brave new world, which has such physicists in it!

Monday, February 10th, 2014

In August I moved away from CERN, and I’ve been back and forth between CERN and Brussels quite a lot since then. In fact right now I’m sitting in the building 40 where people go to drink coffee and have meetings, and I can see the ATLAS Higgs Convener sitting on the next table. All this leaves me feeling a little detached from what is really happening at CERN, as if it’s not “my” lab anymore, and that actually sums up how many people think about particle physics at the moment. With LHC Run I we found the Higgs boson. It was what most people expected to see, and by a large margin it was the most probable thing we would have discovered. Things will be different for Run II. Nobody has a good idea about what to expect in terms of new particles (and if they say they do have a good idea, they’re lying.) In that sense it’s not “our” dataset, it’s whatever nature decides it should be. All we can do is say what is possible, not what is probable. (Although we can probably say one scenario is more probable than another.)

The problem we now face is that there is no longer an obvious piece that’s missing, but there are still many unanswered questions, which means we have to move from an era of a well constrained search to an era of phenomenology, or looking for new effects in the data. That’s not a transition I’m entirely comfortable with for several reasons. It’s often said that nature is not spiteful, but it is subtle and indifferent to our expectations. There’s no reason to think that there “should” be new physics for us to discover as we increase the energy of the LHC, and we could be unlucky enough to not find anything new in the Run II dataset. A phenomenological search also means that we’d be overly sensitive to statistical bumps and dips in the data. Every time there’s a new peak that we don’t expect we have to exercise caution and skepticism, almost to the point where it stops being fun. Suppose we find an excess in a dijet spectrum. We may conclude that this is due a new particle, but if we’re going to be phenomenologists about it we must remain open minded, so we can’t necessarily expect to see the same particle in a dimuon final state. It would then be prudent to ask if such a peak comes from a poorly understood effect, such as jet energy scales, and those kinds of effects can be hard to untangle if we don’t have a good control sample in data. At least with the discovery of the Higgs boson, the top quark, and the W and Z bosons we knew what final states to expect and what ratios they should exhibit. There’s also something a little unsettling about not having a roadmap of what to expect. When asked to pick between several alternative scenarios that are neither favoured by evidence nor disfavoured by lack of evidence it’s hard to decide what to prioritise.

Take your pick of new physics!  Each scenario will have new phase space to explore in LHC Run II [CMS]

Take your pick of new physics! Each scenario will have new phase space to explore in LHC Run II [CMS]

On the other hand there is reason to be excited. Since we don’t know what to expect in LHC Run II, anything we do discover will change our views considerably, and will lead to a paradigm shift. If we do discover a new particle, or even better, a new sector of particles, it could help frame the Standard Model as a subset of something more elegant and unified. If that’s the case then we can look forward to decades of intense and exciting research, that would make the Higgs discovery look like small potatoes. So the next few years at the LHC could be either the most boring or the most exciting time in the history of particle physics, and we won’t know until we look at the data. Will nature tantalise us with hints of something novel, will it give us irrefutable evidence of a new resonance, or will it leave us with nothing new at all? For my part I’m taking on the dilepton final states. These are quick, clean, simple, and versatile signatures of something new that are not tied down to a specific model. That’s the best search I can perform in an environment of such uncertainty and with a lack of coherent direction. Let’s hope it pays off, and paves the way for even more discoveries.

What's happening at 325GeV at CDF?  Only more data can tell us! (CDF)

What’s happening at 325GeV at CDF? Only more data can tell us. Based on what the LHC has seen, this is probably a statistical fluctuation. (CDF)

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Higgs Convert

Friday, November 29th, 2013

Since 4th July 2012, the physicists at CERN have had a new boson to play with. This new boson was first seen in the searches that were optimised to find the world famous Higgs boson, and the experiments went as far as to call it a “Higgs-like” boson. Since then there has been an intense program to study its spin, width, decay modes and couplings and so far it’s passed every test of Higgs-ness. Whether or not the new boson is the Standard Model Higgs boson is one of the most pressing questions facing us today, as there is still room for anomalous couplings. Whatever the answer is, a lot of physicists will be pleased. If we find that the properties match those of a Standard Model Higgs boson exactly then we will hail it as a triumph of science and a fitting end to the quest for the Standard Model which has taken the work of thousands of physicists over many decades. If we find some anomaly in the couplings this would be a hint to new physics hiding “just around the corner” and tease is with what we may see at higher energies when the LHC turns on again in 2015.

