The R&D activities for the Linear Collider TPC (LCTPC) are currently focused on the adoption of the Micro-Pattern Gaseous Detectors (MPGDs). Different MPGD modules which are commissioned on the ...endplate of a Large Prototype TPC (LPTPC) at DESY, were tested with a 5 GeV electron beam, under a 1 T magnetic field. During the tests, reduced signal sensitivity as well as distortion in the reconstructed track, were observed at the boundary of these modules. We have numerically investigated the origin of the track distortions observed close to the edges of the Micromegas modules. The study clearly shows that the electric field non-uniformity near the inter-modular gaps is responsible for such track distortion. We have been able to simulate the observed patterns and magnitudes of distortion successfully. The obtained agreements with 2015 beam test data encourage us to continue with the study and, to propose module design modifications that can alleviate the problem of electrostatic field distortion at the module boundaries.
An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, ptvecmiss, due to the production of unobserved weakly interacting ...particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated luminosity of 18.5 inverse femtobarns. The dimensionless kinematic variable alphaT is used to discriminate between events with genuine ptvecmiss associated with unobserved particles and spurious values of ptvecmiss arising from jet energy mismeasurements. No excess of event yields above the expected standard model backgrounds is observed. The results are interpreted in terms of constraints on the parameter space of several simplified models of supersymmetry that assume the pair production of top squarks. The search provides sensitivity to a broad range of top squark decay modes, including the two-body decay top squark to c chi0, where c is a charm quark and chi0 is the lightest neutralino, as well as the four-body decay top squark to b f bar-f' chi0, where b is a bottom quark and f and bar-f' are fermions produced in the decay of an intermediate off-shell W boson. These modes dominate in scenarios in which the top squark and lightest neutralino are nearly degenerate in mass. For these modes, top squarks with masses as large as 260 and 230 GeV are excluded, respectively, for the two- and four-body decays.
A dedicated search is presented for new phenomena in inclusive eight- and ten-jet final states with low missing transverse momentum, with and without identification of jets originating from b quarks. ...The analysis is based on data from proton-proton collisions corresponding to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector at the LHC at sqrt(s) = 8 TeV. The dominant multijet background expectations are obtained from low jet multiplicity control samples. Data agree well with the standard model background predictions, and limits are set in several benchmark models. Colorons (axigluons) with masses between 0.6 and 0.75 (up to 1.15) TeV are excluded at 95% confidence level. Similar exclusion limits for gluinos in R-parity violating supersymmetric scenarios are from 0.6 up to 1.1TeV. These results comprise the first experimental probe of the coloron and axigluon models in multijet final states.
A search is presented for narrow resonances decaying to dijet final states in proton-proton collisions at sqrt(s)=13 TeV using data corresponding to an integrated luminosity of 12.9 inverse ...femtobarns. The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet ascalars below 3.0 TeV, W' bosons below 2.7 TeV, Z' bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.
The Fourier coefficients v2 and v3 characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at sqrt(sNN)= 5.02 TeV are measured with data collected ...by the CMS experiment. The measurements cover a broad transverse momentum range, pt= 1-100 GeV. The analysis focuses on pt > 10 GeV range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60x% most central events. The v2 coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to the initial-state fluctuations. The values of both methods remain positive up to pt ~ 70 GeV, in all examined centrality classes. The v3 coefficient, only measured with the scalar product method, tends to zero for pt >~ 20 GeV. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations.
The decay B+ to psi(2S) phi(1020) K+ is observed for the first time using data collected from pp collisions at sqrt(s) = 8 TeV by the CMS experiment at the LHC, corresponding to an integrated ...luminosity of 19.6 inverse femtobarns. The branching fraction of this decay is measured, using the mode B+ to psi(2S) K+ as normalization, to be (4.0+/- 0.4 (stat) +/- 0.6 (syst) +/- 0.2 (B)1E-6, where the third uncertainty is from the imprecision in the normalization channel.
The total and differential cross sections for inclusive production of B(+) hadrons are measured as a function of the B(+) transverse momentum pTB and rapidity yB in pp collisions at a centre-of-mass ...energy of 13 TeV, using data collected by the CMS experiment that correspond to an integrated luminosity of 49.4 inverse-picobarns. The measurement uses the exclusive decay channel B(+) to J/psi K(+), with J/psi mesons that decay to a pair of muons. The results show a reasonable agreement with theoretical calculations within the uncertainties.