Showing papers by "Universidad Iberoamericana Ciudad de México published in 2011"
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TL;DR: In this article, the transverse momentum balance in dijet and γ/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transversal momentum resolution.
Abstract: Measurements of the jet energy calibration and transverse momentum resolution in CMS are presented, performed with a data sample collected in proton-proton collisions at a centre-of-mass energy of 7TeV, corresponding to an integrated luminosity of 36pb−1. The transverse momentum balance in dijet and γ/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transverse momentum resolution. The results are presented for three different methods to reconstruct jets: a calorimeter-based approach, the ``Jet-Plus-Track'' approach, which improves the measurement of calorimeter jets by exploiting the associated tracks, and the ``Particle Flow'' approach, which attempts to reconstruct individually each particle in the event, prior to the jet clustering, based on information from all relevant subdetectors
750 citations
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TL;DR: In this article, the authors studied the effect of collision centrality on the transverse momentum of PbPb collisions at the LHC with a data sample of 6.7 inverse microbarns.
Abstract: Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.
621 citations
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TL;DR: In this article, a new measurement of the inclusive forward-backward t{bar t} production asymmetry and its rapidity and mass dependence was presented, with data corresponding to an integrated luminosity of 5.3 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV.
Abstract: We present a new measurement of the inclusive forward-backward t{bar t} production asymmetry and its rapidity and mass dependence. The measurements are performed with data corresponding to an integrated luminosity of 5.3 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, recorded with the CDF II Detector at the Fermilab Tevatron. Significant inclusive asymmetries are observed in both the laboratory frame and the t{bar t} rest frame, and in both cases are found to be consistent with CP conservation under interchange of t and {bar t}. In the t{bar t} rest frame, the asymmetry is observed to increase with the t{bar t} rapidity difference, {Delta}y, and with the invariant mass M{sub t{bar t}} of the t{bar t} system. Fully corrected parton-level asymmetries are derived in two regions of each variable, and the asymmetry is found to be most significant at large {Delta}y and M{sub t{bar t}}. For M{sub t{bar t}} {ge} 450 GeV/c{sup 2}, the parton-level asymmetry in the t{bar t} rest frame is A{sup t{bar t}} = 0.475 {+-} 0.114 compared to a next-to-leading order QCD prediction of 0.088 {+-} 0.013.
327 citations
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TL;DR: In this paper, a search for events with jets and missing transverse energy is performed in a data sample of pp collisions collected at 7 TeV by the CMS experiment at the LHC.
Abstract: A search for events with jets and missing transverse energy is performed in a data sample of pp collisions collected at sqrt(s) = 7 TeV by the CMS experiment at the LHC. The analyzed data sample corresponds to an integrated luminosity of 1.14 inverse femtobarns. In this search, a kinematic variable, alphaT, is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. No excess of events over the standard model expectation is found. Exclusion limits in the parameter space of the constrained minimal supersymmetric extension of the standard model are set. In this model, squark masses below 1.1 TeV are excluded at 95% CL. Gluino masses below 1.1 TeV are also ruled out at 95% CL for values of the universal scalar mass parameter below 500 GeV.
300 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2193 more•Institutions (152)
TL;DR: In this article, the authors measured the Upsilon production cross section in proton-proton collisions at 7 TeV using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3.1 +/- 0.81 nb.
Abstract: The Upsilon production cross section in proton-proton collisions at sqrt(s) = 7 TeV is measured using a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 3.1 +/- 0.3 inverse picobarns. Integrated over the rapidity range |y|<2, we find the product of the Upsilon(1S) production cross section and branching fraction to dimuons to be sigma(pp to Upsilon(1S) X) B(Upsilon(1S) to mu+ mu-) = 7.37 +/- 0.13^{+0.61}_{-0.42}\pm 0.81 nb, where the first uncertainty is statistical, the second is systematic, and the third is associated with the estimation of the integrated luminosity of the data sample. This cross section is obtained assuming unpolarized Upsilon(1S) production. If the Upsilon(1S) production polarization is fully transverse or fully longitudinal the cross section changes by about 20%. We also report the measurement of the Upsilon(1S), Upsilon(2S), and Upsilon(3S) differential cross sections as a function of transverse momentum and rapidity.
241 citations
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TL;DR: In this paper, a measurement of W and Z production cross sections in pp collisions at 7 TeV is presented, where electron and muon decay channels are analyzed in a data sample collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns.
