LHC research program launched with 7 TeV collisions

March 30, 2010 | 6:30 am

At 1:06 p.m. Central European Summer Time (CEST) today, the first protons collided at 7 TeV in the Large Hadron Collider. These first collisions, recorded by the LHC experiments, mark the start of the LHC’s research program. For more information about this milestone event, the LHC’s physics potential at 7 TeV and American participation in the project, read the press releases below. You can also tune in live to CERN’s LHC First Physics webcast before 12:15 p.m. Eastern time (6:15 p.m. CEST) today.

Text of the press release issued by Brookhaven National Laboratory and Fermilab:

Physics Begins at the Large Hadron Collider

Batavia, IL and Upton, NY – The Large Hadron Collider has launched a new era for particle physics. Today at 1:06 p.m. Central European Summer Time (CEST) at CERN in Geneva, Switzerland, the first particles collided at the record energy of seven trillion electron volts (TeV). These collisions mark the start of a decades-long LHC research program, and the beginning of the search for discoveries by thousands of scientists around the world.

“Today’s first 7 TeV collisions are a great start for LHC science,” said Dr. Dennis Kovar, Associate Director of Science for High Energy Physics at the U.S. Department of Energy. “We eagerly anticipate the work of the world’s physicists as they begin their search for dark matter, extra dimensions, and the ever-elusive Higgs boson.”

Today’s proton collisions were recorded by the LHC experiments’ particle detectors, known by their acronyms: ATLAS, CMS, ALICE and LHCb.  While the LHC accelerator brings the protons up to their maximum energy and steers them around the 17-mile ring into collision, the experiments use massive particle detectors to record and analyze the collision debris.

“The LHC experiments are the world’s largest and most complex scientific instruments, and scientists from American universities and laboratories have made vital contributions to each of them,” said Dr. Edward Seidel, Acting Assistant Director of the National Science Foundation’s Directorate For Mathematical and Physical Sciences. “We wish all the LHC scientists success in their quest to solve some of the most profound mysteries of our universe.”

More than 1,700 scientists, engineers, students and technicians from 89 American universities, seven U.S. Department of Energy (DOE) national laboratories, and one supercomputing center helped design, build and operate the LHC accelerator and its four massive particle detectors. American participation is supported by the DOE’s Office of Science and the National Science Foundation (NSF).

Now, the real work begins for the LHC teams. Over the next 18 to 24 months, the LHC accelerator will deliver enough collisions at 7 TeV to enable significant advances in a number of research areas. As data begins to pour from their detectors, more than 8,000 LHC scientists around the world will sift through the flood in search of the tiny signals that could indicate discovery.

“It’s a great day to be a particle physicist,” said CERN Director General Rolf Heuer. “A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends.”

The DOE’s Brookhaven National Laboratory and Fermi National Accelerator Laboratory are the host laboratories for the U.S. groups participating in the ATLAS and CMS experiments, respectively. Scientists from American universities and laboratories, who comprise more than 20% of the ATLAS collaboration and 35% of CMS, have played major roles in the construction of both detectors, and join thousands of international colleagues as they operate the detector and analyze the collision data that will be collected in the coming years.  In addition, Lawrence Berkeley National Laboratory is the host laboratory for U.S. groups participating in ALICE, with American scientists contributing 10% of the ALICE collaboration.

The United States is also home to major national and regional computing centers that, as part of the Worldwide LHC Computing Grid, enable scientists in the United States and around the world to access the enormous amount of data generated by the LHC experiments. Brookhaven National Laboratory and Fermi National Accelerator Laboratory, host to major “Tier-1” computing centers, are the first stop in the U.S. for data from the ATLAS and CMS experiments, respectively. The data are further distributed to smaller NSF and DOE-funded “Tier-2” and “Tier-3” computing centers across the country, where physicists will conduct the analyses that may lead to LHC discoveries.

Text of the CERN Press Release:

LHC research programme gets underway

Geneva 30 March 2010. Beams collided at 7 TeV in the LHC at 13:06 CEST, marking the start of the LHC research programme. Particle physicists around the world are looking forward to a potentially rich harvest of new physics as the LHC begins its first long run at an energy three and a half times higher than previously achieved at a particle accelerator.

“It’s a great day to be a particle physicist,” said CERN Director General Rolf Heuer. “A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends.”

“With these record-shattering collision energies, the LHC experiments are propelled into a vast region to explore, and the hunt begins for dark matter, new forces, new dimensions and the Higgs boson,” said ATLAS collaboration spokesperson, Fabiola Gianotti. “The fact that the experiments have published papers already on the basis of last year’s data bodes very well for this first physics run.”