A candidate for a Higgs boson decaying to two tau leptons (ATLAS)

A candidate for a Higgs boson decaying to two tau leptons (ATLAS)

For those who have read my blog for a long time, you may remember that I wrote a post saying how I was skeptical that we would find the Standard Model Higgs boson. In fact I even bet a friend $20 that we wouldn’t find the Standard Model Higgs boson by 2020, and until today I’ve been holding on to my money. This week I found that ATLAS announced the results of their search for the Higgs boson decaying to two tau leptons, and the results agree with predictions. When we take this result alongside the decays to bosons, and the spin measurements it’s seems obvious that this is the Higgs boson that we were looking for. It’s not fermiophobic, and now we have direct evidence of this. We have see the ratio of the direct ferimonic couplings to direct bosonic couplings, and they agree very well. We’d had indirect evidence of fermionic couplings from the gluon fusion production, but it’s always reassuring to see the direct decays as well. (As a side note I’d like to point out that the study of the Higgs boson decaying to two tau leptons has been the result of a huge amount of very hard work. This is one of the most difficult channels to study, requiring a huge amount of knowledge and a wide variety of final states.)

Now the reason for my skepticism was not because I thought the Standard Model was wrong. In fact the Standard Model is annoyingly accurate in its predictions, making unexpected discoveries very difficult. What I objected to was the hyperbole that people were throwing around despite the sheer lack of evidence. If we’re going to be scientists we need to rely on the data to tell us what is real about the universe and not what some particular model says. If we consider an argument of naturalness (by which I mean how few new free terms we need to add to the existing edifice of data) then the Higgs boson is the best candidate for a new discovery. However that’s only an argument about plausibility and does not count as evidence in favour of the Higgs boson. Some people would say things like “We need a Higgs boson because we need a Brout-Englert-Higgs mechanism to break the electroweak symmetry.” It’s true that this symmetry needs to be broken, but if there’s no Higgs boson then this is not a problem with nature, it’s a problem with our models!

The fact that we’ve seen the Higgs boson actually makes me sad to a certain extent. The most natural and likely prediction has been fulfilled, and this has been a wonderful accomplishment, but it is possible that this will be the LHC’s only new discovery. As we move into LHC Run II will we see something new? Nobody knows, of course, but I would not be surprised if we just see more of the Standard Model. At least this time we’ll probably be more cautious about what we say in the absence of evidence. If someone says “Of course we’ll see strong evidence of supersymmetry in the LHC Run II dataset.” then I’ll bet them $20 we won’t, and this time I’ll probably collect some winnings!

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Nobel Dreams

Friday, October 4th, 2013

The liveblog

Greeting from Brussels! This is my liveblog of the Nobel Prize Announcement Ceremony, bringing you the facts and the retweets as they happen.

14:14: Press Conference ongoing. “This is a great day for young people.”

13:56: A moving statement from Kibble (source):

I am glad to see that the Swedish Academy has recognized the importance of the mass-generating mechanism for gauge theories and the prediction of the Higgs boson, recently verified at CERN. My two collaborators, Gerald Guralnik and Carl Richard Hagen, and I contributed to that discovery, but our paper was unquestionably the last of the three to be published in Physical Review Letters in 1964 (though we naturally regard our treatment as the most thorough and complete) and it is therefore no surprise that the Swedish Academy felt unable to include us, constrained as they are by a self-imposed rule that the Prize cannot be shared by more than three people. My sincere congratulations go to the two Prize winners, François Englert and Peter Higgs. A sad omission from the list was Englert’s collaborator Robert Brout, now deceased.

