Quantum Diaries

Aidan Randle-Conde | USLHC | USA

This week the Earth has seen some increased magnetic activity in the upper atmosphere, and that means we got to see aurore! Across Northern Europe and the Northern USA people looked to the skies to see the northern lights. An aurora is one of the most beautiful sights in the natural world, and a phenomenon that actually tells us a lot about the Earth and how it interacts with its environment.

Those who followed me on Twitter (@aidanatcern) may have already seen some of the wonderful images of aurorae. There are dedicated webcams that capture the night sky, and you can see some sample images at the Aurora Webcam archive.

Aurora over Alaska (wikimedia)

When charged particles accelerate or decelerate, or recombine in pairs, they emit electromagnetic radiation, and it is this radiation that we see in the aurora. The color of the light depends on the wavelength of the radiation, and the intensity of the light depends on how much radiation is emitted. That means that there is always an aurora above us, but if the energy of the radiation is too low, or the intensity is too weak, we won’t see anything. Once we know how to interpret the light we can learn something about the radiation that is emitted. Usually we see a variety of colors in an aurora and each color corresponds to a different wavelength, so if we can see a region of the sky that is all one color, we know that the wavelength (and hence the energy, ignoring the effects of aberration) must be the same. That means we can “map” the sky and find contours of wavelength.

Since the particles are accelerating, there must be something that causes the acceleration. The Earth’s core is made of (among other materials) molten iron. The rotation of the Earth means that this core is also rotating, and a rotating fluid magnetic medium creates a magnetic dipole, giving the Earth magnetic North and South poles. These poles are aligned near the geographic North and South poles of the Earth, but not exactly. (In fact, magnetic North and South keep moving and from time to time they even swap places. The exact mechanism behind this is not yet fully understood, but geological records show it happens every few hundred thousand years. Simulations suggest that the rotating magnetic fluid is a chaotic system, so the reversals occur at stochastic, or random, intervals of time.)

The sun produces a stream of particles, known as the solar wind, and they create their own electromagnetic field. The two fields, from the Earth and the sun, interact and they force charged particles in the upper atmosphere along curved paths. As the particles move along these paths they accelerate, decelerate and recombine, and that is what produces the aurorae. The most recent increase in magnetic activity can be traced back to a huge coronal mass ejection that arrived from the sun. This video shows the arrival of the flare:

The effect looks impressive, but don’t be scared, solar winds like this are perfectly harmless. Far bigger winds have hit the Earth in the past few billions years and life has continued to flourish in spite of them. Life has adapted to the Earth’s magnetic field and this field protects us from the high energy particles.

It turns out that while looking up at the night sky is a beautiful and moving experience in itself, it is also important to particle physicists. Some of the most important discoveries in the last century came from a different phenomena, cosmic rays. Cosmic rays are very high energy particles (usually protons) that travel huge interstellar distances and rain down on the Earth in much the same way that the solar wind does. They interact with the upper atmosphere to create cascades of particles, and usually the muons are the only detectable particles that reach sea level. Interactions of these cosmic rays gave rise to the discovery of the muon (“Who ordered that?!”), the pion and the kaon, the lightest forms of mesonic matter. It was around this time that large scale accelerators were developed, and we found hundreds of new mesons and baryons. Cosmic rays gave us a very small glimpse into a rich “zoo” of particles that has occupied physicists ever since.

Eventually, when we have exhausted our ability to accelerate particles to higher energies we might need to rely on cosmic rays again. There are proposals to develop ground based detectors to study the interactions of extremely high energy particles from outer space. Those particles have the potential to reach energy regimes we can only dream of at the moment. (Incidentally, this is one of the ways that we know for sure that the LHC cannot destroy the world. The universe creates much more energetic particles than we could ever hope to create in our accelerators, and since the universe seems to be in one piece we can conclude that the LHC is safe on Earth!)

An aurora from above (Expedition 28 on board the International Space Station)

If you’re fortunate enough to see an aurora then take a few moments to think about the huge forces at work, the vast distances involved, and how the colors tell us so much about how the Earth and solar wind behave. It really is one of the most beautiful phenomena in the universe.

Tags: aurora, Nature, science
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Getting layed

Friday, January 20th, 2012

On a past blog post I came across the most wonderful comment from Kelly, one of our readers:

Lay people are far smarter than it is supposed, they are also fickle and quick to get bored or offended if talked down to

This got me thinking about the last time I spoke to an expert in another field about their research, about the last time I got “layed”, if you’ll excuse the awful pun. I also hope you’ll excuse an excursion into biochemistry for one post.

Alex and Kia, relaxing in the sun

I was in Manchester for the weekend, spending the evening with Alex and Kia, a couple of friends from undergraduate and we had a lot of catching up to do! They’re both biochemistry graduate students and they work in the same lab, although in different areas. We stayed up all night over tea and biscuits (how British), discussing our research, using analogies, looking at diagrams, and coming up with all sorts of thought experiments to try to understand what was happening. They had a lot of questions about how the detector works, how we reconstruct particles (including the Higgs!) and why it takes so long to find it.

