7811061
Atomic-weight dependence of the production of hadron pairs by 800-GeV/c protons on nuclear targets.
Fermilab experiment 711 has investigated proton-nucleus collisions in which two high-transverse-momentum hadrons are produced forming high-mass ++, +{minus}, and {minus}{minus} charged states, using an 800-GeV/{ital c} proton beam on targets of beryllium, aluminum, iron, and tungsten. Our data cover the range in dihadron mass from 6 to 15 GeV/{ital c}{sup 2}. We show here that the dependence of the cross section on atomic weight {ital A} can be parametrized as {ital A}{sup {alpha}} where {alpha}=1.043{plus minus}0.011(stat){plus minus}0.025 (syst), and is independent of the charge state of the dihadron system.
122705388
Measurement of the Muon Stopping Power in Lead Tungstate
A large sample of cosmic ray events collected by the CMS detector is exploited to measure the specific energy loss of muons in the lead tungstate of the electromagnetic calorimeter. The measurement spans a momentum range from 5 GeV/c to 1 TeV/c. The results are consistent with the expectations over the entire range. The calorimeter energy scale, set with 120 GeV/c electrons, is validated down to the sub-GeV region using energy deposits, of order 100 MeV, associated with low-momentum muons. The muon critical energy in lead tungstate is measured to be 160+5/-6 plus or minus 8 GeV, in agreement with expectations. This is the first experimental determination of muon critical energy.
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.
209834639
Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV
Results are presented from a search for physics beyond the standard model based on events with large missing transverse energy, at least three jets, and at least one, two, or three b-quark jets. The study is performed using a sample of proton-proton collision data collected at sqrt(s)=7 TeV with the CMS detector at the LHC in 2011, with the missing transverse energy distribution as the principal search variable. The integrated luminosity of the sample is 4.98 inverse femtobarns. The observed number of events is found to be consistent with the standard model expectation, which is evaluated using control samples in the data. The results are used to constrain cross sections for the production of supersymmetric particles decaying to b-quark-enriched final states in the context of simplified model spectra.
40497104
Performance of CMS muon reconstruction in $pp$ collision events at $\sqrt{s}=7$ TeV
The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta)<2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.
122635454
Calibration of the CMS drift tube chambers and measurement of the drift velocity with cosmic rays
This paper describes the calibration procedure for the drift tubes of the CMS barrel muon system and reports the main results obtained with data collected during a high statistics cosmic ray data-taking period. The main goal of the calibration is to determine, for each drift cell, the minimum time delay for signals relative to the trigger, accounting for the drift velocity within the cell. The accuracy of the calibration procedure is influenced by the random arrival time of the cosmic muons relative to the LHC clock cycle. A more refined analysis of the drift velocity was performed during the offline reconstruction phase, which takes into account this feature of cosmic ray events.
45798253
Aspects of the chiral quark model.
We point out intriguing connections between the chiral quark model in which the nucleon is treated as a soliton and the ordinary potential-binding quark model. The axial-vector coupling comes out near the value (5/3 rather than around 0.7 as in the Skyrme description and can be easily ''fine-tuned'' to its experimental value. A ''linear potential'' in some sense is generated as a collective effect of the ''meson cloud.'' Contact with QCD is made by introducing a gluonium field so as to satisfy the trace-anomaly equation. In the simplest treatment of this field one predicts a scalar-isoscalar state at 900 MeV in agreement with a recent analysis of experiments. The model is used to discuss how a ''nontrivial winding number'' emerges for the meson fields. A number of additional features of the model are treated.
36956553
Scale anomaly and the scalars.
We investigate the properties of a possible low-lying scalar glueball as well as the ordinary scalar-quark states using an effective chiral Lagrangian which satisfies the trace anomaly and U(1)/sub A/ anomaly of QCD. An interesting mass bound for the lightest particle in the scalar-singlet channel is discussed. Detailed arguments against the existence of a very light (less than 400 MeV) scalar glueball are presented. It is shown that the introduction of a derivative-coupling term in the usual type of linear sigma model cures the problem of excessively large widths for the ordinary (nonet) scalar mesons. In fact, chiral symmetry enables one to nicely correlate the widths of the entire scalar nonet. It is noted that the same derivative-coupling term allows a heavy (1-2 GeV) scalar glueball to have sufficiently narrow width to permit its observation as an ordinary resonance, in contrast with a recent claim. Our model can naturally explain the unusually large partial width for the etaeta' mode of the glueball candidate G(1590). A symmetrical ansatz for the anomaly terms is suggested which enables one to successfully calculate the eta' mass as the ratio of gluon condensate to pion-decay constant. In addition, the theoretically interesting limit where the glueballmore » becomes a true dilaton is formulated in a new and illustrative way.« less
23146513
Bag formation in the presence of vector mesons. II. Inclusion of scalars.
We construct an effective Lagrangian of pions, the vector mesons rho and ..omega.., as well as a scalar meson and a scalar glueball which incorporates chiral symmetry and the QCD trace anomaly. The scalar sector is set up so that it contains particles in a realistic mass range with physically narrow widths. We calculate static nucleon properties and demonstrate that shallow bags with typical confinement sizes of Rapprox.1/2 fm are favored by phenomenology.
32539092
Measurement of the mass of the tau lepton.
The mass of the [tau] lepton has been measured at the Beijing Electron-Positron Collider using the Beijing Spectrometer. A search near threshold for [ital e][sup +][ital e[minus]][r arrow][tau][sup +][tau][sup [minus]] was performed. Candidate events were identified by requiring that one [tau] decay via [tau][r arrow][ital e][nu][bar [nu]], and the other via [tau][r arrow][mu][nu][bar [nu]]. The mass value, obtained from a fit to the energy dependence of the [tau][sup +][tau][sup [minus]] cross section, is [ital m][sub [tau]]=1776.9[sub [minus]0.5][sup +0.4][plus minus]0.2 MeV.
36028712
Driven response of a trapped particle beam.
The dynamics of a metastable beam of particles injected'' into artificially excited resonance islands in the Fermilab Tevatron is studied. Evolution of the captured beam distribution is measured by an externally detectable coherent signal. Dynamical partitions observed in the control space of amplitude and tune of a focusing modulation are consistent with an equivalent mode of an ensemble of driven gravity pendula. The model's single parameter, the island tune {ital Q}{sub {ital I}} of small oscillations, is inferred as the central frequency of resonant detrapping under this weak drive.