13:37: CERN are holding a press conference at 14:00 (CET) link

13:22: Commentary continues at the Nobel Prize page. Currently discussing why the boson was so hard to find. “This particle has been looked for at every accelerator that has existed.”

13:20: As expected, so many news sites have been created: CMS, ATLAS, ULB, Edinburgh

13:14: I think my twitter account has exploded with tweets. Also, some Belgian news pages are down, probably due to high traffic. Wow!

13:11: Wow, what a great announcement. Too short though!

13:08: Find out more about the physics at Brussels, where the Brout-Englert-Higgs mechanism was born! The IIHE and the Nobel Prize

13:01: Englert is on the phone. Good to hear from him :)

12:59: Animation of the boson appearing, cool!

12:57: We just opened the champagne here at ULB!

12:52: Text for the announcement:

“For the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”

12:48: The award goes to Englert and Higgs!

12:44: One minute to go!

12:39: We all know what the Brout-Englert-Higgs mechanism is and what the boson discovery means, so let’s instead take a look at the other likely awards. The prize could go to the discovery of extra solar planets. 51 Pegasi b was an extra solar planet discovered in 1995, orbiting a sun-like star. This discovery could have far reaching implications. What would happen if we saw spectral lines suggesting the presence amino acids coming from the planet? (I’m not sure such a phenomenon is even possible, but if it is it would be a very strong indicator of RNA-like life from another planet.) That discovery took place 18 years ago, and the Brout-Englert-Higgs boson was discovered only one year ago. Either discovery would certainly be worthy of the prize.

12:33: A quantum approach to the delay problem:

Someone go observe the academy and make them leave this terrible superposition. (@lievenscheire)

12:32: Another possible reason for the delay:

There’ll be a new hunt for the #Higgs. He’s gone to the Highlands to avoid the fuss if he wins #nobelprize. Maybe reason for delay. (@BBCPallab)

12:31: The Nobel Prize committee are stalling by suggesting we look at previous awards. At least they are trying to keep up amused while we wait :)

12:29: Around the world people are patiently waiting. People from the US have been awake since 5:00am. In Marakech the ATLAS Collaboration looks on. Here are ULB/IIHE the cafeteria seem deserted. (I’m glad there’s a coffee machine on the desk next time mine.) I’m starting to think this is a plot to get some more media attention for what is bound to be a controversial year for physics. There are many good choices of topic this year, and even some of the topics have controversial choices of Laureates.

12:21: Some humourous speculation about the delay:

The Academy only has 3 #sigma evidence of more votes for than against, waiting for more data (@SethZenz)

They can’t get Comic Sans installed on the Academy’s computer (@orzelc)

The committee were mobbed trying to get across a cocktail party. (@AstroKatie)

12:07: The announcement is delayed until 12:45 CET. People are complaining about the background music!

11:58: The announcement is delayed until 12:30 CET.

11:44: According to the Guardian (source) there will be a delay of 30 minutes.

11:42: Just over two minutes to go. This could be a very exciting year for Belgium.

11:33: See the livecast.

Other info

On Tuesday October 8th the recipient(s) of the 2013 Nobel Prize in Physics will be announced. There has already been a lot of speculation about who might be the Nobel Laureates this year, and there is a lot of interest in the likely contenders! Each year Thomson Reuters publishes predictions of who might receive the Nobel Prizes, and this year they have narrowed the scope down to three likely awards in physics:

  • ‣ Francois Englert and Peter Higgs, for their prediction of the Brout-Englert-Higgs mechanism. (Brout is deceased and the Nobel Prize is not awarded posthumously.)
  • ‣ Hideo Hosono, for his discovery of iron-based superconductors.
  • ‣ Geoffrey Marcy, Michel Mayor, and Didier Queloz, for their discoveries of extrasolar planets.
The 2012 Nobel Prize Award Ceremony (Copyright © Nobel Media AB 2012 Photo: Alexander Mahmoud)

The 2012 Nobel Prize Award Ceremony (Copyright © Nobel Media AB 2012 Photo: Alexander Mahmoud)

There has also been speculation that either Anderson or Nambu may receive a second Nobel Prize for their work related to spontaneous symmetry breaking.