Having a discussion about something technical with an expert is not only lots of fun, but it also tells you a lot about your own skills when it comes to explaining concepts. As Kelly mentioned in her comment, there’s a temptation to talk down to people, but I find it’s more rewarding for all involved if we match our discussion to the intelligence of the audience. I’d like to think that most people who read Quantum Diaries and US LHC Blogs are here because they’re intelligent, they’re not scared of nuance, they want to read more than what a press release will tell them, and they may even be a scientist too. Once we find the right level of discussion for a given audience things get much more rewarding!

From the outside biochemistry is such a wonderful field of research. Their work is instantly relevant to the fight against disease and cancer, the field is expanding so rapidly that what students learn one year may be out of date a couple of years later, and there’s no end to the range of different topics you can research. It’s about as fast paced as you can get! It must have its frustrations, like any area of research, but being a layperson I got a chance to appreciate the concepts without the hard work, and that made it sound amazing.

The watered down version of what they told me went something like this:

HIV and T cells

What HIV looks like (Telegraph)

The HIV virus is extremely dangerous for one reason- it infects the white blood cells (T cells) that fight disease in the body. This in itself isn’t a huge problem, but when a person with HIV have some infection then things become very serious. It’s not so much that the white blood cells don’t function anymore, it’s more that they use so many of their resources building more copies of the virus. The virus attaches itself via a protein, and a small percentage of the population have a different form of the protein, which has a different shape. In principle, if a person could get a complete blood transfusion then they could be given the white blood cells with the other protein and may become immune to HIV. An easier way to do this would be to have a bone marrow transplant from another person, as the bone marrow creates the white blood cells. Naturally there are dangers associated with any procedure like this, so it’s not something to be taken lightly. Still, in the course of an hour or so my friends gave me a wonderful insight into how HIV works and some of the discoveries in the fight against the disease.

Genetic diseases

While on the topic of diseases with risky treatments we also discussed a family of genetic diseases (known as mucopolysaccharide diseases, a name I could not remember) which cause premature aging or degradation of the body. The diseases are associated with the failure of the body to break down certain sugars, so the cells get clogged up, do not function as well and then part of the body ages. The exact type of disease manifests in different ways, and sometimes they can only be identified once the disease has progressed. So I asked why children aren’t just screened for this at birth, as they are for many other diseases. It turns out that the cost of the test isn’t low enough and rate of incidence of the disease isn’t high enough for that to become a realistic option yet. Putting groundbreaking, life saving research in that kind of context is rather chilling. I’m glad physicists don’t have to deal with those kinds of choices!

Kia was kind enough to link to one of the charities, so I could find out more about the disease and how it affects us: The MPS Society.

The immune system

But we weren’t done yet! We also talked about the immune system and cancer. Having heard so much about T cells, I was curious about where they came from and why they only attacked foreign objects in the body. It turns out that T cells spend much of their time in the thymus where they are trained to learn what cells in the body look like. When the T cells are produced there is some shuffling of genes and each T cell ends up a little different. If a T cell latches onto part of the thymus it gets destroyed and isn’t allowed into the rest of the body. Otherwise the T cell is let out into the bloodstream. If it finds a cell it “thinks” is attractive, it latches on and releases chemicals into the blood stream. Other T cells respond to the chemical gradient and they too latch on. After a short while the foreign body is overwhelmed and dies.

A red blood cell, a platelet and a T-cell, side by side (Wikipedia)

Well that’s how it works in principle, and there are many ways in which it can go wrong. Some viruses are adept at mutating so that their appearance changes. (On the subject of mutations, my friends also treated me to a discussion of “frame shifts” and how you can get two proteins from one gene!) If one of these viruses gets identified and overwhelmed, one copy may mutate into another form, and the T cells are back to square one again. Another “nightmare scenario” is when a cancerous growth releases a different kind of chemical which essentially says “All fine over here! Carry on!” to the T cells. If that happens then things can go quite seriously wrong quite quickly. If all that wasn’t complicated enough, T cells can also get “confused” and latch on cells from their host body, giving rise to auto immune diseases. The immune system is so amazingly intricate that you could easily spend a whole evening just scratching the surface of the subject. At the same time it also seems immensely fragile and wonderfully robust. Although the apparatus for making an immune system is inherited, the good work it does fighting disease isn’t. If those ideas doesn’t blow your mind then I don’t know what will!

The PhD problem

To round off the evening we also discussed how our PhDs had progressed. Biochemistry seems less forgiving than physics, and they told me that between them and two other mutual friends, two of them had to find new topics, new funding and new institutions. Sometimes, when a research idea doesn’t work out and the funding disappears, even if it’s through no fault of the student, the student has no choice but to start again. I faced a similar situation with my own PhD, as funding for the experiment was cut short and I suddenly found myself with 18 months left, no research topic and no service task. My colleagues rallied round, asked questions, contacted people and helped me find a new topic and a new service task on the same experiment. I finished about 9 months later than expected (but still within four years!) with a decent thesis and some glowing letters of recommendation. Once again, I was glad to be in the cozy realm of physics! It’s differences like these that aren’t at all obvious, and make us realize just how much we have to learn from each other. (My friends were also amazed to find I had about a hundred papers with my name on!)

PhDs are elastic... (PhD Comics)

When did you last get layed?

So for a few hours I was a layperson with two experts at my disposal, and it was one of the most entertaining evenings I’ve had in a long time. So to the lay people reading this blog, if you don’t find the term “layperson” pejorative, it would be great to hear about your experiences. What discussions particularly excited you? How you deal with being patronized or, perhaps worse, overwhelmed with ideas? Or for that matter, if you’re an expert in another area, what are your experiences telling other people about your work? In short, tell us happened last time you got “layed”.

