Posts Tagged ‘conference’

Summer Conference Coverage: Lepton Photon 2011

Monday, August 22nd, 2011

Brian Dorney

The summer conference season may be winding down, but that doesn’t mean we are quite done yet. Today was the first day of the Lepton Photon 2011 (LP2011) Conference; which is taking place in Mumbai, India all this week. The proceedings of LP2011 are available via webcast from CERN (although Mumbai is ~10 hours ahead if you are in the Eastern Standard Timezone). But if you’re a bit of a night owl and wish to participate in the excitement, then this is the link for the webcast.

The complete schedule for the conference can be found here.

But what was shown today? Today was a day of Higgs & QCD Physics. I’ll try to point out some of the highlights of the day in this post. So let’s get to it.

The Hunt for the Higgs

Today’s update on the CMS Collaboration’s search for the ever elusive Higgs boson made use of ~110-170 trillion proton-proton collisions (1.1-1.7 fb ^-1); covering eight separate decay channels and a Higgs mass range of 110-600 GeV. The specific channels studied and the corresponding amount of data used for each are shown in the table at left. Here l represents a charged lepton and v represents a neutrino.

The CMS Collaboration has not reported a significant excess of events in the 110-600 GeV range at LP2011. However, the exclusion limits for the Higgs boson mass range were updated from our previously reported values at EPS2011. By combining the results of the eight analyses mentioned above the CMS Collaboration produced the following plot summarizing the current state of Higgs exclusion (which I have taken from the Official CMS Press Release, Ref. 1; and CMS PAS HIG-11-022, Ref. 2. Please see the PAS for full analysis details):

: Standard Model Higgs boson combined confidence levels showing current exclusion regions, image courtesy of the CMS Collaboration (Ref 1 & 2).

But how do you interpret this plot? Rather than re-inventing the wheel, I suggest you take a quick look at Aidan‘s nice set of instructions in this post here.

Now then, from the above plot we can see that the Standard Model Higgs boson has been excluded at 95% confidence level (C.L.) in the ranges of 145-216, 226-288 and 310-400 GeV [1,2]. At a lower CL of 90%, the Collaboration has excluded the SM Higgs boson for a mass window of 144-440 GeV [1,2].

These limits shown at LP2011 improve the previous limits shown at EPS2011 (using 1.1 fb^-1). The previous exclusion limits were 149-206 and 300-440 GeV at 95% C.L., or 145-480 GeV at 90% C.L.

While the LP2011 results did not show a Higgs discovery, the CMS Collaboration is removing places for this elusive boson to hide.

QCD Physics

Today’s other talks focused on quantum chromodynamics (QCD). With the CMS Collaboration’s results shown for a variety of QCD related measurements.

One of the highlights of these results is the measurement of the inclusive jet production cross section. The measurement was made for a jet transverse momentum over a range of ~20-1100 GeV. The range in cross-section covers roughly ten orders of magnitude!

: Measurement of the inclusive jet cross-section made with the CMS Collaboration, here data are the black points, the theoretical prediction is given by the red line. Image courtesy of the CMS Collaboration (Ref. 3).

In this plot above each of the data series are “binned” by what is known as a jet’s rapidity (denoted by the letter y). Or in this case the absolute value of the jets rapidity. Rapidity is a measure of where a jet is located in space.

The CMS detector is a giant cylinder, with the collisions taking place in the center of the cylinder. If I bisect the detector at the center with a plane (perpendicular to the cylinder’s axis), objects with lower rapidities make a small angle with this plane. Whereas objects with higher rapidities make a large angle with this plane.

As we can see from the above plot, the theoretical prediction of QCD matches the experimental data rather well.

Another highlight of CMS Collaboration’s results shown at LP2011 is the measurement of di-jet production cross-section

: Measurement of the dijet production cross-section made with the CMS Collaboration. Again, data are the black points, the theoretical prediction is given by the red line. Image courtesy of the CMS Collaboration (Ref. 3).

Here the CMS results shown cover an invariant dijet mass of up to ~4 TeV, that’s over half the CoM collision energy! Again, the theory is in good agreement with the experimental data!

And the last highlight I’d like to show is the production cross section of isolated photons as recorded by the CMS Detector (this is a conference about leptons and photons after all!).

: Measurement of the isolated photon production cross-section made with the CMS Collaboration. Again, data are the black points, the theoretical prediction is given by the red line. Image courtesy of the CMS Collaboration (Ref. 3).