With so many different predictions and so many opinions it can be hard to keep up with all the latest news and blogs! I know that a lot of people plan to share their views and experiences of the day, so I’ll be keep a list of bloggers and tweeters that you can follow.

Seth Zenz:

See Seth’s excellent post about the Nobel Prize, Englert and Higgs, and CERN. You can also follow his twitter account: @SethZenz

James Doherty:

See James’s great post about the Nobel Prize, He’s on twitter too: @JimmyDocco

Guardian liveblog

Other twitter accounts to follow:

@CERN

@aidanatcern

@kylecranmer

@kenbloomunl

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Gauge transformation

Tuesday, October 1st, 2013

“Welcome to CMS,” my friend said, “it’s exactly the same as ATLAS, except the fluctuations are downward.” It was a light hearted, almost flippant remark and to an extent it summarised my feelings about the two experiments. So when I moved from the ATLAS experiment to the CMS experiment the biggest changes were not related to the physics. After all, we see the same physics, publish very similar results and analyse the same beams colliding over and over again. The big news that both experiments celebrate the most is, of course, the new boson. ATLAS saw a little more events than they expected in the main channels, and CMS saw a little fewer, and otherwise they both saw the same effect, confirming that it was real.

Aidan at ATLAS

Aidan at CMS

Same experience, different detectors. Nothing really changes!

What really changes is everything surrounding the work. I’ve moved across the world a few times to follow my career, first to California where we analysed collisions at SLAC, and then to CERN to work on ATLAS. This time I moved to ULB in Brussels, the capital of Europe, and that meant a new home, a new nation, a new university, and a new experiment. In fact the only thing that stayed the same were the protons. For me that’s perfect, after all the last thing I want to do is stagnate, doing the same thing day after day. A change like this is refreshing, gives a chance to open up new horizons and reinvent oneself a little. Having those tiny little protons be the only source of continuity is actually quite reassuring in a way. That’s what I’m here for, after all. To keep studying those protons I’ll let everything else around me change and welcome the state of flux.

So as well as all those “auxiliary” changes I decided to change the physics topic as well. I have previously searched for the Higgs boson, starting up and leading a new analysis from scratch before handing it over to the ATLAS machine. This time I’m looking for the Z prime boson, which has a clean signature and if it is seen, it is seen very soon after taking new data. There are several models out there, but given the relative ease and speed of discovery it’s more a matter of “Find now, ask questions later!” Within the first few weeks of taking data we will be poring over the results, looking for any hints of new physics, competing in a head to head race with ATLAS and with each other to find the peak first. If if exists, we’ll find it, and it’ll shake our view of physics at the TeV scale. This is a very different kind of physics for me, and at first it was not I felt particularly comfortable pursuing. I was used to having an airtight model that told me what to expect and how much of it to expect and even where to expect it. This time the data is telling the story and that’s a tricky idea to get used to. Then again this whole transition is about changing my outlook, so why not change analysis style too?

Grand Place

Finding the best table in Brussels and having dinner with a visiting friend.

For those who noticed my absence, I’m sorry! It’s taken a few months from the start of a job search in a very difficult job market, applying to positions on three different experiments, in four different countries. The move from one place to another is never particularly “clean” either, as there are loose ends from my old job, and it takes a while to get started in my new position. Then there are all those small changes, like a different ID card, a different currency, a slightly different style of French. I’ve let it take longer than I should have before returning to blogging because to be honest the break has been a very welcome one. CERN is a very busy place with long days and huge demands. Moving to Brussels was hard work at first, but now I find myself with more space, more time and more opportunities to catch up with everything in my life that was put on the back-burner. A decade of photos to sort, all those books I bought and put on the shelf, the half-finished ideas that got archived for when I got around to it. Contributing to this blog again is part of the grand plan. There are so many topics I want to touch on, and I set a very high bar with the Advent Calendar last year! I also want to look beyond science to the pursuit of knowledge itself and its implications on theology (something I never felt comfortable tackling when working for a US institute.)

