Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method

Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum

Search for baryon number violation in top quark decays

A search for baryon number violation (BNV) in top-quark decays is performed using pp collisions produced by the LHC at View the MathML source. The top-quark decay considered in this search results in one light lepton (muon or electron), two jets, but no neutrino in the final state. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.5 fb 121. The event selection is optimized for top quarks produced in pairs, with one undergoing the BNV decay and the other the standard model hadronic decay to three jets. No significant excess of events over the expected yield from standard model processes is observed. The upper limits at 95% confidence level on the branching fraction of the BNV top-quark decay are calculated to be 0.0016 and 0.0017 for the muon and the electron channels, respectively. Assuming lepton universality, an upper limit of 0.0015 results from the combination of the two channels. These limits are the first that have been obtained on a BNV process involving the top quark

Use of the gLite-WMS in CMS for production and analysis

The CMS experiment at LHC started using the Resource Broker (by the EDG and LCG projects) to submit Monte Carlo production and analysis jobs to distributed computing resources of the WLCG infrastructure over 6 years ago. Since 2006 the gLite Workload Management System (WMS) and Logging \& Bookkeeping (LB) are used. The interaction with the gLite-WMS/LB happens through the CMS production and analysis frameworks, respectively ProdAgent and CRAB, through a common component, BOSSLite. The important improvements recently made in the gLite-WMS/LB as well as in the CMS tools and the intrinsic independence of different WMS/LB instances allow CMS to reach the stability and scalability needed for LHC operations. In particular the use of a multi-threaded approach in BOSSLite allowed to increase the scalability of the systems significantly. In this work we present the operational set up of CMS production and analysis based on the gLite-WMS and the performances obtained in the past data challenges and in the daily Monte Carlo productions and user analysis usage in the experiment

Search for supersymmetry in pp collisions at sqrt(s) = 8 TeV in events with a single lepton, large jet multiplicity, and multiple b jets

Results are reported from a search for supersymmetry in pppp collisions at a center-of-mass energy of 8 TeV, based on events with a single isolated lepton (electron or muon) and multiple jets, at least two of which are identified as b jets. The data sample corresponds to an integrated luminosity of 19.3 fb 121recorded by the CMS experiment at the LHC in 2012. The search is motivated by supersymmetric models that involve strong-production processes and cascade decays of new particles. The resulting final states contain multiple jets as well as missing transverse momentum from weakly interacting particles. The event yields, observed across several kinematic regions, are consistent with the expectations from standard model processes. The results are interpreted in the context of simplified supersymmetric scenarios with pair production of gluinos, where each gluino decays to a top quark\u2013antiquark pair and the lightest neutralino. For the case of decays via virtual top squarks, gluinos with a mass smaller than 1.26 TeV are excluded for low neutralino masses

Measurement of the muon charge asymmetry in inclusive pp -> W+X production at sqrt(s) = 7 TeV and an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp\u2192W+X production at s 1a=7\u2009\u2009TeV are presented. The data sample corresponds to an integrated luminosity of 4.7\u2009\u2009fb 121 recorded with the CMS detector at the LHC. With a sample of more than 20 million W\u2192\u3bc\u3bd events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10 123 to 10 121. These measurements and the recent CMS measurement of associated W+charm production are used together with the cross sections for inclusive deep inelastic e\ub1p scattering at HERA in a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved, and the strange-quark distribution is probed directly through the leading-order process g+s\u2192W+c in proton-proton collisions at the LHC

Search for new physics in events with same-sign dileptons and jets in pp collisions at sqrt(s) = 8 TeV

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb 121. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models

Measurement of the properties of a Higgs boson in the four-lepton final state

The properties of a Higgs boson candidate are measured in the H\u2192ZZ\u21924\u2113 decay channel, with \u2113=e, \u3bc, using data from pp collisions corresponding to an integrated luminosity of 5.1\u2009\u2009fb 121 at the center-of-mass energy of s 1a=7\u2009\u2009TeV and 19.7\u2009\u2009fb 121 at s 1a=8\u2009\u2009TeV, recorded with the CMS detector at the LHC. The new boson is observed as a narrow resonance with a local significance of 6.8 standard deviations, a measured mass of 125.6\ub10.4(stat)\ub10.2(syst)\u2009\u2009GeV, and a total width 643.4\u2009\u2009GeV at the 95% confidence level. The production cross section of the new boson times its branching fraction to four leptons is measured to be 0.93+0.26 120.23(stat)+0.13 120.09(syst) times that predicted by the standard model. Its spin-parity properties are found to be consistent with the expectations for the standard-model Higgs boson. The hypotheses of a pseudoscalar and all tested spin-1 boson hypotheses are excluded at the 99% confidence level or higher. All tested spin-2 boson hypotheses are excluded at the 95% confidence level or higher

Search for the associated production of the Higgs boson with a top-quark pair

A search for the standard model Higgs boson produced in association with a top-quark pair (tt\uafH) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb 121 and 19.7 fb 121 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H \u2192 hadrons, H \u2192 photons, and H \u2192 leptons. The results are characterized by an observed tt\uafH signal strength relative to the standard model cross section, \u3bc=\u3c3/\u3c3 SM,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is \u3bc = 2.8 \ub1 1.0 for a Higgs boson mass of 125.6 GeV

Measurement of the t-channel single-top-quark production cross section and of the |Vtb| CKM matrix element in pp collisions at sqrt(s) = 8 TeV

Measurements are presented of the t-channel single-top-quark production cross section in proton-proton collisions at s 1a = 8 TeV. The results are based on a data sample corresponding to an integrated luminosity of 19.7 fb 121 recorded with the CMS detector at the LHC. The cross section is measured inclusively, as well as separately for top (t) and antitop (t\uaf), in final states with a muon or an electron. The measured inclusive t-channel cross section is \u3c3t-ch. = 83.6 \ub1 2.3 (stat.) \ub1 7.4 (syst.) pb. The single t and t\uaf cross sections are measured to be \u3c3t-ch.(t) = 53.8 \ub1 1.5 (stat.) \ub1 4.4 (syst.) pb and \u3c3t-ch.(t\uaf) = 27.6 \ub1 1.3 (stat.) \ub1 3.7 (syst.) pb, respectively. The measured ratio of cross sections is Rt-ch. = \u3c3t-ch.(t)/\u3c3t-ch.(t\uaf) = 1.95 \ub1 0.10 (stat.) \ub1 0.19 (syst.), in agreement with the standard model prediction. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element Vtb is extracted and, in combination with a previous CMS result at s 1a = 7 TeV, a value |Vtb| = 0.998 \ub1 0.038 (exp.) \ub1 0.016 (theo.) is obtained

Search for invisible decays of Higgs bosons in the vector boson fusion and associated ZH production modes

A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a bb\uaf\uaf\uaf quark pair. The searches use the 8\u252c\ue1TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7\u252c\ue1fb 121. Certain channels include data from 7\u252c\ue1TeV collisions corresponding to an integrated luminosity of 4.9\u252c\ue1fb 121. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at mH=125\u252c\ue1GeV is found to be 0.58\u252c\ue1(0.44) at 95\u252c\ue1% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions