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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>
Search for heavy long-lived charged particles with the ATLAS detector in pp collisions at s=7 TeV
ATLAS Collaboration,Aad, G.,Abbott, B.,Abdallah, J.,Abdelalim, A.A.,Abdesselam, A.,Abdinov, O.,Abi, B.,Abolins, M.,Abramowicz, H.,Abreu, H.,Acerbi, E.,Acharya, B.S.,Adams, D.L.,Addy, T.N.,Adelman, J. North-Holland Pub. Co 2011 Physics letters: B Vol.703 No.4
A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb<SUP>-1</SUP> from pp collisions at s=7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stable τ@? sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N<SUB>5</SUB>=3, m<SUB>messenger</SUB>=250 TeV, sign(μ)=1 and tanβ=5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of R-hadrons produced as g@?-balls.
CMS Collaboration,Chatrchyan, S.,Khachatryan, V.,Sirunyan, A.M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Ero, J.,Fabjan, C.,Friedl, M.,Fruhwirth, R.,Ghete, V.M.,Hammer, J.,Hoch, M.,Hormann, N North-Holland Pub. Co 2012 Physics letters. Section B Vol.709 No.1
The difference in angular distributions between top quarks and antiquarks, commonly referred to as the charge asymmetry, is measured in pp collisions at the LHC with the CMS experiment. The data sample corresponds to an integrated luminosity of 1.09 fb<SUP>-1</SUP> at a centre-of-mass energy of 7 TeV. Top-quark pairs are selected in the final state with an electron or muon and four or more jets. At least one jet is identified as originating from b-quark hadronization. The charge asymmetry is measured in two variables, one based on the pseudorapidities (η) of the top quarks and the other on their rapidities (y). The results A<SUB>C</SUB><SUP>η</SUP>=-0.017+/-0.032 (stat.)<SUB>-0.036</SUB><SUP>+0.025</SUP>(syst.) and A<SUB>C</SUB><SUP>y</SUP>=-0.013+/-0.028 (stat.)<SUB>-0.031</SUB><SUP>+0.029</SUP>(syst.) are consistent within uncertainties with the standard-model predictions.
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>
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 European Physical Journal C Vol.77 No.12
<P>A search is presented for an excess of events with heavy-flavor quark pairs (t (t) over bar and b (b) over bar) and a large imbalance in transverse momentum in data from proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 2.2 fb(-1) collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in t (t) over bar and b (b) over bar final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states.</P>
Adam, J.,Adamová,, D.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S.U.,Aimo, I.,Aiola, S.,Ajaz, M.,Akindinov, A.,Alam, S.N.,Aleksandrov, D.,Alessandro, B.,Alexand North-Holland Pub. Co 2017 Physics letters. Section B Vol.768 No.-
<P><B>Abstract</B></P> <P>The first study of <I>ϕ</I>-meson production in p–Pb collisions at forward and backward rapidity, at a nucleon–nucleon centre-of-mass energy <SUB> s NN </SUB> = 5.02 TeV , has been performed with the ALICE apparatus at the LHC. The <I>ϕ</I>-mesons have been identified in the dimuon decay channel in the transverse momentum ( <SUB> p T </SUB> ) range 1 < <SUB> p T </SUB> < 7 GeV / c , both in the p-going ( 2.03 < y < 3.53 ) and the Pb-going ( − 4.46 < y < − 2.96 ) directions — where <I>y</I> stands for the rapidity in the nucleon–nucleon centre-of-mass — the integrated luminosity amounting to 5.01 ± 0.19 <SUP> nb − 1 </SUP> and 5.81 ± 0.20 <SUP> nb − 1 </SUP> , respectively, for the two data samples. Differential cross sections as a function of transverse momentum and rapidity are presented. The forward–backward ratio for <I>ϕ</I>-meson production is measured for 2.96 < | y | < 3.53 , resulting in a ratio ∼0.5 with no significant <SUB> p T </SUB> dependence within the uncertainties. The <SUB> p T </SUB> dependence of the <I>ϕ</I> nuclear modification factor <SUB> R pPb </SUB> exhibits an enhancement up to a factor 1.6 at <SUB> p T </SUB> = 3 – 4 GeV / c in the Pb-going direction. The <SUB> p T </SUB> dependence of the <I>ϕ</I>-meson cross section in pp collisions at s = 2.76 TeV , which is used to determine a reference for the p–Pb results, is also presented here for 1 < <SUB> p T </SUB> < 5 GeV / c and 2.5 < y < 4 , for a 78 ± 3 <SUP> nb − 1 </SUP> integrated luminosity sample.</P>
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 Institute of Physics Pub 2017 The journal of high energy physics Vol.2017 No.10