The way I see it, moving experiment is just like a gauge transformation. No matter what happens, any physical phenomenon must be the same after a gauge transformation. This kind of transformation is a subtle mathematical change that has no classical analog. By making a phenomenon gauge invariant we can introduce new forces that mop up all the differences, so that ultimately, we all see the same thing, no matter how we look at it. In this case, what stays the same is the underlying nature of those colliding protons. That’s the gauge invariance, and everything else, the movement from place to place, from one experiment to another, are just the fields swooshing about as we perform our own personal gauge transformations. It turns out life is complex.

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Margaret Thatcher, politician, scientist

Monday, April 15th, 2013

Early last week Margaret Thatcher, former British Prime Minister, passed away, aged 87. She was a charismatic figure who was known internationally for being a strong and decisive leader. She had close political ties with President Ronald Reagan, she opposed the communist policies in Eastern Europe, and she was skeptical of increasing integration of the UK with Western Europe. Her actions and legacy are entwined with the global political stage at the time. However, in the UK she was very divisive and at times controversial, and even to this day there is a mixture of high praise a bitter resentment about her policies. Much has been said about her legacy over the past few days, and I think that, regardless of one’s own views, one of the best things we can say about Thatcher is that she knew what her vision was, and she pursued it with a great deal of energy and enthusiasm.

Thatcher, the politician (Mirror)

Thatcher, the politician (Mirror)

During her undergraduate years, Thatcher was a chemist at the University of Oxford. It was only later that she studied law and became a politician, so from her very early career she had an appreciation for science. She knew about the care and attention needed to make discoveries, the frustration of waiting for data, and the need for peer review and skepticism. Given her status as an international leader, she had the opportunity to visit CERN in the early 1980s, but as a scientist she took so much more away from the visit than we could have expected.

Thatcher, the chemist (popsci)

Thatcher, the chemist (popsci)

She’d asked to be treated like a fellow scientist, and her questions showed that she had taken her background reading about CERN seriously. She asked why the proposed accelerator, LEP, would be circular and not linear. This is not an easy question to answer unless the person asking has knowledge about how accelerators work. After a discussion with Herwig Schopper, then Director General, she came back to the UK as an ambassador for CERN and LEP was approved in the UK shortly afterwards. One of her questions was very astute. When told that the LEP tunnel would be the last at CERN she knew from experience that scientists will usually want to go further with their research and in particle physics at the energy frontier, further usually means larger. It’s true that CERN has reused the LEP tunnels for the LHC, but there are also proposals for even larger projects that will probe even higher center of mass energies.

Thatcher must have made a very good impression on Schopper during her visit. A recent Scientific American article has revealed that she was told about the discovery of the W and Z bosons before the information was made public. This letter shows that Schopper kept his promise and trusted Thatcher to keep the tantalizing and preliminary evidence to herself:

Schopper writes to Thatcher (Scientific American)

Schopper writes to Thatcher (Scientific American)

When the news of the \(W\) boson discovery was public she wrote to Peter Kalmus of Queen Mary College, London, to offer her congratulations. Naturally she made a point to mention that there was a significant British effort behind the discovery:

Thatcher's letter to Kalmus

Thatcher's letter to Kalmus

On the one hand, Thatcher was genuinely excited about CERN and the research, but on the other she was a fiscally conservative politician with monetarist policies and she had to defend the spending to her colleagues, and to herself. She had to make sure that the physicists at CERN were using the funding effectively, and delivering high quality scientific results for the spending. During a visit to the Super Proton Synchrotron she spoke John Ellis, who introduced himself as a theoretical physicist. The conversation continued:

Thatcher: “What do you do?”
Ellis: “Think of things for the experiments to look for, and hope they find something different.”
Thatcher: “Wouldn’t it be better if they found what you predicted?”
Ellis: “Then we would not learn how to go further!”

Once again Thatcher knew what question to ask, and Ellis knew what answer to give. Thatcher seemed convinced and knew that the people at CERN has the right attitude when it comes to discovery and use of public money. You can see some media coverage of her visit to the UA1 (Underground Area 1) site on the CERN Document Server.