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A new year, a new outlook

Saturday, December 31st, 2011

2011 has been a year of change and excitement. We’ve had plenty of good news and bad news to deal with. The new year doesn’t mean just another calendar on the wall, it means a new way of looking at physics. There’s no better way to bring in the new year than watching the fireworks in central London, surrounded by friends. There’s usually a fantastic display, because London is not only one of the most important cities in the world, but it’s also home of universal time. With the Greenwich Meridian running through the capital, we’re reminded of the role that timekeeping has played in the development our history and our science. But this year was even more special, since London is literally inviting the world to its streets this year for the Olympics. So I got caught up in the excitement of it all my thoughts turned to what we’ve seen in the world of physics, and where we’re going next.

New year fireworks in London (New York Times)

2011 got off to a start with ATLAS announcing a startling asymmetry in the jet momenta in heavy ion collisions. However, the joy was tainted by a leaked abstract from an internal document. That document never made it through internal review and should never have been made public. We were faced with several issues of confidentiality, ethics and biases, and how having several thousand people, all armed with the internet and with friends on competing experiments makes the work tough for all of us. In the end we followed the right course, subjected all the analyses to the rigors of internal and external review, and presented some wonderful papers.

There was more gossip over the CDF dijet anomaly presented at Blois. CDF saw a bump, and D0 didn’t. Before jumping to any conclusions it’s important to remember why we have two experiments at Tevatron in the first place! These kinds of double checks are exactly what we need and they represent the high standard of scientific research that we expect and demand. The big news for Tevatron was, of course, the end of running. We’re all sad that the shutdown had to happen and grateful for such a long, productive run, but lets look to the future in the intensity frontier.

Meanwhile both ATLAS and CMS closed in on the Higgs boson, excluding the vast majority of the allowed regions. The combinations and results just got better and better, until eventually on December 13th we saw the result of 5fb^-1 from each experiment. The world watched as the presentations were made and quite a few people were left feeling a little deflated. But that’s not the message we should take away. If the Higgs boson is there (and it probably is) then we’ll see by the end of the year. There’s no more of saying “Probably within a year, if we’re lucky”, or “Let’s not get ahead of ourselves”. This time we can be confident that this time next year we’ll have uncovered every reasonable stone. The strategies will change and we narrow the search. We may have new energies to explore, and we’ll tweak our analyses to get more discriminating power from the data. Now is the time to get excited! The game has changed and the end is definitely in sight.

Raise a glass as we say farewell to a great year of physics, and welcome another

It’s been a good year for heavy flavor physics as well. LHCb has gone from strength to strength, probing deeper and deeper into the data. We’ve seen the first new particle at the LHC, a state of bottomonium. Precision measurements of heavy flavor physics give some of the most sensitive tests of new physics models, and it’s easy to forget the vital role they play in discover.

ALICE has been busy exploring different questions about our origins, and they’ve studied the quark gluon plasma in great detail. The findings have told us that the plasma acts like a fluid, while showing unexpected suppression of excited bottomonium states. With even more data from 2011 being crunched we can expect even more from ALICE in 2012.

The result that came completely out of left field was the faster than light neutrinos from OPERA. After seeing neutrinos break the cosmic speed limit, OPERA repeated the measurements with finer proton bursts and got the same result. Something interesting is definitely happening with that result. Either it’s a subtle mistake that has eluded all the OPERA physicists and their colleagues across the world, or our worldview is about to be overturned. I don’t think we’ll get the answers in the immediate future, so let’s keep an eye out for results from MINOS and OPERA.

Finally it’s been an incredible year for public involvement. It’s been a pleasure to have such a responsive audience and to see how many people all across the world have been watching CERN and the LHC. A couple of years ago I would not have thought that the LHC and Higgs boson would get so much attention, and it’s been a of huge benefit to everyone. The discoveries we share with the world are not only captivating us all, they’re also inspiring the next generation of physicists. We need a constant supply of fresh ideas and new students to keep the cutting edge research going. If we can reach out to teenagers in schools and inspire some of them to choose careers in science then we’ll continue to answer the most fascinating, far reaching and beautiful questions about our origins.

So when you a raise a glass to the new year, don’t forget that we’ve had an incredible 2011 for physics, and that 2012 is going to deliver even more. We don’t even know what’s out there, but it’s going to be amazing. To physics!

Tags: ALICE, ATLAS, CERN, CMS, Intensity Frontier, LHC, LHCb, Tevatron
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Higgs seminar discussion

Tuesday, December 13th, 2011

Shortly after the Higgs Seminar, Seth Zenz and I had a short, impromptu discussion about the results and what they mean for physics in the near future. Check out the video:

(Due to a technical problem, we lost the first two seconds of audio, so there is a slightly abrupt start.)

Tags: ATLAS, CERN, CMS, Higgs, LHC, seminar, video
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Higgs Liveblog

Tuesday, December 13th, 2011

Seminar / Webcast / My Twitter

Slides available

Go to the Seminar page for the slides that there presented today.

The liveblog

(For details about the seminar, see below. Some links to photos on the twitter feed.)

The most recent updates are at the top of the page. All times are CERN times.

More updates will be posted as they arrive. Thanks for reading!

Questions

15:49: Rolf says “No more questions, so final remarks”. Great to have first results, remember they are preliminary and with small numbers. “Keep in mind we’re also running next year.” “The window is getting smaller and smaller, but it’s still alive!” “Stayed tuned for next year”.

(G) means that Guido answered, (F) means that Fabiola answered. Thanks to Rozmin Daya for providing more detailed transcripts of the questions and answers. (Questions are ordered so that the most recent question is at the top of the post.)

Q: Regarding the crystal calorimeter, by how much has this improved your endcap H->gamma gamma mass resolution? Did I understand that you understand the scale to 0.1%?
A(G): No. for the scale, if you take a look at the plot on slide 33, this rms is what you’re able to acheive. In the endcap there’s a lot of progress, the scale does not evolve in big jumps. We have lots of room to improve. Up to now we were limited by this phenomena related to transparencies. Our tracker is fantastic but introduces extra material. Have to understand material and conversions more. We did this for barrel but must do more aggresively for barrel.

Q: For ATLAS, you have exclusion at 115.5 GeV. Is there a way to have some kind of Look Elsewhere effect for negative fluctuations? For CMS, you have excess everywhere between 115-135 GeV. Can it be that you’re simply misunderstimating background?
A(G): it could be, but we should be really precise. I cannot exclude but I’ll give small probability to this. Atlas: as far as I know we don’t have a LEE for this exclusion, but it’s an exclusion at the 95% confidence level.

Q: In the 4l final state analysis, how much would you lose if we count only 2/3 events (to ATLAS)
A(F): It would go down to 1.5sigma to 1.6sigma
Note: This question was motivated by fact that now there is discrepancy between ATLAS and CMS that wasn’t there at HCP time.

Q: What is the ultimate scale energy energy scale precision in the gamma gamma, because you were showing 0.5GeV from the Z.
A(F): Uncertainty on photon energy scale is more. It’s a few parts per million on the Z peak, but it’s below 1%. When we transfer to the photon, we have to take into account that we use the Monte Carlo simulation. We vary the material in the simulation, and we end up with a few parts per million to 1%.

Q: it’s interesting to understand what are the signal resolution for the few events in the 4 lepton final state.
A(F): The mass resolution is typically about 1.9 GeV for muons, and 1.7GeV for electrons.

Q: Question for CMS. Did you try to extract the 90% exclusion limit for gamma gamma? It’s a bit close to the ATLAS excess. Don’t understand the strategy for W->lnulnu.
A(G): We use continuous approach: cut based, and then the invariant mass of two leptons in a boosted decision tree.

Q: I’d like to understand looking at gam gam fit and the use of exponenetials to describe the background. Choice in CMS was not to do that. How confident are you to do that, knowing that QCD bg not well modeled by exponential?
A(F): You’ll find the slide in the spares. We tried several functions. We tried using background coming from Monte Carlo simulation, and also adopted a conservative estimation on background by taking as background uncertainty in a bin of 4GeV the difference between exponential and the expectation from Monte Carlo generator. We get consistent results using other functions.

Talks

15:36: Finish and applause. Rolf gives overview and opens up the floor to questions.

15:34: Two excesses at 119.5GeV and 124GeV. Both excesses seem compatible with a Standard Model Higgs. 95% confident limits include 127-600GeV. Some excess is present in all 5 channels. Statistical significance of 2.6sigma locally and 1.9sigma with Look Elsewhere Effect taken into account.

15:30: Modes split by resolution. Low and high resolution channels agree that something is happening around 125GeV. Maximum local significance is 2.6sigma. With look elsewhere effect it’s 1.9sigma in low mass region. Expect 2-3 sigma effect in region 115-127GeV. Look for best fit of Higgs cross section, shows best agreement at 124GeV.

15:29: CMS more sensitive than Tevatron experiments combined! Expected exclusion is 117-543GeV, observed is 127-600GeV. What is stopping CMS getting lower limit? There’s some kind of bump there in the low mass region…

15:26: First glance at invariant mass plot. Exclusion plot looks like it shows excess at 125GeV, but deficiency at around 128GeV. Interesting, given what ATLAS saw!

15:25: H->gamma gamma analysis. Improvements in the vertex identification, energy resolution. Vertex finding efficiency gives roughly 80% or better in all data periods. Resolution measured using Z, W decays and pi0 decays. Laser signals used to correct for transparency measurements. A lot of work has gone into understanding these issues!

15:20: Putting limits using H->ZZ* mode, one of the most powerful modes. Expected to exclude the ranges 130-160GeV, 182-420GeV, observed exclusion in 134-156GeV, 180-395GeV and 340 460GeV.

15:19: H->ZZ*(llll) and H->gammagamma have excellent resolution. H->ZZ* is the “golden channel”. Expect 67 events, observer 72 events in full mass range. In the low mass region (mH<160GeV) CMS has observed 13 events, expected 9.5 events.

15:13: H->bb mode. Very challenging! Huge background from QCD processes. Look for associated production of a boson with the Higgs boson. Better sensitivity, but lower efficiency. Require a very boosted W or Z produced in association. (pT of 100-160GeV) 5 sub channels of H->bb with associated production.

15:12: H->tautau mode. Slight hints of excess. Limit plot shows gentle excess across the low mass region (110-150GeV) compared to expectation.