<P>A search for dark matter is performed looking for events with large missing transverse momentum and a Higgs boson decaying either to a pair of bottom quarks or to a pair of photons. The data from proton-proton collisions at a center-of-mass energy of 13TeV, collected in 2015 with the CMS detector at the LHC, correspond to an integrated luminosity of 2.3 fb(-1). Results are interpreted in the context of a Z'-two-Higgs-doublet model, where the gauge symmetry of the standard model is extended by a U(1) Z' group, with a new massive Z' gauge boson, and the Higgs sector is extended with four additional Higgs bosons. In this model, a high-mass resonance Z' decays into a pseudoscalar boson A and a light SM-like scalar Higgs boson, and the A decays to a pair of dark matter particles. No signi fi cant excesses are observed over the background prediction. Combining results from the two decay channels yields exclusion limits in the signal cross section in the m(Z')-m(A) phase space. For example, the observed data exclude the Z' mass range from 600 to 1860 GeV, for Z' coupling strength gZ' = 0: 8, the coupling of A with dark matter particles g(X) = 1, the ratio of the vacuum expectation values tan beta = 1, and m(A) = 300GeV. The results of this analysis are valid for any dark matter particle mass below 100 GeV.</P>
Beam energy dependence of rapidity-even dipolar flow in Au+Au collisions
Adam, J.,Adamczyk, L.,Adams, J.R.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Ajitanand, N.N.,Alekseev, I.,Anderson, D.M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Ashraf, M.U.,A North-Holland Pub. Co 2018 Physics letters. Section B Vol.784 No.-
<P><B>Abstract</B></P> <P>New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient <SUB> v 1 </SUB> , are presented for transverse momenta <SUB> p T </SUB> , and centrality intervals in Au+Au collisions recorded by the STAR experiment for the center-of-mass energy range <SUB> s N N </SUB> = 7.7 – 200 GeV. The measurements underscore the importance of momentum conservation, and the characteristic dependencies on <SUB> s N N </SUB> , centrality and <SUB> p T </SUB> are consistent with the expectations of geometric fluctuations generated in the initial stages of the collision, acting in concert with a hydrodynamic-like expansion. The centrality and <SUB> p T </SUB> dependencies of v 1 even , as well as an observed similarity between its excitation function and that for <SUB> v 3 </SUB> , could serve as constraints for initial-state models. The v 1 even excitation function could also provide an important supplement to the flow measurements employed for precision extraction of the temperature dependence of the specific shear viscosity.</P>
Search for leptonic decays of W′ bosons in pp collisions at $ \sqrt {s} = {7} $ TeV
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.,Hammer, J.,Hö,rmann, N.,Hrubec, Springer-Verlag 2012 Journal of high energy physics Vol.2012 No.8
<P>A search for a new heavy gauge boson W' decaying to an electron or muon, plus a low mass neutrino, is presented. This study uses data corresponding to an integrated luminosity of 5.0 fb(-1), collected using the CMS detector in pp collisions at a centre-of-mass energy of 7TeV at the LHC. Events containing a single electron or muon and missing transverse momentum are analyzed. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the lepton-neutrino system, and upper limits for cross sections above different transverse mass thresholds are presented. Mass exclusion limits at 95% CL for a range of W' models are determined, including a limit of 2.5TeV for right-handed W' bosons with standard-model-like couplings and limits of 2.43-2.63 TeV for left-handed W' bosons, taking into account their interference with the standard model W boson. Exclusion limits have also been set on Kaluza-Klein W-KK states in the framework of split universal extra dimensions.</P>
CMS Collaboration,Chatrchyan, S.,Khachatryan, V.,Sirunyan, A.M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Ero, J.,Fabjan, C.,Friedl, M.,Fruhwirth, R.,Ghete, V.M.,Hammer, J.,Hormann, N.,Hrubec, North-Holland Pub. Co 2013 Physics letters: B Vol.718 No.3
A search is presented for physics beyond the standard model (BSM) in final states with a pair of opposite-sign isolated leptons accompanied by jets and missing transverse energy. The search uses LHC data recorded at a center-of-mass energy s=7 TeV with the CMS detector, corresponding to an integrated luminosity of approximately 5 fb<SUP>-1</SUP>. Two complementary search strategies are employed. The first probes models with a specific dilepton production mechanism that leads to a characteristic kinematic edge in the dilepton mass distribution. The second strategy probes models of dilepton production with heavy, colored objects that decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield in excess of the standard model expectations is found. Upper limits on the BSM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing specific models of BSM physics not considered in this Letter.