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Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Asilar, E.,Bergauer, T.,Brandstetter, J.,Brondolin, E.,Dragicevic, M.,Erö,, J.,Flechl, M.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N Springer-Verlag 2017 Journal of high energy physics Vol.2017 No.7
<P>A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying tau lepton, and at least two jets, using a root s = 13 TeV pp collision data sample corresponding to an integrated luminosity of 12: 9 fb(-1) collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and beta(2), where beta is the branching fraction of leptoquark decay to a tau lepton and a bottom quark. Assuming beta = 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, N-R, and right-handed W bosons, W-R, arising in a left-right symmetric extension of the standard model. In this search, W-R bosons are assumed to decay to a tau lepton and N-R followed by the decay of the N-R to a tau lepton and an off-shell W-R boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, W-R boson masses below 2.9 TeV are excluded at 95% confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with tau leptons in the final state.</P>
Chatrchyan, S.,Khachatryan, V.,Sirunyan, A. M.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Fabjan, C.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N.,Hrubec, J.,Jeitler, M. Institute of Physics Pub 2015 The journal of high energy physics Vol.2015 No.3
<P>The production of Z bosons is studied in the dimuon and dielectron decay channels in PbPb and pp collisions at root s(NN) = 2.76TeV, using data collected by the CMS experiment at the LHC. The PbPb data sample corresponds to an integrated luminosity of about 166 mu b(-1), while the pp data sample collected in 2013 at the same nucleon-nucleon centre-of-mass energy has an integrated luminosity of 5.4 pb(-1). The Z boson yield is measured as a function of rapidity, transverse momentum, and collision centrality. The ratio of PbPb to pp yields, scaled by the number of inelastic nucleon-nucleon collisions, is found to be 1.06 +/- 0.05 (stat) +/- 0.08 (syst) in the dimuon channel and 1.02 +/- 0.08 (stat) +/- 0.15 (syst) in the dielectron channel, for centrality-integrated Z boson production. This binary collision scaling is seen to hold in the entire kinematic region studied, as expected for a colourless probe that is unaffected by the hot and dense QCD medium produced in heavy ion collisions.</P>
Chatrchyan, S.,Khachatryan, V.,Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Fabjan, C.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hö,rmann, N.,Hrubec, J.,Jeitler, Springer Berlin Heidelberg 2013 The European physical journal. C, Particles and fi Vol.73 No.12
<P>Characteristics of multi-particle production in proton-proton collisions at [FORMULA OMISSION] are studied as a function of the charged-particle multiplicity, <I>N</I><SUB>ch</SUB>. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity |<I>η</I>|<2.4 and transverse momentum <I>p</I><SUB>T</SUB>>0.25 GeV/<I>c</I>. Jets are reconstructed from charged-particles only and required to have <I>p</I><SUB>T</SUB>>5 GeV/<I>c</I>. The distributions of jet <I>p</I><SUB>T</SUB>, average <I>p</I><SUB>T</SUB> of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of <I>N</I><SUB>ch</SUB> and compared to the predictions of the <SMALL>PYTHIA</SMALL> and <SMALL>HERWIG</SMALL> event generators. Predictions without multi-parton interactions fail completely to describe the <I>N</I><SUB>ch</SUB>-dependence observed in the data. For increasing <I>N</I><SUB>ch</SUB>, <SMALL>PYTHIA</SMALL> systematically predicts higher jet rates and harder <I>p</I><SUB>T</SUB> spectra than seen in the data, whereas <SMALL>HERWIG</SMALL> shows the opposite trends. At the highest multiplicity, the data–model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.</P>
Khachatryan, V.,Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Fabjan, C.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N.,Hrubec, J.,Jeitler, M.,K Institute of Physics Pub 2015 The journal of high energy physics Vol.2015 No.1
<P>The ratio of the production cross sections times branching fractions (sigma(B-c(+/-))B(B-c(+/-) -> J/psi pi(+/-)))/(sigma(B-+/-)B(B-+/- -> J/psi K-+/-)) is studied in proton-proton collisions at a center-of-mass energy of 7TeV with the CMS detector at the LHC. The kinematic region investigated requires B-c(+/-) and B-+/- mesons with transverse momentum p(T) > 15 GeV and rapidity vertical bar y vertical bar < 1.6. The data sample corresponds to an integrated luminosity of 5.1 fb(-1). The ratio is determined to be [0.48 +/- 0.05 (stat) +/- 0.03 (syst) +/- 0.05 (tau(Bc))]%. The B-c(+/-) -> J/psi pi(+/-)pi(+/-)pi(-/+) decay is also observed in the same data sample. Using a model-independent method developed to measure the efficiency given the presence of resonant behaviour in the three-pion system, the ratio of the branching fractions B-c(+/-) -> J/psi pi(+/-)pi(+/-)pi(-/+)/B(B-c(+/-) -> J/psi pi(+/-)) is measured to be 2.55 +/- 0.80 (stat) +/- 0.33 (syst)(-0.01)(+0.04) (tau(Bc)), consistent with the previous LHCb result.</P>
Khachatryan, V.,Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N.,Hrubec, J.,Jeitler, M.,Kiesenhofer, American Physical Society 2015 PHYSICAL REVIEW D - Vol.91 No.5
<P>A search is performed for long-lived particles that decay into final states that include a pair of electrons or a pair of muons. The experimental signature is a distinctive topology consisting of a pair of charged leptons originating from a displaced secondary vertex. Events corresponding to an integrated luminosity of 19.6 (20.5) fb(-1) in the electron (muon) channel were collected with the CMS detector at the CERN LHC in proton-proton collisions at root s TeV. No significant excess is observed above standard model expectations. Upper limits on the product of the cross section and branching fraction of such a signal are presented as a function of the long-lived particle's mean proper decay length. The limits are presented in an approximately model-independent way, allowing them to be applied to a wide class of models yielding the above topology. Over much of the investigated parameter space, the limits obtained are the most stringent to date. In the specific case of a model in which a Higgs boson in the mass range 125-1000 GeV/c(2) decays into a pair of long-lived neutral bosons in the mass range 20-350 GeV= c(2), each of which can then decay to dileptons, the upper limits obtained are typically in the range 0.2-10 fb for mean proper decay lengths of the long-lived particles in the range 0.01-100 cm. In the case of the lowest Higgs mass considered (125 GeV/c(2)), the limits are in the range 2-50 fb. These limits are sensitive to Higgs boson branching fractions as low as 10(-1).</P>
Khachatryan, V.,Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N.,Hrubec, J.,Jeitler, M.,Kiesenhofer, Springer Berlin Heidelberg 2015 European Physical Journal C Vol.75 No.4
<P>A search has been performed for long-lived particles that could have come to rest within the CMS detector, using the time intervals between LHC beam crossings. The existence of such particles could be deduced from observation of their decays via energy deposits in the CMS calorimeter appearing at times that are well separated from any proton–proton collisions. Using a data set corresponding to an integrated luminosity of 18.6[FORMULA OMISSION] of 8[FORMULA OMISSION] proton–proton collisions, and a search interval corresponding to 281 h of trigger livetime, 10 events are observed, with a background prediction of [FORMULA OMISSION] events. Limits are presented at 95 % confidence level on gluino and top squark production, for over 13 orders of magnitude in the mean proper lifetime of the stopped particle. Assuming a cloud model of R-hadron interactions, a gluino with mass [FORMULA OMISSION]1000[FORMULA OMISSION] and a top squark with mass [FORMULA OMISSION]525[FORMULA OMISSION] are excluded, for lifetimes between 1 [FORMULA OMISSION]s and 1000[FORMULA OMISSION]. These results are the most stringent constraints on stopped particles to date.</P>
Khachatryan, V.,Sirunyan, A. M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Erö,, J.,Fabjan, C.,Friedl, M.,Frü,hwirth, R.,Ghete, V. M.,Hartl, C.,Hö,rmann, N.,Hrubec, J.,Jeitler, M.,K Springer Berlin Heidelberg 2014 The European physical journal. C, Particles and fi Vol.74 No.9
<P>A measurement of the cross section for the production of top quark–antiquark pairs ([FORMULA OMISSION]) in association with a vector boson V (W or Z) in proton-proton collisions at [FORMULA OMISSION][FORMULA OMISSION] is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb[FORMULA OMISSION] recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and [FORMULA OMISSION]) channels: a same-sign dilepton analysis targeting [FORMULA OMISSION] events, and trilepton and four-lepton analyses designed for [FORMULA OMISSION] events. In the same-sign dilepton channel, the [FORMULA OMISSION] cross section is measured as [FORMULA OMISSION], corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the [FORMULA OMISSION] cross section, [FORMULA OMISSION], is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive [FORMULA OMISSION] process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.</P>