15:08: Using multivariate analyses for the H->WW* state. Cut and count analysis shows most backgrounds removed by a handful of cuts. (Standard Model WW production dominates to the end. Expected exclusion is 129-236GeV, observed is 132-238GeV. Then using a boosted decision tree, split samples into different topologies. Look for discrepancies in the BDT spectrum Expected exclusion is 127-270GeV, observed is 129,-270GeV. Looks like a small excess just below 127GeV!

15:06: Now onto H->WW* analysis. Large non-resonant background from Standard Model WW processes. Angle between leptons can be used as a discriminant. Leptons emitted in small angle, so invariant mass of leptons not very large (it's all about spins of boson!) MET can be used to discriminate against background.

15:03: Monte Carlo simulation plots shown for events. Topological constraints useful for removing background. H->ZZ(ll,qq) mode extended to low mass region. Study at high mass includes H->ZZ(ll,tautau). 10.2 expected background events, 10 observed, so not sensitive in this mode yet.

14:58: 8 independent decay channels modes shown in a big table, with their sensitivities. 4.6-4.7fb^-1 of luminosity used for each of the 5 main modes (H->gamma gamma, ZZ*, WW*, tautau, bb) Resolution is 1-3% for gamma gamma and ZZ* final states. All 8 analyses made it to preliminary results to be shown today.

14:56: More than 90% data taking efficiency in each mode, and 91% overall. Impressive! Analysis requires good understanding of backgrounds and object reconstruction. Good agreement with data for identification efficiencies up to hundreds of GeV. Standard Model cross section plot shown. CMS agrees with data across all the processes, with a slight deficiency in ZZ production.

14:50: Guide starts, outlining the CMS collaboration and the detector. Overview of the Standard Model Higgs boson. Showing results up to 600GeV. Different production modes give different sensitivity.

14:52: Flashback to slides from a year ago, showing expectations. Expected sensitivity down to Standard Model across the whole range when combining channels. Projected significance decreases sharply in the low mass range. Sensitivity will come from combining channels.

14:48: Finish and applause! Guido takes the microphone. And goes through Fabiola's slides by mistake!

14:45 With current data set ATLAS has excluded 112.7-115.5GeV and 131-453GeV (except for 237-251GeV) ATLAS is now competing with LEP's low mass results! There is a large deviation in p0-values at 126GeV. 1.9e-4, or an excess of 3.6sigma (gamma gamma 2.8 has sigma, ZZ* has 2.1, WW* has 1.4sigma)

Updating all other analyses for full data set. We need more data in 2012 in order to confirm if this is the Higgs. 126GeV is a nice mass for the Higgs- it can be probed with lots of modes (gamma gamma, ZZ*, WW*, bb, tautau).

14:40: Apologies, connectivity issues.

Now discussing H->ZZ* analysis. Statistics limited background studies for SM ZZ processes. Electron identification efficiency comes from J/psi, W and Z decays. Covers wide range of transvere energy (up to 50GeV). Monte Carlo simulation tracks particle identification well as pileup increases- we understand the detector very well. Isolated muons selected, isolation performance looks impressive, even as pileup increases.

Simultation gives mass resolution of about 2GeV, 85% of signal falls within two standard deviations of mass point. 71 events seen in the full range, expected background is 62 events. In the low mass region (gamma gamma at 126GeV is 2.8sigma! If it's due to background only, it's a very large fluctuation. There are nine categories of photon, with the background modeled with an exponential function, and Crystal ball+Gaussian for signal. Excess shown at 126GeV

14:27: Discussion of the angle measurement. Need to know position performance in the calorimeter. Resolution of position of primary vertex is ~1.5cm. Potentially large background from jets and hadrons. The faking is rare, but the rate of production of jets is orders of magnitude larger than the rate of Higgs boson production.

14:26: Sensitive at lower energies. Different from previous channel, need good resolution of photon measurements. Irreducible background from Standard Model gamma gamma, also some fake gammas from jets. Mass resolution and positive robust against pileup. About 5GeV width in the invariant gamma gamma mass (in simulation, based on knowledge of detector.) Energy scale known to 0.5%, about 1% for linearity and uniformity. Z->ee mass shown, good performance there. Knowledge of how electrons interact inform energy scale for photons.

14:19: Discussion of Standard Model backgrounds for WW* channel. Turn on of ttbar background for this mode at Missing Energy (MET)>50GeV. MET strongly affected by pileup.

Expected background: 76 events, Data seen: 94 events, Expected signal :19 events. Cannot improve limit with this mode alone.

14:17: There are lots of backgrounds to consider! Concentrating on the gamma gamma, WW* and ZZ* modes. Backgrounds are jets, photons and W/Z bosons.

14:16: Huge efforts go into understanding the detector. As the regions of the Higgs search change, the requirements of the analyses change.

14:12: Outline of Higgs search motivation. The two photon sample is most sensitive at low mass ranges. Massive vector bosons sensitive at higher masses. Theorists have been working hard to update their expectations. The allowed region is small. We'll make it even more smaller today, and maybe see something very interesting in there as we do!

14:10: "The Standard Model works at 7TeV. Very Good." Good performance of Standard Model processes. We must understand these to understand the backgrounds, and also to calbirate measurements.

