Search for the standard model Higgs boson produced in association with a W or a Z boson and decaying to bottom quarksThe CMS Collaboration * Abstract A search for the standard model Higgs boson (H) decaying to bb when produced in association with a weak vector boson (V) is reported for the following channels: W(µν)H, W(eν)H, W(τν)H, Z(µµ)H, Z(ee)H, and Z(νν)H. The search is performed in data samples corresponding to integrated luminosities of up to 5.1 fb −1 at √ s = 7 TeV and up to 18.9 fb −1 at √ s = 8 TeV, recorded by the CMS experiment at the LHC. An excess of events is observed above the expected background with a local significance of 2.1 standard deviations for a Higgs boson mass of 125 GeV, consistent with the expectation from the production of the standard model Higgs boson. The signal strength corresponding to this excess, relative to that of the standard model Higgs boson, is 1.0 ± 0.5.Published in Physical Review D as 2 Detector and simulated samples signal region. These regions also test the accuracy of the modeling of kinematic distributions in the simulated samples.Upper limits at the 95% CL on the pp → VH production cross section times the H → bb branching fraction are obtained for Higgs boson masses in the 110-135 GeV range. These limits are extracted by fitting the shape of the output distribution of a boosted-decision-tree (BDT) discriminant [14,15]. The results of the fitting procedure allow to evaluate the presence of a Higgs boson signal over the expectation from the background components. The significance of any excess of events, and the corresponding event yield, is compared with the expectation from a SM Higgs boson signal. Detector and simulated samplesA detailed description of the CMS detector can be found elsewhere [16]. The momenta of charged particles are measured using a silicon pixel and strip tracker that covers the pseudorapidity range |η| < 2.5 and is immersed in a 3.8 T axial magnetic field. The pseudorapidity is defined as η = − ln[tan(θ/2)], where θ is the polar angle of the trajectory of a particle with respect to the direction of the counterclockwise proton beam. Surrounding the tracker are a crystal electromagnetic calorimeter (ECAL) and a brass/scintillator hadron calorimeter (HCAL), both used to measure particle energy deposits and consisting of a barrel assembly and two endcaps. The ECAL and HCAL extend to a pseudorapidity range of |η| < 3.0. A steel/quartzfiber Cherenkov forward detector extends the calorimetric coverage to |η| < 5.0. The outermost component of the CMS detector is the muon system, consisting of gas-ionization detectors placed in the steel return yoke of the magnet to measure the momenta of muons traversing through the detector. The two-level CMS trigger system selects events of interest for permanent storage. The first trigger level, composed of custom hardware processors, uses information from the calorimeters and muon detectors to select events in less than 3.2 µs. The high-level trigger software algorithms, executed on a farm of commercial processor...
A study of vector boson scattering in pp collisions at a center-of-mass energy of 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.4 fb −1 collected with the CMS detector. Candidate events are selected with exactly two leptons of the same charge, two jets with large rapidity separation and high dijet mass, and moderate missing transverse energy. The signal region is expected to be dominated by electroweak same-sign W-boson pair production. The observation agrees with the standard model prediction. The observed significance is 2.0 standard deviations, where a significance of 3.1 standard deviations is expected based on the standard model. Cross section measurements for W AE W AE and WZ processes in the fiducial region are reported. Bounds on the structure of quartic vector-boson interactions are given in the framework of dimension-eight effective field theory operators, as well as limits on the production of doubly charged Higgs bosons.
Measurements are presented of the t-channel single-top-quark production cross section in proton-proton collisions at √ s = 8 TeV. The results are based on a data sample corresponding to an integrated luminosity of 19.7 fb −1 recorded with the CMS detector at the LHC. The cross section is measured inclusively, as well as separately for top (t) and antitop (t), in final states with a muon or an electron. The measured inclusive tchannel cross section is σ t-ch. = 83.6 ± 2.3 (stat.) ± 7.4 (syst.) pb. The single t and t cross sections are measured to be σ t-ch. (t) = 53.8 ± 1.5 (stat.) ± 4.4 (syst.) pb and σ t-ch. (t) = 27.6 ± 1.3 (stat.) ± 3.7 (syst.) pb, respectively. The measured ratio of cross sections is R t-ch. = σ t-ch. (t)/σ t-ch. (t) = 1.95±0.10 (stat.)±0.19 (syst.), in agreement with the standard model prediction. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element V tb is extracted and, in combination with a previous CMS result at √ s = 7 TeV, a value |V tb | = 0.998 ± 0.038 (exp.) ± 0.016 (theo.) is obtained.
