Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (eta) and azimuthal angle (phi). Short-range correlations in Delta(eta), which are studied in minimum bias events, are characterized using a simple "independent cluster" parametrization in order to quantify their strength (cluster size) and their extent in eta (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb(-1) data set at 7TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p(T) of 1-3 GeV/c, 2.0

A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For tt events under typical 2011 pileup conditions, the average trackreconstruction efficiency for promptly-produced charged particles with transverse momenta of p T > 0.9 GeV is 94% for pseudorapidities of |η| < 0.9 and 85% for 0.9 < |η| < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of p T = 100 GeV emitted at |η| < 1.4, the resolutions are approximately 2.8% in p T , and respectively, 10 µm and 30 µm in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10-12 µm in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung.

A detailed description is reported of the analysis used by the CMS Collaboration in the search for the standard model Higgs boson in pp collisions at the LHC, which led to the observation of a new boson. The data sample corresponds to integrated luminosities up to 5.1 fb −1 at √ s = 7 TeV, and up to 5.3 fb −1 at √ s = 8 TeV. The results for five Higgs boson decay modes γγ, ZZ, WW, τ τ , and bb, which show a combined local significance of 5 standard deviations near 125 GeV, are reviewed. A fit to the invariant mass of the two high resolution channels, γγ and ZZ → 4 , gives a mass estimate of 125.3 ± 0.4 (stat.) ± 0.5 (syst.) GeV. The measurements are interpreted in the context of the standard model Lagrangian for the scalar Higgs field interacting with fermions and vector bosons. The measured values of the corresponding couplings are compared to the standard model predictions. The hypothesis of custodial symmetry is tested through the measurement of the ratio of the couplings to the W and Z bosons. All the results are consistent, within their uncertainties, with the expectations for a standard model Higgs boson. The CMS collaboration 106 Keywords: Hadron-Hadron Scattering IntroductionThe standard model (SM) [1-3] of particle physics accurately describes many experimental results that probe elementary particles and their interactions up to an energy scale of a few hundred GeV [4]. In the SM, the building blocks of matter, the fermions, are comprised of quarks and leptons. The interactions are mediated through the exchange of force carriers: the photon for electromagnetic interactions, the W and Z bosons for weak interactions, and the gluons for strong interactions. All the elementary particles acquire mass through their interaction with the Higgs field [5][6][7][8][9][10][11][12][13]. This mechanism, called the "Higgs" or "BEH" mechanism [5][6][7][8][9][10], is the first coherent and the simplest solution for giving mass to W and Z bosons, while still preserving the symmetry of the Lagrangian. It is realized by introducing a new complex scalar field into the model. By construction, this field allows the W and Z bosons to acquire mass whilst the photon remains massless, and adds to the model one new scalar particle, the SM Higgs boson (H). The Higgs scalar field and its conjugate can also give mass to the fermions, through Yukawa interactions [11][12][13] The discovery or exclusion of the SM Higgs boson is one of the primary scientific goals of the LHC. Previous direct searches at the LHC were based on data from protonproton collisions corresponding to an integrated luminosity of 5.1 fb −1 collected at a centreof-mass energy of 7 TeV. The CMS experiment excluded at 95% CL masses from 127 to 600 GeV [20]. The ATLAS experiment excluded at 95% CL the ranges 111. . Within the remaining allowed mass region, an excess of events between 2 and 3 standard deviations (σ) near 125 GeV was reported by both experiments. In 2012, the proton-proton centre-of-mass energy was increased to 8 TeV, and by the end of June, an...

