2,180 research outputs found
W and Z Cross Sections at the Tevatron
The CDF and D0 experiments at the Tevatron have used p-pbar collisions at
sqrt(s)=1.96 TeV to measure the cross section of W and Z boson production using
several leptonic final states. An indirect measurement of the total W width has
been extracted, and the lepton charge asymmetry in Drell-Yan production has
been studied up to invariant masses of 600 GeV/c^2.Comment: 4 pages, 6 figures, proceedings of Moriond QCD 2003, Les Arcs 22-29
march 2003, to be published by World Scientific (ed. T.T.Vanh
Recent Results of the CMS Experiment
The CMS collaboration has recently produced results of a number of searches
for new physics processes using data collected during the 2011 run of the Large
Hadron Collider. Up to 5 inverse femtobarns of proton-proton collisions at 7
TeV centre-of-mass energy have been used to search for the standard model Higgs
boson in five different decay modes, divided in 42 independent sub-channels.
The combination of the results has allowed CMS to set 95% confidence-level
limits on the Higgs boson mass, constraining it to lay in the region
114.4600 GeV. An excess of events with a local
significance of 3.1 standard deviations is observed for M(H)=124 GeV; the
global significance of observing such an effect anywhere in the search range
110-600 GeV is estimated to be 1.5 standard deviations. A number of signatures
of supersymmetric particles have also been investigated, significantly
restricting the parameter space of natural low-scale theories. A search for the
rare decays of neutral bottom mesons to muon pairs, Bs to mu mu and Bd to mu
mu, has achieved the tightest limits to date, and is approaching the
sensitivity to measure the standard model branching ratios. As it happens,
though, the highly informative results extracted from 2011 data produce more
questions than answers; this doubles expectations for the 2012 run of LHC,
which will conclusively answer several of them.Comment: 33 pages, 20 figures. Contribution to the Proceedings of the 50th
International Winter Meeting on Nuclear Physics, Bormio (Italy) 23-27 January
201
Observation of Z Decays to b Quark Pairs at the Tevatron Collider
A search for Z boson decays to pairs of b-quark jets has been performed in
the full dataset collected with the CDF detector at the Tevatron
proton-antiproton collider. After the selection of a pure sample of bb events
by means of the identification of secondary vertices from b-quark decays, we
have used two kinematic variables to further discriminate the electroweak bb
production from QCD processes, and sought evidence for the Z decay in the dijet
invariant mass distribution. An absolute background prediction allows the
extraction of an excess of events inconsistent with the background predictions
by 3.23 sigma but in good agreement with the amount and characteristics of the
expected signal. We then fit the mass distribution with an unbinned likelihood
technique, and obtain a Z -> bb signal amounting to 91+-30+-19 events.Comment: 12 pages, 8 .eps figure
Recent CMS Results
The CMS experiment obtained a large number of groundbreaking results from the
analysis of 7- and 8-TeV proton-proton collisions produced so far by the Large
Hadron Collider at CERN. In this brief summary only a sample of those results
will be discussed. A new particle with mass m(H) = 125.3 +- 0.4(stat.) +-
0.5(syst.) GeV and characteristics compatible with those expected for a
standard model Higgs boson has been observed in its decays to photon pairs, WW
pairs, and ZZ pairs. Searches for the rare decays B_d -> mu mu and B_s -> mu mu
have allowed to set limits on the branching fractions which are close to
standard model predictions, strongly constraining new physics models. The top
quark has been studied with great detail, obtaining among other results the
world's best measurement of its mass as m(top) = 173.49 +- 0.43(stat. + JES) +-
0.98(syst.) GeV. New physics models have been strongly constrained with the
available data.Comment: 13 pages. Proceedings of the 1st International Conference on Frontier
Physics, Kolymbari, Crete (GR) June 201
The Inverse Bagging Algorithm: Anomaly Detection by Inverse Bootstrap Aggregating
For data sets populated by a very well modeled process and by another process
of unknown probability density function (PDF), a desired feature when
manipulating the fraction of the unknown process (either for enhancing it or
suppressing it) consists in avoiding to modify the kinematic distributions of
the well modeled one. A bootstrap technique is used to identify sub-samples
rich in the well modeled process, and classify each event according to the
frequency of it being part of such sub-samples. Comparisons with general MVA
algorithms will be shown, as well as a study of the asymptotic properties of
the method, making use of a public domain data set that models a typical search
for new physics as performed at hadronic colliders such as the Large Hadron
Collider (LHC).Comment: 8 pages, 5 figures. Proceedings of the XIIth Quark Confinement and
Hadron Spectrum conference, 28/8-2/9 2016, Thessaloniki, Greec
Geometry optimization of a muon-electron scattering detector
Abstract A high-statistics determination of the differential cross section of elastic muon-electron scattering as a function of the transferred four-momentum squared, d σ e l ( μ e → μ e ) / d q 2 , has been argued to provide an effective constraint to the hadronic contribution to the running of the fine-structure constant, Δ α h a d , a crucial input for precise theoretical predictions of the anomalous magnetic moment of the muon. An experiment called ''MUonE'' is being planned at the north area of CERN for that purpose. We consider the geometry of the detector proposed by the MUonE collaboration and offer a few suggestions on the layout of the passive target material and on the placement of silicon strip sensors, based on a fast simulation of elastic muon-electron scattering events and the investigation of a number of possible solutions for the detector geometry. The employed methodology for detector optimization is of general interest as it may be applied to the design of task-specific detectors for high-energy physics, nuclear physics, and astro-particle physics applications
Hadron Collider Searches for Diboson Resonances
This review covers results of searches for new elementary particles that
decay into boson pairs (dibosons), performed at the CERN Large Hadron Collider
in proton-proton collision data collected by the ATLAS and CMS experiments at
7-, 8-, and 13-TeV center-of-mass energy until the year 2017. The available
experimental results of the analysis of final states including most of the
possible two-object combinations of W and Z bosons, photons, Higgs bosons, and
gluons place stringent constraints on a variety of theoretical ideas that
extend the standard model, pushing into the multi-TeV region the scale of
allowed new physics phenomena.Comment: 76 pages, 16 figures. To be published in Progress of Particle and
Nuclear Physic
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