ATLAS celebrating the International Women’s day!

Today ATLAS celebrates the role of women in physics its own way.  ATLAS has encouraged its staff and users to place as many women as possible on shift in the control room and to serve as guides for official visits.  These women are well qualified and trained in the corresponding tasks. The result can not be better described than in the message of Rolf Heuer, CERN Director General:

“The fact that we can do this easily may come as a surprise to those who don’t know us better, but it’s no surprise to me. Curiosity, the main prerequisite for being a researcher, is a shared characteristic of all mankind and that’s reflected in the CERN community. Men and women from all over the world come here to pursue their research, and the diversity they bring is one of our greatest assets.”

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Circulating beams in ATLAS.

With the beginning of the new long run, the ATLAS physicists are getting quickly used to the circulating proton beams in their detector. The shift crew in the ATLAS control room is keeping the detector operational continuously during the current phase of LHC beam tuning before the beam is further accelerated to higher energies. In the CCC (the LHC control room) our colleagues steer the beam injection, measure beam orbit parameters and test the safety procedures to ensure safe operation in the coming months. All happens in a perfect coordination with the ATLAS control room to guarantee the detector safety as well.
ATLAS is performing very well in these days, catching even the few particles created by the circulating beams passing by.
From time to time the shifters look at the ATLAS control panels which show the monitored beam position, eagerly awaiting the moment when the beams are crossing again and new proton-proton collision events can be collected.

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A Titan Awakes

At approximately 2:40 am Central European Time, ATLAS saw particles from the LHC for the first time in 2010.  As in previous LHC turn-on periods the first thing we see are beam splashes from the LHC beams as they slowly thread the beam through the LHC ring for the first time.  ATLAS is located at Point 1 (there are eight points all together) on the ring, and the injection points for the two beams are on either side of Point 1.  Therefore ATLAS is the last point along the ring to see the beam.  This year they start with Beam 2.  This beam is injected between Point 1 and Point 2.  It then gets steered into closed collimators and beam dumps as the LHC Control Room carefully adjusts various beam parameters to get the beam to circulate all the way through the machine with out losing any particles or scrapping into the magnets.

The ATLAS Detector: lit up like a Christmas tree!

This Atlantis event view is from one of the splash events we got later in the day.  One can see that all of the elements of the detector are lit up (compare this with other typical event views, obtainable from the ATLAS public web page).  This indicates that the trigger was well timed (good job guys!).  We will use these events to do some fine tuning and final checks of readout timing of the detector, as well as search for any dead channels that we may not have found before (hopefully we don’t find many!).  So the next step is for the LHC to do some more tests and checkouts of beam protection; add even more bunches to the beams and then a short run of collisions at 900 GeV center-of-mass energy; and finally ramp up the beams to 3.5 TeV and start colliding them to start off the Physics Program at the LHC!  All of that is planned to happen in a little less than a month!  So the next couple of weeks will see a busy Control Room.

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The Calm Before the Storm

The Control Room is quiet. The configurations are set. The trigger menu is uploaded. The shifters are ready. All that is left is for the LHC to deliver beam. http://public.web.cern.ch/public/

The ATLAS Control Room (ACR) just hours before the 2010 beam splashes.

Pretty soon the ATLAS Control Room will be filling up with experts, managers, shifters, and other fellow collaborators as the LHC begins to deliver 10 beam splash events from both beams (10 from beam one, followed by 10 from beam 2). A beam splash is when the LHC steers the beam into the beam collimators just upstream from ATLAS. This creates of splash of muons, pions, protons, and whole bunch of other junk that basically lights up the entire detector all at once. It is literally a spray of particles. Hence the term “Beam Splash”. This will be the third time that ATLAS has gotten beam splash events. The two previous times was when the LHC had previously turned on. Once in September 2008, once in November 2009. So this is an old bag for us now. This is a unique opportunity for the detector to check its timing and is the first big step for commissioning the detector before the LONG 2010/2011 LHC physics run.

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Gearing-up for the 2010 run!!

ATLAS has been taking cosmic rays data this month exercising new features of the data acquisition, including protocols to start and control the run.

To be prepared to the high collision rate we expect to have soon, the trigger system needs to be exercised. Higher trigger rate (especially for the fast first level of decision) means larger potential physics output. A stress test has then been performed with up to 50,000 random events per second in the first Level of the trigger (decision time of a couple of microseconds). Inner detector, calorimeters and muon systems were integrated in the run and operated stably in these conditions.

The protocol to start the run has been improved and tested. It is based on a so-called “warm start”. Once all the detectors are in a safe state, the shift leader gives the “Injection Permit” to LHC. ATLAS is safe for injection and beam commissioning when muon detectors and SCT are in “standby” mode (voltage lower than nominal), Pixels are switched off and the rest of the apparatus is at nominal conditions.  The data taking then begins with a “standby trigger menu” that accounts for these not standard conditions.  Once the beam is injected and it is declared “stable” by the LHC control room, muon detectors, Pixel and SCT are set to nominal conditions and the trigger menu is changed to “physics mode” without stopping the run.

This procedure, which allows to minimize the downtime, is currently exercised at each run start, even if there is no beam yet.

Another very important step to increase the (already very satisfactory) data acquisition efficiency is to repair parts “on the fly” without stopping the whole ATLAS.  This is the so called “stop-less removal & recovery” option.

During a long run, it might happen that some of the read-out drivers (ROD’s) become busy, i.e. they do not reply correctly to the trigger as they have lost the configuration, are desynchronized or part of the detector they are connected to becomes noisy. A protocol has been implemented to remove and re-include them without stopping the run. Therefore solving the problem of a ROD interferes very little with the run. The conditions are recorded in the databases so that the analysis can take into account that the detector configuration was different for a little while. This “stop-less removal & recovery” protocol is working for the large majority of the ATLAS detectors (and soon it will be working for all).

Together with the upgrade described above, ATLAS is collecting since early February cosmic ray events. These allow for final tuning of the operation of the whole ATLAS with particles and readiness for first collisions.

Laura and Jeremy working on calibration runs to study the performance of the MDT BEE chambers when the Toroidal Magnetic field is ON.

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First Integrated Run in 2010

[Spanish version in the bottom]

Today ATLAS has started the integrated runs.  This has happen before, nevertheless this is the first time ATLAS subdetectors get together after the winter break, a lot of work has been done since then. The new settings, after learning from the last year collisions, have been installed in the subsystems, updates on software have been tested, upgrades on hardware have been done.

We have the complexity of the subsystems of the Inner Detector, the Calorimeters, the muon systems, the trigger, the data acquisition and some other services that have to be integrated. Part by part with small steps to let the detector synchronize the clocks. Starting from inside to outside of the detector. First the inner part of the detector gets integrated: Pixels, SCT, and TRT, then the calorimeters L1Calo, LArg, and Tile. Later the rest.

And now running test smoothly.

Spanish version

PRIMERA CORRIDA GLOBAL DE ATLAS EN EL 2010

———————

Hoy es el primer día que hay una corrida integrada de ATLAS , es decir todos los subdetectores al tiempo. Después de las vacaciones la gente de los diferentes subdetecores  ha trabajado mucho para entender el detector con la información que dejaron las colisiones que se tuvieron el año pasado.

Se han hecho cambios en las configuraciones, en los programas, en los visualizadores, y hoy después de que cada subsistema de cada subdetector han probado la estabilidad de estas actualizaciones están listos para integrarse.

ATLAS se integra de adentro hacia afuera. Hoy por la mañana, el detector interno (Inner Detector)  se integró: SCT, Pixels y TRT. Más tarde vendrán los calorímetros (L1Calo, LArg, Tile), y después el sistema de muones.

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All Bunched Up!

Us High Energy Physicists have been waiting for many years to see the LHC turn on.  Now that it has been turned on, the network of physicists around the world have quickly been harnessed.  It can be considered a phase transition in particle physics. One of the characteristics of the LHC (or any other synchrotron ) is that they have a radio frequency (R-F) structure to the beams.  It basically looks like a series of buckets if one looks at it on an oscilliscope.  One R-F bucket will hold one bunch of protons.  The LHC has a train of about 3600 bunches per beam.  Due to technical machine safety reasons a block of about a third of these bunches are not filled (this is commonly refered to as the abort gap).  So that leaves about 2400 possible bunches that can be filled into the LHC.  But a machine as complex as the LHC will not simply run with a full beam from day one. The plan is to gradually increase the number bunches.  For the first several weeks the LHC operated with what is called safe beam.  This is simply a single bunch of about 1×10^9 protons.  Then they went quickly to 2 bunches per beam.  Then they doubled that again soon after to 4 bunches.  That was the first time that all four experiments were able to see collisions during the same Fill (a fill is litterally an operation of the LHC with the same beam, everytime a new beam has be injected, or filled, a new Fill is declared, there have been > 900 Fills this year alone).  On Tuesday December 14th at 10pm the LHC performed its first test with 16 bunches per beam.  This means that we get 8 bunches crossing at Point 1 per orbit (an orbit is simply one cycle of the beam in the LHC, just like the Earth does one orbit per year).  This was the most intense beam the LHC had seen and this is just the tip of the iceberg.

This plot shows the beam intensities of the first 16 bunch collision run at the LHC.

As you recall they have several thousand bunches to go.  The LHC must proceed cautiously because as you add more bunches to the beam, the beams will start to interact with themselves (refered to as beam-beam interactions).  These beam-beam interactions are manifestations of basic electro-dynamic physical phenomena (but I won’t go into that now).  Basically as the currents in the machine get bigger, the LHC will have to adjust its tuning of orbits (small tweaks of special magnets in the machine will take care of these adjustments).

ATLAS was very happy to see the increase in bunches because it means that we get that many more collisions, we see it as a very encouraging sign of more good things to come!

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More collisions at 2.36 TeV

This early morning Dec.14 at 2.40, after a 8 minutes ramp, the energy of the two LHC beams has been brought up to 1.18 TeV again. They started then to collide for about 3 hours with a collision trigger rate of around 1 Hz. Both the magnetic fields of ATLAS were on (they were both off when the first few collisions at this energy were collected on Dec. 8). All the detectors which could be switched safely on in these beam conditions were operational and taking data.

Beam energy (in GeV) during ramping

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Just a taste

At 21:32 pm on December 8th, the LHC did something that no other accelerator has ever done before. It collided particles with a center of mass energy of 2.36 Tera-electron Volts (TeV). The previous world record was 1.96 TeV from the Tevatron in the US.

The LHC was being very coy about it though. They decided to try to do some ramping studies, quietly, by just injecting one bunch per beam, and then ramping up the energy of the beams. No one was told they would ramp to the highest energy that they were willing to safely go (i.e. 1.18 TeV per beam) nor that the beams were going to collide. ATLAS was quietly taking data (as we have quickly learned to just take data no matter what) when this event appeared on the event display.

The many tracks from particles passing through the detector are shown by the coloured lines. The innermost silicon detectors are sensitive to any radiation accompanying the beam. And since these collisions occurred during machine studies, the LHC had not sent what is known as the stable beam flag, so they were in standby. But, ATLAS has an inner sub-detector that is less sensitive to damage from radiation from the beam, so it was on and recording data. That’s why we were able to see tracks despite the fact that the collisions occurred when no stable beam flag had been declared. Some people might wonder why the tracks are straight. That is because our solenoid magnet was off due to a minor cryogenic problem (consider this growing pains of a brand new detector), and the electric current in the magnet was switched off to keep it safe. The problem has been fixed and the solenoid was on for the next set of collisions recorded today.

However, the most interesting feature can be seen in the lego-like plot, which shows the energy deposited in the calorimeter. It rather looks like ATLAS was able to record the first ever event containing 2 jets seen at 2.36TeV! The jets have an uncalibrated transverse energy of 32 and 16 GeV. The collisions only lasted for 2 minutes but they were a lovely appetizer of just how exciting the LHC is going to be.

JD&HG

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ATLAS increases its active channel count by one order of magnitude

On Sunday December 6, 2009 at 8.00 the ATLAS Pixel Detector has measured, for the first time, tracks emerging from LHC collisions. It has been a very smooth start. The whole detector has been switched on and put in operational conditions in matter of minutes. Hits appeared on the screen and tracks were immediately fitted through them. It is hard to describe the emotion of the happy few who happened to be present in this historic moment. More than 100 people worked tirelessly for more than 15 years to conceive, build and operate this very complex “eye” devoted to the observation of the details of the proton-proton interactions. To do so (and in particular to detect short lived particles) in the harsh LHC environment this “eye” is made of 80 million of individual tiny sensors. This makes the Pixel detector by far the highest channel count detector in ATLAS (~90% of the ATLAS read-out channels are in the Pixel) even if it is the smallest in size of those covering the full acceptance. A jewel of technology out of which we expect to extract precious physics measurements.

The” happy few Pixelers” who happened to be present when the first LHC interactions were recorded with the Pixel detector on Sunday morning, Dec 6. The crew stands in front of one of the first LHC events recorded by the Pixel Detector. The three project leaders who have directed the detector construction, integration and operation over the last 12 years did not miss this historic moment (Kevin Einsweiler, Beniamino di Girolamo and Leonardo Rossi, respectively 2nd, 3rd and 4th from left).

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