A simulated collision of lead ions, courtesy the ALICE experiment at CERN
The joint news release that follows is issued by the Department of Energy’s three national laboratories that host U.S. collaborations in experiments at CERN’s Large Hadron Collider (LHC)—Lawrence Berkeley National Laboratory for ALICE, Brookhaven National Laboratory for ATLAS, and Fermi National Accelerator Laboratory for CMS.
The LHC has completed many successful months of colliding protons (hydrogen ions) at record-breaking energies and now begins four weeks of colliding much more massive lead ions, giving access to different physical phenomena. ALICE is designed specifically to study these heavy-ion collisions, which give rise to a unique phase of matter, the quark-gluon plasma. Berkeley Lab scientists led development of ALICE’s Electromagnetic Calorimeter (EMCal) component, which enables efficient study of jet quenching, a phenomenon not yet discovered when ALICE was originally designed. Only part of EMCal is in place for this first lead-lead run.
Berkeley Lab is also a major participant in the ATLAS experiment, one of the other LHC experiments that will study lead-lead collisions. ATLAS will capture a broad range of products of the hot, dense medium formed when heavy ions collide.
Batavia, IL, Berkeley, CA and Upton, NY—The Large Hadron Collider’s first record-setting run of high-energy proton collisions ended today, and scientists are now readying the accelerator to meet its next challenge: the world’s highest-energy collisions of lead ions.
“Over the last seven months, the intensity of the LHC’s proton beams has increased 200,000 times, and the scientists from the LHC experiments have quickly converted proton collisions into scientific results,” says Dennis Kovar, Associate Director of Science for High Energy Physics at the U.S. Department of Energy. “This is excellent progress for the brand-new accelerator and detectors, and bodes well for discoveries in the years to come.”
The LHC at the CERN particle physics laboratory in Geneva, Switzerland will spend the next month colliding lead ions—atoms of lead with all of their electrons stripped off during the acceleration process. The teams operating three of the four major LHC experiments—ALICE, ATLAS and CMS—will record and analyze data from these record-setting “heavy-ion” collisions, in which up to 10,000 particles will stream from each high-energy collision. This next phase of the LHC will provide the first full test of the capabilities of the ALICE experiment, which was designed specifically to record heavy-ion collision data. The lead-ion collisions will be used to investigate the quark gluon plasma, a state of matter that physicists believe existed millionths of a second after the Big Bang.
“The LHC’s lead-ion collisions may generate temperatures up to 500,000 times hotter than the center of the sun,” said Timothy Hallman, Associate Director of Science for Nuclear Physics at the U.S. Department of Energy. “The LHC experiments’ investigations into how the quark gluon plasma behaves at such temperatures will provide vital insight into why and how quarks and gluons cool from such high temperatures to bind together to form more complex particles and thus how our universe evolved into the form it has today.”
Following the lead-ion collision period, the LHC will shut down for about two months for yearly maintenance before resuming high-energy collisions with protons in 2011.
The LHC’s first high-energy proton-collision run was a scientific success. Scientists from the LHC experiments used the first few months’ worth of collision data to verify that their sophisticated new detectors worked as designed—no easy task for devices weighing thousands of tons and containing millions of individual sensors. Scientists measured known particles at higher energies than ever before, which confirmed that the detectors worked correctly while providing brand-new information to the physics community and laying the groundwork for longer-term searches for new particles like the Higgs boson. For example, the ATLAS and CMS collaboration measured the production of W bosons, elementary particles heavier than atoms of iron, and the LHCb collaboration measured the production of b-quarks, particles that may give us clues as to why nature prefers matter over anti-matter.
“The experiments are already providing an exciting glimpse of the new frontier”, said Sergio Bertolucci, CERN’s Director for Research and Computing. “This rapid delivery of the first physics measurements at 7 TeV is a direct result of the excellent performance of the detectors, the high efficiency of the data collection and the swift distribution of data via the Worldwide LHC Computing Grid for analysis at centers across the globe.”
Hard on the heels of these new measurements of known particles were searches for never-before-seen particles. While no new particles have yet been discovered, scientists from both the ATLAS and CMS experiments have placed new limits on the production of certain hypothetical particles, such as excited quarks and the supersymmetric partners of elementary particles called gluons.
“The eyes of the world might be on the hunt for the Higgs boson, but the scientists from the LHC experiments have shown that there is a wealth of physics research being done using the LHC’s proton collisions,” says National Science Foundation Physics Division Director Joseph Dehmer. “And while the accelerator might take a short break at the end of the year, thousands of LHC scientists will continue poring over this first run’s data in the hopes of confirming some theories, disproving others, and spotting the first evidence for a new particle.”
The LHC has also seen its first unexpected measurement, announced in September by the CMS collaboration. In collisions of protons in which more than 100 charged particles were produced, scientists from the CMS experiment saw indications that some of the particles were associated with each other at the time of their creation, despite traveling away from the collision with very different angles. This phenomenon had never before been observed in proton collisions. Effects with intriguing similarities have been seen in collisions of heavy ions, such as those recorded at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider, which have been interpreted as being possibly due to the creation of strongly interacting, hot dense matter.
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). The DOE’s Brookhaven National Laboratory, Fermi National Accelerator Laboratory and Lawrence Berkeley National Laboratory are the host laboratories for the U.S. groups participating in the ATLAS, CMS and ALICE experiments, respectively.
Media contacts:
Brookhaven National Laboratory: Kendra Snyder, [email protected], 631-344-8191
Fermi National Accelerator Laboratory: Elizabeth Clements, [email protected], 630-399-1777
Lawrence Berkeley National Laboratory: Paul Preuss, [email protected], 510-486-6249
CERN: James Gillies, [email protected], +41 22 767 4101
Notes for editors:
Lead-ion collision photos, animations and video are available at: http://www.uslhc.us/Images/Heavy_Ion_Event_Displays
The full list of the 97 U.S. universities, national laboratories and computing centers participating in the Large Hadron Collider project is available at: http://www.uslhc.us/The_US_and_the_LHC/Collaborating_Institutions
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California. Visit our website at http://www.lbl.gov.
Brookhaven National Laboratory is operated and managed for the Department of Energy’s Office of Science by Brookhaven Science Associates and Battelle. Visit Brookhaven Lab’s electronic newsroom for links, news archives, graphics, and more: http://www.bnl.gov/newsroom.
Fermilab is a U.S. Department of Energy Office of Science national laboratory, operated under contract by the Fermi Research Alliance, LLC. The U.S. Department of Energy Office of Science is the nation’s single-largest supporter of basic research in the physical sciences. Visit Fermilab’s website at http://www.fnal.gov.
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.