14:08: Discussion of pileup, the price we pay for high luminosity. We increase the number of events we record at once by having several interactions per beam crossing. A big challenge at working at the LHC, and a challenge we meet. Triggers are closely monitored to pick out the most interesting results.

14:06: Understanding of the search is "well advanced". Fabiola expresses thanks to the LHC team. Data taking efficiency is 93.5%. Good quality data fraction is greater than 90% for all analyses.

14:05: First two slides. Fabiola explains the importance and difficult of Higgs searches. The first slide shows plots from several different analyses with data and Monte Carlo simulation.

14:01: Rolf introducing Fabiola and Guido. Huge round of applause for all the experts and LHC team. Building up the moment with a great sense of community. In spite of the competition between ATLAS and CMS, we're here together to present and see the results together.

Before the talks

13:59: One minute to go. Both talks and both speakers ready.

13:54: Just spotted Guido Tonelli, the Spokesperson for CMS and the second speaker today! Both he and Fabiola are looking smart, and ready to give us the facts.

13:45: Fabiola's talk has been copied and it is ready for her. She taking a sip of water and chatting with Rolf and technical support.

13:41: Experts from the LHC are here too. They have worked very hard to make sure the machine works for us, and we've had fantastic running this year. We must not forget their role in this work!

13:40: Fabiola Gianotti, the ATLAS Spokesperson is here. She will give the first talk in about 20 minute's time. She's chatting to the Director General of CERN, Rolf Heuer. She's smiling, but if I was in her position I'd be quite nervous right now! She's taking off her coat, looking at the microphone and so on. She's given many talks before, so she knows what's she's doing. Still, it must be nerve-wracking for her!

13:32: The webcast is now available! http://webcast.web.cern.ch/webcast/

13:30: A “delegation” of very smartly dressed people are arriving in the front rows! They’re more smartly dressed than most physicists, and they have reserved seats, so they are probably management, dignitaries etc.

13:27: Of course big names from CMS are here as well, including Albert de Roeck, Jim Virdee, and Gigi Rolandi! (Being an ATLAS member, it’s easier to recognize other ATLAS members!)

13:22: ATLAS Higgs Group Conveners, including Bill Murray and Eilam Gross, arriving now. These are the people in charge of the various Higgs searches at ATLAS. Some of the analysts are here as well. Lots of big names arriving.

13:14: Some thoughts about the media, science, and what we can expect to see today. The physicist sitting next to me asked about my blog and twitter feed, and we started discussing how pressure from the media can affect what scientists do. While it’s true that we love the media to be informed, we don’t change our results or interpretation based on public opinion. The results we see today are going to be exciting, but we need to be careful and do a proper job. If it’s not 5σ yet, it’s not a discovery yet. We’ve been searching for the Higgs boson for decades, so we want to get it right and we don’t want to sacrifice our standards for the sake of getting in a few months early. If we see the Higgs in the summer (and we probably will, if the rumors are to be believed) it will be the most important discovery in high energy physics since the W was discovered in 1983!

(If we don’t see the Higgs, that will also be an important observation, as it will tell us there is something else out there . Convincing bumps have been known to disappear when we add more data.)

12:53: The projector is being tested. As soon as the webcast is available I’ll update to let you know.

12:51: Katie snapped a photo of me and Pauline! It’s on yfrog.

12:28: I’ve just heard that the security staff at the door are no longer allowing more people to enter.

12:27: This seminar is one that should not be missed. Looking through the audience I’m glad to see most of my closest colleagues have found somewhere to sit, including @marktibbetts, Matt, Tina, Rozmin, Catrin and Sudan. We are normal physicists, fighting for whatever seats we can get. The first three rows have been reserved for special guests, representatives etc. There are people sitting on all the stairs. We’ve all heard the rumors. None of us has heard the official results form both experiments yet.

11:57: There are lot of people from the blogging community here, including Pauline Gagnon (to my right), Anna Phan (to my left) and Seth Zenz (in front of me)! You can follow Seth’s tweets, @sethzenz

11:42: Seating is at a premium, I just someone bring their own chair in!

11:31: I’ve been here for an hour now, and the auditorium is nearly full. There are roughly 10 seats left (none of them have desks, or power supplies.) Nearly everyone here has their laptop with them, it’s like a commercial for Apple! Staff are checking IDs at the door. There is a lot of chatter here.

Details about the seminar

Today sees CERN’s seminar on the update of the Higgs search. I’ll be updating this page as the information comes in. Refresh this page to get the updates! The most important points will be also be tweeted.

Time

The seminar will begin at 14:00 CERN time. (08:00 East Coast, 05:00 Pacific)

There will be a talk from the ATLAS spokesperson 14:00-14:40 giving updates on the ATLAS search, and then a talk from the CMS spokesperson 14:40-15:20. There will then be questions and answers to both speakers until 16:00.

Links

Here are the links to:
Seminar page

Webcast video

Follow the updates on twitter using the hashtag #higgsliveblog (my account there is @aidanatcern.)

The seminar page also has a chat room!

Shortlink for this page: http://bit.ly/u0wALv

Shortlink for the seminar page: http://bit.ly/s5X4Zm

Shortlink for the webcast: http://bit.ly/q2QB

Connectivity

We’re expecting a lot of internet traffic at CERN today, so there is a small possibility the network may get jammed for a few seconds from time to time. Thank you to Kevin for allowing caching of this page so that it can still be accessible in case of any problems.

