Large Hadron Collider Pauses Protons; Looks
Ahead to Lead
November 4, 2010
Simulation of a lead-ion collision in the ALICE detector. Image
courtesy CERN.
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,” said 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 centres 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,” said 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, ksnyder@bnl.gov,
631-344-8191
Fermi National Accelerator Laboratory: Elizabeth Clements, lizzie@fnal.gov,
630-399-1777
Lawrence Berkeley National Laboratory: Paul Preuss, paul_preuss@lbl.gov,
510-486-6249
CERN: James Gillies, james.gillies@cern.ch,
+41 22 767 4101
Notes for editors:
Lead-ion collision photos, animations and video are available on
the LHC
website.
The full list of the 97 U.S. universities, national laboratories
and computing centers participating in the Large Hadron Collider
project is available on the
LHC website.
SOURCE
