Edgar Carrera (BU)

CMS one of the 1st collision events at 7 TeV

After years of hard work by many people, after several weeks of intense work for preparation, and after several hours of holding our breaths, we finally got stable colliding beams at the record center-of-mass energy of 7 TeV.  Today, Tuesday 30th of March of 2010, CMS captured these beautiful collision candidate events!!!

You will see them appearing  here soon!!!

A new era of exciting physics (hopefully discoveries) has just started, a renaissance of science, which will most certainly change the way we perceive our universe and trigger an enhancement of our own humanism.

Cheers for particle physics and for humankind!!

Edgar Carrera (Boston University)

]]> http://www.quantumdiaries.org/2010/03/30/cms-first-7-tev-collision-candidate-events/feed/ 3 http://www.quantumdiaries.org/2010/03/30/where-will-the-collisions-be-at-cms/ http://www.quantumdiaries.org/2010/03/30/where-will-the-collisions-be-at-cms/#comments Tue, 30 Mar 2010 06:08:48 +0000 Edgar Carrera http://blogs.uslhc.us/?p=4157 These are plots of the horizontal and vertical positions at CMS where collisions will be expected to happen.  They were measured from “beam gas” events by experts from the CMS Collaboration.  There is a small offset of about 100 microns in one of the directions.  This information is being passed to the LHC operators.   The moment of truth approaches, stay tuned….

Edgar Carrera (BU)

]]> http://www.quantumdiaries.org/2010/03/30/where-will-the-collisions-be-at-cms/feed/ 0 http://www.quantumdiaries.org/2010/03/29/stable-non-colliding-beams-at-3-5-tev/ http://www.quantumdiaries.org/2010/03/29/stable-non-colliding-beams-at-3-5-tev/#comments Mon, 29 Mar 2010 23:29:41 +0000 Edgar Carrera http://blogs.uslhc.us/?p=4151 We will enjoy about one hour of stable non-colliding beams at 3.5 TeV.  When was the last time we saw all those indicators “true” and “green”?  It looks beautiful; congratulations LHC, and thanks!!….. we can’t wait for collisions!!

Edgar Carrera(BU)

lhc stable non-colliding beams at 3.5 TeV per beam

It’s 01:15am and I just got home after a quite long day of work (although shorter than I expected).  Everything needs to be ready before we get collisions, so the efforts have to double.  As part of the high level trigger team in CMS, my work this week consists in making sure that we are able to accept all the good collision events (data).  After a few days of intensive testing from different groups and people, we hope we will deploy the final version of the trigger “menu” tomorrow, or on Thursday the latest.  The high level trigger is a key component of being able to accept data.  It is basically a collection of code that runs online, live, to discriminate what information is put into tape and what is not.

It is very likely that  we will have lower energy collisions (900 GeV) during the weekend as a preamble for the historic 7 TeV smashings. We also need the trigger to catch beam gas events from 3.5 TeV circulating stable beams (no collisions), maybe on Sunday.

The adrenaline is starting to flow here at CERN.  It is somehow difficult to sleep, thinking about all this, for people like me who are on-call.  Most of the improvements, fixes, upgrades, etc, that we made after the learning experience of last year’s collisions are now in place, and ready for prime time.   We will do just fine.  I am sure.

Edgar F. Carrera (Boston University)

Do you think the LHC is a worthwhile scientific endeavor? Will it help answer important questions about the nature of our universe?

Of course, my simple answers would be: yes and yes!  However, since  the IEEE is one of the most important (if not the most important) association related to technology and engineering,  it might be worthwhile elaborating on the answer.  Apparently anyone can make a comment to the address indicated in the magazine.

Enjoy!

Edgar Carrera (Boston University)

I haven’t been paying much attention, and I don’t know the statistics, but I have the feeling that there’s usually a good mix of women and man in the control room. As a matter of fact, this past week (when I was on-call and I had to go to P5 every day) both run field managers were women and I guess they continue for this week.

The fun part of today was that they managed to schedule women for 32 out of the 34 shift positions required to run the CMS experiment; or at least that’s what I was told.  I am sure those two other spots were not filled in with women because the women that can cover them are very busy.  Like my boss, for example, who were supposed to be here for this day but couldn’t make it because she is rather busy with some other CMS responsibilities in the US.

Now, I am curious if they could manage to do the inverse though, i.e., have mostly man scheduled for shifts.  That would be an interesting exercise; it won’t be easy for sure, as many women in CMS have essential expertise in many areas.

All in all it was a good day,  it definitely felt like a special day, and that’s always a lot of fun.  It smelled very nice too!

Hope all women had a good day !!

Edgar Carrera (Boston University)

I took a block of 4  day data acquisition (DAQ) shifts during the last weekend (Thu-Sat) at CMS point 5 (where all the action happens).  I was lucky to have a trainee who is also a good friend of mine.  My mission was to prepare him to take DAQ shifts by himself and be able to run the whole CMS experiment (that’s what DAQ shifters do, and that’s why it is so much fun).

My friend, as all of us, had to read and study the documentation about how to run the different applications that are used to run the experiment.  Being able to comprehend the data flow, understand how the sub-detectors interconnect , and quickly identify potential problems are tasks that require some training and practice.  The good side is that we do love to do this; every day is a learning experience.