What happens in isolated photon production is a quark in one proton interacts with a gluon in the other proton. This interaction is mediated by a quark propogrator (which is a virtual quark). The outgoing particles are a quark and photon. Essentially this process is a joining of QCD and QED, an example of the Feynman Diagram for isolated photon production is shown below (with time running vertically):

From the above plot, the theoretical predictions for isolated photon production are, again, in good agreement with the experimental data!

These and other experimental tests of QCD shown at LP2011 (and other conferences) are illustrating that the theory is in good agreement with the data, even at the LHC’s unprecedented energy level. Some tweaks are still needed, but the theorists really deserve a round of applause.

But I encourage anyone with the time or interest to tune into the live webcast all this week! Perhaps I’ll be able to provide an update on the other talks/poster sessions in the coming days (If not check out the above links!).

Until Next Time,

-Brian

References

[1] CMS Collaboration, “New CMS Higgs Search Results for the Lepton Photon 2011 Conference,” http://cms.web.cern.ch/cms/News/2011/LP11/, August 22^nd 2011.

[2] CMS Collaboration, “Combination of Higgs Searches,” CMS Physics Analysis Summary, CMS-PAS-HIG-11-022, http://cdsweb.cern.ch/record/1376643/, August 22^nd 2011.

[3] James Pilcher, “QCD Results from Hadron Colliders,” Proceedings of the Lepton Photon 2011 Conference, http://www.ino.tifr.res.in/MaKaC/contributionDisplay.py?contribId=122&sessionId=7&confId=79, August 22^nd 2011.

Tags: CMS, conference, first results, Higgs, LP2011
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DPF 2011, tweet tweet!

Friday, August 5th, 2011

Ken Bloom

I know, I know, everyone has been focusing on the EPS and Lepton-Photon conferences (not to mention repeatedly putting in hyperlinks to their Web sites), but let’s not forget that the 2011 Meeting of the Division of Particles and Fields of the American Physical Society (DPF 2011, for short) starts this coming Tuesday. This will be the largest conference exclusively focused on particle physics in the United States this year, and it’s organized by the nation’s grass-roots membership organization of physicists, the APS. There are currently more than 450 people registered, so a large slice of the US particle-physics community will be there. This will be the fourth time that I’ve been to a DPF meeting, and I really do enjoy them — they are large enough to cover a broad range of topics, yet still small enough that you don’t get lost in the crowd.

For the first time ever, I find myself giving two presentations at the same conference — one on behalf of the CMS Collaboration (on the status of our distributed computing operation) and one on behalf of the D0 Collaboration at the Tevatron (on measurements of spin correlations in top-antitop production). On top of that, I’m also co-organizing a lunchtime panel discussion on “physics and the modern media.” What you are reading right now is a form of modern media, of course. We’re going to be talking with science journalists, communicators and bloggers about where communication about science is going…and what these sorts of people think of each other!

Since we’re going to talk about modern media, we figured that we should jump in with both feet, and that means Twitter. I must admit that I haven’t done much Twitter (although I do now have an account), but it seems to be all the rage. So, we’re encouraging Twitter users who will be attending the conference, and those who aren’t but want to keep up with what’s going on, to tweet away using the hash tag #DPF2011. If you are interested in the modern-media panel, feel free to tweet to us on Tuesday at 12:30 PM Eastern time; we’ll be keeping an eye on the feed and relaying interesting comments and questions to the panel.

More next week from fabulous Providence, Rhode Island!

Tags: conference, culture, DPF, publicity, Twitter
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DZero results hit the conference runway

Monday, April 4th, 2011

Fermilab

It’s been a very exciting winter conference season here at DZero, one of the two huge experiments at the Fermilab Tevatron Collider.

The massive size of the DZero detector is evident in comparison to the size of the man standing near the top of the image. Credit: Fermilab

What’s the winter conference season? We pretty much take data all the time, and we analyze the data and produce dozens of results every year. These analyses are ongoing, but there are two big events in the year where experiments here and at the Large Hadron Collider at CERN aim to roll out new results. That’s the winter and summer conferences. It’s kind of like when the fashion designers send their latest creations down the runway, hoping to turn as many heads as possible. These conferences are where we introduce to the world our latest and greatest insights about the nature of the universe.

The biggest winter conference is “Rencontres de Moriond” held in the Italian Alps, and it just completed two weeks ago. The big summer conference changes from year to year, and last year it was the International Conference on High Energy Physics, or ICHEP, in Paris. I was fortunate to give a talk for DZero at that one (yes, a perk of being a physicist is that every now and then you get to go somewhere nice).

