A search is presented for a heavy vector-like quark, decaying into a b quark and a W boson, which is produced singly in association with a light flavor quark and a b quark. The analysis is performed ...using a data sample of proton-proton collisions at a center-of-mass energy of sqrt(s) = 13 TeV collected at the LHC in 2015. The data set used in the analysis corresponds to an integrated luminosity of 2.3 inverse-femtobarns. The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in the forward region of the detector, and missing transverse momentum. No excess over the standard model prediction is observed. Upper limits are placed on the production cross section of heavy exotic quarks: a T quark with a charge of 2/3, and a Y quark with a charge of -4/3. For Y quarks with coupling of 0.5 and B(Y to bW) = 100%, the observed (expected) lower mass limits are 1.40 (1.0) TeV. This is the most stringent limit to date on the single production of the Y vector-like quark.
A search for heavy narrow resonances decaying into four-lepton final states from cascade decays of a Z' boson has been performed using proton-proton collision data at sqrt(s) = 8 TeV collected by the ...CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. No excess of events over the standard model background expectation is observed. Upper limits for a benchmark model on the product of cross section and branching fraction for the production of these heavy narrow resonances are presented. The limit excludes leptophobic Z' bosons with masses below 2.5 TeV within the benchmark model. This is the first result to constrain a leptophobic Z' resonance in the four-lepton channel.
The WZ production cross section in proton-proton collisions at sqrt(s) = 13 TeV is measured with the CMS experiment at the LHC using a data sample corresponding to an integrated luminosity of 2.3 ...inverse femtobarns. The measurement is performed in the leptonic decay modes WZ to l nu l' l', where l, l'= e, mu. The measured cross section for the range 60 < ml'l' < 120GeV is sigma(pp to WZ = 39.9 +/- 3.2 (stat) +2.9/-3.1 (syst) +/- 0.4 (theo) +/- 1.3 (lum) pb, consistent with the standard model prediction.
The CMS Collaboration presents the first measurement of the differential cross section of jets from charm quarks produced in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of ...sqrt(sNN) = 5.02 TeV, as well as results from charm quark jets in proton-proton (pp) collisions at sqrt(s)= 2.76 and 5.02 TeV. By comparing the yields of the pPb and pp collision systems at the same energy, a nuclear modification factor for charm jets in pPb collisions at sqrt(sNN) = 5.02 TeV of RpA = 0.92 +/- 0.07 (stat) +/- 0.11 (syst) is obtained. This is consistent with an absence of final-state energy loss for charm quarks in pPb collisions. In addition, the fraction of jets coming from charm quarks is found to be consistent with that predicted by PYTHIA 6 for pp collisions at sqrt(s)= 2.76 and 5.02 TeV, and is independent of the jet transverse momentum from 55 to 400 GeV.
The production yields of Upsilon(1S), Upsilon(2S), and Upsilon(3S) quarkonium states are measured through their decays into muon pairs in the CMS detector, in PbPb and pp collisions at the ...centre-of-mass energy per nucleon pair of 2.76 TeV. The data correspond to integrated luminosities of 166 inverse microbarns and 5.4 inverse picobarns for PbPb and pp collisions, respectively. Differential production cross sections are reported as functions of Upsilon rapidity $y$ up to 2.4, and transverse momentum pt up to 20 GeV/c. A strong centrality-dependent suppression is observed in PbPb relative to pp collisions, by factors of up to ~2 and 8, for the Upsilon(1S) and Upsilon(2S) states, respectively. No significant dependence of this suppression is observed as a function of y or pt. The Upsilon(3S) state is not observed in PbPb collisions, which corresponds to a suppression for the centrality-integrated data by at least a factor of ~7 at a 95% confidence level. The observed suppression is in agreement with theoretical scenarios modeling the sequential melting of quarkonium states in a quark gluon plasma.