Please report any errors in the transcript of this blog post in the comments.

Aidan Randle-Conde

Tags: CERN, Higgs, liveblog, seminar
Posted in Latest Posts | 19 Comments »

CERN Higgs seminar liveblog!

Wednesday, December 7th, 2011

Follow the liveblog here!

On Tuesday December 13th, there will be a seminar at CERN about the search for the Higgs boson using the 2011 dataset.

Physicists at ATLAS and CMS have been working very hard all year (and are still working) to show the results for 5fb^-1 each. This means that we will have 5 times the amount of data available since the last update, and we can expect the exclusion of the Higgs to be even more impressive than what we saw in the summer.

Watch the video on youtube!

Since this an important milestone in the search for the Higgs boson, I will be liveblogging the event, from the main auditorium here at CERN. There will be a webcast available for those of us not at CERN. (The webcast details will appear on the seminar page on the day of the seminar.) So please join me on Tuesday, watch the webcast and follow the liveblog for minute by minute updates of the search for the Higgs boson.

If you want to know more about the Higgs boson I’d recommend you look at Flip’s recent post.

Check out the link to the Seminar page.

Follow the updates with the Twitter hashtag #higgsliveblog.

Tags: ATLAS, CERN, CMS, Higgs, LHC
Posted in Latest Posts | 14 Comments »

Change of state

Friday, November 25th, 2011

A few weeks ago I bumped into one my group’s former students, Rozmin. She’s still jetlagged from her journey here and she had the look on her face that told me she’d been through the change of state. She’d transitioned from a grad student to a postdoc. The metamorphosis is not an easy one, and in fact no matter how much time you spend preparing for it, and how long it takes, there are always some surprises.

A while back she was still editing her thesis. Today she is finding her feet in a new role, one with more responsibilities, more challenges and fewer safety nets. From now on, students will look to her for help, and expect to get answers. I should point out that grad students do a great deal of the work here at ATLAS, and they answer a lot of the questions we have, and perform a lot of the studies that we need. But they’re here primarily to learn, the postdocs are primarily here to work, and at the back of our minds we have prejudices about our roles. As a postdoc I feel that I should be mentoring students and helping them, rather than having them help me, even though I spent most of my first year here playing catch up with students who knew the experiment inside out. As a student on BaBar, what mattered most was getting the thesis written, and I felt that it was okay to make mistakes, ask for help and tell people I didn’t really know what I was doing.

Becoming a postdoc

The difference between being a student and a postdoc is mostly cosmetic, and a lot of the time it’s hard to tell whether someone has graduated yet. The real difference is one of attitude. When Rozmin was a student she was impressed that I seemed to know a little bit about every part of particle physics, especially the history. She would ask me how I knew about the history of CP violation and the tau-theta puzzle, and I’d reply knowingly “It’s a postdoc thing.” “Like a special power?” “Yeah, postdoc power!” Of course at that point she knew it was a bit of an act. I knew little more than she did, but I said it with confidence, and that inspires confidence in others. I’ve had quite a few roles where I had to put on an act of confidence like that. One of my favorite examples was when I worked for a telephone helpline where there was a locked desk drawer full of secret help for the coordinators. When I finally saw what was inside I was surprised to find nothing but a bottle of gin, some chocolate, and an electric drill. I asked what the drill was for and they replied “To stop volunteers messing around with it.” Huh. It looks like sometimes we need to be told that the only source of reassurance is feigned confidence.

Sometimes this is all the help you get...

There’s no magic solution, no ancient wisdom and in research, everything is new. Once you realize that, and once you realize that everyone is out of their depth and everyone is working without a safety net, life becomes much easier. Then you can tell your grad students what they need to hear. “That’s an interesting question, let’s look it up online” means “I don’t know any more than you do”, “Let’s talk to Frank about this over coffee” means “I have no idea how to even get started on this problem, but I could use a break”, and “A similar study was tried at UA1″ means “I have a tiny amount of information about this from a long time ago, but at least that means it’s not completely new.” And so on. It’s takes a while to get used to. I even managed to get a taste of life as a Professor recently. When faced with a particularly challenging problem the head of our department told me simply “Welcome to the world of supervision!” In that world, the stakes are higher, the help is rarer and it takes even more courage to make decisions with so much uncertainty.

Naturally there are more changes than a slightly different day job. Rozmin has had to move house (to a different continent) again and settle down somewhere new. This is one of the most traumatizing experiences a person can go through, so doing it in French, when your husband is thousands of miles away and you’ve got a high pressure job (as well as your student’s high pressure job) taking up all your time, it can get even more tricky. The dynamic of our friendship has changed since she got back, as we spend more time together, going for a coffee or a drink, talking about our respective jobs and problems. The shift in our friendship has brought us closer and now we’re both free of our theses, and can focus on what we came here for, the physics.

It's all about the small achievements

It’s challenging, it’s scary, it’s all about the unknown and even the unknowable. But it’s like I always say: We don’t these things because they’re easy, we do them because they’re hard.

