1,722,545 research outputs found
Measurement of Differential Cross Sections at 7 TeV
No full textA measurement is presented of the normalized differential cross sections of top-quark pair production in pp collisions at a center of mass energy of 7 TeV, using 1.1 fb of data collected in 2011 by the CMS experiment. The measurement is performed using five different final states with one or two muons or electrons in the final state. The event selections yield high purity samples. Kinematic reconstructions are performed to obtain full information of the top quarks, the
system and the final state leptons. The results are compared to several QCD predictions up to next-to-leading order
Studies of +X at CMS
No full textThis talk is dedicated to the most recent measurements of the processes that feature the production of a top quark pair either with an electroweak standard model boson, or another pair of top, bottom or light quarks. For the measurement of the production cross-section of top quark pair in association with a photon, 19.7 of proton-proton collision data collected by CMS detector at = 8 TeV is used, while for four top production, + bb, + jj, W and Z the data collected at = 13 TeV amounting to 35.9 , is used. The measurement of is performed in the fiducial phase space corresponding to the semileptonic decay chain of the top quark pair, and the cross section is measured relative to the inclusive top quark pair production cross section. The fiducial cross section for this process is found to be 127 27 (stat + syst) fb. The most recent search for the four top quark production, that explores the same-sign dilepton final state, set the upper observed (expected) limit to 4.6 () times predicted standard model cross section. The measured cross section of the top pair production with two b quarks is found to be ( + bb) = 3.9 0.6 (stat) 1.3 (syst) pb in the full phase space. The measurement of the W and Z processes combines three final states with two same-sign, three and four leptons. The W and Z production cross sections are measured to be (Z) = pb and (W) = pb with an expected (observed) significance of 4.6 (5.5) and 9.5 (9.9) standard deviations from the background-only hypothesis. The latter measurements are used to constrain the Wilson coefficients for four dimension-six operators describing interactions of new physics that would modify W and Z production
Reflexió crítica sobre RM/T
No full textS'analitza el nou model relacional RM/T d'En Codd, criticant-ne diferents punts, en particular els referents al paper de les "entitats", i situant-lo en relació a altres recerques
Reflexió crítica sobre RM/T
No full textS'analitza el nou model relacional RM/T d'En Codd, criticant-ne diferents punts, en particular els referents al paper de les "entitats", i situant-lo en relació a altres recerques.Postprint (published version
Reflexió crítica sobre RM/T
No full textS'analitza el nou model relacional RM/T d'En Codd, criticant-ne diferents punts, en particular els referents al paper de les "entitats", i situant-lo en relació a altres recerques.Postprint (published version
Measurements of , production, and production at CMS
No full textThe most recent CMS measurements of the production of pairs with two additional jets, or two additional b quarks, are presented. These two processes are important for several reasons: they can allow a better modeling of Monte Carlo simulations, because of the different energy scale associated to b-jets and generic jets; they are important backgrounds to other standard model processes; and they might be related to new physics. In addition, the search for the production of two pairs is discussed, along with its connection to the Yukawa coupling of top quarks to the Higgs boson
B-meson hadroproduction in the SACOT- scheme
Get PDFWe apply the SACOT- general-mass variable flavour number scheme
(GM-VFNS) to the inclusive B-meson production in hadronic collisions at
next-to-leading order in perturbative Quantum Chromodynamics. In the GM-VFNS
approach one matches the fixed-order heavy-quark production cross sections,
accurate at low transverse momentum (), with the zero-mass cross
sections, accurate at high . The physics idea of the SACOT- scheme is to do this by accounting for the finite momentum transfer
required to create a heavy quark-antiquark pair throughout the calculation. We
compare our results with the latest LHC data from proton-proton and proton-lead
collisions finding a very good agreement within the estimated theoretical
uncertainties. We discuss also scheme-related differences and their impact on
the scale uncertainties.Comment: Version that matches with the one accepted for publicatio
Energy dependence of light neutral meson spectrum produced in pp collisions at the LHC measured in ALICE
No full textWe present the measurement of light neutral mesons, and , in pp collisions at different center-of-mass energies obtained with the ALICE experiment at the LHC. The and mesons are measured via photons reconstructed by the electromagnetic calorimeters and the central tracking system. The invariant cross-section of and mesons are measured in a broad range at and 8 TeV. The spectra of and mesons measured in pp collisions at different collision energies show -scaling at high and violation of -scaling at low . The smaller -scaling exponents of our measurements compared to RHIC may hint at a reduced importance of higher twist processes at LHC
Quantification of the low- pion excess in heavy-ion collisions at the LHC and top RHIC energy
Get PDFA Bayesian inference analysis is performed to quantify the pion excess in the
low transverse momentum () regime in heavy-ion collisions. This
quantification is conducted across centrality classes and collision systems at
the LHC and top RHIC energy. The analysis is based on the relativistic fluid
dynamics description of spectra of identified charged hadrons. A
range scan investigation to determine the optimal range for the
pion spectra with respect to a fluid dynamic description is
performed, finding 0.5~~2.0~GeV. A significant low- pion excess is computed across all centrality classes and collision systems
investigated, indicating that a clear low- component arises from
different physics mechanisms, rather than thermal production. Further
comparison with measurements by the PHOBOS Collaboration confirms the
persistence of the pion excess into very low-, with no enhancement
observed in kaons and protons within the current experimental precision.Comment: 9 pages, 6 figure
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