Publications (40)0 Total impact
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: A search for pair production of first-generation scalar leptoquarks is performed in the final state containing two electrons and two jets using proton-proton collision data at sqrt(s)=7 TeV. The data sample used corresponds to an integrated luminosity of 33 inverse picobarns collected with the CMS detector at the CERN LHC. The number of observed events is in good agreement with the predictions for the standard model background processes, and an upper limit is set on the leptoquark pair production cross section times beta^2 as a function of the leptoquark mass, where beta is the branching fraction of the leptoquark decay to an electron and a quark. A 95% confidence level lower limit is set on the mass of a first-generation scalar leptoquark at 384 GeV for beta=1, which is the most stringent direct limit to date.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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[hide abstract]
ABSTRACT: A measurement of the b-hadron production cross section in proton-proton collisions at sqrt(s)=7 TeV is presented. The dataset, corresponding to 85 inverse nanobarns, was recorded with the CMS experiment at the LHC using a low-threshold single-muon trigger. Events are selected by the presence of a muon with transverse momentum greater than 6 GeV with respect to the beam direction and pseudorapidity less than 2.1. The transverse momentum of the muon with respect to the closest jet discriminates events containing b hadrons from background. The inclusive b-hadron production cross section is presented as a function of muon transverse momentum and pseudorapidity. The measured total cross section in the kinematic acceptance is sigma(pp to b+X to mu + X') =1.32 +/- 0.01 (stat) +/- 0.30 (syst) +/- 0.15 (lumi) microbarns.
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Serguei Chatrchyan,
Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: A search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 inverse picobarns. No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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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 pb-1 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 --> WX) X B(W--> ln) = 9.95 +/- 0.07 (stat.) +/- 0.28 (syst.) +/- 1.09 (lumi.) nb and sigma(pp --> ZX) X B(Z --> ll) = 0.931 +/- 0.026 (stat.) +/- 0.023 (syst.) +/- 0.102 (lumi.) nb, where l stands for either e or mu. 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.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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[hide abstract]
ABSTRACT: A search for pair production of second-generation scalar leptoquarks in the final state with two muons and two jets is performed using proton-proton collision data at sqrt(s) = 7 TeV collected by the CMS detector at the LHC. The data sample used corresponds to an integrated luminosity of 34 inverse picobarns. The number of observed events is in good agreement with the predictions from the standard model processes. An upper limit is set on the second-generation leptoquark cross section times beta^2 as a function of the leptoquark mass, and leptoquarks with masses below 394 GeV are excluded at a 95% confidence level for beta = 1, where beta is the leptoquark branching fraction into a muon and a quark. These limits are the most stringent to date.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Giovanni Polese,
Don Reeder,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: Bose-Einstein correlations between identical particles are measured in samples of proton-proton collisions at 0.9 and 7 TeV centre-of-mass energies, recorded by the CMS experiment at the LHC. The signal is observed in the form of an enhancement of number of pairs of same-sign charged particles with small relative momentum. The dependence of this enhancement on kinematic and topological features of the event is studied.
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Serguei Chatrchyan,
Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: A new heavy gauge boson, W', decaying to a muon and a neutrino, is searched for in pp collisions at a centre-of-mass of 7 TeV. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 36 inverse picobarns. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the muon-neutrino system. Masses below 1.40 TeV are excluded at the 95% confidence level for a sequential standard-model-like W'. The W' mass lower limit increases to 1.58 TeV when the present analysis is combined with the CMS result for the electron channel.
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Serguei Chatrchyan,
Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl, [......],
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Francesco Palmonari,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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[hide abstract]
ABSTRACT: A search for large extra spatial dimensions via virtual-graviton exchange in the diphoton channel has been carried out with the CMS detector at the LHC. No excess of events above the standard model expectations is found using a data sample collected in proton-proton collisions at sqrt(s) = 7 TeV and corresponding to an integrated luminosity of 36 inverse picobarns. New lower limits on the effective Planck scale in the range of 1.6-2.3 TeV at the 95% confidence level are set, providing the most restrictive bounds to date on models with more than two large extra dimensions.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
[show abstract]
[hide abstract]
ABSTRACT: A search for a heavy gauge boson W' has been conducted by the CMS experiment at the LHC in the decay channel with an electron and large transverse energy imbalance, using proton-proton collision data corresponding to an integrated luminosity of 36 inverse picobarns. No excess above standard model expectations is seen in the transverse mass distribution of the electron-(missing E_T) system. Assuming standard-model-like couplings and decay branching fractions, a W' boson with a mass less than 1.36 TeV/$c^2$ is excluded at 95% confidence level.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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[hide abstract]
ABSTRACT: The result of a search at the LHC for heavy stable charged particles produced in pp collisions at sqrt(s) = 7 TeV is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 inverse picobarns. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398 GeV/c2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Giovanni Polese,
Don Reeder,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Jessica Leonard,
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
Giovanni Polese,
Don Reeder,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: A measurement of the underlying activity in scattering processes with pT scale in the GeV region is performed in proton-proton collisions at $\sqrt{s}$ = 0.9 TeV, using data collected by the CMS experiment at the LHC. Charged hadron production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged hadrons with pseudorapidity |h| <2, pT >0.5 GeV/c, and azimuthal direction transverse to that of the leading object.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
William Parker,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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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.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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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.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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ABSTRACT: A measurement of the angular correlations between beauty and anti-beauty hadrons (B B-bar) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential B B-bar production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 inverse picobarns, shows that a sizable fraction of the B B-bar pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of b b-bar production.
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Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
Christos Lazaridis,
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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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 K0_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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Serguei Chatrchyan,
Vardan Khachatryan,
Albert M. Sirunyan,
Armen Tumasyan,
Wolfgang Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl, [......],
Jessica Leonard,
Richard Loveless,
Ajit Mohapatra,
Francesco Palmonari,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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[hide abstract]
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 Adam,
Thomas Bergauer,
Marko Dragicevic,
Janos Erö,
Christian Fabjan,
Markus Friedl,
Rudolf Fruehwirth, [......],
David Lomidze,
Richard Loveless,
Ajit Mohapatra,
William Parker,
Don Reeder,
Ian Ross,
Alexander Savin,
Wesley H. Smith,
Joshua Swanson,
Marc Weinberg
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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.