As the LHC has been playing with the beams (injection, tuning, dumping, beta beats, optics, etc, etc) in order to prepare for energy ramp-up, there were many occasions for my friend to learn and adapt to being a DAQ shifter.  He quickly picked up the basics on how to incorporate or drop sub-detectors in/from the CMS run; how to read and understand the no-less-than 7 monitors (3 keyboards) used for the DAQ system; how to interpret the big screens that announce the current LHC and CMS conditions; how to start, end, pause a CMS run; how to load the appropiate conditions to run a cosmic run, splash events, circulating beams (and eventually collisions); how to issue resynch signals to the different components; how to debug more complicated problems like loss of synch and back-pressure (data flow stuck); and most importantly, become confident and comfortable to know that a 2+ billion dollars experiment like CMS is, in great part, in his hands while driving the DAQ.

Despite him being an experienced professional physicist, I can’t avoid being impressed of how, in general, we humans learn.  It is a marvelous thing, an amazing skill to have.  It propels great things like this experiment, it is so much fun, but it also comes with a great deal of responsibility.

Edgar F. Carrera (Boston University)

It was scheduled that professor Peter Higgs (one of the proponents of the Standard Model EWSB mechanism) would recieve the prestigious Sakurai Prize for theoretical physics along with many other great theorists that were involved in developing such formalism.  I was really looking forward to see professor Higgs giving one of the acceptance talks, but unfortunately he did not make it to the APS meeting on Monday: it was a Higgsless APS meeting!!! As Higgsless as the models we are trying to study, isn’t that neat??

There are many physical and even philosophical reasons (well, let me say more like aesthetic reasons) for which many of us believe that we will not find the “Higgs” particle per se, i.e., not as a fundamental scalar particle but maybe as composite or none at all (although something must be there).  One of these reasons is, for example, that we have never seen a fundamental scalar particle in nature before.  I dislike the idea of the Higgs boson being a special component, why would that be?  …. Well, I guess we are at the brink of finding out… stay tuned as the LHC will resume very soon!!!!

Edgar Carrera (Boston University)

With the Tevatron’s first direct constraint on the mass of the Higgs boson beyond good-old LEP’s this past week, physicists in all LHC experiments are getting ready and more excited to re-start operations and finally gather some data that allow them to search for new physics and hopefully complement or surpass very quickly the astonishing Tevatron results.  Meanwhile, LHC physicists and engineers are finalizing the improvements in the quench protection systems that will allow us to run at the energy of 3.5 TeV/beam, starting middle February.

My two cents, as always, consists of collaborating in putting the CMS trigger system in the best condition possible to start taking good data.  This time though, we are using “real” data from last year’s operations as opposed to using “simulated” data.  No more relying entirely on Monte Carlo, no more tweaking and tuning and speculating about our computer simulations.  This is the real deal guys!!

What we do with the data is to skim it off-line into a collection of good and interesting events, then we feed them into our on-line system and run the trigger menu to check its performance.  These data has all the information, event by event, that the detector collected (in the form of electronic signals) from those proton-proton collisions we had last year.  For these past month or so, we have been capable of touching nature’s primary constituents over and over in order to adapt our detectors and tune them to be able to better sense the most fantastic petals of life: particles!

Edgar Carrera (Boston University)

K_short meson

One of the most amazing characteristics of science is reproducibility, i.e., experimental results can be reproduced by independent tests.  So, the first thing to check in any physics experiment is to see if you can reproduce what older, well tested, experiments have found running in similar conditions.  CMS did this very quickly last November when it presented its beautiful di-photon resonance peak, but the story does not end there.

Since December, CMS has taken advantage of the technical stop scheduled for the LHC in order to improve the reliability for the cooling system in the end-caps of the detector and, meanwhile, physicists have put a lot of effort in analyzing the data gathered during those few weeks of operation, mostly at 900 GeV of energy.

The results are quite fantastic.  I mean, ok, we know these particles (resonances) for quite some time now (most of them have been known for more than 40 years) and we can easily “google” them and obtain all their information, but to see them coming alive in our detector is probably only second to experiencing the actual discovery.  To make this succint, we know now that our detector is capable of reconstructing, with an astonishing precision,  the invariant mass of many mesons and baryons ["vintage" Kaon (short) resonance is shown in the plot as an example!!], such as pions, eta mesons, kaons, lambda baryons, etc, that were seen and studied many years ago by different experiments around the world.  Seeing these beloved resonances is not only cool, but they are necessary to calibrate the detector and to be in a much better shape for the next round of operations of the LHC, which will happen most likely in middle February.  Stay tuned, the next big thing will be seeing  Z/W bosons, for example, and from then a plethora (hopefully) of new and exciting physics (particles).

Edgar Carrera (Boston University)

All the hardware subsystems in the CMS experiment have two kind of people taking care of operations.  The ones in the front-line are the so-called “shifters”, operators who sit in front of several computer screens in the control room and whose job is to monitor closely the performance of each component, and take rapid action in case something goes wrong.  Each shift is usually of 8 hours and there is always someone doing this; the operations are 24/7.  The other kind are the “experts”, who are on-call 24/7 in case there is a major problem or a more involved task that needs to be done.  For this first week, however, shifters and experts were intensively working together in the control room making sure everything works as planned.