A deluge of data:

As a scientist on DZero and head of the team that runs the data handling for many Fermilab experiments, things get busy in many ways when we gear up for the conference seasons. For example, physicists run computer programs to analyze the mountain of data that comes from the detector. The computers are always busy, but before the conferences they get super busy as people try to finish up their analyses. For those weeks we deliver around 200 terabytes of data per day! The amount of data in 200 terabytes is equivalent to watching a high-definition television station non-stop for 2 ½ years (that reminds me that my 5-year-old daughter needs to watch less TV)!! Our data-handling system is very robust and tends to run itself. But, this season the demand for data was so great that some future plans to make it more efficient had to get implemented very quickly. Fortunately, that all worked and now it’s ready for even greater demands that may be coming in the summer.

The Results:

A smattering of results from DZero for the 2011 winter conferences. Click on image to make it larger. Credit: DZero

I’m also a “subgroup” convener, which means I organize a small group of analyses and the people doing them. Probably the most exciting result being presented this winter is the Tevatron mass exclusion for the Higgs boson, which was written about previously in Quantum Diaries. But there are lots of other new results as well, including two from my subgroup.

One result is an updated result, which means we’ve analyzed more data, from an analysis that looks for collisions that produce two Z bosons (ZZ). These events are very, very, very rare. In fact in the Standard Model, the theory that describes sub-atomic particles, the Higgs is the next rarer process. Showing that we can find ZZ proves that we really understand our detector and our data. And, in fact, the result shows that we find ZZ at the level the Standard Model predicts.

The other analysis looks for events that have a W boson and a photon (the latter is a particle of light). We now see a few hundred of these events and have a clear picture of the “radiation amplitude zero”, which is an interesting effect predicted by the Standard Model that says that the W and photon fly off in some directions more often than others.

I mentioned I was lucky enough to give a talk at last year’s big summer conference. It was exciting to be in Paris, which is my favorite foreign city and where I’m reminded how much of my high school French I’ve forgotten. But it was also exciting because that was the conference where the new LHC experiments showed their first results.

This winter they had more results and joined us in comparing experiment with theory. While the LHC is just starting, as you may have heard, the Tevatron will wind down soon. But that doesn’t mean we’re done. We will have lots more data and lots more analyses, including possibly some new ones. The results from our final data set will be appearing at many summer and winter conferences to come!

– Adam Lyon

Tags: conference, D0, DZero, Energy Frontier
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ICHEP’s Biggest Day

Tuesday, July 27th, 2010

Seth Zenz

Yesterday was, I suppose, the biggest and most formal day here at the 35th International Conference of High Energy Physics. I wore my suit, and took some ribbing from some of my colleagues for dressing up so much, but I’ve worn it for far less excuse and am not sorry in the slightest. It’s not every day, or even every ICHEP, that one hears an address from the President of the French Republic!

Mr. Sarkozy’s speech was great to hear. He is a very emotive, enthusiastic, and informal speaker, which made him relatively easy to understand for those in the audience (like me) with limited French. He didn’t claim to know the details of our work, and seemed to think we’re all a little weird, but spoke mostly about the importance of fundamental questions about the universe and his support for basic research. This was very well received indeed. He also talked a bit about the contributions of the French labs to the LHC and other projects, which is fair: France plays one of the central roles at CERN, and the French particle physics community has made significant contributions throughout the field. This is reflected in the excellent and informative conference that they’re hosting here in Paris.

If there was one thing I would ask to be improved for the next ICHEP, however, I wish there had been a bit more food at the banquet! You can see the banquet, which was held in the National Natural History Museum, at right. It was a very impressive museum — the main hall reminds me of the ATLAS cavern, and seems to be just about the same size — and the food was certainly varied and interesting. But the lines were long to get even a little of it, and we had to go out to dinner afterwards to be full.

Yesterday was also the final talk on the combined Tevatron Higgs results. Fermilab sent out the press release while we were still on coffee break, so I saw the excluded mass range on Twitter before going into the talk. (I overcame the temptation to shout out the answer at the start.) It was still a very entertaining talk, and obviously the details of how the measurement was done were as important to see as the final numbers. Of course, we all wish there had been more to see than mass limits in the expected range and a few possible tantalizing hints. We also had talks from the CERN’s Director for Accelerators and Technology on the LHC and from the spokespeople of the LHC experiments. Although we haven’t seen anything really new at the LHC yet, it’s clear that the accelerator and experiments are all making great progress in getting ready to make the exciting discoveries that we’ll see at future conferences!

