From CERN Courier – May 2012 – Important Articles
LHC yields data rapidly at new collision energy of 8 TeV
“At 12.38 a.m. on 5 April, the LHC shift crew declared “stable beams” as two 4 TeV proton beams were brought into collision at the LHC’s four interaction points. This signalled the start of physics data-taking by the LHC experiments for 2012. The collision energy of 8 TeV is a new world record. By 11 April the LHC had already delivered a total integrated luminosity of 0.2 fb–1 to the experiments. Last year, it took six weeks achieve the same number.” Read the rest.
The rarest B decay ever observed
“As announced at the “Moriond” conference on 10 March, the LHCb collaboration has made the first observation of the decay B+ → π+μ+μ–. With a branching ratio of about 2 per 100 million decays, this is the rarest decay of a B hadron ever observed.
The LHCb experiment is designed to search for new physics in the rare decays and CP-violation of particles with heavy flavour, i.e. those containing the c or b quark. Such decays have previously been studied by the B-factory experiments BaBar and Belle, but LHCb is taking the field further as a result of two major advantages: not only are all of the varieties of heavy-flavour hadrons produced in the LHC’s high-energy collisions, but they are also produced at an enormous rate.” Read the rest.
ATLAS and CMS search for new gauge bosons
The ATLAS and CMS collaborations are carrying out a large-scale hunt for hypothetical heavy partners of the Standard Model gauge bosons, the W and the Z. The two experiments were designed to be sensitive to the decays of such particles, which are called, appropriately, W’ and Z’. The latest findings presented at the recent winter conferences show that so far these searches probe for W’ and Z’ particles with masses more than 20 times larger than those of their well known Standard Model counterparts.” Read the rest.
New developments in the search for SUSY
“Although no sign of supersymmetry (SUSY) has been observed so far, it is still the front-runner as a signal for new physics that could be discovered at the LHC. Not only does it neatly solve several shortcomings of the Standard Model, it also provides a candidate for the as-yet undiscovered dark-matter particle. Unfortunately, the masses of the SUSY particles are not constrained by theory, but it does provide some interesting hints. For SUSY to solve in a natural way the fine-tuning problems that arise in the Standard Model from the presence of a low-mass Higgs, the lightest of the two supersymmetric partners of the top quark (stop quarks) should have a mass not too much beyond that of the Standard Model counterpart, and the mass of the gluon’s superpartner (gluino) should not be too far above that of the stop quarks.
Both the ATLAS and CMS collaborations have made significant progress in searching for possibly light third-generation squarks (stop and sbottom), produced either directly or in the decays of gluinos, and first results based on the full data set recorded in 2011, equivalent to about 5 fb–1, have been released. CMS has presented a search for events containing multiple b-quarks and two leptons of the same charge, thus effectively eliminating most of the Standard Model backgrounds. ATLAS has released a novel interpretation of its updated multi-jet analysis, which explores events with up to nine high-transverse-momentum jets.” Read the rest.