“We’ve all been impressed with the way the LHC has performed so far,” said Guido Tonelli, spokesperson of the CMS experiment, “and it’s particularly gratifying to see how well our particle detectors are working while our physics teams worldwide are already analysing data. We’ll address soon some of the major puzzles of modern physics like the origin of mass, the grand unification of forces and the presence of abundant dark matter in the universe. I expect very exciting times in front of us.”

“This is the moment we have been waiting and preparing for”, said ALICE spokesperson Jürgen Schukraft. “We’re very much looking forward to the results from proton collisions, and later this year from lead-ion collisions, to give us new insights into the nature of the strong interaction and the evolution of matter in the early Universe.”

“LHCb is ready for physics,” said the experiment’s spokesperson Andrei Golutvin, “we have a great research programme ahead of us exploring the nature of matter-antimatter asymmetry more profoundly than has ever been done before.”

CERN will run the LHC for 18-24 months with the objective of delivering enough data to the experiments to make significant advances across a wide range of physics channels. As soon as they have  ”re-discovered” the known Standard Model particles, a necessary precursor to looking for new physics, the LHC experiments will start the systematic search for the Higgs boson. With the amount of data expected, called one inverse femtobarn by physicists, the combined analysis of ATLAS and CMS will be able to explore a wide mass range, and there’s even a chance of discovery if the Higgs has a mass near 160 GeV. If it’s much lighter or very heavy, it will be harder to find in this first LHC run.

For supersymmetry, ATLAS and CMS will each have enough data to double today’s sensitivity to certain new discoveries. Experiments today are sensitive to some supersymmetric particles with masses up to 400 GeV. An inverse femtobarn at the LHC pushes the discovery range up to 800 GeV.

“The LHC has a real chance over the next two years of discovering supersymmetric particles,” explained Heuer, “and possibly giving insights into the composition of about a quarter of the Universe.”

Even at the more exotic end of the LHC’s potential discovery spectrum, this LHC run will extend the current reach by a factor of two. LHC experiments will be sensitive to new massive particles indicating the presence of extra dimensions up to masses of 2 TeV, where today’s reach is around 1 TeV.

“Over 2000 graduate students are eagerly awaiting data from the LHC experiments,” said Heuer.  “They’re a privileged bunch, set to produce the first theses at the new high-energy frontier.”

Following this run, the LHC will shutdown for routine maintenance, and to complete the repairs and consolidation work needed to reach the LHC’s design energy of 14 TeV following the incident of 19 September 2008. Traditionally, CERN has operated its accelerators on an annual cycle, running for seven to eight months with a four to five month shutdown each year. Being a cryogenic machine operating at very low temperature, the LHC takes about a month to bring up to room temperature and another month to cool down. A four-month shutdown as part of an annual cycle no longer makes sense for such a machine, so CERN has decided to move to a longer cycle with longer periods of operation accompanied by longer shutdown periods when needed.

“Two years of continuous running is a tall order both for the LHC operators and the experiments, but it will be well worth the effort,” said Heuer. “By starting with a long run and concentrating preparations for 14 TeV collisions into a single shutdown, we’re increasing the overall running time over the next three years, making up for lost time and giving the experiments the chance to make their mark.”

Katie Yurkewicz

21 Comments »

Time-lapse: Watch an excavator eat a building

March 24, 2010 | 10:50 am

Bite by bite, the prehistoric-looking excavator demolished the old cooling tower. It’s an image that took me back to childhood playing with toy dinosaurs as they rampaged through the buildings I’d made with wooden blocks until everything was leveled. Many of us watched with childhood glee as the building was eaten away.

Sometimes particle physics labs get a bit old and creaky around the edges. A cooling tower at SLAC National Accelerator Laboratory had been around since the 1960s and needed replacing. But taking out such a large building with so many vital connections to the rest of the lab is tricky. After more than a year of planning, the facilities and safety people embarked on removing a decades-old fixture of the SLAC skyline.

Enjoy the show!

The video was made by Brad Plummer and Rod Reape at SLAC, and you can read more about the cooling tower demolition. Brad set up a high-end digital SLR, taking photos every 30 seconds, on the roof of a nearby building. Rod took video from ground level, and they combined the photos and footage into the time-lapse.

David Harris

2 Comments »

First 7 TeV LHC collisions scheduled for March 30

March 23, 2010 | 6:03 am

CERN has announced that the first attempt to collide protons in the Large Hadron Collider at the record energy of 7 TeV (3.5 TeV per beam) will take place on March 30. A live webcast will be available on the day dubbed “LHC First Physics” from 8:30 a.m. to 6:00 p.m. Central European Time (2:30 a.m. to 12:00 p.m. Eastern time). More information about the webcast will be available soon at the LHC First Physics Web site.

Text of today’s CERN Press Release:

CERN sets date for first attempt at 7 TeV collisions in the LHC

Geneva, 23 March 2010. With beams routinely circulating in the Large Hadron Collider at 3.5 TeV, the highest energy yet achieved in a particle accelerator, CERN has set the date for the start of the LHC research programme. The first attempt for collisions at 7 TeV (3.5 TeV per beam) is scheduled for 30 March.

“With two beams at 3.5 TeV, we’re on the verge of launching the LHC physics programme,” explained CERN’s Director for Accelerators and Technology, Steve Myers. “But we’ve still got a lot of work to do before collisions. Just lining the beams up is a challenge in itself: it’s a bit like firing needles across the Atlantic and getting them to collide half way.”

Between now and 30 March, the LHC team will be working with 3.5 TeV beams to commission the beam control systems and the systems that protect the particle detectors from stray particles. All these systems must be fully commissioned before collisions can begin.

“The LHC is not a turnkey machine,” explained Myers. “The machine is working well, but we’re still very much in a commissioning phase and we have to recognize that the first attempt to collide is precisely that. It may take hours or even days to get collisions.”

The last time CERN switched on a major new research machine, the Large Electron Positron collider, LEP, in 1989 it took three days from the first attempt to collide to the first recorded collisions.

The current LHC run began on 20 November 2009, with the first circulating beam at 0.45 TeV. Milestones were quick to follow, with twin circulating beams established by 23 November and a world record beam energy of 1.18 TeV being set on 30 November. By the time the LHC switched off for 2009 on 16 December, another record had been set with collisions recorded at 2.36 TeV and significant quantities of data recorded. Over the 2009 part of the run, each of the LHC’s four major experiments, ALICE, ATLAS, CMS and LHCb recorded over a million particle collisions, which were distributed smoothly for analysis around the world on the LHC computing grid. The first physics papers were soon to follow. After a short technical stop, beams were again circulating on 28 February 2010, and the first acceleration to 3.5 TeV was on 19 March.

Once 7 TeV collisions have been established, the plan is to run continuously for a period of 18-24 months, with a short technical stop at the end of 2010. This will bring enough data across all the potential discovery areas to firmly establish the LHC as the world’s foremost facility for high-energy particle physics.

A webcast will be available on the day of the first attempt to collide protons at 7TeV. More details will be available at: http://press.web.cern.ch/press/lhc-first-physics/

Contact CERN Press Office
press.office@cern.ch
+41 22 767 34 32
+41 22 767 21 41

CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.

Katie Yurkewicz

1 Comment »

Needed: Participants for study of women in HEP

March 22, 2010 | 6:10 am

How do cultural and societal factors impact the careers of female physicists?

It’s a question Teresa Embry would like to answer–and she needs your help. For her PhD thesis at the University of Arizona, Embry would like to compare the career paths of female HEP physics from the United States and Italy, and investigate how cultural and social factors might impact the career progression and perseverance of these women. Her study is partly spurred by the fact that there are more Italian women than US women participating in international HEP experiments.

If you are a female particle physicist or PhD student participating in an HEP experiment at CERN or SLAC National Accelerator Laboratory, and would be interested in assisting Embry, please contact her at tembry (at) grad.arizona.edu. Interviewees will need to have lived and completed their education in either the United States or Italy,  must provide their CV and give a one- to two-hour interview.

Embry notes that while her study is gender based, her study aims to identify positive aspects that have created environments where women have been successful in this field; not to focus on struggles that women face in a male-dominated field.

Calla Cofield

2 Comments »

LHC Page 1—decoded!

March 19, 2010 | 1:53 pm

Today the CERN Bulletin decodes the LHC'S Page 1 using a display from this morning's energy ramp to 3.5 TeV.

Earlier today the Large Hadron Collider ramped up to a new energy level of 3.5 TeV, and may be only weeks away from colliding particles at this record-breaking energy. As things progress during this exciting period, you can keep track of the changes at the LHC with the same LHC Page 1 display the experts use to monitor the accelerator.

LHC accelerator engineers and physicists use Page 1 to display the overall status of the accelerator. The page changes throughout the day with the changing activity of the machine. LHC operators update the page to incorporate comments on the current task and operations mode such as preparing for beam, testing an accelerator system, or providing experimental collisions.

