A search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra measured with the CMS detector at the LHC. The data set corresponds to 5 fb −1 of integrated luminosity collected in pp collisions at √ s = 7 TeV. No narrow resonances or quantum black holes are observed. Modelindependent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E 6 diquarks (3.75 TeV), and on the masses of W (1.92 TeV) and Z (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.

A search is performed for heavy resonances decaying to two long-lived massive neutral particles, each decaying to leptons. The experimental signature is a distinctive topology consisting of a pair of oppositely charged leptons originating at a separated secondary vertex. Events were collected by the CMS detector at the LHC during pp collisions at √ s = 7 TeV, and selected from data samples corresponding to 4.1 (5.1) fb −1 of integrated luminosity in the electron (muon) channel. No significant excess is observed above standard model expectations, and an upper limit is set with 95% confidence level on the production cross section times the branching fraction to leptons, as a function of the long-lived massive neutral particle lifetime. . This Letter presents the first search using data from the Compact Muon Solenoid (CMS) for massive, long-lived exotic particles X that decay to a pair of oppositely charged leptons. We search for events containing a pair of oppositely charged electrons or muons (dileptons) originating from a common secondary vertex within the volume of the CMS tracker, that is significantly transversely displaced from the event primary vertex. These leptons are assumed to originate from a 2-body decay of a long-lived particle, and so are required to form a narrow resonance in the dilepton mass spectrum. This topological -1 - Keywords: Hadron-Hadron Scattering JHEP02(2013)085signature has the potential to provide clear evidence for physics beyond the standard model (SM). It is also very powerful in suppressing backgrounds from standard model processes.This signature is sensitive to a wide class of models. However, for the purpose of establishing a signal benchmark, a specific model of a long-lived, spinless, exotic particle X which has a non-zero branching fraction to dileptons is used. In this particular model, the X is pair-produced in the decay of a Higgs boson, i.e. H 0 → 2X, X → + − [5], where the Higgs boson is produced through gluon-gluon fusion. This model predicts up to two displaced dilepton vertices in the tracking volume per event.The D0 Collaboration has performed searches for leptons from delayed decays in its tracker volume [6, 7], but these searches are sensitive to a much smaller kinematic phase space region than CMS. The ATLAS Collaboration has performed searches that are sensitive to decay lengths up to about 20 m by exploiting the ATLAS muon spectrometer [8,9], using different decay channels from those considered in this Letter. The CMS detectorThe central feature of the CMS apparatus [10] is a superconducting solenoid of 6 m internal diameter providing an axial field of 3.8 T. Within the field volume are the silicon pixel and strip tracker, the lead-tungstate crystal electromagnetic calorimeter (ECAL), and the brass/scintillator hadron calorimeter. Muons are identified in gas-ionisation detectors embedded in the steel magnetic-flux return yoke of the solenoid.The silicon tracker is composed of pixel detectors (three barrel layers and two forward disks on either end of ...

Results are presented from a search for heavy bottom-like quarks, pair-produced in pp collisions at √ s = 7 TeV, undertaken with the CMS experiment at the LHC. The b quarks are assumed to decay exclusively to tW. The b b → tW − tW + process can be identified by its distinctive signatures of three leptons or two leptons of same charge, and at least one b-quark jet. Using a data sample corresponding to an integrated luminosity of 4.9 fb −1 , observed events are compared to the standard model background predictions, and the existence of b quarks having masses below 611 GeV/c 2 is excluded at 95% confidence level. Submitted to the Journal of High Energy Physics IntroductionThe total number of fermion generations is assumed to be three in the standard model (SM), though the model does not provide an explanation of why this should be the case. Thus the possible existence of a fourth generation remains an important subject for experimental investigation. Adding a fourth generation of massive fermions to the model may strongly affect the Higgs and flavour sectors [1][2][3][4][5]. A fourth generation of heavy quarks would enhance the production of Higgs bosons [6], while the indirect bound from electroweak precision data on the Higgs mass would be relaxed [7,8]. Additional massive quarks may provide a key to understanding the matter-antimatter asymmetry in the universe [9].Various searches for fourth-generation fermions have already been reported. Experiments have shown that the number of light neutrino flavours is equal to three [10][11][12][13], but the possibility of additional heavier neutrinos has not been excluded. A search for pair-produced bottom-like quarks (b ) by the ATLAS collaboration excludes a b -quark mass of less than 480 GeV/c 2 [14]. Earlier studies setting mass limits on possible fourth-generation quarks, from experiments at the Tevatron and the Large Hadron Collider (LHC), can be found in Ref. [15][16][17][18][19][20][21].Using the Compact Muon Solenoid (CMS) detector, we have searched for a heavy b quark that is pair-produced in pp collisions at a centre-of-mass energy of 7 TeV at the LHC. We assume that the mass of the b quark (M b ) is larger than the sum of the top quark and the W-boson masses. If the b quark couples principally to the top quark, the decay chain b b → tW − tW + → bW + W − bW − W + will dominate [22]. Given the 11% branching fraction for a W-boson to each lepton, distinctive signatures of b b production are expected, specifically those of two isolated leptons with the same charge ("same-charge dileptons") or three isolated leptons ("trileptons"). Although occurring very rarely in the standard model, these two signatures may be present in 7.3% of the b b events. An earlier search by CMS [17] in the same-charge dilepton and the trilepton channels, utilizing a data set corresponding to an integrated luminosity of 34 pb −1 , set a lower limit on the mass of the b quark of 361 GeV/c 2 at the 95% confidence level (CL). Here we present an update of this search using a much larg...

A measurement of the mass difference between the top and the antitop quark (∆m t = m t − m t ) is performed using events with a muon or an electron and at least four jets in the final state. The analysis is based on data collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.96±0.11 fb −1 , and yields the value of ∆m t = −0.44 ± 0.46 (stat.) ± 0.27 (syst.) GeV. This result is consistent with equality of particle and antiparticle masses required by CPT invariance, and provides a significantly improved precision relative to existing measurements.

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