Results are presented from a search for the rare decays Bs(0)→μ+ μ- and B(0)→μ+ μ- in pp collisions at sqrt[s]=7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20 fb(-1), respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction B(Bs(0)→μ+ μ-)=(3.0(-0.9)(+1.0))×10(-9), where the uncertainty includes both statistical and systematic contributions. An excess of Bs(0)→μ+ μ- events with respect to background is observed with a significance of 4.3 standard deviations. For the decay B(0)→μ+ μ- an upper limit of B(B(0)→μ+ μ-)<1.1×10(-9) at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.
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model (SM) of particle physics is generally considered to be valid only at low energy scales and is expected to be superseded by a more complete theory at higher scales.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.
Angular distributions of the decay B 0 → K * 0 µ + µ − are studied using a sample of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb −1 . An angular analysis is performed to determine the P 1 and P 5 parameters, where the P 5 parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the P 1 and P 5 parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model.
We examine systematically the (in)consistency between cosmological constraints as obtained from various current data sets of the expansion history, large-scale structure (LSS), and cosmic microwave background (CMB) temperature and polarization from Planck. We run (dis)concordance tests within each set and across the three sets using a recently introduced index of inconsistency (IOI) capable of dissecting inconsistencies between two or more data sets. First, we compare the constraints on H0 from five different methods and find that the IOI drops from 2.85 to 0.88 (on Jeffreys's scales) when the local H0 measurements is removed. This seems to indicate that the local measurement is an outlier compared to the others, thus favoring a systematics-based explanation. We find a moderate inconsistency (IOI=2.61) between Planck temperature and polarization data sets. We find that current LSS data sets including the WiggleZ power spectrum, SDSS redshift space distortion, CFHTLenS weak lensing, CMB lensing, and cluster count from SZ effect, are consistent one with another and also when all combined. However, we find a persistent moderate inconsistency between Planck and individual or combined LSS probes. For Planck TT+lowTEB versus individual LSS probes, the IOI spans the range 2.92-3.72 and increases to 3.44-4.20 when the polarization data is added in. The joint LSS versus the combined Planck temperature and polarization has an IOI of 2.83 in the most conservative case. But if Planck low-temperature and polarization is also added to the joint LSS to constrain τ and break degeneracies, the inconsistency between Planck and joint LSS data increases to the high end of the moderate range with IOI=4.81. Whether due to systematic effects in the data or to the underlying model, these inconsistencies need to be resolved. Finally, we perform forecast calculations using the Large Sky Synoptic Survey (LSST) and find that the discordance between Planck and future LSS data, if it persists as present, can rise up to a high IOI of 17, thus falling in the strong range of inconsistency.
A measurement of the single-top-quark t-channel production cross section in pp collisions at √ s = 7 TeV with the CMS detector at the LHC is presented. Two different and complementary approaches have been followed. The first approach exploits the distributions of the pseudorapidity of the recoil jet and reconstructed top-quark mass using background estimates determined from control samples in data. The second approach is based on multivariate analysis techniques that probe the compatibility of the candidate events with the signal. Data have been collected for the muon and electron final states, corresponding to integrated luminosities of 1.17 and 1.56 fb −1 , respectively. The single-topquark production cross section in the t-channel is measured to be 67.2±6.1 pb, in agreement with the approximate next-to-next-to-leading-order standard model prediction. Using the standard model electroweak couplings, the CKM matrix element |V tb | is measured to be 1.020 ± 0.046 (meas.) ± 0.017 (theor.). Keywords: Hadron-Hadron Scattering Conclusions 21The CMS collaboration 27 IntroductionSingle top quarks can be produced through charged-current electroweak interactions. Due to the large top-quark mass, these processes are well suited to test the predictions of the standard model (SM) of particle physics and to search for new phenomena. Measurements of the single-top-quark production cross section also provide an unbiased determination of the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V tb |. Single-top-quark production was observed in proton-antiproton collisions at the Tevatron collider with a centre-of-mass energy of 1. by a factor of 20 at the Large Hadron Collider (LHC) with respect to the Tevatron. The first measurements of the single-top-quark production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV were performed by the Compact Muon Solenoid (CMS) [4] and ATLAS [5,6] experiments.Previous measurements are compatible with expectations based on approximate nextto-leading-order and next-to-next-to-leading-logarithm (NLO+NNLL) perturbative quantum chromodynamics (QCD) calculations. In these calculations, three types of parton scattering processes are considered: t-channel and s-channel processes, and W-associated single-top-quark production (tW). The dominant contribution to the cross section is expected to be from the t-channel process with a cross section of σ th t-ch. = 64.6 +2.1 −0.7for a top-quark mass of m t = 172.5 GeV/c 2 .This paper extends the previous CMS measurement [4] of the t-channel cross section. The single-top-quark production cross section measurement is based on pp collision data at √ s = 7 TeV collected during 2011 with the CMS experiment, corresponding to integrated luminosities of 1.17 and 1.56 fb −1 with muon and electron final states, respectively. Events with leptonically decaying W bosons are selected: t → bW → b ν ( = e or µ). This measurement is used to determine the CKM matrix element |V tb |.The t-channel event signature (figure 1)...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.