—
An overview presents the recent results of the CMS collaboration on the dimuon physics at the proton–proton collisions, starting with the precision measurements of Drell–Yan differential cross ...sections and rare processes, and extending into the search for narrow heavy resonances and other effects beyond the Standard model in the dimuon channel.
The physics program of the CMS experiment is aimed at testing the Standard Model on the new energy scale of the order of TeV and at searching for new physical objects and phenomena beyond the ...Standard Model. At present, in the dilepton channels, where the search for new physics is going on, the established limits on the invariant masses of dileptons reach a few TeV. At high energies, one of the problems in the search for new heavy Z
'
resonances is the presence of background processes, e.g., the production of
WZ
and
ZZ
dibosons, in which muons are produced. The dimuons formed from these muons can be misinterpreted as candidates for heavy resonances, which makes the problem of the background elimination even more topical. To this end, the analyses for isolating and reducing the backgrounds were performed in this work.
A systematic study of the factorization of long-range azimuthal two-particle correlations into a product of single-particle anisotropies is presented as a function of pT and η of both particles and ...as a function of the particle multiplicity in PbPb and pPb collisions. The data were taken with the CMS detector for PbPb collisions at √sNN=2.76 TeV and pPb collisions at √sNN=5.02 TeV, covering a very wide range of multiplicity. Factorization is observed to be broken as a function of both particle pT and η. When measured with particles of different pT, the magnitude of the factorization breakdown for the second Fourier harmonic reaches 20% for very central PbPb collisions but decreases rapidly as the multiplicity decreases. The data are consistent with viscous hydrodynamic predictions, which suggest that the effect of factorization breaking is mainly sensitive to the initial-state conditions rather than to the transport properties (e.g., shear viscosity) of the medium. The factorization breakdown is also computed with particles of different η. The effect is found to be weakest for mid-central PbPb events but becomes larger for more central or peripheral PbPb collisions, and also for very-high-multiplicity pPb collisions. The η-dependent factorization data provide new insights to the longitudinal evolution of the medium formed in heavy ion collisions.
A
bstract
A measurement is performed of the cross section of top quark pair production in association with a W or Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the ...LHC. The data sample corresponds to an integrated luminosity of 35.9 fb
−1
, collected by the CMS experiment in 2016. The measurement is performed in the same-sign dilepton, three- and four-lepton final states. The production cross sections are measured to be
$$ \sigma \left(\mathrm{t}\overline{\mathrm{t}}\mathrm{W}\right)={0.77}_{-0.11}^{+0.12}{\left(\mathrm{stat}\right)}_{-0.12}^{+0.13}\left(\mathrm{syst}\right)\mathrm{p}\mathrm{b} $$
σ
t
t
¯
W
=
0.77
−
0.11
+
0.12
stat
−
0.12
+
0.13
syst
p
b
and
$$ \sigma \left(\mathrm{t}\overline{\mathrm{t}}\mathrm{Z}\right)={0.99}_{-0.08}^{+0.09}{\left(\mathrm{stat}\right)}_{-0.10}^{+0.12}\left(\mathrm{syst}\right)\mathrm{p}\mathrm{b} $$
σ
t
t
¯
Z
=
0.99
−
0.08
+
0.09
stat
−
0.10
+
0.12
syst
p
b
. The expected (observed) signal significance for the
$$ \mathrm{t}\overline{\mathrm{t}}\mathrm{W} $$
t
t
¯
W
production in same-sign dilepton channel is found to be 4.5 (5.3) standard deviations, while for the
$$ \mathrm{t}\overline{\mathrm{t}}\mathrm{Z} $$
t
t
¯
Z
production in three- and four-lepton channels both the expected and the observed significances are found to be in excess of 5 standard deviations. The results are in agreement with the standard model predictions and are used to constrain the Wilson coefficients for eight dimension-six operators describing new interactions that would modify
$$ \mathrm{t}\overline{\mathrm{t}}\mathrm{W} $$
t
t
¯
W
and
$$ \mathrm{t}\overline{\mathrm{t}}\mathrm{Z} $$
t
t
¯
Z
production.
The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (Pb-Pb) collisions at a center-of-mass energy of ...sqrts_{NN}=5.02 TeV per nucleon pair, using the decay chain X(3872)→J/ψπ^{+}π^{-}→μ^{+}μ^{-}π^{+}π^{-}. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb^{-1}. The measurement is performed in the rapidity and transverse momentum ranges |y|<1.6 and 15<p_{T}<50 GeV/c. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to ψ2S yield ratio is found to be ρ^{Pb-Pb}=1.08±0.49(stat)±0.52(syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.
Recent progress in the investigation of the material parameters of Al Al2O3systems leads to an increase in the possibilities for using embedded TaOXN1-X layers. The use of Al-sheets as mechanical ...strength carriers in combination with vacuum-deposited Al-layers and electrochemically anodized Al2O3 structure requires study. This was found to create a periodic multilayer Al Al2O3 structure. The material qualities of this system allow optimization in order to achieve high speed data processing and signal propagation. The existing studies using Al and Ta combination as well as the high resistance qualities of the modified TaOXN1-X layers have shown satisfactory results. It can be concluded that the development of this new layer combination is possible in the multilayer carrier structures. Some preliminary research studies show a proper adhesion and satisfactory characteristics of the two integrated resistive planes in the multilayer combination Al Al2O3 TaOXN1-X Ta2O5 Al.
Electroweak Measurements at CMS Lanyov, Alexander
Moscow University physics bulletin,
04/2022, Letnik:
77, Številka:
2
Journal Article
Recenzirano
Odprti dostop
This report presents the recent results by the CMS Collaboration on the electroweak sector of the Standard Model, including single boson and Drell–Yan production, as well as multiboson processes. ...Detailed studies included measurements of differential cross sections and many other observables, such as asymmetries, ratios for lepton flavor universality, anomalous gauge couplings, etc.
Measurements of two- and four-particle angular correlations for charged particles emitted in pPb collisions are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding ...to an integrated luminosity of approximately 31 nb−1, were collected during the 2013 LHC pPb run at a nucleon–nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. The results are compared to 2.76 TeV semi-peripheral PbPb collision data, collected during the 2011 PbPb run, covering a similar range of particle multiplicities. The observed correlations are characterized by the near-side (|Δϕ|≈0) associated pair yields and the azimuthal anisotropy Fourier harmonics (vn). The second-order (v2) and third-order (v3) anisotropy harmonics are extracted using the two-particle azimuthal correlation technique. A four-particle correlation method is also applied to obtain the value of v2 and further explore the multi-particle nature of the correlations. Both associated pair yields and anisotropy harmonics are studied as a function of particle multiplicity and transverse momentum. The associated pair yields, the four-particle v2, and the v3 become apparent at about the same multiplicity. A remarkable similarity in the v3 signal as a function of multiplicity is observed between the pPb and PbPb systems. Predictions based on the color glass condensate and hydrodynamic models are compared to the experimental results.
The results of searches for supersymmetry by the CMS experiment are interpreted in the framework of simplified models. The results are based on data corresponding to an integrated luminosity of 4.73 ...to 4.98 fb super(-1). The data were collected at the LHC in proton-proton collisions at a center-of-mass energy of 7 TeV. This paper describes the method of interpretation and provides upper limits on the product of the production cross section and branching fraction as a function of new particle masses for a number of simplified models. These limits and the corresponding experimental acceptance calculations can be used to constrain other theoretical models and to compare different supersymmetry-inspired analyses.
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