2,864 research outputs found
Measurements of the inclusive production cross section at the ATLAS and CMS experiments
The results of the most recent measurements of the inclusive
cross section performed by the ATLAS and CMS experiments at
the CERN LHC are summarized. These include results obtained in proton-proton
collisions at different centre-of-mass energies, and the first observation of
production in proton-lead collisions. A new result at
by the CMS Collaboration is presented for the
first time at this conference. In this analysis, the total cross section is
determined both for a fixed top quark mass value in the simulation of
, and simultaneously with
.Comment: Proceedings for 11th International Conference on Top Quark Physic
Measuring standard model parameters using top-quark cross sections in ATLAS and CMS
Theoretical predictions of top-quark cross sections depend on the values of
the parameters of the quantum chromodynamics Lagrangian, such as the strong
coupling constant and the mass of the top quark, but also on parameters of the
electroweak sector of the standard model and parton distribution functions.
Comparisons between state-of-the-art calculations and recent measurements at
the ATLAS and CMS experiments at the CERN LHC allow for the precise
determination of these parameters. In this proceeding, the most recent results
by the two collaborations are summarized and discussed.Comment: Presented at the 13th International Workshop on Top Quark Physics,
Durham UK (videoconference), 14-18 September 202
Probing QCD using top quark pair production at in CMS
Measurements of the top quark-antiquark pair production cross section,
, can be used to constrain the strong coupling
constant, , the top quark mass, , and the parton
distribution functions (PDFs). In this poster, the two most recent relevant
results published by the CMS Collaboration are presented. The analyses are
performed using proton-proton collision data at a centre-of-mass energy of 13
TeV recorded by the CMS detector at the CERN LHC in 2016, corresponding to an
integrated luminosity of . In the first one,
and are extracted independently from a measurement
of the inclusive , using next-to-next-to-leading
order theoretical predictions. In the second, a measurement of the normalized
triple-differential cross section is performed; the result
is then used together with HERA deep-inelastic scattering data to perform a
simultaneous determination of , , and the PDFs, at
next-to-leading order. As a result, the uncertainty in the gluon PDF and its
correlation with are significantly reduced at high parton momentum
fraction, the kinematic range probed by production. The
result also yields the most precise determination of the top quark pole mass,
to date.Comment: To appear in the Proceedings of the European Physical Society
Conference on High Energy Physics (EPS-HEP 2019), Ghent, Belgium, 10-17 July
201
First experimental investigation of the running of the top quark mass
The first experimental investigation of the running of the top quark mass is
presented. The running, defined in the modified minimal subtraction
() renormalization scheme, is extracted from a
measurement of the differential top quark-antiquark ()
production cross section as a function of the invariant mass of the
system using theoretical predictions at next-to-leading
order. The measurement is performed using proton-proton collisions at a
centre-of-mass energy of recorded by the CMS detector at the
CERN LHC in 2016, corresponding to an integrated luminosity of
. Candidate events are selected in
the final state with an electron and a muon of opposite charge, and the
differential cross section is determined at the parton level by means of a
maximum-likelihood fit to multidifferential distributions. The extracted
running is found to be compatible with the solution of the corresponding
renormalization group equation, up to a scale on the order of
Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV
The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
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