A search for new physics is performed in multijet events with large missing transverse momentum produced in proton-proton collisions at √ s = 8 TeV using a data sample corresponding to an integrated luminosity of 19.5 fb −1 collected with the CMS detector at the LHC. The data sample is divided into three jet multiplicity categories (3-5, 6-7, and ≥8 jets), and studied further in bins of two variables: the scalar sum of jet transverse momenta and the missing transverse momentum. The observed numbers of events in various categories are consistent with backgrounds expected from standard model processes. Exclusion limits are presented for several simplified supersymmetric models of squark or gluino pair production. 3 Sample selectionAll these backgrounds are determined using the data, with as little reliance on simulation as possible. The CMS detector and event reconstructionThe CMS detector is a multipurpose apparatus, described in detail in Ref. [5]. The CMS coordinate system is defined with the origin at the centre of the detector and the z axis along the anticlockwise beam direction. The polar angle θ is measured with respect to the z axis, and the azimuthal angle φ (measured in radians) in the plane perpendicular to that axis. Chargedparticle trajectories are measured with a silicon pixel and strip tracker, covering |η| < 2.5, where the pseudorapidity η is defined as η = − ln[tan(θ/2)]. Immersed in the 3.8 T magnetic field provided by a 6 m diameter superconducting solenoid, which also encircles the calorimeters, the tracking system provides transverse momentum (p T ) resolution of approximately 1.5% for charged particles with p T ∼ 100 GeV. A lead-tungstate crystal electromagnetic calorimeter and a brass-and-scintillator hadron calorimeter surround the tracking volume and cover the region |η| < 3. Steel and quartz-fibre hadron forward calorimeters extend the coverage to |η| ≤ 5. Muons are identified in gas ionization detectors embedded in the steel flux return yoke of the magnet. The events used for this search are recorded using a two-level trigger system described in Ref. [5].The recorded events are required to have at least one well-identified interaction vertex with z position within 24 cm from the nominal centre of the detector and transverse distance from the z axis less than 2 cm. The primary vertex is the one with the largest sum of p T -squared of all the associated tracks, and is assumed to correspond to the hard-scattering process. The events are reconstructed using a particle-flow (PF) algorithm [23]. This algorithm reconstructs a list of particles in each event, namely charged and neutral hadrons, photons, muons, and electrons, combining the information from the tracker, the calorimeters, and the muon system. These particles are then clustered into jets using the anti-k T clustering algorithm [24] with a size parameter of 0.5. Contributions from additional pp collisions overlapping with the event of interest (pileup) are mitigated by discarding charged particles not associated with the primary vert...

Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of √ s = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |η| < 0.5 to |η| < 2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distribution at √ s = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with √ s is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies. Keywords: Hadron-Hadron ScatteringOpen Access, Copyright CERN, for the benefit of the CMS Collaboration The CMS collaboration 21 IntroductionThe charged hadron multiplicity, or number of primary charged hadrons, n, is a basic global observable characterising final states in high-energy-collision processes. The multiplicity distribution, P n , is the probability to produce n charged hadrons in an event, either in full phase space or in restricted phase space domains. In this paper we report measurements of P n in non-single-diffractive [1] proton-proton collisions, at centre-of-mass energies √ s = 0.9, 2.36, and 7 TeV at the Large Hadron Collider (LHC) [2]. The measurements are based on events recorded by the Compact Muon Solenoid (CMS) [3] experiment, using a minimumbias trigger.Energy-momentum and charge conservation significantly influence the multiplicity distribution for the full phase space. The distribution in restricted phase space, which is less affected by such constraints, is expected to be a more sensitive probe of the underlying dynamics and can be used to better constrain phenomenological models. Comprehensive reviews on the subject can be found in [1,4,5]. The measurements described in this paper are performed for intervals of increasing extent in pseudorapidity from |η| < 0.5 up to |η| < 2.4, where η is defined as −ln[tan(θ/2)], and θ is the polar angle of the particle with respect to -1 - JHEP01(2011)079the counterclockwise beam direction. In these measurements primary charged hadrons are defined as all charged hadrons produced in the interaction, including the products of the decays of objects with life-time less than 10 −10 seconds; products of longer-lived particles, such as K 0 S and Λ, and hadrons originating from secondary interactions are excluded. Independent emission of single particles yields a Poissonian P n . Deviations from this shape, therefore, reveal correlations. These correlations are predominantly short range in rapidity, attributed to cluster decays, and reflect local conservation of quantum numbers in the hadronisation process. In hadron-hadron interactions, additional large long-range rapidity correlations are observed, wh...