A search for supersymmetry is presented based on events with large missing transverse energy, no isolated electron or muon, and at least three jets with one or more identified as a bottom-quark jet. ...A simultaneous examination is performed of the numbers of events in exclusive bins of the scalar sum of jet transverse momentum values, missing transverse energy, and bottom-quark jet multiplicity. The sample, corresponding to an integrated luminosity of 19.4 fb−1, consists of proton–proton collision data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the LHC in 2012. The observed numbers of events are found to be consistent with the standard model expectation, which is evaluated with control samples in data. The results are interpreted in the context of two simplified supersymmetric scenarios in which gluino pair production is followed by the decay of each gluino to an undetected lightest supersymmetric particle and either a bottom or top quark–antiquark pair, characteristic of gluino mediated bottom- or top-squark production. Using the production cross section calculated to next-to-leading-order plus next-to-leading-logarithm accuracy, and in the limit of a massless lightest supersymmetric particle, we exclude gluinos with masses below 1170 GeV and 1020 GeV for the two scenarios, respectively.
Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top quark (the top squark) ...and the Higgs boson (Higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 fb-1 of proton-proton collision data at s=8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the top squark mass below 360 to 410 GeV, depending on the Higgsino mass.
Charged kaon mass measurement using the Cherenkov effect Graf, N.; Lebedev, A.; Abrams, R.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2010, Letnik:
615, Številka:
1
Journal Article
Recenzirano
The two most recent and precise measurements of the charged kaon mass use X-rays from kaonic atoms and report uncertainties of 14 and 22
ppm yet differ from each other by 122
ppm. We describe the ...possibility of an independent mass measurement using the measurement of Cherenkov light from a narrow-band beam of kaons, pions, and protons. This technique was demonstrated using data taken opportunistically by the Main Injector Particle Production experiment at Fermi National Accelerator Laboratory which recorded beams of protons, kaons, and pions ranging in momentum from
+
37
to
+
63
GeV
/
c
. The measured value is
491.3
±
1.7
MeV
/
c
2
, which is within
1.4
σ
of the world average. An improvement of two orders of magnitude in precision would make this technique useful for resolving the ambiguity in the X-ray data and may be achievable in a dedicated experiment.
Measurements are presented of the associated production of a W boson and a charm-quark jet (W + c) in pp collisions at a center-of-mass energy of 7 TeV. The analysis is conducted with a data sample ...corresponding to a total integrated luminosity of 5 inverse femtobarns, collected by the CMS detector at the LHC. W boson candidates are identified by their decay into a charged lepton (muon or electron) and a neutrino. The W + c measurements are performed for charm-quark jets in the kinematic region ptjet > 25 GeV, abs(eta) < 2.5, for two different thresholds for the transverse momentum of the lepton from the W-boson decay, and in the pseudorapidity range abs(etaell) < 2.1. Hadronic and inclusive semileptonic decays of charm hadrons are used to measure the following total cross sections: sigma(pp to W + c + X) times B(W to ell nu) = 107.7 +/- 3.3 (stat.) +/- 6.9 (syst.) pb (ptell > 25 GeV) and sigma(pp to W + c + X) times B(W to ell nu) = 84.1 +/- 2.0 (stat.) +/- 4.9 (syst.) pb (ptell > 35 GeV), and the cross section ratios sigma(pp to W+ + c + X)/sigma(pp to W- + c + X) = 0.954 +/- 0.025 (stat.) +/- 0.004 (syst.) (ptell > 25 GeV) and sigma(pp to W+ + c bar + X)/sigma(pp to W- + c + X) = 0.938 +/- 0.019 (stat.) +/- 0.006 (syst.) (ptell > 35 GeV). Cross sections and cross section ratios are also measured differentially with respect to the absolute value of the pseudorapidity of the lepton from the W-boson decay. These are the first measurements from the LHC directly sensitive to the strange quark and antiquark content of the proton. Results are compared with theoretical predictions and are consistent with the predictions based on global fits of parton distribution functions.