Abstract: A measurement of inclusive W and Z production cross sections in pp collisions at sqrt(s)=7 TeV is presented. The electron and muon decay channels are analyzed in a data sample collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. The measured inclusive cross sections are sigma(pp-> WX) B(W-> l nu) = 10.30 +/- 0.02 (stat.) +/- 0.10 (syst.) +/- 0.10 (th.) +/- 0.41 (lumi.) nb and sigma(pp -> ZX) B(Z-> l^+l^-) = 0.974 +/- 0.007 (stat.) +/- 0.007 (syst.) +/- 0.018 (th.) +/- 0.039 (lumi.) nb, limited to the dilepton invariant mass range 60 to 120 GeV. The luminosity-independent cross section ratios are [sigma(pp->WX) B(W-> l nu)]/[sigma(pp-> ZX) B(Z->l^+l^-)] = 10.54 +/- 0.07 (stat.) +/- 0.08 (syst.) +/- 0.16 (th.) and [sigma(pp->W^+X) B(W^+ -> l^+nu)] / [sigma(pp->W^- X) B(W^- -> l^- nu)] = 1.421 +/- 0.006 (stat.) +/- 0.014 (syst.) +/- 0.029 (th.). The measured values agree with next-to-next-to-leading order QCD cross section calculations based on recent parton distribution functions.
227 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2184 more•Institutions (150)
TL;DR: In this article, the W and Z boson production cross sections in pp collisions at 7 TeV are presented, based on 2.9 inverse picobarns of data recorded by the CMS detector at the LHC.
Abstract: Measurements of inclusive W and Z boson production cross sections in pp collisions at sqrt(s)=7 TeV are presented, based on 2.9 inverse picobarns of data recorded by the CMS detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give sigma(pp to WX) times B(W to muon or electron + neutrino) = 9.95 \pm 0.07(stat.) \pm 0.28(syst.) \pm 1.09(lumi.) nb and sigma(pp to ZX) times B(Z to oppositely charged muon or electron pairs) = 0.931 \pm 0.026(stat.) \pm 0.023(syst.) \pm 0.102(lumi.) nb. Theoretical predictions, calculated at the next-to-next-to-leading order in QCD using recent parton distribution functions, are in agreement with the measured cross sections. Ratios of cross sections, which incur an experimental systematic uncertainty of less than 4%, are also reported.
225 citations
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TL;DR: In this paper, a comparison of the relative yields of upsilon resonances in the mu(+) mu(-) decay channel in PbPb and pp collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV, is performed with data collected with the CMS detector at the LHC.
Abstract: A comparison of the relative yields of Upsilon resonances in the mu(+) mu(-) decay channel in PbPb and pp collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV, is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4 GeV/c and pseudorapidity below 2.4, the double ratio of the Upsilon(2S) and Upsilon(3S) excited states to the Upsilon(1S) ground state in PbPb and pp collisions,(Upsilon(2S+3S)/Upsilon(1S)[PbPb])/(Upsilon(2S+3S)/Upsilon(1S)[pp]), is found to be 0.31 - 0.15 + 0.19 (stat.) +/- 0.03 (syst.). The probability to obtain the measured value, or lower, if the true double ratio is unity, has been calculated to be less than 1%.
202 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2222 more•Institutions (151)
TL;DR: In this article, the multiplicity distribution of primary charged hadron multiplicity distributions for non-single-diffractive events in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |eta|<0.5 to |eta |<2.4.
Abstract: Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |eta|<0.5 to |eta|<2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distribution at sqrt(s) = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with sqrt(s) is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies.
181 citations
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2184 more•Institutions (152)
TL;DR: In this article, the production of J/psi mesons from b-hadron decays at the LHC was studied in pp collisions at 6.5 to 30 GeV/c and in three rapidity ranges.
Abstract: The production of J/psi mesons is studied in pp collisions at sqrt(s)=7 TeV with the CMS experiment at the LHC. The measurement is based on a dimuon sample corresponding to an integrated luminosity of 314 inverse nanobarns. The J/psi differential cross section is determined, as a function of the J/psi transverse momentum, in three rapidity ranges. A fit to the decay length distribution is used to separate the prompt from the non-prompt (b hadron to J/psi) component. Integrated over J/psi transverse momentum from 6.5 to 30 GeV/c and over rapidity in the range |y| < 2.4, the measured cross sections, times the dimuon decay branching fraction, are 70.9 \pm 2.1 (stat.) \pm 3.0 (syst.) \pm 7.8(luminosity) nb for prompt J/psi mesons assuming unpolarized production and 26.0 \pm 1.4 (stat.) \pm 1.6 (syst.) \pm 2.9 (luminosity) nb for J/psi mesons from b-hadron decays.
175 citations
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TL;DR: In this article, a measurement of the lepton charge asymmetry in WX production at 7 TeV was presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns.
Abstract: A measurement of the lepton charge asymmetry in inclusive pp to WX production at sqrt(s)= 7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. This high precision measurement of the lepton charge asymmetry, performed in both the W to e nu and W to mu nu channels, provides new insights into parton distribution functions.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2155 more•Institutions (136)
TL;DR: The first measurement of the cross section for top-quark pair production in pp collisions at the LHC at center-of-mass energy sqrt(s)= 7 TeV has been performed using 3.1 {\pm} 0.3 inverse pb of data recorded by the CMS detector as discussed by the authors.