The cross section for coherent J/psi photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS ...experiment in ultra-peripheral PbPb collisions at sqrt(sNN) = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 inverse microbarns, collected during the 2011 PbPb run. The J/psi mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is d sigmacoh,Xn0n/d y(J/psi) = 0.36 +/- 0.04\ (stat) +/- 0.04 (syst) mb in the rapidity interval 1.8<abs(y)<2.3. Using a model for the relative rate of coherent photoproduction processes, this Xz,n,z measurement gives a total coherent photoproduction cross section of d sigmacoh/d y(J/psi) = 1.82 +/- 0.22 (stat) +/- 0.20 (syst) +/- 0.19 (theo) mb. The data strongly disfavour the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/psi photoproduction in gamma + Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.
The cross section for the production of single top quarks in the t channel is measured in proton-proton collisions at 13 TeV with the CMS detector at the LHC. The analyzed data correspond to an ...integrated luminosity of 2.3 inverse-femtobarns. The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 232 +/- 13 (stat) +/- 28 (syst) pb and a ratio of top quark and top antiquark production of Rt-ch. = $ 1.81 +/- 0.18 (stat) +/- 0.15 (syst). From the total cross section the absolute value of the CKM matrix element Vtb is calculated to be 1.03 +/- 0.07 (exp) +/- 0.02 (theo). All results are in agreement with the standard model predictions.
The invariance of the standard model (SM) under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the ...top quark and antiquark (Delta mt = mt - mt-bar) that are produced in pp collisions at a center-of-mass energy of 8 TeV, using events with a muon or an electron and at least four jets in the final state. The analysis is based on data corresponding to an integrated luminosity of 19.6 inverse-femtobarns collected by the CMS experiment at the LHC, and yields a value of Delta mt = -0.15 +/- 0.19 (stat) +/- 0.09 (syst) GeV, which is consistent with the SM expectation. This result is significantly more precise than previously reported measurements.
The differential cross section for inclusive particle production as a function of energy in proton-proton collisions at a center-of-mass energy of 13 TeV is measured in the very forward region of the ...CMS detector. The measurement is based on data collected with the CMS apparatus at the LHC, and corresponds to an integrated luminosity of 0.35 inverse microbarns. The energy is measured in the CASTOR calorimeter, which covers the pseudorapidity region -6.6<eta<-5.2. The results are given as a function of the total energy deposited in CASTOR, as well as of its electromagnetic and hadronic components. The spectra are sensitive to the modeling of multiparton interactions in pp collisions, and provide new constraints for hadronic interaction models used in collider and in high energy cosmic ray physics.
Intraoperative frozen section examination of the sentinel node in breast cancer patients is associated with a high number of incorrect negative results with the sentinel node becoming positive in the ...permanent examination and necessitating a secondary axillary lymph node dissection. A reoperation of the axilla following skin-sparing mastectomy and immediate autologous tissue reconstruction may compromise the vascular pedicle of the flap and should be avoided.
Eighty breast cancer patients underwent skin-sparing mastectomy with immediate autologous reconstruction and sentinel node biopsy followed by axillary lymph node dissection irrespective of the result of the frozen section of the sentinel node. The goal of the study was to identify a subgroup of patients with incorrect negative sentinel node(s) in the frozen section who may forego a secondary axillary lymph node dissection due to a low risk of positive nonsentinel nodes.
Frozen section examination of the sentinel node was negative in 58 patients and positive in 22 patients. Permanent histologic examination revealed tumor in 13 of 58 (22.4 percent) sentinel node(s) found negative in the frozen section. None of these 13 patients showed positive nodes in the axillary specimen, whereas nine of 22 patients with their metastases in the sentinel node found through intraoperative frozen section examination had additional positive nonsentinel node(s) (p = 0.001).
Patients with incorrect negative sentinel node(s) found in the frozen section examination had a significantly decreased risk for additional positive nonsentinel node(s) compared with patients with sentinel node metastases found in the frozen section. However, to avoid a secondary axillary lymph node dissection, the authors suggest performing sentinel node biopsy before mastectomy under local anesthesia to have the permanent result of the sentinel node available before a planned reconstruction.
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