In December, the Large Hadron Collider, the world's largest particle
accelerator, shattered the world record for highest energy particle collisions.
 | | Screen capture of proton-proton collision events in the CMS detector at an energy of 2.36 TeV. Photo - Photo: CERN |
A team led by researchers from MIT,
CERN and the KFKI Research Institute for Particle and Nuclear Physics in Budapest,
Hungary, completed work on the first scientific paper analyzing the results
of those collisions last week. Its findings show that the collisions produced
an unexpectedly high number of particles called mesons — a factor that
will have to be taken into account when physicists start looking for more rarer
particles and for the theorized Higgs boson.
“This is the very first step in a long road to performing extremely sensitive
analyses that can detect particles produced only in one in a billion collisions,”
says Gunther Roland, MIT associate professor of physics and an author of the
new paper.
Roland and MIT professors Wit Busza and Boleslaw Wyslouch, who are members
of the CMS (compact muon solenoid) collaboration, were among the study leaders.
The CMS collaboration runs one of four detectors at the collider.
The Large Hadron Collider (LHC), located underground near Geneva, Switzerland,
started its latest run in late November. On Dec. 8, the proton beams around
the 17-mile ring collided at a peak energy of 2.36 tera electron volts (TeV),
breaking the previous record of 1.96 TeV achieved at the Fermi National Accelerator
Lab. Because of Einstein's equation, E=mc2, which correlates mass and
energy, higher energy levels should produce heavier particles — possibly
including some never seen before.
In the new paper, submitted to the Journal of High Energy Physics by CMS, the
physicists analyzed the number of particles produced in the aftermath of the
high-energy collisions. When protons collide, their energy is predominantly
transformed into particles called mesons — specifically, two types of
mesons known as pions and kaons.
To their surprise, the researchers that the number of those particles increased
faster with collision energy than was predicted by their models, which were
based on results of lower-energy collisions.
Taking the new findings into account, the team is now tuning its predictions
of how many of those mesons will be found during even higher energy collisions.
When those high-energy experiments are conducted, it will be critical to know
how many such particles to expect so they can be distinguished from more rare
particles.
“If we're looking for rare particles later on, these mesons will
be in the background,” says Roland. “These results show us that
our expectations were not completely wrong, but we have to modify things a bit.”
Using the Large Hadron Collider, physicists hope to eventually detect the Higgs
boson, a particle that is theorized to give all other particles their mass,
as well as evidence for other physical phenomena such as supersymmetry, extra
dimensions of space and the creation of a new form of matter called quark-gluon
plasma (QGP). The new data provide an important reference point when CMS will
look for signatures of QGP creation in collisions of lead ions at the LHC later
this year.
The CMS team, which includes more than 2,000 scientists around the world, has
45 members (including faculty, students and research scientists) from the MIT
Laboratory for Nuclear Science's Particle Physics Collaboration and heavy-ion
research groups.
The Large Hadron Collider is capable of creating collisions up to 14 TeV, but
scientists are gradually easing the machine up to that level to try to avoid
safety issues that have arisen in the past. In September 2008, the collider
had to be shut down for several months after a connector joining two of the
collider's magnets failed, causing an explosion and leakage of the liquid
helium that cools the magnets.
During the collider's next run in March, researchers hope to create collisions
of 7 TeV, says Roland. The success of the latest effort “makes us extremely
optimistic about the detector,” he says. “It performed beautifully
during the run.”
Posted February 8th, 2010
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