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Edgar Carrera | USLHC | USA

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What are we doing right now?: Rediscoverying physics

Sunday, January 17th, 2010
K_short meson

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)

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Memories of the first CMS collisions

Saturday, December 5th, 2009

I happened to be on-call for the CMS High Level Trigger (HLT) system during the week all LHC experiments saw their first collisions, so here I describe (after having some time to breath) my experience.

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)

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Live from CMS P5: LHC Candidate Collision Event in CMS!!

Monday, November 23rd, 2009
Candidate Collision Event at CMS

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)

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Pushing the Red Button (Live from CMS CR at P5)

Saturday, November 21st, 2009
Beam splash event.  CMS detector side view

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)

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Live from CMS CR at P5 (the BBC is in)…

Friday, November 20th, 2009
Beam splash event from Beam 2 (beam onto collimator), CMS detector

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)

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Live from the CMS control room at P5….

Friday, November 20th, 2009

I am the secondary on-call expert for the High Level Trigger system, therefore I am backing up the primary expert at P5.

Everyone is so excited around here.  We are waiting for the beams to reach P5.  They will eventually circulate around the LHC ring and that will allow their alignment, etc.  The monitor that shows the beam status from the LHC machine reads “Injection Probe Beam”.

It is a great feeling to be here, to make history, to contribute a little bit to the improvement of our knowledge, to the improvement of our own humanity.

http://cmsdoc.cern.ch/cms/performance/FirstBeam/cms-e-commentary09.htm (I am the guy typing standing in one of the pics 🙂 )

Edgar Carrera (Boston University)

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Symmetry restoration at the LHC, heating it up a notch

Wednesday, November 11th, 2009

In particle physics, it seems that all the work we do is devoted to finding out how to understand the original symmetry of our universe. If you have been following some of the latest entries in this blog, you know what I am talking about. If not, think about this, at the very beginning everything was very uniform (in the sense of very symmetric); in simplified words, there was probably just one “thing” with a single type of interaction (force). However, as the universe cooled down, it began a process of breaking this nice symmetry to the state in which we are today. I understand this is a little complicated to comprehend, and since this is a blog, I will try to share one of my oversimplified analogies; maybe it will help understand all this business about symmetries and the universe.

I sometimes think of our universe as a pot of glue made out of flour (try it, it is fun!) At the beginning, when you first prepare it with boiling water, you can nicely mix all the ingredients and you can tell it has a nice symmetric looking aspect. However, after you turn off the stove and let it cool down, little lumps start to appear (some of them here, some of them over there), breaking the symmetry of the mixture. If, after it has been cold for a while, you start warming it up again (increased temperature = more energy), you can see how the symmetry slowly gets restored as everything starts to gradually merge properly into the original state. You can actually follow, step by step, the restoration process.

In some sense, this is what we do with particle colliders. We warm up the “goo” to recover the symmetries that have been hidden for billions of years in the hope that we can understand the original state. We have made a lot of progress so far, and the LHC is just one (very important) step above in temperature (energy).

Edgar Carrera (Boston University)

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DAQ shifts and those sneaky neutrinos

Monday, October 26th, 2009

It is almost 40 minutes past midnight.  I just came back from my last CMS DAQ (Data Acquisition) trainee shift.  Strangely, I still have a lot of energy, so the first thing that comes to mind, after eating something (shifts make me hungrier than usual), is to keep doing something productive.  However, I need to get up early in the morning (well, it is effectively the morning already) to cover my first solo shift at 7 am, so I know I need to get some rest.  The problem is not the amount of rest needed, however, it is just that I am not used to waking up that early!

It won’t be easy to fall asleep though.  It seems that sometimes I get these bursts of energy out of air, particularly during the night.  Maybe that is why I do not drink coffee like every other physicist I know (besides it makes your teeth yellow).  Then, I think I should write while the energy “euphoria” lasts.  Write in a more natural way, that is; in a more spontaneous way.  Maybe it will be fun to read this entry again when the sun is up… I’ve been thinking about doing that for a while….

DAQ shifts are fun: you have the “control” of all the CMS detectors; everything passes trough DAQ’s hands. I liked them at the Tevatron and like them now at the LHC.  Besides, it is nice to be at P5 (point 5) where the CMS detector is located (in Cessy, France).  There, in the control room, I feel at home.  I like the excitement, and I can only imagine it being multiplied by 100 times, once first collisions come.