Today’s CERN Bulletin offers a quick guide to understanding Page 1 using a display from last night’s ramp to 3.5 TeV. The Bulletin describes the main features of the display, including the status of the overall accelerator and the energy and intensity of each beam of protons.

For a more technical walkthrough, visit the LHC portal’s explanation of Page 1. The Portal breaks down two other display examples; one for beam circulation and dump and a second from an injection test. A glossary helps translate the acronyms and shorthand used by the LHC’s operators in the CERN Control Centre.

This concludes our three-part LHC decoded series. Earlier this week, we described how physicists at the LHC display particle collisions at the CMS and ATLAS experiments.

by Daisy Yuhas

Symmetry Intern

1 Comment »

LHC sets another world record, accelerates beams to 3.5 TeV

March 19, 2010 | 4:33 am

CERN announced this morning that the Large Hadron Collider has broken its own world record for proton beam energy. At just after 5:20 a.m. Central European Time, beams circulated in both directions in the LHC at an energy of 3.5 trillion electron volts (TeV). This energy breaks the LHC’s previous record of 1.18 TeV established on November 30, 2009.

The acceleration of beams to 3.5 TeV is the last major milestone on the way to the ultimate goal for 2010: collisions of protons at 7 TeV (3.5 TeV per beam) in the center of the LHC experiments. The first 7 TeV collisions will mark the beginning of the LHC’s research program. The date for the first attempt at 7 TeV collisions will be announced by CERN in the next few weeks.

Following the first 7 TeV collisions, the LHC will run continuously for a period of 18 to 24 months, with only a short maintenance shutdown at the end of 2010. By the end LHC’s first long physics run, the LHC experiments will have collected enough collision data to make advances in a number of research areas, including the hunts for the Higgs boson and dark matter particles. In late 2011 a shutdown of approximately one year will begin, which will be used to fix problems with connections between LHC magnets that prevent the accelerator from running at its design energy of 7 TeV, as well as to carry out regular maintenance and repairs.

Visit the US LHC Web site to learn about the contributions by scientists from four Department of Energy national laboratories and one American university to the construction of and continuing R&D for the LHC accelerator.

Katie Yurkewicz

No Comments »

ATLAS event display – decoded!

March 18, 2010 | 2:40 am

Yesterday we introduced you to the collision event displays used by Large Hadron Collider physicists, and explained one type of display used by the CMS experiment. Today we’ll delve into the details of this ATLAS experiment event display.

First things first

Check out the title and text at the bottom left of the event display. The ATLAS Experiment logo lets you know which particle physics collaboration produced the display – an important distinction when there are four massive experiments recording and analyzing LHC collision data.

Next, the title tells you what type of collision event you’re viewing. This event display shows the production of jets from the collision of two protons, each of which had an energy of 1.18 trillion electron volts (TeV). Jets—sprays of particles that fly out from certain high-energy collisions—indicate that two protons have collided head-on. These violent collisions are the ones that are likely to produce new, heavy particles, and thus physicists expect to see jets in the signatures of almost every interesting LHC collision.

Finally, there is the date, time, run and event numbers. This collision was recorded on December 14, 2009 at 4:30 a.m. Central European Time (the time zone of the CERN laboratory in Geneva, Switzerland). Run and event numbers are used by physicists to catalog their data. Run numbers are unique. The first ATLAS run was recorded years before the LHC circulated its first beam, and run number will increase throughout the decades-long life of ATLAS. The event number resets to zero every time a new run starts.

Split screens

Now let’s move on to the display itself. This event display shows three different views of the same proton collision. The three views help convey all the information about a three-dimensional event on a two-dimensional surface.

Physicists on ATLAS use interactive versions of this and other event displays to delve deeply into the details of any collision event. Static images such as the one decoded here are created to be shown to scientists from other collaborations and the general public, and thus may be cropped, rotated, or differently colored compared to the views the physicists use on a daily basis.

View A shows the ATLAS detector from the side. Onto this lengthwise slice of the ATLAS detector is projected all of the information collected by the different detector systems.

View B shows a beams-eye view of the ATLAS detector. All of the information collected by the different detector systems is projected onto this cross-wise slice of the detector.

View C shows information only from two of ATLAS’ detector systems, the calorimeters. The different detector systems are not shown in this view.

Breaking down views A and B

The ATLAS detector is made up of a number of smaller sub-detector systems that each specialize in measuring certain properties of certain types of particle. The colors of the sub-detector systems are consistent between views A and B.

1: Collision point
Shows the point at which two protons collided in this event.

2: Direction of the particle beams
In view A, the proton beams enter from either side of the detector, cross at the collision point and exit through the opposite side of the detector. In view B, the proton beams travel into and out of the display through the collision point.