Tags: conference, Higgs, Tevatron
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My First Day at ICHEP

Friday, July 23rd, 2010

Seth Zenz

There are probably many blogs where you can read summaries of the ICHEP conference — or if not, there will be soon enough — so I’m going to limit myself to telling you about my day. Getting my poster printed and getting it to Paris in one piece was stressful, but uneventful in the end, and once I got to the conference things were easy. The poster session was the first evening, and you can see me at right standing in front of the thing, ready to explain what’s going on. (I will soon post more about the measurement shown in the poster, but here is the official ATLAS conference note, and here is an old summary of some of the concepts.) I didn’t get an overwhelming number of people asking questions — there were an awful lot of posters, which gave me a new perspective on how my work is one tiny facet of our overall effort to understand particle physics — but I did have a few good discussions with interested folks, and the psoter will be up all week.

As for the rest of the conference, I mostly went to the “early LHC experience” sessions, along with a few talks in the Standard Model session. I found the ATLAS and CMS measurments of the W and Z bosons interesting, but mostly because they show how the experiments are getting going. The theory of these particles is very well understood, and the experiments are consistent with it — in fact, if the experiments disagreed the theory at this point, we’d conclude that something had gone wrong with the experiments. When the detectors are solidly understood and working toward precision measurements, they may discover subtle differences from theoretical predictions in this area, but that will be years from now.

And now for another day of conference talks!

Tags: conference, track jets
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ICHEP: what to watch for

Wednesday, July 21st, 2010

Ken Bloom

At long last, the 35th International Conference on High Energy Physics begins tomorrow. It’s the largest particle-physics conference of the year, and the first major conference since the start of LHC operations at 7 TeV, If the US LHC blog has seemed to be a bit quiet lately, it might be because so many bloggers have been working hard to get results ready. Now, it’s highly unlikely that there will be any surprising LHC discoveries announced there; we just don’t have nearly enough data yet. But that doesn’t mean that this conference will be boring! Here are a few things that you might want to be watching for:

How well are the experiments keeping up with the LHC? The LHC has now delivered about 350 nb-1 of integrated luminosity to the experiments. What fraction of that data will the experiments show? This is a measure of the operational efficiency of the experiments, and of their ability to get the data through reconstruction and analysis. If the experiments are able to show a large fraction of the delivered data, then we can be optimistic about how quickly results will come out as the collision rates rise.
How competitive is the LHC with the Tevatron? The Tevatron experiments have collected a huge amount of data over the past nine years, and have an excellent understanding of how their detectors work. They will still be in the lead on many, many physics topics. (Disclaimer: I also work on one of the Tevatron experiments.) However, because of the LHC’s higher collision energy, there might be a few measurements for which the LHC can produce stronger results, even with a tiny amount of data. Will there be any such results, and what will they be?
How competitive is the Tevatron with the LHC? Everyone is eager to hear the latest limits on the standard-model Higgs boson from the Tevatron. The excluded Higgs masses are the ones that would have been the easiest for the LHC to see too. How much harder will new Higgs limits make it to find a Higgs at the LHC?
Any surprises from elsewhere? Let’s not forget that this conference covers all of particle physics, and there’s a lot more going on out there than just the LHC!
How tired do the presenters look? A lot of that 350 nb-1 came at the last minute — did everyone stay up all night to finish their data analysis?

I won’t be attending the conference, but I’ll try to provide some commentary from lovely Lincoln as events unfold. Good luck to all involved — this is going to be a lot of fun!

Tags: conference, first results, ICHEP, LHC, Tevatron
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Almost There

Monday, July 19th, 2010

Seth Zenz

The official ATLAS conference note describing the analysis I worked on was approved on Saturday morning. My poster was finalized, approved, and printed — possibly not in that order — just in the past few hours. Now the only challenge left is to get myself and my poster through a French air traffic controllers’ strike and to the Palais de Congrès by Thursday morning.

Tags: collaboration, conference, travel
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Track Jets for ICHEP

Friday, July 9th, 2010

Seth Zenz

Along with many other particle physicists, I’ve been working hard lately to prepare results for the 35th International Conference on High Energy Physics, which will be held in Paris starting on July 22nd. That means I am again going through the complexities of reviewing my work with my (3000+) collaborators, to make sure that the work I’ve done is something we all have confidence in. After all, everyone’s name will be on it!

So far, things are going well, and it looks like (cross your fingers) the analysis will be out and ready. I just designed a poster this week, and some of the plots might also appear in one of the ATLAS talks given by one of my colleagues. The approval process has also been a great opportunity to get feedback — some of which has been included in the current analysis, and some of which will be added as we update and improve the results for a complete paper.