In 1993, three years after Thatcher left office, David Miller from UCL came up with an analogy for the Higgs field where Thatcher played the central role. Essentially we can think of the Higgs field like a room full of people milling around at a cocktail party. Someone famous and popular enters the room, and all of a sudden people crowd around, making this person’s journey through the room harder. They take longer to get up to a good walking speed, and when they are walking they become harder to stop. That’s essentially what mass is- a measure of hard it is to change an object’s velocity. The analogy goes further, to include rumors being spread from the vicinity of this famous person. They would spread in small groups of people, and each group would have its own “mass”, which is what the Higgs boson is, it’s just an excitation of the field in the presence of matter. Who was the famous person in this analogy? Margaret Thatcher, of course!

Thatcher and the Higgs field (Quantum Tangents)

Thatcher and the Higgs field (Quantum Tangents)

So her legacy with CERN is one of a scientist and a politician. She was genuinely excited to see the discoveries take place, she met with the scientists personally and interacted with them as another scientist. She took the time to understand the questions and answers, and even challenged the physicists with more questions. At the same time she put the projects in context. She had to defend the experiments, so she had to challenge the physicists to give her the information she needed to get the support from the UK. In a sense she knew the need for public outreach, to open up CERN’s scientific program to scrutiny from the public so that when we want to push back the frontiers even further we can count on their support.

If we’re to keep pursuing scientific discoveries in the future, we need scientifically literate and inspired politicians. It would be tempting to say that they are becoming more and more rare, but in reality I think things are more favorable than they have been before. With the recent discoveries we’re in a golden age of physics that has made front page news. Multimedia outlets and the internet have helped spread the good word, so science is high in the public consciousness, and justifying further research is becoming easier. However before the modern internet era and the journalistic juggernaut that comes to CERN each time there’s a big announcement it fell on the shoulders of a few people, and Thatcher was one of them.

(I would like to thank John Ellis for providing help with his quote, and for giving the best answer when asked the question!)

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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.

Questions

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)

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The Substandard Model of Particle Physics

Monday, April 1st, 2013

Now that we are on the verge of completing the Standard Model of Particle Physics, it’s time to look to the future of the field. Five physicists at CERN present their new state of the art* theory: The Substandard Model of Physics!

“It’s easy to understand but questionably accurate.” Mandy Baxter (Marine Biogeochemical Microbiologist, USCB)

Thanks to the actors.
The Substandard Model Task Force:
Androula Alekou (Neutrino Expert)
Katie Malone (Higgs Expert)
Stephen Ogilvy (Flavor Expert)
Aidan Randle-Conde (QCD Expert)
Lee Tomlinson (QFT Expert)

Steve Marsden (Standard Model Expert)
Helen Lambert (Environmental Sanitization Team)

You can find Steve and Aidan on youtube and twitter:

http://www.youtube.com/signifyingsomething

http://www.youtube.com/aidanatcern

@sigsome @aidanatcern

Visit the US LHC Blogs at Quantum Diaries:

http://www.quantumdiaries.org/lab-81

Music: Off to Osaka, Kevin Macleod, http://www.incompetech.com

Images taken from CKMFitter (http://ckmfitter.in2p3.fr), UTFit (http://www.utfit.org), Wikimedia.

This video does not reflect the views of CERN. It does not even reflect the views of the actors. In fact I’d be surprised if it reflected the views of anyone at all.

Thanks to Adam Davidson for inspiring the name. It was a off handed comment you made about 7 years ago that stuck with me ever since. Finally it has become a reality!

Apologies for the slightly out of focus footage and extra frame. Some small technical glitches always get through.

(*We’re just not sure what kind of a state, and what kind of art it is.)

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Tweeting the Higgs

Wednesday, January 23rd, 2013

Back in July two seminars took place that discussed searches for the Higgs boson at the Tevatron and the LHC. After nearly 50 years of waiting an announcement of a \(5\sigma\) signal, enough to claim discovery, was made and all of a sudden the twitter world went crazy. New Scientist presented an analysis of the tweets by Domenico et al. relating to the Higgs in their Short Sharp Scient article Twitter reveals how Higgs gossip reached fever pitch. I don’t want to repeat what is written in the article, so please take a few minutes to read it and watch the video featured in the article.