Happy Thanksgiving Weekend! Thanks to Jorg Cham for the comics. PHD Comics

Tags: postdoc life, science, transition
Posted in Latest Posts | 2 Comments »

In the shadow of Shiva

Thursday, November 10th, 2011

In front of one of CERN’s most imposing and industrious buildings stands a statue of Dancing Shiva. During the day it’s a beautiful reminder of the friendship between CERN and India, celebrating the cosmic ballet that surrounds us all. By night it casts an ominous shadow over building 40, where discoveries are made, decisions are taken, results are shared and gossip is spread. But what does Shiva represent to us?

Working in the shadow of Shiva

The Dancing Shiva represents the changes in the universe around us, as matter and energy constantly bump into each other, create and destroy systems and keep renewing the world. I suppose we can attach any meaning we like to this, the constant chatter of culture, the renewal of our population as people die and children and born, the violent cosmological events that keep reorganizing the universe. Any and all of these interpretations are beautiful, powerful and majestic, but for me there is one interpretation which excites me more than any other and holds a very deep truth in it. This cosmic dance is the interaction of matter and antimatter.

Whenever we create new particles we create them in matter-antimatter pairs. They are literally equal and opposite components that make up everything we see. When they meet, they destroy each other in a burst of energy. If that was all there was to matter and antimatter, it would make a rather beautiful cosmic ballet, but not an interesting one. The fascinating part of the story is when we remember that we have more matter than antimatter, which means that this particular cosmic ballet is unbalanced, and the statue is a constant reminder of this fact.

The universe knows something we don't. And it acts on cosmic scales.

We don’t know why nature prefers to matter to antimatter, and until we know why we can’t really claim to understand how the universe works. We know how one mechanism has a preference (the weak force interacting with quarks) but this is much too small to explain the whole story. Whenever collide protons together at the LHC we have to live with the fact that we’re colliding matter with more matter in a detector made of matter. The particles that escape are not quite half matter half antimatter, as we might like. After a while, all the particles (except the neutrinos) slow down, decay and hit some rock. They join the rest of the stuff around them and either annihilate or get comfortable and settle in with their surroundings. All we’re really doing is moving matter around in a very complicated way; nature balances the books and every piece of antimatter we created (except the antineutrinos) gets removed from this small part of the universe. The cosmic dance continues, and if we’re lucky we get a small glimpse into how it really works. On the tiny, insignificant scales we work on we don’t see much of an imbalance at all. When we look up to the stars we see matter everywhere we look, across vast distances and far back in time.

Nature’s balance sheet has a few implications for our physics. For example, every time we produce a Higgs boson, we also produce a lot of noise in the detectors as well. In a matter-antimatter collider (such as LEP or Tevatron) this is less of a problem, since the Higgs boson is neither matter nor antimatter, it’s equal amounts of both. To create a Higgs boson we would need to create at least one antiparticle, and that takes a lot of energy. With this extra particle we get a lot more particles “for free”, leading to all kinds of noise!

So in the light of day, when CERN is teeming with life Shiva seems playful, reminding us that the universe is constantly shaking things up, remaking itself and is never static. But by night, when we have more time to contemplate the deeper questions Shiva literally casts a long shadow over our work, a bit like the shadows on Plato’s cave. Shiva reminds me that we still don’t know the answer to one of the biggest questions presented by the universe, and that every time we collide the beams we must take the cosmic balance sheet into account.

It’s rare that we get a symbol that inspires both clarity and beauty. It’s almost poetic. Why does Shiva prefer to destroy antimatter more than matter? The more data we gather the better chance we have of finding the answer to that question. I don’t think we’ll ever stop wondering about this question. It’s the reason there’s something instead of something and antisomething. It’s the reason atoms exist and stars can form. And yet the answer is still out of our grasp.

Tags: CERN, science
Posted in Latest Posts | 6 Comments »

Happy Hallowe’en!

Monday, October 31st, 2011

Thanks to Steve for the inspiration and Rozmin for her help with editing! And, of course, to the LHC team.

Tags: heavy ion physics
Posted in Latest Posts | 1 Comment »

60ns? How about 60mn?

Saturday, October 29th, 2011

In a couple of hour’s time the clocks go back an hour in Geneva, as European daylight savings time ends. Usually this isn’t a big deal. We adjust our watches, the nights get darker earlier, and some of us turn up an hour early for work while the rest enjoy the extra hour of rest! But what happens in the Control Room? It’s not as trivial as you’d think…

The timing of the detector will be okay, as the passage of “normal” time is full of leap seconds and minor corrections here and there. Protons don’t care about that kind of thing, they just care about the amount of absolute time that has elapsed. But when humans get involved it gets more complicated, because we work with the time of day. Our plots show the hour along the x-axis for the past day or so. If we’re going to keep these plots online we’ve got to make a decision, either to double-count the results for that hour (ugh) or repeat the hour on the plots (and see some protons turn up 60 minutes earlier than expected!) It’ll be made even worse when people try to use the log books to recreate the events of the evening. They’ll see that some experts forgot to change their watches, and some didn’t. For those that did change their watches they’ll have 2am occur twice. Does this means we’ll have 2am(A) and 2am(B)? Will my replacement turn up at 6am or 7am? (I hope he turns up at 6am so I can send him to get some coffee while I sit through my extra hour!)

It’s tempting to write something like this in the electronic log book:
02:00: Some neutrinos arrive. Where did they come from?!
02:59: We have beams! We’ll be getting some data soon.
03:01: Wait a minute.

If only ATLAS could detect neutrinos…

Posted in Latest Posts | 2 Comments »

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