For software subsystems, like the HLT, there are also shifters, but who usually sit somewhere else (like in the remote control room across the Atlantic, at the LPC at Fermilab) and who take the usual 8 hours shifts.  The CMS control room at P5 is always connected via video with the other remote stations, including Fermilab, Desy, CMS Meyrin centre, etc.

The experts are of two kinds, the primary and the secondary.  The team of people in charge of expert support rotate between these two states.  The primary is usually the main expert who carries a cell phone all the time in case there is an “emergency” call from the control room.  The secondary is there for backup, in case the primary needs support or if the primary is unreachable for any circumstances. The week before the collisions week I was secondary, and the primary responsibility was transferred to me the day of first collisions, so it was a very exciting (also quite stressful) moment.

The HLT system is a crucial part of the system.  After the first level of triggering (called L1), the HLT is responsible for deciding what goes into tape and what not.  For the expected first collisions, of course, there was no room for mistake.   We had to be able to record these events and make sure we don’t miss them for circumstances like timing synch of the beam with our trigger (L1), timing of the subdetectors, or any other eventuality.  The beam conditions for these first pilot runs are not as stable (and the detectors are not fully calibrated, we need collision events for that!), so we needed to make sure we considered all scenarios.  On Saturday and Sunday, before Monday 23 of November (the day of first collisions), everyone was working very enthusiastically to prepare for this.  I remember sitting down with the Run Coordinator (the person in charge of all operations), together with expert people related to the data acquisition, in order to define a strategy and adapt quickly to the expected (and not so expected) beam conditions.  We worked intensively to make sure the small modifications that needed to be done were carefully executed.

By Monday morning we were ready and very confident that if the delivered beams were to collide at the CMS detector, we were going to be able to see them and record them.  Unfortunately, on Monday afternoon (when most experiments saw their first collisions), CMS did not see any collision candidate;  everything seemed to be consistent with beam gas, or at most something colliding outside the detector.  Worrisomeness and stress could be briefly noticed  in the faces at the  control room.  But there was no time for that, for many it was the culmination of years of work, and for all of us the beginning of and exciting program, so we went back to work to confirm our explanations of what happened.  I could feel the adrenaline flowing in small but appreciable quantities;  I imagine this chemical flooded many physicists’ bodies that day.

Soon, however, we (CMS+LHC) found out that the beams were  not optimized for collisions at P5 during the afternoon, so we tried again in the evening: the LHC circulated two beams again, now optimized for CMS, and it was marvelous.  The displays showed beautiful events.  There were applauses and champagne!! The machine works !!!!

Edgar Carrera (Boston University)

Candidate Collision Event at CMS

http://cmsdoc.cern.ch/cms/performance/FirstBeam/cms-e-commentary09.htm

http://cmsdoc.cern.ch/cms/performance/FirstBeam/pictures221109/CollisionEvent.png

It looks like we recorded a very good collision candidate event!! Enjoy!!

Edgar Carrera (Boston University)

Beam splash event. CMS detector side view

It looks like tonight CMS will be the chosen experiment to press the red button.  The LHC operators have told us that after they perform several tests with the captured beam 1, they will try to run for 20 min with an untouched captured beam 1 (probably meaning they won’t perform any tests) and then CMS will be asked to push the button to dump it!!!!  As I understand, this is a test of this safety feature that each of the experiments has.  After this, they will re-inject.

In all these exciting years of being an experimental particle physicist, whenever I talk about what I do, and in particular when I mention that I have worked in two of the biggest accelerators in the world, people tend to ask me about pushing the “red button”.    I think no one is exactly sure what they mean when they ask, – oh, so you have to push the red button? -, but it always amuses me and triggers my imagination.  I am pretty sure different people imagine different tasks for this big round red thing (the CMS beam abort button, however, is actually pretty small and green.  At least this is what I have heard…)

When I was working in the D0 experiment at the Fermilab’s Tevatron in Chicago, I was aware of many red buttons, but none of them fit my “ideal” red one.  As a data acquisition shifter (the operator who basically runs the data taking), I had to press many, but I don’t remember any being red (or round for that matter) and all of them were within computer graphical interfaces.

As a graduate student, however, a fellow senior graduate student inherited me a RED squared button for my desktop’s keyboard at work when he graduated.  There were many times when I wished the button had a real effect on things (it was a dummy )….. I sometimes pushed it nevertheless.   This button, which read “PANIC” in its legend, had been passed over  for generations ….. I proudly continued the tradition when I graduated.

CMS is running fine, triggering on circulating beams.

Edgar Carrera (Boston University)

Beam splash event from Beam 2 (beam onto collimator), CMS detector

Beam 1 circulated for several minutes and before that we were able to take a a few splash events.  Then after they managed to circulate Beam 2 and they are ready to capture it…

The BBC was here for most of the Beam 2 episode.

-Edgar Carrera (Boston University)