3: Tracking detectors
The innermost portion of the ATLAS detector contains three systems dedicated to measuring the momentum of charged particles: the pixel detector; semiconductor tracker; and transition radiation tracker. (To view the tracking detectors in detail, we recommend opening the event display in a new window and enlarging it.)

Zooming in close to the collision point you see the pixel detector in grey and black. In view A the pixel detector is directly above and below the collision point (1); in view B it directly surrounds the collision point.

Slightly farther from the collision point, also shown in grey and black, is the semiconductor tracker. In both the pixel detector and semiconductor tracker, the passage of a particle is indicated by a colored square. Grey squares show activity in part of the detector that, after more analysis, was not determined to be of interest to physicists.  Black squares indicate no activity in that area of the detector.

Zooming out even more you see the transition radiation tracker in purple. Colored lines that radiate from the collision point through the transition radiation tracker show the passage of a particle that registered in all three tracking detectors.

4: Central solenoid magnet
The ATLAS detector contains two large magnet systems. The innermost magnet (green) is the central solenoid, which curves the tracks of particles as they pass through the tracking detectors. The curvature can be seen in view B, but not in view A, as the magnetic field bends the paths of particles in some directions but not others (in this case, paths are bent perpendicular to the proton beam direction).

Magnetic fields help scientists measure the momentum of charged particles; the more curved the particle track, the lower the particle’s momentum. They also help scientists tell particles apart, as particles with opposite charge bend in opposite directions in the same magnetic field.

The second – and much larger – toroid magnet system is not shown in the event display. This magnet system bends the paths of particles through the outer portions of the ATLAS detector.

5: Liquid argon calorimeter
This detector, shown in grey, measures the energies of electromagnetic particles such as electrons and photons. Energy deposits left by particles are shown as yellow rectangles.

Electrons can be distinguished from photons by the presence or absence of associated tracks in the tracking detectors. Electrons, which are charged, will leave a track before depositing their energy in the liquid argon calorimeter, while photons will leave no track.

6: Tile calorimeter
This detector, shown in red, measures the energies of hadronic particles such as protons and neutrons. Energy deposits are again indicated by yellow rectangles.

Charged hadrons—such as protons—will leave a track in the tracking detectors before depositing their energy in the tile calorimeter, while neutral hadrons—such as neutrons—will not.

7: Muon spectrometer
The muon spectrometer (blue) measures the passage of muons, heavy particles that do not stop in either of the calorimeters. The muon spectrometer is only partially shown in this event display, as this collision did not produce muons. When muons are created in a collision event, they will leave tracks in the tracking systems, and may deposit energy in one or both calorimeters before interacting with the muon system and ultimately traveling out of the detector.

View C – the Lego plot

While views A and B show information from all parts of the ATLAS detector, view C shows only the energy deposits left by particles in the liquid argon calorimeter (red bars) and tile calorimeter (green bars). This view gives an immediate impression of how much energy was carried away from the collision by a particle or jet.

This type of view is known as a “Lego plot” by physicists, as it stacks the energy collected by the calorimeters on top of each other. Yellow circles indicate clusters of energy deposited by particles or jets.

View C takes the guesswork out of matching energy deposits with each other. Presented only with views A and B, it would be very difficult for you to tell which clusters of energy deposits are associated with a given particle. In view B, for example, energy deposits that appear to be right next to each other—and thus associated with the same particle—could be located at opposite ends of the detector when seen in view A. View C shows the energy as a function of two other parameters called η and φ, which are related to the location of particles along and around the detector.

Bringing it all together – a jet

The white circles labeled by the number 8 shows how the same jet of particles looks in the three different views. The circles mark only the energy deposited by the jet in the calorimeters. Tracing back to the collision point in views A and B, you can also see associated tracks left by the particles in the jet as they passed through the tracking detectors before stopping and depositing all their energy in the calorimeters.

That’s it for this ATLAS event display. To view more displays recorded in 2009 by the ATLAS detector, including a “three-dimensional” display of this same event and collisions that created muons, visit the latest events page. For more information about how particles are measured in the ATLAS detector watch this video overview.

And stay tuned for tomorrow’s introduction to the LHC Page 1 display, which will help you follow the LHC accelerator as it ramps up to 7 TeV collisions.

Katie Yurkewicz

4 Comments »

CMS event display — decoded!

March 16, 2010 | 11:40 am

The Large Hadron Collider is once again moving into world-record-setting territory as it gears up to smash protons at the unprecedented energy of seven trillion electron volts. As the accelerator gets ready to speed up and smash particles, the LHC experiments—which record and analyze the debris from high-energy collisions—are running through their final checks and preparing to take center stage.