A search for events with jets and missing transverse energy is performed in a data sample of pp collisions collected at ffiffi ffi s p ¼ 7 TeV by the CMS experiment at the LHC. The analyzed data sample corresponds to an integrated luminosity of 1:14 fb À1 . In this search, a kinematic variable T is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. The standard model (SM) of particle physics is generally considered to be valid only at low energy scales and is expected to be superseded by a more complete theory at higher scales. Supersymmetric (SUSY) extensions to the SM [1-8] introduce a large number of new particles with the same quantum numbers as their SM partners, but differing by half a unit of spin. If R-parity conservation [9] is assumed, supersymmetric particles, such as squarks and gluinos, are produced in pairs and decay to the lightest, stable supersymmetric particle (LSP . This Letter presents a search for SUSY based on a data sample corresponding to an integrated luminosity of 1:14 AE 0:05 fb À1 . The search strategy follows Ref.[23] and is designed to be sensitive to 6 E T signatures in events with two or more energetic jets. The search is not optimized for any particular model of SUSY and is applicable to other new physics scenarios with a 6 E T signature. In this Letter, nevertheless, the results are interpreted in the constrained minimal supersymmetric extension of the standard model (CMSSM) [28][29][30]. The CMSSM is described by the following five parameters: the universal scalar and gaugino mass parameters, m 0 and m 1=2 ; the universal trilinear soft SUSY-breaking parameter, A 0 ; the ratio of the vacuum expectation values of the two Higgs doublets, tan; and the sign of the Higgs mixing parameter, . We consider only parameter sets for which the LSP is the lightest neutralino. The following example parameter set, referred to as LM6, is used to illustrate possible CMSSM yields: m 0 ¼ 85 GeV, m 1=2 ¼ 400 GeV, A 0 ¼ 0, tan ¼ 10, and > 0.A detailed description of the CMS apparatus can be found in Ref. [31]. Its central feature is a superconducting solenoid providing an axial magnetic field of 3.8 T. The bore of the solenoid is instrumented with several particle detection systems. Charged particle trajectories are measured by a silicon pixel and strip tracker system, with full azimuth () coverage and a pseudorapidity () acceptance from À2:5 to þ2:5. Here, À ln½tanð=2Þ and is the polar angle with respect to the counterclockwise beam direction. A lead tungstate crystal electromagnetic calorimeter (ECAL) and a brass or scintillator hadron calorimeter surround the tracking volume and provide coverage in from À3 to þ3. The forward hadron calorimeter extends symmetrically the coverage by a further two units in . Muons are identified in gas ionization detectors embedded in the steel return yoke of the magnet. The CMS detector is nearly hermetic, which allows for momentum-balance measurements in the plane transverse to the beam axis.
A search is reported for massive resonances decaying into a quark and a vector boson (W or Z), or two vector bosons (WW, WZ, or ZZ). The analysis is performed on an inclusive sample of multijet events corresponding to an integrated luminosity of 19.7 fb −1 , collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. The search uses novel jet-substructure identification techniques that provide sensitivity to the presence of highly boosted vector bosons decaying into a pair of quarks. Exclusion limits are set at a confidence level of 95% on the production of: (i) excited quark resonances q * decaying to qW and qZ for masses less than 3.2 TeV and 2.9 TeV, respectively, (ii) a Randall-Sundrum graviton G RS decaying into WW for masses below 1.2 TeV, and (iii) a heavy partner of the W boson W decaying into WZ for masses less than 1.7 TeV. For the first time mass limits are set on W → WZ and G RS → WW in the all-jets final state. The mass limits on q * → qW, q * → qZ, W → WZ, G RS → WW are the most stringent to date. A model with a "bulk" graviton G bulk that decays into WW or ZZ bosons is also studied.Keywords: Jet substructure, Jets, Jet physics, Hadron-Hadron Scattering, Particle and resonance production The CMS collaboration 21 IntroductionSeveral models of physics beyond the standard model (SM) predict the existence of resonances with masses above 1 TeV that decay into a quark and a W or Z vector boson, or into two vector bosons. In proton-proton (pp) collisions at the energies reached at the Large Hadron Collider (LHC), vector bosons emerging from such decays usually would have sufficiently large momenta so that the hadronization products of their qq(') decays would merge into a single massive jet [1]. We present a search for events containing one or two jets of this kind in pp collisions at a centre-of-mass energy of √ s = 8 TeV. The data sample, corresponding to an integrated luminosity of 19.7 fb −1 , was collected with the CMS detector at the LHC.The signal is characterized by a peak in the dijet invariant mass distribution m jj over a continuous background from SM processes, comprised mainly of multijet events from quantum chromodynamic (QCD) processes. The sensitivity to jets from W or Z bosons is enhanced through the use of jet-substructure techniques that help differentiate such jets from remnants of quarks and gluons [2,3], providing the possibility of "W/Z-tagging". This search is an update of a previous CMS study [4] performed using data from pp collisions at √ s = 7 TeV. Besides increased data-sample size and larger signal cross sections from the increase in centre-of-mass energy, this analysis also benefits from an improved W/Z-tagger based on "N -subjettiness" variables, introduced in ref.[5] and defined in section 3.We consider four reference processes that yield one W/Z-tagged or two W/Z-tagged all-jet events: (i) an excited quark q * [6,7] that decays into a quark and either a W or a Z boson, (ii) a Randall-Sundrum (RS) graviton G RS that...
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