A
bstract
A search for microscopic black holes and string balls is presented, based on a data sample of pp collisions at
$ \sqrt{s}=8 $
TeV recorded by the CMS experiment at the Large Hadron Collider ...and corresponding to an integrated luminosity of 12 fb
−1
. No excess of events with energetic multiparticle final states, typical of black hole production or of similar new physics processes, is observed. Given the agreement of the observations with the expected standard model background, which is dominated by QCD multijet production, 95% confidence level limits are set on the production of semiclassical or quantum black holes, or of string balls, corresponding to the exclusions of masses below 4.3 to 6.2 TeV, depending on model assumptions. In addition, model-independent limits are set on new physics processes resulting in energetic multiparticle final states.
A
bstract
Results of searches for heavy stable charged particles produced in pp collisions at
$ \sqrt{s} $
= 7 and 8 TeV are presented corresponding to an integrated luminosity of 5.0 fb
−1
and 18.8 ...fb
−1
, respectively. Data collected with the CMS detector are used to study the momentum, energy deposition, and time-of-flight of signal candidates. Leptons with an electric charge between
e
/3 and 8
e
, as well as bound states that can undergo charge exchange with the detector material, are studied. Analysis results are presented for various combinations of signatures in the inner tracker only, inner tracker and muon detector, and muon detector only. Detector signatures utilized are long time-of-flight to the outer muon system and anomalously high (or low) energy deposition in the inner tracker. The data are consistent with the expected background, and upper limits are set on the production cross section of long-lived gluinos, scalar top quarks, and scalar
τ
leptons, as well as pair produced long-lived leptons. Corresponding lower mass limits, ranging up to 1322 GeV/
c
2
for gluinos, are the most stringent to date.
A
bstract
A search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra measured with the CMS detector at the LHC. The data set corresponds to 5 fb
...−1
of integrated luminosity collected in pp collisions at
$ \sqrt{s}=7 $
TeV. No narrow resonances or quantum black holes are observed. Model-independent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E
6
diquarks (3.75 TeV), and on the masses of W′ (1.92 TeV) and Z′ (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.
A
bstract
Results are presented from a search for third-generation leptoquarks and scalar bottom quarks in a sample of proton-proton collisions at
$ \sqrt{s}=7\;TeV $
collected by the CMS experiment ...at the LHC, corresponding to an integrated luminosity of 4.7 fb
−1
. A scenario where the new particles are pair produced and each decays to a b quark plus a tau neutrino or neutralino is considered. The number of observed events is found to be in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the production cross sections. Leptoquarks with masses below ~450 GeV are excluded. Upper limits in the mass plane of the scalar quark and neutralino are set such that scalar bottom quark masses up to 410 GeV are excluded for neutralino masses of 50 GeV.
The fixed-target Main Injector Particle Production (MIPP) experiment, Fermilab E907, was designed to measure the production of hadrons from the collisions of hadrons of momenta ranging from 5 to 120 ...GeV/c on a variety of nuclei. These data will generally improve the simulation of particle detectors and predictions of particle beam fluxes at accelerators. The spectrometer momentum resolution is between 3% and 4%, and particle identification is performed for particles ranging between 0.3 and 80 GeV/c using dE/dx, time-of-flight, and Cherenkov radiation measurements. MIPP collected 1.42 x 10 super(6) events of 120 GeV Main Injector protons striking a target used in the Neutrinos at the Main Injector facility at Fermilab. The data have been analyzed and we present here charged pion yields per proton on target determined in bins of longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined statistical and systematic relative uncertainties between 5% and 10%.
The aim of this paper was to determine the effect of fiber-reinforced polymer (FRP) strengthening on the dynamic characteristics of reinforced concrete (RC) frames using ambient vibration-based ...automated model updating procedure. Four different structural conditions were examined: undamaged, damaged, "repaired with injections"; and "strengthened with FRP composites". Ambient vibration tests were conducted to extract the experimental dynamic characteristics using enhanced frequency domain decomposition (EFDD) and stochastic subspace identification (SSI) methods. To validate the experimental results, an initial finite element (FE) model was constructed and numerical dynamic characteristics obtained. To eliminate the differences between initial FE and experimental results, global and sensitivity-based automated model updating procedures were applied to account for various uncertain parameters. The maximum differences were reduced from 38.38% to 4.14% and 0.21% with global and automated model updating. The updated FE model was used as the initial model for the damaged condition. This procedure was followed for each structural condition in turn to demonstrate the effect of FRP strengthening.
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