The distribution of tweets around the July 2nd and July 4th announcements (note the log scale)

The distribution of tweets around the July 2nd and July 4th announcements (note the log scale)

Instead of focusing on the impressive number of tweets and how many people were interested in the news I think it’s more useful for me as a blogger to focus on how this gossip was shared with the world. The Higgs discovery was certainly not the only exciting physics news to come out of 2012, and the main reason for this is the jargon that was used. People were already familiar with acronyms such as CERN and LHC. The name “Higgs” was easy to remember (for some reason many struggled with “boson”, calling it “bosun”, or worse) and, much to physicists’ chagrin, “God particle” made quite a few appearances too. It seems that the public awareness was primed and ready to receive the message. There were many fellow bloggers who chose to write live blogs and live tweet the event (I like to think that I started bit of a trend there, with the OPERA faster than light neutrinos result, but that’s probably just wishful thinking!) Following the experiences of December 2011, when the webcast failed to broadcast properly for many users had twitter on standby, with tweets already composed, hungry for numbers. The hashtags were decided in advance and after a little jostling for the top spot it was clear which ones were going to be the most popular. Despite all the preparation we still saw huge numbers of #comicsans tweets. Ah well, we can’t win them all!

The point is that while the world learned about the Higgs results I think it’s just as important that we (the physicists) learn about the world and how to communicate effectively. This time we got it right, and I’m glad to see that it got out of our control as well. Our tweets went out, some questions were asked and points clarified and the news spread. I’m not particularly fond of the phrase “God particle” , but I’m very happy that it made a huge impact, carrying the message further and reaching more people than the less sensational phrase “Higgs boson”. Everyone knows who God is, but who is Higgs? I think that this was a triumph in public communication, something we should be building on. Social media technologies are changing more quickly each year, so we need to keep up.

A map of retweets on July 4th, showing the global spread.

A map of retweets on July 4th, showing the global spread.

I’m glad to see more physicists using Twitter and youtube and other sites to spread the word because that’s where we can build audiences faster. (Incidentally if you want to see why we should be creating new audiences rather than addressing existing ones then see this video by Vihart.) It takes more work and it’s more experimental, but it’s worth the effort. Why did I make an advent calendar? Why tell physics jokes on Twitter? Just to see what works and what doesn’t. I’m not the first person to do these things, and I’m certainly not going to be the last. All I can hope to do is try new ideas out and give other people ideas. I don’t know the people I inspire and those I am inspired by, but that’s also part of the experiment. A lot of my ideas come from people who leave comments or send E-mails or tweets. Occasionally it gets heated and controversial, but if it’s not worth fighting for then it’s not worth saying in the first place. Many comments come from other bloggers too, and we can learn from each other. When I first started to blog someone sent me a few paragraphs of advice and I forgot most of it except one part “Ignore other people’s expectations. Some people will want you to always write about physics, some people will hate that. Write what matters to you.” When I combine that with what Vihart says (essentially “If your content is worth attention then people will pay attention to it.”) then rest is easy. Well, not easy, but less stressful.

But moving back to the main point, the Higgs tweets went global and viral because they were well prepared and the names were simple. Other news included things like the search for the \(B_s\) meson decaying to two muons and the limits that places on SUSY, but how does one make a hashtag for that? I would not want to put the hashtag #bs on my life’s work. It’s always more exciting to announce a discovery than an exclusion too. The measurement of \(\theta_{13}\) was just as exciting in my opinion, but that also suffered the same problem. How is the general public supposed to interpret a Greek character and two numbers? I should probably point out that this is all to do with finding the right jargon for the public, and not about the public’s capacity to understand abstract concepts (a capacity which is frequently underestimated.) Understanding how \(\theta_{13}\) fits in the PMNS mixing matrix is no more difficult than understanding the Higgs mechanism (in fact it’s easier!) It’s just that there’s no nice nomenclature to help spread the news, and that’s something that we need to fix as soon as possible.