Whenever the first 7 TeV collisions happen, particle physicists from the experiments will proudly show off snapshots of the very first collisions in their detectors. These snapshots, known as event displays, show the information recorded by the massively complex detectors. However, much like a baby’s first ultrasound image, it can be hard to make heads or tails of the physicists’ pictured pride and joy.

Over the next few days, we’ll help you decode ATLAS and CMS event displays, tell pixel detectors from particles, and follow the action in the accelerator with tips on reading LHC Page 1.

What is an event display?

Experiments performed at an accelerator like the LHC use collision event displays to trace the paths of particles produced in a collision. Below is an event display from the Compact Muon Solenoid (CMS) experiment at the LHC. Event displays are very helpful in visualizing specific physical processes and for checking that the detector and software are functioning properly.

Looking at the title and text on this image, we can see that this event occurred on December 14, 2009 at 4:46 a.m. Central European Time. This was the 5,686,693^rd event to be recorded in Run 124120. A run is a period of continuous operation in a given part of the detector.

The fourth line tells you that the energy level of the collision was 2.36 trillion electron volts (TeV). This event is significant in that it produced two muons, making this a possible dimuon event. The path of muons can be very clearly reconstructed in the CMS detector and can be produced in multiple kinds of collision processes.

The two muon paths seen in the detector could be the result of a single heavy particle, such as the J/Psi, decaying, or from two separate particles that each decay into a muon. The paths might also be caused by particles that are not muons but appear identical to muons within the detector. For these reasons, it is impossible to define what a single event is with total certainty. Instead, extensive analyses of multiple events can give physicists the probability of what a given event could be. This is why the event is referred to as a candidate.

Split screens

The event display is divided into different screens that give you different views of the split second when collision occurred and the produced particles travelled through the detector. In this display, there are three screens:

View A: On this screen, labeled Rho Phi, we have a beam’s eye view, looking straight at the central collision point (1). The particle beam is running straight through that central point.

View B: In this view, labeled Rho Z, the beam line (2) is running horizontally through the center of the screen and we can see the three main regions of the CMS detector.

View C: This three-dimensional perspective view allows physicists to rotate the collision event display around an axis. Here the beam line is on a diagonal, running from the upper left to the lower right portion of the screen.

These screens trace the paths of particles from the collision point through the detector. The detector records when and where it makes contact with a particle so that computers can reconstruct the particle’s path after the protons collide. Based on their final destination and movements, physicists can determine what kinds of particles were produced in a collision.

Collision and detector components

Surrounding the central collision point, the detector has three main components that record information about particle travel.

1: Collision point
The collision point, what particle physicists call the interaction point, is where the protons collide. You can orient yourself when looking at each screen by spotting the collision point and imagining where the beam line would pass.

2: Beam line
The beam line is the path that protons travel in opposite directions and into collision. On screen B, arrows represent the movement of protons along the beam line and towards the center of the detector for collision.

3: Silicon tracker
The innermost portion of the detector is the silicon tracker, outlined by a thin green line on screen A and screen B, and within the mesh cylinder in 3D view.

The tracker, which includes the pixel and silicon strip detectors, reconstructs the movement of particles point by point. These points are represented by yellow dots (you can also look at event displays of magnified tracker images). When we connect the dots we can see the particle tracks, represented here by red and green lines, tracing a particle’s trajectory.

The tracker detects charged particles, so the tracks you see in this section come only from particles with a charge, namely muons, electrons, and charged hadrons.

Because of the magnetic field in which the inner detector resides, these particle tracks are curved. From the degree of curvature, physicists learn about the particle’s momentum. Physicists can discern whether a particle’s charge is positive or negative from the direction, clockwise or counterclockwise, of the curve.

The magnetic field can bend the path of particles in some but not all directions. This is one reason why seeing the event from multiple angles is important. In screen A, we can clearly see curved tracks but in screen B they are not visible. The program used to create this display can rotate the angle and axis of the 3D image in view C. Doing so gives physicists a better sense of how the particles travel in space.

4: Calorimeters
The next main components of the detector are the electromagnetic and hadronic calorimeters, referred to by physicists as the ECal and HCal, respectively. When particles strike one or both, they leave an energy deposit. These deposits are represented by the bars (red for ECal and blue for HCal) just outside of the tracker. The height of the bar corresponds to the amount of energy deposited.

Particles that stop in the ECal are generally either electrons or photons. The two can be distinguished by the fact that electrons are charged and leave tracks in the tracker while photons are neutral and generally do not appear in the tracker.

