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Margaret Thatcher, politician, scientist

Aidan Randle-Conde
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)

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)

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)

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

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)

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!)

April 2013 AMS Liveblog

Aidan Randle-Conde
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)

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)

The Substandard Model of Particle Physics

Aidan Randle-Conde
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.
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)

@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.)

Shutdown? What shutdown?

Ken Bloom
Sunday, March 24th, 2013

I must apologize for being a bad blogger; it has been too long since I have found the time to write. Sometimes it is hard to understand where the time goes, but I know that I have been busy with helping to get results out for the ski conferences, preparing for various reviews (of both my department and the US CMS operations program), and of course the usual day-to-day activities like teaching.

The LHC has been shut down for about two months now, but that really hasn’t made anyone less busy. It is true that we don’t have to run the detector now, but the CMS operations crew is now busy taking it apart for various refurbishing and maintenance tasks. There is a detailed schedule for what needs to be done in the next two years, and it has to be observed pretty carefully; there is a lot of coordination required to make sure that the necessary parts of the detector are accessible as needed, and of course to make sure that everyone is working in a safe environment (always our top priority).

A lot of my effort on CMS goes into computing, and over in that sector things in many ways aren’t all that different from how they were during the run. We still have to keep the computing facilities operating all the time. Data analysis continues, and we continue to set records for the level of activity from physicists who are preparing measurements and searches for new phenomena. We are also in the midst of a major reprocessing of all the data that we recorded during 2012, making use of our best knowledge of the detector and how it responds to particle collisions. This started shortly after the LHC run finished, and will probably take another couple of months.

There is also some data that we are processing for the very first time. Knowing that we had a two-year shutdown ahead of us, we recorded extra events last year that we didn’t have the computing capacity to process in real time, but could save for later analysis during the shutdown. This ended up essentially doubling the number of events we recorded during the last few months of 2012, which gives us a lot to do. Fortunately, we caught a break on this — our friends at the San Diego Supercomputer Center offered us some time on their facility. We had to scramble a bit to figure out how to include it into the CMS computing system, but now things are happily churning away with 5000 processors in use.

The shutdown also gives us a chance to make relatively invasive changes to how we organize the computing without potentially disrupting critical operations. Our big goal during this period is to make all of the computing facilities more flexible and generic. For the past few years, particular tasks have often been bound to particular facilities, in particular those that host large tape archives. But that can lead to inefficiencies; you don’t want to let computers remain idle at one site just while another site is backed up because it has particular features that are in demand. For instance, since we are reprocessing all of the data events from 2012, we also need to reprocess all of the simulated events, so that they match the real data. This has typically been done at the Tier-1 centers, where the simulated events are archived on tape. But recently we have shifted this work to the Tier-2 centers; the input datasets are still at the Tier 1′s, but we read them over the Internet using the “Any Data, Anytime, Anywhere” technology that I’ve discussed before. That lets us use the Tier 2′s effectively when they might have been otherwise idle.

Indeed, we’re trying to figure out how to use any available computing resource out there effectively. Some of these resources may only be available to us on an opportunistic basis, and taken away from us quickly when they are needed by their owner, on the timescale of perhaps a few minutes. This is different from our usual paradigm, in which we assume that we will be able to compute for many hours at a time. Making use of short-lived resources requires figuring out how to break up our computing work into smaller chunks that can be easily cleaned up when we have to evacuate a site.

But computing resources include both processors and disks, and we’re trying to find ways to use our disk space more efficiently too. This problem is a bit harder — with a processor, when a computing job is done with it, the processor is freed up for someone else to use, but with disk space, someone needs to actively go and delete files that aren’t being used anymore. And people are paranoid about cleaning up their files, in fear of deleting something they might need at an arbitrary time in the future! We’re going to be trying to convince people that many files on disk aren’t getting accessed, and it’s in our interest to automatically clean them up to make room for data that is of greater interest, with the understanding that the deleted data can be restored if necessary.

In short, there is a lot to do in computing before the LHC starts running again in 24 months, especially if you consider that we really want to have it done in 12 months, so that we have time to fully commission new systems and let people get used to them. Just like the detector, the computing has to be ready to make discoveries on the first day of the run!