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TL;DR: In this article, a search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is performed using pp collisions at root s = 7 TeV corresponding to an integrated luminosity of 1 fb(-1), collected by the CMS experiment at the LHC.
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S. Chatrchyan1, Milan Nikolic2, Robin Erbacher2, C. A. Carrillo Montoya3 +2306 more•Institutions (160)
TL;DR: In this paper, a measurement of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair, is presented.
Abstract: A measurement is presented of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair. The data sample is collected using the CMS detector and a minimum-bias trigger, with the CMS solenoid off. The number of charged hadrons is measured both by counting the number of reconstructed particle hits and by forming hit doublets of pairs of layers in the pixel detector. The two methods give consistent results. The charged hadron multiplicity density dN(ch)/d eta, evaluated at eta=0 for head-on collisions, is found to be 1612 +/- 55, where the uncertainty is dominated by systematic effects. Comparisons of these results to previous measurements and to various models are also presented.
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TL;DR: In this article, the authors measured electroweak production of the top quark in pp collisions at 7 TeV, using a dataset collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns.
Abstract: Electroweak production of the top quark is measured in pp collisions at sqrt(s) = 7 TeV, using a dataset collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. With an event selection optimized for t-channel production, two complementary analyses are performed. The first one exploits the special angular properties of the signal, together with background estimates from data. The second approach uses a multivariate analysis technique to probe the compatibility with signal topology expected from electroweak top quark production. The combined measurement of the cross section is 83.6 +/- 29.8 (stat.+syst.) +/- 3.3 (lumi.) pb, consistent with the standard model expectation.
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Vardan Khachatryan1, Albert M. Sirunyan1, Armen Tumasyan1, Wolfgang Adam +2196 more•Institutions (153)
TL;DR: In this article, the spectra of hadrons were measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV.
Abstract: The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV. The K^0_s, Lambda, and Xi^- particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum. The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The transverse momentum distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.
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TL;DR: In this paper, the authors reported the first observation of the baryonic flavor-changing neutral current decay with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations at √s = 1.73 ± 0.42(stat) ± (syst)] × 10(-6).
Abstract: We report the first observation of the baryonic flavor-changing neutral current decay Λ(b)(0)→Λμ(+)μ(-) with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses a pp collisions data sample corresponding to 6.8 fb(-1) at √s = 1.96 TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Λ(b)(0)→Λμ(+)μ(-) are measured. We find B(Λ(b)(0)→Λμ(+)μ(-))=[1.73 ± 0.42(stat) ± (syst)] × 10(-6). We also report the first measurement of the differential branching ratio of B(s)(0)→ϕμ(+)μ(-), using 49 signal events. In addition, we report branching ratios for B(+)→K(+)μ(+)μ(-), B(0)→K(0)μ(+)μ(-), and B→K(*)(892)μ(+)μ(-) decays.
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TL;DR: In this paper, the authors measured the inclusive jet cross section in pp collisions with a center-of-mass energy of 7 TeV at the LHC using the CMS experiment using the data sample corresponds to an integrated luminosity of 34 inverse picobarns.
Abstract: The inclusive jet cross section is measured in pp collisions with a center-of-mass energy of 7 TeV at the LHC using the CMS experiment. The data sample corresponds to an integrated luminosity of 34 inverse picobarns. The measurement is made for jet transverse momenta in the range 18-1100 GeV and for absolute values of rapidity less than 3. The measured cross section extends to the highest values of jet pT ever observed and, within the experimental and theoretical uncertainties, is generally in agreement with next-to-leading-order perturbative QCD predictions.
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TL;DR: In this article, a search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state, based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC.
Abstract: A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.
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TL;DR: In this article, the first measurements of dihadron correlations for charged particles are presented for central PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV over a broad range in relative pseudorapidity, Delta(eta), and the full range of relative azimuthal angle, Delta (phi).
Abstract: First measurements of dihadron correlations for charged particles are presented for central PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV over a broad range in relative pseudorapidity, Delta(eta), and the full range of relative azimuthal angle, Delta(phi). The data were collected with the CMS detector, at the LHC. A broadening of the away-side (Delta(phi) approximately pi) azimuthal correlation is observed at all Delta(eta), as compared to the measurements in pp collisions. Furthermore, long-range dihadron correlations in Delta(eta) are observed for particles with similar phi values. This phenomenon, also known as the "ridge", persists up to at least |Delta(eta)| = 4. For particles with transverse momenta (pt) of 2-4 GeV/c, the ridge is found to be most prominent when these particles are correlated with particles of pt = 2-6 GeV/c, and to be much reduced when paired with particles of pt = 10-12 GeV/c.
