15510570
RECENT QCD RESULTS FROM OPAL
Some recent QCD results from the OPAL Collaboration are summarized. In particular: a test of color reconnection models and a search for glueballs using gluon jets with a rapidity gap; a study of unbiased gluon jet properties using a new technique called jet boost algorithm; a measurement of the strong coupling constant from radiative events.
29757321
Search for physics beyond the standard model in events with a Z boson, jets, and missing transverse energy in pp collisions at √s=7 TeV
A search is presented for physics beyond the standard model (BSM) in events with a Z boson, jets, and missing transverse energy (MET). This signature is motivated by BSM physics scenarios, including supersymmetry. The study is performed using a sample of proton-proton collision data collected at sqrt(s) = 7 TeV with the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 inverse femtobarns. The contributions from the dominant standard model backgrounds are estimated from data using two complementary strategies, the jet-Z balance technique and a method based on modeling MET with data control samples. In the absence of evidence for BSM physics, we set limits on the non-standard-model contributions to event yields in the signal regions and interpret the results in the context of simplified model spectra. Additional information is provided to facilitate tests of other BSM physics models.
122803232
Search for Microscopic Black Hole Signatures at the Large Hadron Collider
A search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 inverse picobarns. Events with large total transverse energy are analyzed for the presence of multiple high-energy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the expected standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities. Limits on the minimum black hole mass are set, in the range 3.5 -- 4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.
121279531
Results of the first integration test of the CMS drift tubes muon trigger
Two drift tubes (DTs) chambers of the CMS muon barrel system were exposed to a 40 MHz bunched muon beam at the CERN SPS, and for the first time the whole CMS Level-1 DTs-based trigger system chain was tested. Data at different energies and inclination angles of the incident muon beam were collected, as well as data with and without an iron absorber placed between the two chambers, to simulate the electromagnetic shower development in CMS. Special data-taking runs were dedicated to test for the first time the Track Finder system, which reconstructs track trigger candidates by performing a proper matching of the muon segments delivered by the two chambers. The present paper describes the results of these measurements.
67783797
The CMS muon barrel drift tubes system commissioning
Abstract The CMS muon barrel drift tubes system has been recently fully installed and commissioned in the experiment. The performance and the current status of the detector are briefly presented and discussed.
209842972
Determination of alpha(s) using jet rates at LEP with the OPAL detector
Hadronic events produced in e(+)e(-) collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure alpha(S) in the LEP energy range by fitting an expression in which O(alpha(2)(S)) calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of alpha(s)(Mz) was determined to be as(Mz) = 0.1177 +/- 0.0006 (stat.) +/- 0.0012 (expt.) +/- 0.0010 (had.) +/- 0.0032 (theo.)
17564718
Top quark mass measurement in the lepton + jets channel using a matrix element method and in situ jet energy calibration.
A precision measurement of the top quark mass m(t) is obtained using a sample of tt events from pp collisions at the Fermilab Tevatron with the CDF II detector. Selected events require an electron or muon, large missing transverse energy, and exactly four high-energy jets, at least one of which is tagged as coming from a b quark. A likelihood is calculated using a matrix element method with quasi-Monte Carlo integration taking into account finite detector resolution and jet mass effects. The event likelihood is a function of m(t) and a parameter Δ(JES) used to calibrate the jet energy scale in situ. Using a total of 1087 events in 5.6 fb(-1) of integrated luminosity, a value of m(t)=173.0 ± 1.2 GeV/c(2) is measured.