Back From Hibernation, and a Puzzling Asymmetry

Monday, March 4th, 2013

I know in my life at least, there are periods when all I want to do is talk to the public about physics, and then periods where all I would like to do is focus on my work and not talk to anyone. Unfortunately, the last 4 or so months falls into the latter category. Thank goodness, however, I am now able to take some time and write about some interesting physics which had been presented both this year and last. And while polar bears don’t really hibernate, I share the sentiments of this one.

Okay, I swear I'm up this time! Photo by Andy Rouse, 2011.

A little while ago, I posted on Dalitz Plots, with the intention of listing a result. Well, now is the time.

At the 7th International Workshop on the CKM Unitarity Triangle, LHCb presented preliminary results

Asymmetry of $$B^{\pm}\to\pi^{\pm}\pi^+\pi^-$$ as a function of position in the Dalitz Plot. Asymmetry is mapped to the z-axis. From LHCb-CONF-2012-028

for CP asymmetry in the channels $$B\to hhh$$, where $$h$$ is either a $$K$$ or $$\pi$$. Specifically, the presentation was to report on searches for direct CP violation in the decays $$B^{\pm}\to \pi^{\pm} \pi^{+} \pi^{-}$$ and $$B^{\pm}\to\pi^{\pm}K^{+}K^{-}$$.  If CP was conserved in this decay, we would expect decays from $$B^+$$ and $$B^-$$ to occur in equal amounts. If, however, CP is violated, then we expect a difference in the number of times the final state comes from a $$B^+$$ versus a $$B^-$$. Searches of this type are effectively “direct” probes of the matter-antimatter asymmetry in the universe.

Asymmetry of $$B^\pm\to\pi^\pm K K$$ as a function position in the Dalitz plot. Asymmetry is mapped onto the z-axis.From LHCb-CONF-2012-028

By performing a sophisticated counting of signal events, CP violation is found with a statistical significance of $$4.2\sigma$$ for $$B^\pm\to\pi^\pm\pi^+\pi^-$$ and $$3.0\sigma$$ for $$B^\pm\to\pi^\pm K^+K^-$$. This is indeed evidence for CP violation, which requires a statistical significance >3$$\sigma$$.The puzzling part, however, comes when the Dalitz plot of the 3-body state is considered. It is possible to map the CP asymmetry as a function of position in the Dalitz plot, which is shown on the right. It’s important to note that these asymmetries are for both signal and background. Also, the binning looks funny in this plot because all bins are of approximately equal populations. In particular, notice red bins on the top left of the $$\pi\pi\pi$$ Dalitz plot and the dark blue and purple section on the left of the $$\pi K K$$ Dalitz plot. By zooming in on these regions, specifically $$m^2(\pi\pi_{high})>$$15 GeV/c$$^2$$ and $$m^2(K K)<$$3 GeV/c$$^2$$, and separating by $$B^+$$ and $$B^-$$, a clear and large asymmetry is shown (see plots below).

Now, I’d like to put these asymmetries in a little bit of perspective. Integrated over the Dalitz Plot, the resulting asymmetries are

$$A_{CP}(B^\pm\to\pi^\pm\pi^+\pi^-) = +0.120\pm 0.020(stat)\pm 0.019(syst)\pm 0.007(J/\psi K^\pm)$$

and

$$A_{CP}(B^\pm\to\pi^\pm K^+K^-) = -0.153\pm 0.046(stat)\pm 0.019(syst)\pm 0.007(J/\psi K^\pm)$$.

Whereas, in the regions which stick out, we find:

$$A_{CP}(B^\pm\to\pi^\pm\pi^+\pi^-\text{region}) = +0.622\pm 0.075(stat)\pm 0.032(syst)\pm 0.007(J/\psi K^\pm)$$

and

$$A_{CP}(B^\pm\to\pi^\pm K^+K^-\text{region}) = -0.671\pm 0.067(stat)\pm 0.028(syst)\pm 0.007(J/\psi K^\pm)$$.

These latter regions correspond to a statistical significance of >7$$\sigma$$ and >9$$\sigma$$, respectively. The interpretation of these results is a bit difficult: the asymmetries are four to five times that of the integrated asymmetries, and are not necessarily associated with a single resonance. We would expect in the $$\rho^0$$ and $$f_0$$ resonances to appear in the lowest region of $$\pi\pi\pi$$ Dalitz plot, in the asymmetry. In the $$K K\pi$$ Dalitz plot, there are really no scalar particles which we expect to give us an asymmetry of the kind we see. One possible answer to both these problems is that the quantum mechanical amplitudes are only partially interfering and giving the structure that we see. The only way to check this would be to do a more detailed analysis involving a fit to all of the possible resonances in these Dalitz plots. All I can say is that this result is certainly puzzling, and the explanation is not necessarily clear.