As a side note, \(\theta_{13}\) is important because it tells us about how the neutrinos mix. Neutrino mixing is beyond the Standard Model physics, so we should be getting more excited about it! If \(\theta_{13}\) is non-zero then that means that we can put another term into the matrix and this fourth term is what gives us matter-antimatter asymmetry in the lepton sector, helping to explain why we still have matter hanging around in the universe, why we have solid things instead of just heat and light. Put like that is sounds more interesting and newsworthy, but that can’t be squeezed into a tweet, let alone a hashtag. It’s a shame that result didn’t get more attention.

It’s great fun and a fine challenge to be part of this whole process. We are co-creators, exploring the new media together. Nobody knows what will work in the near future, but we can look back what has already worked, and see how people passed on the news. Making news no longer stops once I hit “Publish”, it echoes around the world, through your tweets, and reblogs, and we can see its journey. If we’re lucky it gets passed on enough to go viral, and then it’s out of our control. It’s this kind of interactivity that it so rewarding and engaging.

You can read the New Scientist article or the original paper on the arXiV.

Thanks for reading!

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2013: The road ahead

Monday, December 31st, 2012

This time last year I wrote a blog post about what 2011 delivered and what to expect for 2012. It was obvious that we’d get some answers on the Higgs question, so it’s no surprise that we saw some 5 sigma bumps in there. As Rolf Heuer, Director General of CERN said it was a “vintage year” for physics, which I think means “very good”. Personally I think that the choice of word “vintage” is a bit anticlimactic. Surely a vintage anything is best enjoyed after several years have passed, if you have the money for it? It would have been nicer to see a word that reflected the current excitement of being a part of the discovery and seeing physics a living field, rather than comparing it to a bottle of dusty (though very tasty) wine at the back of a cellar somewhere. Oh well, maybe I’m reading too much into one word. Rolf’s article gives a very nice overview of 2012. In short, 2012 was brilliant and delivered as promised.

As usual, the end of the year also marks the end of the LHC run. In 2012 the LHC was ramping up for another year of proton collisions. This year it’s ramping up for weeks heavy ion physics, and then the long shutdown. Long shutdown. There’s so much meaning in those two words. No more data for two years. What will we do with that time? Will people flee from the field? (That would make it easier for the remaining physicists to find good positions!) Will we re-analyze the existing data? Will we work hard on the hardware? Will we revise our theories? First things first: early in 2013 we’ll need to deal with the rest of the Higgs questions for the Moriond conference. Some questions will have to wait to be answered, but most of them can be addressed with the data we have. What are the final states and branching fractions? Can we get a handle on the spin and parity? Do the production mode rates look right? We can get answers to most of these questions and that would be enough to confirm that what we have seen is the Standard Model Higgs boson. If one value comes out significantly “wrong” at both ATLAS and CMS then we’ve got new physics on our hands.

That’s what I’m hoping for. That’s what nearly everyone is hoping for. I hope 2013 is the year that the Standard Model gets broken. I want to see that model fall apart and leave a big new physics shaped hole for us to fill. If we get a Higgs boson and new phenomena then the 2015 data will be worth the wait. The nightmare scenario is seeing the Standard Model Higgs and nothing else. That would be like Columbus sailing West and getting to India. Impressive, somewhat reassuring, but ultimately disappointing. I don’t want a easy route to an old question, I want a whole new continent of discovery. It worked very well for us last time! I don’t know what a discovery of that kind would look like. It would have be in the dataset somewhere though, and once the pressure from the Higgs searches dies down we’ll have a lot more time and labor to look at the data with fresh eyes and comb it for new processes. Keeping the pace going for analysis during the shutdown will be hard, but worth the effort. There will be no media frenzy, the world will not be watching over our collective shoulders. Instead it will be a quieter process, a time to reflect on the implications of what we’re unwinding and what it is telling us.

2012, you’ve been great, but it’s time to move on. Bring it on 2013. Change the landscape for us all over again and tell us where to take the field in the next few years. Enjoy the hibernation, LHC, 2015 will be rough on you.

And of course Happy New Year to all!

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