Improved jet energy scale corrections, based on a data sample corresponding to an integrated luminosity of 19.7 fb −1 collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 8 TeV, are presented. The corrections as a function of pseudorapidity η and transverse momentum p T are extracted from data and simulated events combining several channels and methods. They account successively for the effects of pileup, uniformity of the detector response, and residual data-simulation jet energy scale differences. Further corrections, depending on the jet flavor and distance parameter (jet size) R, are also presented. The jet energy resolution is measured in data and simulated events and is studied as a function of pileup, jet size, and jet flavor. Typical jet energy resolutions at the central rapidities are 15-20% at 30 GeV, about 10% at 100 GeV, and 5% at 1 TeV. The studies exploit events with dijet topology, as well as photon+jet, Z+jet and multijet events. Several new techniques are used to account for the various sources of jet energy scale corrections, and a full set of uncertainties, and their correlations, are provided.The final uncertainties on the jet energy scale are below 3% across the phase space considered by most analyses (p T > 30 GeV and |η| < 5.0). In the barrel region (|η| < 1.3) an uncertainty below 1% for p T > 30 GeV is reached, when excluding the jet flavor uncertainties, which are provided separately for different jet flavors. A new benchmark for jet energy scale determination at hadron colliders is achieved with 0.32% uncertainty for jets with p T of the order of 165-330 GeV, and |η| < 0.8.

This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing detector signals consistent with an electron, photon, muon, τ lepton, jet, or missing transverse energy. A programmable menu of up to 128 object-based algorithms is used to select events for subsequent processing. The trigger thresholds are adjusted to the LHC instantaneous luminosity during data taking in order to restrict the output rate to 100 kHz, the upper limit imposed by the CMS readout electronics. The second level, implemented in software, further refines the purity of the output stream, selecting an average rate of 400 Hz for offline event storage. The objectives, strategy and performance of the trigger system during the LHC Run 1 are described.

The isospin asymmetries of B → Kµ + µ − and B → K * µ + µ − decays and the partial branching fractions of the B 0 → K 0 µ + µ − , B + → K + µ + µ − and B + → K * + µ + µ − decays are measured as functions of the dimuon mass squared, q 2 . The data used correspond to an integrated luminosity of 3 fb −1 from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.

An angular analysis and a measurement of the differential branching fraction of the decay B 0 s → φµ + µ − are presented, using data corresponding to an integrated luminosity of 3.0 fb −1 of pp collisions recorded by the LHCb experiment at √ s = 7 and 8 TeV. Measurements are reported as a function of q 2 , the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range 1 < q 2 < 6 GeV 2 /c 4 , where precise theoretical calculations are available, the differential branching fraction is found to be more than 3 σ below the Standard Model predictions. The LHCb collaboration 30 IntroductionThe decay B 0 s → φµ + µ − is mediated by a b → s flavour changing neutral current (FCNC) transition. In the Standard Model (SM) it is forbidden at tree-level and proceeds via loop diagrams as shown in figure 1. In extensions of the SM, new heavy particles can appear in competing diagrams and affect both the branching fraction of the decay and the angular distributions of the final-state particles.This decay channel was first observed and studied by the CDF collaboration [1, 2] and subsequently studied by the LHCb collaboration using data collected during 2011, corresponding to an integrated luminosity of 1.0 fb −1 [3]. While the angular distributions were found to be in good agreement with SM expectations, the measured branching fraction differs from the recently updated SM prediction by 3.1 σ [4,5]. A similar trend is also seen for the branching fractions of other b → sµ + µ − processes, which tend to be lower than SM predictions [6-8].-1 - JHEP09(2015)179This paper presents an updated analysis of the decay B 0 s → φ(→ K + K − )µ + µ − using data accumulated by LHCb in pp collisions, corresponding to an integrated luminosity of 1.0 fb −1 collected during 2011 at 7 TeV and 2.0 fb −1 collected during 2012 at 8 TeV centreof-mass energy. The differential branching fraction dB(B 0 s → φµ + µ − )/dq 2 is determined as a function of q 2 , the square of the dimuon invariant mass. In addition, a three-dimensional angular analysis in cos θ l , cos θ K and Φ is performed in bins of q 2 . Here, the angle θ K (θ l ) denotes the angle of the K − (µ − ) with respect to the direction of flight of the B 0 s meson in the K + K − (µ + µ − ) centre-of-mass frame, and Φ denotes the angle between the µ + µ − and the K + K − decay planes in the B 0 s meson centre-of-mass frame. Compared to the previously published fit of the one-dimensional projections of the decay angles [3], the full three-dimensional angular fit gives improved sensitivity and allows access to more angular observables.The decay B 0 s → φµ + µ − is closely related to the decay B 0 → K * 0 µ + µ − , which has been studied extensively by LHCb [6,9, 10]. Although B 0 s meson production is suppressed with respect to the B 0 meson by the fragmentation fraction ratio f s /f d ∼ 1/4, the narrow φ resonance allows a clean selection with low background levels. Furthermore, the contribution from the S wave, w...

The second-order azimuthal anisotropy Fourier harmonics, v 2 , are obtained in p-Pb and PbPb collisions over a wide pseudorapidity (η) range based on correlations among six or more charged particles. The p-Pb data, corresponding to an integrated luminosity of 35 nb −1 , were collected during the 2013 LHC p-Pb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. A sample of semiperipheral PbPb collision data at ffiffiffiffiffiffiffi ffi s NN p ¼ 2.76 TeV, corresponding to an integrated luminosity of 2.5 μb −1 and covering a similar range of particle multiplicities as the p-Pb data, is also analyzed for comparison. The six-and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the v 2 coefficients, extending previous studies of two-and four-particle correlations. For both the p-Pb and PbPb systems, the v 2 values obtained with correlations among more than four particles are consistent with previously published four-particle results. These data support the interpretation of a collective origin for the previously observed long-range (large Δη) correlations in both systems. The ratios of v 2 values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a p-Pb system dominated by fluctuations in the positions of participant nucleons. These results provide new insights into the multiparticle dynamics of collision systems with a very small overlapping region. DOI: 10.1103/PhysRevLett.115.012301 PACS numbers: 25.75.Gz Measurements at the CERN LHC have led to the discovery of two-particle azimuthal correlation structures at large relative pseudorapidity (long range) in protonproton (pp) [1] and proton-lead (p-Pb) [2][3][4][5] collisions. Similar long-range structure has also been observed for ffiffiffiffiffiffiffi ffi [6,7]. The results extend previous studies of relativistic heavy-ion collisions, such as for the copper-copper [8], gold-gold [8][9][10][11][12], and lead-lead (PbPb) [13][14][15][16][17][18] systems, where similar long-range, two-particle correlations at small relative azimuthal angle jΔϕj ≈ 0 were first observed. A fundamental question is whether the observed behavior results from correlations exclusively between particle pairs, or if it is a multiparticle, collective effect. It has been suggested that the hydrodynamic collective flow of a strongly interacting and expanding medium [19][20][21] is responsible for these long-range correlations in central and midcentral heavy-ion collisions. The origin of the observed long-range correlations in collision systems with a small overlapping region, such as for pp and p-Pb collisions, is not clear since for these systems the formation of an extended hot medium is not necessarily expected. Various theoretical models have been proposed to interpret the pp [22,23] and p-Pb results, including initial-state gluon saturation without any final state interactions [24,25] and, similar to what is thought to occur in heavi...