Zoom onto $$m^2(\pi\pi)$$ lower axis (left) and $$m^2(K K)$$ axis (right) . Up triangles are $$B^+$$, down are $$B^-$$

Hangout with CERN, anyone?

Seth Zenz
Tuesday, February 12th, 2013

I’m helping organize the ongoing Hangout with CERN series of events, and this Thursday I get to host. To make the event a success, I need your help! Interested? Read on…

Hangout with CERN happens each week at 17:00 CET, 11 AM EST, or whatever you want to call that time. It’s an informal Google+ hangout in which physicists, engineers, IT experts, and other folks from CERN connect to tell you about what we do here. In our latest format, we devote two weeks to each topic. The first week introduces the topic and lets you hear experts describe their work, along with a quiz and a few questions from the public. (We monitor comments on Twitter and YouTube the whole time.) The second week – which is the part I work on – is even more informal: we try to have a few guest members of the public, get to more questions, and so on.

Here’s last week’s video, entitled “LHC and the Grid – The world is our calculator,” which discusses the worldwide computing system we use to analyze all the data from the LHC:

Next week’s event on Google+ is here. We’ll be discussing the same topic, and we want to hear your questions about it. Do you have a question? Might you want to participate live in the hangout and ask your question directly? Let me know in the comments!

A Change of Pace

Seth Zenz
Monday, February 4th, 2013

Some physicists and engineers from Purdue and DESY, and me, at the beamline we used to test new pixel designs

Every so often, a physicist needs a vacation from doing data analysis for the Higgs boson search. A working vacation, something that gets you a little closer to the actual detector you work on. So last week, I was at the DESY laboratory in Hamburg, Germany, helping a group of physicists and engineers study possible changes to the design of individual pixels in the CMS Pixel Detector. (I’ve written before about how a pixel detector works.) We were at DESY because they had an electron beam we could use, and we wanted to study how the new designs performed with actual particles passing through them. Of course, the new designs can’t be produced in large scale for a few years — but we do plan to run CMS for many, many years to come, and eventually we will need to upgrade and replace its pixel detector.

What do you actually do at a testbeam? You sit there as close to 24 hours a day as you can — in shifts, of course. You take data. You change which new design is in the beam, or you change the angle, or you change the conditions under which it’s running. Then you take more data. And you repeat for the entire week.

So do any of the new designs work better? We don’t know yet. It’s my job to install the software to analyze the data we took, and to help study the results, and I haven’t finished yet. And yes, even “working on the detector” involves analyzing data — so maybe it wasn’t so much of a vacation after all!

Higgs to light video comes to light

Ken Bloom
Thursday, January 31st, 2013

Just a quick note here on something that isn’t really mine: CMS has now released some video footage from the internal meetings where the results of the search for a Higgs particle decaying to a pair of photons (light) were first presented to the collaboration. I think it’s pretty interesting to watch this little bit of science history.

Here is the context: the Higgs searches were done “blind”, in that every little bit of the analysis was done without examining the actual detector data sample where the Higgs might be observed. Using simulations and data samples that are similar to, but not actually, the data in question are used to design the Higgs search, to understand what the experimental uncertainties are, and to give an expectation of what would be seen in the data if there were a Higgs (or not). Everyone avoids looking at the key data samples to avoid biasing the search based on what is seen. (The fear is that if you see a small signal, you might start to make changes in the analysis to enhance the signal…which could turn out to be a statistical fluctuation in the end.)

Then, in the late stages of the data analysis, we finally take a look at the “signal” sample. Of course, someone has to be the first person to do this, which means that for a brief moment, that’s the only person in the world who knows a new scientific fact. And then there is a lot of suspense for everyone else! In the video, someone who was among the first to see the result, just hours beforehand, is presenting it to the rest of the collaboration. You can certainly see how excited the presenters are about that moment.

I suppose there isn’t any suspense now, since we know what the answer is, but try to put yourself in the mindset of the audience in the room…and enjoy!

Tweeting the Higgs

Aidan Randle-Conde
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)

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.

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.