3,368 research outputs found
Z boson production in p+Pb collisions at sNN√=5.02 TeV measured with the ATLAS detector
The ATLAS Collaboration has measured the inclusive production of Z bosons via their decays into electron and muon pairs in p+Pb collisions at √ sNN = 5.02 TeV at the Large Hadron Collider. The measurements are made using data corresponding to integrated luminosities of 29.4 nb−1 and 28.1 nb−1 for Z → ee and Z → µµ, respectively. The results from the two channels are consistent and combined to obtain a cross section times the Z → `` branching ratio, integrated over the rapidity region |y ∗ Z | < 3.5, of 139.8 ± 4.8 (stat.) ± 6.2 (syst.) ± 3.8 (lumi.) nb. Differential cross sections are presented as functions of the Z boson rapidity and transverse momentum, and compared with models based on parton distributions both with and without nuclear corrections. The centrality dependence of Z boson production in p+Pb collisions is measured and analyzed within the framework of a standard Glauber model and the model’s extension for fluctuations of the underlying nucleon-nucleon scattering cross sectionFil: Aad, G.. Aix-Marseille Université; FranciaFil: Abbott, B.. Oklahoma State University; Estados UnidosFil: Abdallah, J.. Academia Sinica; ChinaFil: Abdinov, O.. Azerbaijan Academy of Sciences; AzerbaiyánFil: Aben, R.. University of Amsterdam; Países BajosFil: Alconada Verzini, María Josefina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Alonso, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Arduh, Francisco Anuar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Dova, Maria Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Monticelli, Fernando Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Wahlberg, Hernan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Otero y Garzon, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Piegaia, Ricardo Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Reisin, Hernan Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Sacerdoti, Sabrina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Zieminska, D.. Indiana University; Estados UnidosFil: Zimine, N. I.. Joint Institute for Nuclear Research ; RusiaFil: Zimmermann, C.. Universität Mainz; AlemaniaFil: Zimmermann, S.. Albert-Ludwigs-Universität; AlemaniaFil: Zinonos, Z.. Georg-August-Universität; AlemaniaFil: Zinser, M.. Universität Mainz; AlemaniaFil: Ziolkowski, M.. Universität Siegen ; AlemaniaFil: Živković, L.. University of Belgrade; SerbiaFil: Zobernig, G.. University of Wisconsin; Estados UnidosFil: Zoccoli, A.. Università di Bologna; ItaliaFil: Nedden, M. zur. Humboldt University; AlemaniaFil: Zurzolo, G.. Università di Napoli; ItaliaFil: Zwalinski, L.. Cern - European Organization For Nuclear Research; SuizaFil: The ATLAS Collaboration. No especifica
Measurement of the production of a W boson in association with a charm quark in pp collisions at sqrt(s)=7 TeV with the ATLAS detector
The production of a W boson in association with a single charm quark is studied using 4.6 fb^-1 of pp collision data at sqrt(s)=7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26 -0.30 at Q^2=1.9 GeV^2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W^+ + bar{c})/sigma(W^- + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-bar{s} quark asymmetry.Fil: ATLAS Collaboration, G. AAd, F. Monticelli, et al. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Cern - European Organization For Nuclear Research; Suiz
Measurement of the parity-violating asymmetry parameter αb and the helicity amplitudes for the decay Λ0b→J/ψ+Λ0 with the ATLAS detector
A measurement of the parity-violating decay asymmetry parameter, αb, and the helicity amplitudes for the decay Λb0→J/ψ(μ+μ-)Λ0(pπ-) is reported. The analysis is based on 1400 Λb0 and Λ¯b0 baryons selected in 4.6 fb-1 of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the Λb0 and Λ¯b0 samples under the assumption of CP conservation, the value of αb is measured to be 0.30±0.16(stat)±0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.Fil: F. Monticelli.Fil: Atlas Collaboration
Lambda hyperon production and polarization in collisions of p(3.5 GeV) + Nb
Results on hyperon production are reported for collisions of p(3.5
GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at
SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse
mass distributions in rapidity bins are well described by Boltzmann shapes with
a maximum inverse slope parameter of about MeV at a rapidity of ,
i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions,
. The rapidity density decreases monotonically with increasing
rapidity within a rapidity window ranging from 0.3 to 1.3. The
phase-space distribution is compared with results of other experiments and with
predictions of two transport approaches which are available publicly. None of
the present versions of the employed models is able to fully reproduce the
experimental distributions, i.e. in absolute yield and in shape. Presumably,
this finding results from an insufficient modelling in the transport models of
the elementary processes being relevant for production, rescattering
and absorption. The present high-statistics data allow for a genuine
two-dimensional investigation as a function of phase space of the
self-analyzing polarization in the weak decay . Finite negative values of the polarization in the order of
are observed over the entire phase space studied. The absolute value of the
polarization increases almost linearly with increasing transverse momentum for
MeV/c and increases with decreasing rapidity for .Comment: accepted by Eur. Phys. J.
Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy
Data on inclusive pion and eta production measured with the dielectron
spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV
are presented. Our results, obtained with the photon conversion method,
supplement the rather sparse information on neutral meson production in
proton-nucleus reactions existing for this bombarding energy regime. The
reconstructed e+e-e+e- transverse-momentum and rapidity distributions are
confronted with transport model calculations, which account fairly well for
both pi0 and eta production.Comment: 12 pages, 9 figures, submitted to Physical Review
Searching a Dark Photon with HADES
We present a search for the e+e- decay of a hypothetical dark photon, also
names U vector boson, in inclusive dielectron spectra measured by HADES in the
p (3.5 GeV) + p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction.
An upper limit on the kinetic mixing parameter squared epsilon^{2} at 90% CL
has been obtained for the mass range M(U) = 0.02 - 0.55 GeV/c2 and is compared
with the present world data set. For masses 0.03 - 0.1 GeV/c^2, the limit has
been lowered with respect to previous results, allowing now to exclude a large
part of the parameter region favoured by the muon g-2 anomaly. Furthermore, an
improved upper limit on the branching ratio of 2.3 * 10^{-6} has been set on
the helicity-suppressed direct decay of the eta meson, eta-> e+e-, at 90% CL
Inclusive Dielectron Production in Ar+KCl Collisions at 1.76 AGeV studied with HADES
Results of the HADES measurement of inclusive dielectron production in Ar+KCl
collisions at a kinetic beam energy of 1.76 AGeV are presented. For the first
time, high mass resolution spectroscopy was performed. The invariant mass
spectrum of dielectrons is compared with predictions of UrQMD and HSD transport
codes.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering
We have measured the spin-dependent structure function in inclusive
deep-inelastic scattering of polarized muons off polarized protons, in the
kinematic range and . A
next-to-leading order QCD analysis is used to evolve the measured
to a fixed . The first moment of at is .
This result is below the prediction of the Ellis-Jaffe sum rule by more than
two standard deviations. The singlet axial charge is found to be . In the Adler-Bardeen factorization scheme, is
required to bring in agreement with the Quark-Parton Model. A
combined analysis of all available proton and deuteron data confirms the
Bjorken sum rule.Comment: 33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical
Review
Future perspectives at SIS-100 with HADES-at-FAIR
Currently, the HADES spectrometer undergoes un upgrade program to be prepared
for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the
current status of the HADES di-electron measurements at the SIS-18 and our
future plans for SIS-100.Comment: Invited contribution presented at the XLVII International Winter
Meeting on Nuclear Physics, Bormio (Italy), Jan. 26-30, 200
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