Hadrons pass through the ECal but are stopped in the HCal. Charged hadrons leave tracks in the tracker while neutral hadrons do not.

It is also possible for the tracker or calorimeters to record signals that do not get reconstructed as particle trajectories or energies. Further analysis can help physicists decide whether these signals come from particles or other processes in the detector.

There is another particle that sometimes deposits energy in one or both calorimeters. This particle is the muon.

5: Muon chambers
The third and outermost components of the detector are the muon system‘s muon chambers, so named because they are designed to study muons. A muon can pass through the tracker, calorimeters, and solenoid magnet (not visible in the displays but lying just beyond the calorimeters) to reach the muon chambers.

Muon chambers are visible in screen B as red and blue blocks and the chambers through which a muon has passed have been highlighted. On screen C, only those chambers through which a muon has passed are visible.

6: Muons
This event display illustrates a dimuon event or the production of two muons in a collision. The paths of the muons are shown by the thin red lines on each screen. The muons left signals that were reconstructed into tracks in the silicon tracker, deposited a little energy in the calorimeters, and passed through the muon chambers.

For a good summary of the parts of the CMS detector and the particles that pass through them, take a look at the CMS Detector slice.

Interested in learning more about event displays? Check back tomorrow to learn how to decode an event display from CMS’s sister experiment, ATLAS.

by Daisy Yuhas

Symmetry Intern

7 Comments »

Atom and Eve: Fermilab’s First International Women’s Day

March 15, 2010 | 2:17 pm

Monday, March 8th, dawned gloomy and forbidding at Fermi National Accelerator Laboratory. Thick curtains of gray fog obscured Wilson Hall’s upper floors, giving the high rise the look of a modern-day retreat for a Tolkien villain. But the bleak atmosphere out of doors didn’t extend beyond the building’s sturdy walls. At least not inside the ROC, Fermilab’s remote operations center for the Large Hadron Collider’s CMS experiment, where some two-and-a-half dozen people gathered to kick off the laboratory’s first ever celebration of International Women’s Day.

Perhaps it was all the free coffee, or the palpable sense that, after weeks of intense planning, this thing was actually (finally!) happening, but the mood was downright convivial―more befitting a Friday evening cocktail hour than an overcast Monday morning.

To kick off Fermilab’s first International Women’s Day, deputy-director Young-Kee Kim greets CERN luminaries as director Pier Oddone and a roomful of Fermilab employees look on.

At around 8:30 a.m., the crowd fanned out around one of the command center’s enormous computer screens, and the day’s festivities officially began. Via video conference, scientists from CERN sent a warm, trans-Atlantic greeting to their female colleagues, and, after some brief speeches on the importance of diversity, handed the floor over to Fermilab.
Deputy-director Young-Kee Kim highlighted women’s contributions to particle physics research over the laboratory’s lifetime. She also looked to the future. “I hope this day is not only a celebration, but an inspiration to young women considering a career in science,” she said.

Echoing Kim’s remarks, Director Pier Odonne wrapped up the video conference, and called upon the particle physics community to try to bring more women to the field.

After a round of applause and a flurry of camera flashes, the Europeans said adieu, and much of the Fermilab contingency filed next door for more coffee and a go at a box of pastries. Although women comprise only around 20% of Fermilab’s 1900 employees, there was momentary equal representation at the breakfast spread.

Particle physicist Pushpa Bhat lingered behind in the ROC, chatting with a knot of female colleagues. A 20-year Fermilab veteran who participated in the discovery of the top quark and managed Tevatron luminosity upgrades, Bhat said she thought a day recognizing women was a good thing. “Maybe in 10 or 20 years it won’t be an issue. But for now, it’s important. It’s a way to remind our male colleagues that we are a minority here, and we need their support,” Bhat said. “Sometimes you are the only woman in important meetings, and that can be challenging.”

But not everyone agrees with Bhat. International Women’s Day has been a source of controversy and even anger for some women, who don’t want to be singled out because of their gender or minority status. Some of the women at Fermilab want to be known as scientists—not women scientists.

But, despite the mixed feelings, the day was dedicated to women’s achievements. And to see some of those achievements first hand, a group of journalists milled around in the atrium just after lunch, hard hats tucked under their arms. They were waiting for a shuttle to take them to another of the day’s featured events—the underground tour, highlighting some of Fermilab’s neutrino experiments, where women are contributing at every stage.