Then I think about neutrinos.  Those sneaky neutrinos that have been making me think a lot during the weekend.  Those sneaky neutrinos that we, at CMS, cannot detect directly but simply infer their presence by the imbalance of transverse energy in the detector.  I’ve been thinking about them because of this recent and excellent article about relic neutrinos, and how much closer to us they seem to come from compared to the relic photons. Those sneaky and skinny (their mass is really tiny) relic neutrinos, almost as old as the Universe.  I am sure they have great stories to tell about the past. They are like the grandpas of the Universe. If we could only get them to like us, to interact with us somehow.  But no, trillions of them pass through my body without me even noticing.  Maybe they keep the secret of the origins, the answer to the question that drove most of us into this, apparently, endless quest.

Edgar Carrera (Boston University)

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Juggling Scientists

Sunday, October 18th, 2009

Recently, I came across a BBC article about juggling.  Apparently, it can increase the white matter of your brain by as much as 5%.  I have not done much juggling in my life, so I really hope that the juggling I am doing now as a postdoctoral researcher counts! Let me explain…

The position title Postdoctoral Researcher is given to someone who has completed his doctoral degree but who is not quite ready to be hired as Professor or Researcher at some university.  It is the transition from being a Ph.D. student, who was told almost always what to do, to this mature scientist who can take decisions by his own and can lead a particular project of research.  I became a “postdoc” not too long ago, after a rather quick period of doctoral training, which made it a very tough enterprise.  Like any other Ph.D. student, I sometimes felt really exhausted with my academic work and its intensity, so I have to admit that I was a little scared about becoming a postdoc.

In fact, the life of a young postdoc does not become any easier, on the contrary, you are being demanded a lot more than when you were a student.  Basically, you have to juggle with many activities that range from aiding graduate students with their physics analysis (something really new that requires a different mind set) to working on your own physics analysis.  In between, you are expected to complete little service projects in a fraction of the time you spent in a similar project as a student.  To summarize, stress does not decrease.

Life is now much better though. It is maybe that I found that learning how to lead and how to abandon that advisor-dependency is much more enriching and fulfilling.  I still have a long way to go, but so far, I have been having quite some fun with this new postdoc life.

Edgar Carrera (Boston University)

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Rio 2016!!

Sunday, October 4th, 2009

Despite of what TV makes us believe about scientists (and in particular about physicists), several of us, like a great percentage of the world population, are very much passionate about sports.  In my case, although I enjoy other disciplines as well, football (soccer) occupies a special place in my life.  In fact, I was very happy I was invited to participate in the CERN’s futsal tournament this year.  My team, “El Equipo-A”,  just played its first game last week against the defending champions.  Having not played more than twice with each other before, we did really good for the first game; our rivals were very lucky to tie the game at the end! 😉  It is a lot of fun…

I bring all this up because last week it was announced that Rio de Janeiro will host the 2016 Summer Olympics and Paralympics.  Earlier, FIFA had announced that Brazil will host the 2014 FIFA World Cup as well.  Being South American, I am, of course, very excited for my continent and I entertained the idea of going there to work for a few years (for “those” years 🙂 ).

But there is a little problem.  I found this web page, after a quick Google search for particle accelerators, which basically tells me that there is no particle colliders in the South American continent, and just a couple of very small particle accelerators for condensed matter research.  My first thought was: quick!! we need to build a particle collider in Rio soon 🙂 !

Science (collider physics in particular) and the Olympics usually have common (luckily not many) detractors.  They say that we should not spend that much money doing these activities while there are starving kids in the world.  Of course, those who think this way seem not to understand their own humanity and also are a little confused.  Why do we compete in sports? Why do humans pursue the understanding of how things work at most elementary level?  Maybe there is not a very simple answer to these questions, but I am sure the majority of us sense the need of such activities for achieving a better civilization, a better society, and above all, to improve our own humanity.

Since the (my) perfect world, in which there would be one cutting-edge particle collider at least in each continent, is not possible for the moment, my plans for working in Rio during the exciting sporty times might not become true.  At the same time, I realize how lucky I am to be at CERN right now and be part of the extraordinary LHC adventure.

TAGLINE: The amount of money spent on the LHC is just a fraction of the money spent in organizing a Summer Olympics.  Moreover, the total money put into these activities is a very small fraction of the yearly amount spent in weapons in the world.

Edgar Carrera (Boston University)

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