g****g
发帖数: 1828 | 1 March 15, 2011 | 4:34 am
CMS scientists observed an excess in their data consistent with the
production of single top quarks after combining just a couple of variables.
Image courtesy of the CMS Collaboration.
CMS scientists observed an excess in their data consistent with the
production of single top quarks after combining just a couple of variables.
Image courtesy of the CMS Collaboration.
For the first time, scientists at the Large Hadron Collider have spotted
single top quark production.
It took Fermilab scientists at the Tevatron more than 13 years to observe
the particle in its solo state after they discovered it paired with its
antiparticle in 1995. The CMS experiment teased signs of the single top out
of 36 inverse picobarns of collision data, roughly what Tevatron experiments
collect over three days.
“We were surprised we saw it so soon,” said CMS physicist Philip Coleman
Harris, who announced the accomplishment on Monday at the Rencontres de
Moriond conference. The ATLAS experiment also made public impressive limits
on the single top quark.
Scientists took the news as one of many signs that experiments at the LHC
are prepared to make great strides in the coming years.
Energy makes all the difference. Rare single top quarks appear buried in
background particles in collisions at the Tevatron, which have a center-of-
mass energy of about 2 TeV. The LHC’s center-of-mass energy in 2010 was
more than three times that high, at 7 TeV. At that energy, the production
gap between the number of single top quarks and the number of background
particles widens significantly, making them much easier to pick from the
pack.
CMS scientists also found evidence of the single top quark through a
multivariate analysis using 37 variables. Image courtesy of the CMS
Collaboration.
CMS scientists also found evidence of the single top quark through a
multivariate analysis using 37 variables. Image courtesy of the CMS
Collaboration.
At the Tevatron, the CDF and DZero experiments shook single top quarks from
their data through a multivariate process, in which scientists combine data
about dozens of variables in an algorithm to infer new information. At the
LHC, CMS needed to look at only two variables. This simpler search gives
scientists a new understanding of what they’ve found, said CMS Physics
Coordinator Gigi Rolandi.
“When you have fewer variables, you understand the search better,” he said
. “You can see if it shows the right behavior. A multivariate search is
less intuitive.”
The CMS collaboration also found the single top quark using a multivariate
search. But it’s the additional success of the simpler search that gives
scientists the most hope for future hunting for new physics. |
|