Everyone trooped off the bus at the MINOS (Main Injector Neutrino Oscillation Search) above-ground facility, awkwardly adjusting hard hats. Aria Meyhoefer, the laboratory’s underground coordinator, delivered a safety briefing, and the journalists got a crash course in neutrino physics from Yale University physicist and MicroBooNE experiment spokesperson Bonnie Fleming.

In particle physics, a spokesperson is a leader on an experiment, democratically nominated and elected by all the scientists in the collaboration; election signifies deep involvement in the physics and leadership in the field. Five of the laboratory’s eight neutrino experiments currently have, or have had, female spokespersons.

MicroBooNE spokesperson Bonnie Fleming explains the secrets of neutrinos to a group of journalists inside the MINOS above-ground facility.

Once Fleming explained the basics of neutrinos—the funny little particles that rarely interact with anything, but may hold the key to understanding why we live in a matter-dominated universe―the group piled into a large elevator for the shaky ride down through 330 feet of rock.

“I don’t deal well with heights,” one reporter said a little nervously. Just two minutes later, the elevator doors opened and the group emerged (unscathed) into the cathedral-sized hall that houses the massive detectors for Fermilab’s neutrino and dark matter experiments.

The smell of fresh concrete and fresh welds mingled with the smell of a male reporter’s cologne, motors and compressors roared, and physicist Debbie Harris, co-spokesperson for the MINERvA neutrino experiment, led the group on a dizzying trip through the bowels of a contraption the size of a small apartment building. She explained the experiment’s intricacies with infectious enthusiasm as she went. Up stairwells, down the other side, the tour wound past vast arrays of cables and wiring, blinking green lights, through the innards of the stop-sign-shaped neutrino detector―the ghostly particles’ first stop on their split second journey through the earth to a mine deep beneath northern Minnesota.

On the way back to the elevator, Harris pointed out three people up on lifts and ladders working on the detector; two of them were women. “That’s not because it’s Women’s Day, that’s just because it’s Monday,” Harris explained, laughing.

As the press prepared to leave, University of Rochester technician Janina Gielata climbed down from her perch to grab some fresh fiber-optic cables.

With safety glasses balanced on the brim of her hard hat, Gielata said she was familiar with the idea of a Women’s Day. “I’m from Poland,” she explained, where it’s a strong tradition, “so it’s nothing new to me,” she said. “Usually, the men you work with bring you a flower. A flower or a pastry. Something little,” she said. She shrugged. “Nothing big.”

To see the people and events in the story, view this photo gallery, chronicling International Women’s Day at Fermilab and CERN.

[Show as slideshow]

[View with PicLens]

By Andrea Mustain

Symmetry Intern

No Comments »

The “strangest” thing we’ve ever seen

March 12, 2010 | 2:23 pm

CMS has observed the Ξ baryon by looking for events containing both lambda baryons and pi mesons. If these two particles are observed and came from a single parent particle, we expect to see a narrow peak in our data. This measurement used data taken in December, including the data taken during the period when the LHC ran at record-breaking energy, 20 percent higher than the Tevatron.

Some things are far stranger than others, and this week I’m reporting on the strangest thing CMS has seen so far. “Strange” in this context doesn’t mean “weird” but rather describes something about the quarks inside the newly rediscovered particle.

There are many particles that are produced at the LHC. One particular type is called the baryon. Baryons are a class of particles that contain exactly three quarks. The most familiar baryons are the proton and neutron, which are made of up and down quarks. Indeed, the up and down quarks are all that is necessary to make up our universe. However, we know that four other kinds of quarks exist: strange, charm, bottom and top. Finding particles with these additional quarks is an important way-station in the CMS collaboration’s journey to fully understanding our detector.

One interesting particle is the Ξ (the Greek letter xi) baryon. Discovered in 1964, this type of particle is also called the cascade particle because of its distinctive decay pattern. All baryons contain three quarks, but in order to be a Ξ baryon, two of those quarks must be strange quarks. Scientists observe these particles by their decay into a π (pi) meson and a λ (lambda) baryon. The lambda baryon contains a single strange quark and CMS collaborators observed the lambda baryon in December.

CMS physicists searched in their data, looking for collisions in which lambda baryons and pi mesons were created. They then asked the question “If these two particles were the decay product of a single particle, what would be the mass of the parent particle?” They then plotted the mass of the potential parent. If the two particles didn’t have a single parent, all masses would occur with nearly equal frequency. However, if they had a single parent, we expect to see a narrow peak on a wide background. As seen in the figure above, these scientists clearly observed the Ξ baryon with the mass we expect from earlier measurements.

With this success, CMS continues its rediscovery of the Standard Model.

By Don Lincoln

This story first appeared in Fermilab Today on March 12, 2010.

Guest author

No Comments »