2,376 research outputs found
"Eyes Like Stars": Exclusive Author Interview
No full textExclusive Author Interview with Lisa Matchev) with Mellissa Forge
Uncovering quasi-degenerate Kaluza-Klein Electro-Weak gauge bosons with top asymmetries at the LHC
No full textBy exploiting the correlation between charge and spin polarisation asymmetries in t-tbar, we show that combining the two observables could identify the presence of quasi-degenerate states in a resonant signal at the LHC. As an example, we investigate experimental signatures emerging in top-antitop final states in the context of a model where the Standard Model Electro-Weak sector is allowed to propagate in large extra--dimensions of TeV-1 size while the colour sector is localised. Assuming current experimental constraints from the 7 and 8 TeV runs and taking into account the estimated top (anti-top) reconstruction efficiencies, we find that the 14 TeV upgraded LHC with the planned integrated luminosity L=100 fb-1 could access these quasi-degenerate multiple resonances and explore for the first time the rich phenomenology in the asymmetry observables. The main outcome would be having measurable quantities, complementary to the usual total and differential cross sections, capable of distinguishing a quasi-degenerate multiply resonant spectrum from a 'standard' single resonance that could present a similar signal in a bump hunt analysis
Observation of the Λ b 0 → J / ψ Ξ - K + decay
No full textAbstract Using proton–proton collision data corresponding to an integrated luminosity of 140 fb - 1 collected by the CMS experiment at s = 13 Te V , the Λ b 0 → J / ψ Ξ - K + decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the Λ b 0 → ψ ( 2 S ) Λ decay, is measured to be B ( Λ b 0 → J / ψ Ξ - K + ) / B ( Λ b 0 → ψ ( 2 S ) Λ ) = [ 3.38 ± 1.02 ± 0.61 ± 0.03 ] % , where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in B ( ψ ( 2 S ) → J / ψ π + π - ) and B ( Ξ - → Λ π - )
Slepton Mass Measurements at the LHC
No full textWe first discuss the motivation for measuring slepton masses at the LHC, emphasizing their importance for cosmology. Next we investigate the possibility of making slepton mass determinations at the LHC in neutralino decays. We demonstrate that by studying the shape of the dilepton invariant mass distribution in the decay neutralino_2 -> neutralino_1 + l^+ + l^-, one can determine whether the slepton is real or virtual. Furthermore, in case of virtual sleptons, it is possible to bound the slepton mass within a limited range. We conclude by discussing future avenues for investigation
Measurement of the CP-violating phase phi(s) in the B-s(0) -> J/psi phi(1020) -> mu(+)mu-K+K- channel in proton-proton collisions at root s=13 TeV
No full textThe CP-violating weak phase ?s and the decay width difference ??s between the light and heavy B0s mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed B0s? J/I) d (1020) ?11+11? K+K? events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4 fb?1, collected in proton-proton collisions at ?s = 13 TeV in 2017?2018. To extract the values of ?s and ??s, a time-dependent and flavor-tagged angular analysis of the 11+11?K+K? final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ?s = ?11 ?50 (stat) ? 10 (syst) mrad and ??s = 0.114 ? 0.014 (stat)? 0.007 (syst) ps?1, in agreement with the standard model predictions. When combined with the previous CMS measurement at ?s = 8 TeV, the following values are obtained: ?s = ?21 ? 44 (stat) ? 10 (syst) mrad, ??s = 0.1032 ? 0.0095 (stat) ? 0.0048 (syst) ps?1, a significant improvement over the 8 TeV result. ? 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY licens
Study of charm hadronization with prompt Λ c + baryons in proton-proton and lead-lead collisions at s NN = 5.02 TeV
No full textAbstract The production of prompt Λ c + baryons is measured via the exclusive decay channel Λ c + → p K − π + at a center-of-mass energy per nucleon pair of 5.02 TeV, using proton-proton (pp) and lead-lead (PbPb) collision data collected by the CMS experiment at the CERN LHC. The pp and PbPb data were obtained in 2017 and 2018 with integrated luminosities of 252 and 0.607 nb −1, respectively. The measurements are performed within the Λ c + rapidity interval |y| 10 GeV/c are strongly suppressed in PbPb collisions. The level of suppression depends significantly on the collision centrality. The Λ c + /D0 production ratio is similar in PbPb and pp collisions at p T > 10 GeV/c, suggesting that the coalescence process does not play a dominant role in prompt Λ c + baryon production at higher p T
Test of lepton flavor universality in B ± → K ± μ + μ − and B ± → K ± e + e − decays in proton-proton collisions at s = 13 TeV
No full textA test of lepton flavor universality inB±→K±μ+μ-andB±→K±e+e-decays, as well as a measurement of differential and integrated branching fractions of a nonresonantB±→K±μ+μ-decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions ats=13TeVrecorded in 2018, by the CMS experiment at the LHC, using a special high-rate data stream designed for collecting about 10 billion unbiased b hadron decays. The ratio of the branching fractionsB(B±→K±μ+μ-)toB(B±→K±e+e-)is determined from the measured double ratioR(K)of these decays to the respective branching fractions of theB±→J/ψK±withJ/ψ→μ+μ-ande+e-decays, which allow for significant cancellation of systematic uncertainties. The ratioR(K)is measured in the range1.1<6.0GeV2, whereqis the invariant mass of the lepton pair, and is found to beR(K)=0.78-0.23+0.47, in agreement with the standard model expectationR(K)≈1. This measurement is limited by the statistical precision of the electron channel. The integrated branching fraction in the sameq2range,B(B±→K±μ+μ-)=(12.42±0.68)×10-8, is consistent with the present world-average value and has a comparable precision
Measurement of masses in the t(t)over-bar system by kinematic endpoints in pp collisions at √s=7 TeV
No full textThis article is the pre-print version of the final published paper that is available from the link below.A simultaneous measurement of the top-quark, W-boson, and neutrino masses is reported for tt events selected in the dilepton final state from a data sample corresponding to an integrated luminosity of 5.0 fb−1 collected by the CMS experiment in pp collisions at √s = 7 TeV. The analysis is based on endpoint determinations in kinematic distributions. When the neutrino and W-boson masses are constrained to their world-average values, a top-quark mass value of Mt = 173.9 ± 0.9 (stat.)+1.7−2.1 (syst.) GeV is obtained. When such constraints are not used, the three particle masses are obtained in a simultaneous fit. In this unconstrained mode the study serves as a test of mass determination methods that may be used in beyond standard model physics scenarios where several masses in a decay chain may be unknown and undetected particles lead to undercon-strained kinematics
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