I’ll be able to show you the latest results once the ICHEP conference starts, but for now I at least have some plots of track jets from last year’s 900 GeV run, one of which is shown here at right. You can click the image for more and bigger pictures, but I don’t promise that the text will be too comprehensible! I’ve written a more understandable explanation of the track jet analysis here. The plot on this page shows the momentum of track jets we found in the 900 GeV data (black points) and compares it to the momentum of simulated track jets (yellow graph). You can tell a few things from it: first, there are a lot more low-momentum jets than high-momentum jets, which is exactly what we expect; second, that the data and the simulation agree pretty well; third, that they don’t agree perfectly.

There are two basic reasons why data and simulation might not agree: one is that we aren’t simulating our detector accurately enough, and the other is that we’re not simulating the underlying physics that comes out of the collision well enough. Working out which is which, and coming up with our best guess as to what really happened when the protons collided, is the hard work of data analysis. How did it go? To find out, come see my poster at the ICHEP conference, or just stay tuned here!

Tags: ATLAS, collaboration, conference
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Collaborating Isn’t Always Easy

Monday, March 1st, 2010

Seth Zenz

Hi, Seth here. It’s been a while since I’ve written about my work, mostly because my work lately has been time-consuming and a bit complicated to write about. Nevertheless, I’m going to take a stab at it. About two weeks ago now, I gave a talk at the APS conference (which Regina gave a talk at also). Preparing for the talk was a more challenging process than I had expected; I knew what I wanted to say, but what I showed also had to fit within the goals of ATLAS as a whole.

I had originally written in my abstract for the talk that I was going to describe the method for my track jet measurement, but I had always hoped that I would be able to show some initial collision data in order to demonstrate things were going well. And indeed, I had that data, and things looked pretty good to me. But of course, when any ATLAS collaboration member shows the results of our work outside the experiment, we are relying on years of hard work by thousands of people, and we are speaking for everyone in the experiment. That means that my colleagues had a say, as they should, in what I would show in my talk and how I would show it.

Showing my plans and simulated results wasn’t a big deal, in part because ATLAS has special rules for “work-in-progress” by students. But there were definitely questions and discussions on whether we ought to show plots based on real collision data. Let me summarize a few of the potential issues:

My talk was very early. Except for an initial flurry of quick plots right when we got first data, ATLAS is showing its next round of more polished plots of detector performance in March. Did it make sense to release some of that work ahead of schedule?
Was there time to make sure my results were correct?
My own plots rely heavily on the work done for our experiment’s first paper, the “minimum bias” analysis. (It shows the distributions of charged particles in our detector, including as many events as possible — hence, “minimum bias.”) That paper isn’t out yet (but the one from CMS is). Did it make sense to show work that depended on other, not-yet-published work that might change?

These are important questions. Some of my collaborators thought the answer was yes and some didn’t, and the resulting discussions took time and energy. In the end, I did get to show some of what I wanted, but not all of it. I can’t say I was completely happy about that, but I did end up getting to show some of my work only a few months after we collected data, and that’s cool.

I fully agree with the need for ATLAS to have a set of procedures to make sure that our work is presented appropriately and that it’s correct. A big experiment relies on consensus, so obviously I won’t always be completely satisfied with the outcome. As as an experiment, we’re also still in the process of figuring how to apply those procedures now that we have real data to discuss. It may not have been easy, but reaching agreement on my talk was an educational experience.

The plots from my APS talk aren’t posted anywhere, but you’ll get to see improved versions of them soon — I’ll let you know.

Tags: ATLAS, collaboration, conference, culture
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ATLAS in Bern

Wednesday, July 9th, 2008

Peter Steinberg

Believe it or not, this is a photo just outside the ATLAS meeting in Bern, Switzerland that Monica and I are both attending this week. We’d never met before, but I found myself sitting behind her, so introduced myself by pointing out that ATLAS has put us both on their “Blogs” outreach page. Gee, I have to get posting more.

But about that soccer field, the meeting itself is being held at the Stade de Suisse, just outside downtown Bern. The UEFA EURO2008 tournament just ended of course (which I believe inspired the locale), and just in time for an ATLAS-on-ATLAS soccer match tomorrow. Stay tuned for photos posted to my Flickr set. You can also see some photos in and around Bern, which is a lovely place. And some nice mountains nearby, that my wife and I hiked in and on and over last week.

Tags: ATLAS, conference
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