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TL;DR: A search for Z bosons in the mu+mu- decay channel has been performed in PbPb collisions at a nucleon-nucleon center of mass energy = 2.76 TeV with the CMS detector at the LHC, in a 7.2 inverse microbarn data sample as mentioned in this paper.
Abstract: A search for Z bosons in the mu^+mu^- decay channel has been performed in PbPb collisions at a nucleon-nucleon centre of mass energy = 2.76 TeV with the CMS detector at the LHC, in a 7.2 inverse microbarn data sample. The number of opposite-sign muon pairs observed in the 60--120 GeV/c^2 invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of (33.8 +/- 5.5 (stat) +/- 4.4 (syst)) 10^{-8}, in the |y|<2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.
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TL;DR: In this paper, the invariant mass distribution of jet pairs produced in association with a W boson was studied and the observed distribution has an excess in the 120-160 GeV/c(2) mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties.
Abstract: We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb(-1). The observed distribution has an excess in the 120-160 GeV/c(2) mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this Letter, we report studies of the properties of this excess.
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TL;DR: Please cite this paper as: Mier‐Cabrera J, Jiménez‐Zamudio L, García‐Latorre E, Cruz‐Orozco O, Hernández‐Guerrero C.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2143 more•Institutions (135)
TL;DR: In this paper, a search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV was conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 inverse picobarns.
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TL;DR: In this article, a search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC.
Abstract: A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets.
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TL;DR: It is established, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.
Abstract: A first measurement of the polarization of W bosons with large transverse momenta in pp collisions is presented. The measurement is based on 36 pb(-1) of data recorded at root s = 7 TeV by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions (f(L), f(R), and f(0), respectively) of W bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: (f(L) - f(R))(-) = 0.240 +/- 0.036(syst) +/- 0.031(syst) and f(0)(-) = 0.183 +/- 0.087(stat) +/- 0.123(syst) for negatively charged W bosons and (f(L) - f(R))(+) = 0.310 +/- 0.036(syst) +/- 0.017(syst) and f(0)(+) = 0.171 +/- 0.085(syst) +/- 0.099(syst) for positively charged W bosons. This establishes, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.
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TL;DR: In this paper, the main characteristics of electrochemistry as a promising green methodology for organic synthesis are described and exemplified, and their relationship with the twelve green chemistry principles is described.
Abstract: Over the last decade, organic electrosynthesis has become recognized as one of the methodologies that can fulfill several important criteria that are needed if society is to develop environmentally compatible processes. It can be used to replace toxic or dangerous oxidizing or reducing reagents, reduce energy consumption, and can be used for the in situ production of unstable and hazardous reagents. These are just a few of the most important attributes that render electrochemistry environmentally useful. In this review the main characteristics of electrochemistry as a promising green methodology for organic synthesis are described and exemplified. Herein we provide basic information concerning the nature of electrosynthetic processes, paired electrochemical reactions, electrocatalytic reactions, reactions carried out in ionic liquids, electrogeneration of reactants, electrochemical reactions that use renewable starting materials (biomass), green organic electrosynthesis in micro- and nano-emulsions, the synthesis of complex molecules using an electrosynthetic key step, and conclude with some insights concerning the future. Throughout the review the “green aspects” of these topics are highlighted and their relationship with the twelve green chemistry principles is described.
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TL;DR: In this article, a measurement of the underlying activity in scattering processes with a hard scale in the several GeV region is performed in proton-proton collisions at squarert(s) = 0.9 and 7 TeV.
Abstract: A measurement of the underlying activity in scattering processes with a hard scale in the several GeV region is performed in proton-proton collisions at sqrt(s) = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |eta| 0.5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-pT sum of the particles in the transverse region is observed with increasing pT of the leading track-jet, followed by a much slower rise above a few GeV/c. For track-jet pT larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in PYTHIA are compared to the data.
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Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam1 +2209 more•Institutions (152)
TL;DR: In this paper, the authors measured the total and differential cross sections with respect to transverse momentum and rapidity for B+ mesons produced in pp collisions at square root(s) = 7 TeV.
Abstract: Measurements of the total and differential cross sections with respect to transverse momentum and rapidity for B+ mesons produced in pp collisions at sqrt(s) = 7 TeV are presented. The data correspond to an integrated luminosity of 5.8 inverse picobarns collected by the CMS experiment operating at the LHC. The exclusive decay B+ to J/psi K+, with the J/psi decaying to an oppositely charged muon pair, is used to detect B+ mesons and to measure the production cross section as a function of the transverse momentum and rapidity of the B. The total cross section for p_t(B) > 5 GeV and |y(B)| < 2.4 is measured to be 28.1 +/- 2.4 +/- 2.0 +/- 3.1 microbarns, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement.