Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE, 2010
In view of a possible extension of the forward CMS muon detector system and future LHC luminosity... more In view of a possible extension of the forward CMS muon detector system and future LHC luminosity upgrades, Micro-Pattern Gas Detectors (MPGDs) are an appealing technology. They can simultaneously provide precision tracking and fast trigger information, as well as sufficiently fine segmentation to cope with high particle rates in the high-eta region at LHC and its future upgrades. We report on the design and construction of a full-size prototype for the CMS endcap system, the largest Triple-GEM detector built to-date. We present details on the 3D modeling of the detector geometry, the implementation of the readout strips and electronics, and the detector assembly procedure.
The charged particle transverse momentum (p T) spectra are presented for pp collisions at √ s = 0... more The charged particle transverse momentum (p T) spectra are presented for pp collisions at √ s = 0.9 and 7 TeV. The data samples were collected with the CMS detector at the LHC and correspond to integrated luminosities of 231 µb −1 and 2.96 pb −1 , respectively. Calorimeter-based high-transverse-energy triggers are employed to enhance the statistical reach of the high-p T measurements. The results are compared with leading and next-toleading order QCD and with an empirical scaling of measurements at different collision energies using the scaling variable x T ≡ 2p T / √ s over the p T range up to 200 GeV/c. Using a combination of x T scaling and direct interpolation at fixed p T , a reference transverse momentum spectrum at √ s = 2.76 TeV is constructed, which can be used for studying high-p T particle suppression in the dense QCD medium produced in heavy-ion collisions at that centre-of-mass energy.
Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of i... more Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at √ s = 7 TeV. The W boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both lefthanded and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W → tb, leading to a final state signature with a single electron or muon, missing transverse energy, and jets, at least one of which is identified as a b-jet. A W boson that couples to the right-handed (left-handed) chiral projections of the fermions with the same coupling constants as the W is excluded for masses below 1.85 (1.51) TeV at the 95% confidence level. For the first time using LHC data, constraints on the W gauge couplings for a set of left-and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.
A search for microscopic black hole production and decay in pp collisions at a centerof-mass ener... more A search for microscopic black hole production and decay in pp collisions at a centerof-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb −1. Events with large total transverse energy are analyzed for the presence of multiple highenergy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the expected standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities. Limits on the minimum black hole mass are set, in the range 3.5-4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.
A search for a heavy gauge boson W has been conducted by the CMS experiment at the LHC in the dec... more A search for a heavy gauge boson W has been conducted by the CMS experiment at the LHC in the decay channel with an electron and large transverse energy imbalance E miss T , using proton-proton collision data corresponding to an integrated luminosity of 36 pb −1. No excess above standard model expectations is seen in the transverse mass distribution of the electron-E miss T system. Assuming standard-model-like couplings and decay branching fractions, a W boson with a mass less than 1.36 TeV/c 2 is excluded at 95% confidence level.
A search for narrow resonances at high mass in the dimuon and dielectron channels has been perfor... more A search for narrow resonances at high mass in the dimuon and dielectron channels has been performed by the CMS experiment at the CERN LHC, using pp collision data recorded at √ s = 7 TeV. The event samples correspond to integrated luminosities of 40 pb −1 in the dimuon channel and 35 pb −1 in the dielectron channel. Heavy dilepton resonances are predicted in theoretical models with extra gauge bosons (Z) or as Kaluza-Klein graviton excitations (G KK) in the Randall-Sundrum model. Upper limits on the inclusive cross section of Z (G KK) → + − relative to Z → + − are presented. These limits exclude at 95% confidence level a Z with standard-modellike couplings below 1140 GeV, the superstring-inspired Z ψ below 887 GeV, and, for values of the coupling parameter k/M Pl of 0.05 (0.1), Kaluza-Klein gravitons below 855 (1079) GeV.
A measurement of the angular correlations between beauty and anti-beauty hadrons (BB) produced in... more A measurement of the angular correlations between beauty and anti-beauty hadrons (BB) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential BB production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 pb −1 , shows that a sizable fraction of the BB pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of bb production.
A search is presented for physics beyond the standard model (SM) in final states with opposite-si... more A search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 pb −1. No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.
A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into... more A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into a final state containing two quark jets and two leptons, H → ZZ(*) → q $ \overline {\text{q}} $ ℓ − ℓ + is presented. Results are based on data corresponding to an integrated luminosity of 4.6 fb−1 of proton-proton collisions at $ \sqrt {s} = 7 $ TeV, collected with the CMS detector at the LHC. In order to discriminate between signal and background events, kinematic and topological quantities, including the angular spin correlations of the decay products, are employed. Events are further classified according to the probability of the jets to originate from quarks of light or heavy flavor or from gluons. No evidence for the Higgs boson is found, and upper limits on its production cross section are determined for a Higgs boson of mass between 130 and 600 GeV.
Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data ... more Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 pb -1 . Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
A search for pair-produced bottom-like quarks in pp collisions at √ s = 7 TeV is conducted with t... more A search for pair-produced bottom-like quarks in pp collisions at √ s = 7 TeV is conducted with the CMS experiment at the LHC. The decay b → tW is considered in this search. The b b → tW − tW + process can be identified by the distinctive signature of trileptons and same-sign dileptons. With a data sample corresponding to an integrated luminosity of 34 pb −1 , no excess above the standard model background predictions is observed and a b quark with a mass between 255 and 361 GeV/c 2 is excluded at the 95% confidence level.
A new heavy gauge boson, W , decaying to a muon and a neutrino, is searched for in pp collisions ... more A new heavy gauge boson, W , decaying to a muon and a neutrino, is searched for in pp collisions at a centre-of-mass energy of 7 TeV. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 36 pb −1. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the muon-neutrino system. Masses below 1.40 TeV are excluded at the 95% confidence level for a sequential standard-model-like W. The W mass lower limit increases to 1.58 TeV when the present analysis is combined with the CMS result for the electron channel.
A measurement of the double-differential inclusive dijet production cross section in proton-proto... more A measurement of the double-differential inclusive dijet production cross section in proton-proton collisions at √ s = 7 TeV is presented as a function of the dijet invariant mass and jet rapidity. The data correspond to an integrated luminosity of 36 pb −1 , recorded with the CMS detector at the LHC. The measurement covers the dijet mass range 0.2 TeV to 3.5 TeV and jet rapidities up to |y| = 2.5. It is found to be in good agreement with next-to-leading-order QCD predictions.
with typographical errors in an author name in Refs. [4] and [9]. Reference [4] should read as ''... more with typographical errors in an author name in Refs. [4] and [9]. Reference [4] should read as ''U. Baur, I. Hinchliffe.. .'' and Ref. [9] should read as ''E. Eichten, I Hinchliffe,.. ..'' The references have been corrected as of 6 January 2011. The references are incorrect in the printed version of the journal.
We present a search for the standard model Higgs boson produced in association with a W boson in ... more We present a search for the standard model Higgs boson produced in association with a W boson in ffiffi ffi s p ¼ 1:96 TeV p p collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of 9:45 fb À1 . In events consistent with the decay of the Higgs boson to a bottomquark pair and the W boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the WH production cross section times the H ! b b branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV=c 2 , we observe (expect) a limit of 4.9 (2.8) times the standard model value.
A study of events with missing transverse energy and an energetic jet is performed using pp colli... more A study of events with missing transverse energy and an energetic jet is performed using pp collision data at a centre-of-mass energy of 7 TeV. The data were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb −1. An excess of these events over standard model contributions is a signature of new physics such as large extra dimensions and unparticles. The number of observed events is in good agreement with the prediction of the standard model, and significant extension of the current limits on parameters of new physics benchmark models is achieved.
A search for quark compositeness in the form of quark contact interactions, based on hadronic jet... more A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV, is described. The data sample of the study corresponds to an integrated luminosity of 2:9 pb À1 collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the standard model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.
Evidence is presented for the associated production of a single top quark and W boson in pp colli... more Evidence is presented for the associated production of a single top quark and W boson in pp collisions at ffiffi ffi s p ¼ 7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4:9 fb À1. The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the t t background from the signal. The observed signal has a significance of 4:0 and corresponds to a cross section of 16 þ5 À4 pb, in agreement with the standard model expectation of 15:6 AE 0:4 þ1:0 À1:2 pb.
Measurements of dijet azimuthal decorrelations in pp collisions at ffiffi ffi s p ¼ 7 TeV using t... more Measurements of dijet azimuthal decorrelations in pp collisions at ffiffi ffi s p ¼ 7 TeV using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of 2:9 pb À1. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.
A search for Z bosons in the µ + µ − decay channel has been performed in PbPb collisions at √ s N... more A search for Z bosons in the µ + µ − decay channel has been performed in PbPb collisions at √ s NN = 2.76 TeV with the CMS detector at the LHC, in a 7.2 µb −1 data sample. The number of opposite-sign muon pairs observed in the 60-120 GeV/c 2 invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of (33.8 ± 5.5(stat) ± 4.4(syst)) × 10 −8 , in the |y| < 2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE, 2010
In view of a possible extension of the forward CMS muon detector system and future LHC luminosity... more In view of a possible extension of the forward CMS muon detector system and future LHC luminosity upgrades, Micro-Pattern Gas Detectors (MPGDs) are an appealing technology. They can simultaneously provide precision tracking and fast trigger information, as well as sufficiently fine segmentation to cope with high particle rates in the high-eta region at LHC and its future upgrades. We report on the design and construction of a full-size prototype for the CMS endcap system, the largest Triple-GEM detector built to-date. We present details on the 3D modeling of the detector geometry, the implementation of the readout strips and electronics, and the detector assembly procedure.
The charged particle transverse momentum (p T) spectra are presented for pp collisions at √ s = 0... more The charged particle transverse momentum (p T) spectra are presented for pp collisions at √ s = 0.9 and 7 TeV. The data samples were collected with the CMS detector at the LHC and correspond to integrated luminosities of 231 µb −1 and 2.96 pb −1 , respectively. Calorimeter-based high-transverse-energy triggers are employed to enhance the statistical reach of the high-p T measurements. The results are compared with leading and next-toleading order QCD and with an empirical scaling of measurements at different collision energies using the scaling variable x T ≡ 2p T / √ s over the p T range up to 200 GeV/c. Using a combination of x T scaling and direct interpolation at fixed p T , a reference transverse momentum spectrum at √ s = 2.76 TeV is constructed, which can be used for studying high-p T particle suppression in the dense QCD medium produced in heavy-ion collisions at that centre-of-mass energy.
Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of i... more Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at √ s = 7 TeV. The W boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both lefthanded and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W → tb, leading to a final state signature with a single electron or muon, missing transverse energy, and jets, at least one of which is identified as a b-jet. A W boson that couples to the right-handed (left-handed) chiral projections of the fermions with the same coupling constants as the W is excluded for masses below 1.85 (1.51) TeV at the 95% confidence level. For the first time using LHC data, constraints on the W gauge couplings for a set of left-and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.
A search for microscopic black hole production and decay in pp collisions at a centerof-mass ener... more A search for microscopic black hole production and decay in pp collisions at a centerof-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb −1. Events with large total transverse energy are analyzed for the presence of multiple highenergy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the expected standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities. Limits on the minimum black hole mass are set, in the range 3.5-4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.
A search for a heavy gauge boson W has been conducted by the CMS experiment at the LHC in the dec... more A search for a heavy gauge boson W has been conducted by the CMS experiment at the LHC in the decay channel with an electron and large transverse energy imbalance E miss T , using proton-proton collision data corresponding to an integrated luminosity of 36 pb −1. No excess above standard model expectations is seen in the transverse mass distribution of the electron-E miss T system. Assuming standard-model-like couplings and decay branching fractions, a W boson with a mass less than 1.36 TeV/c 2 is excluded at 95% confidence level.
A search for narrow resonances at high mass in the dimuon and dielectron channels has been perfor... more A search for narrow resonances at high mass in the dimuon and dielectron channels has been performed by the CMS experiment at the CERN LHC, using pp collision data recorded at √ s = 7 TeV. The event samples correspond to integrated luminosities of 40 pb −1 in the dimuon channel and 35 pb −1 in the dielectron channel. Heavy dilepton resonances are predicted in theoretical models with extra gauge bosons (Z) or as Kaluza-Klein graviton excitations (G KK) in the Randall-Sundrum model. Upper limits on the inclusive cross section of Z (G KK) → + − relative to Z → + − are presented. These limits exclude at 95% confidence level a Z with standard-modellike couplings below 1140 GeV, the superstring-inspired Z ψ below 887 GeV, and, for values of the coupling parameter k/M Pl of 0.05 (0.1), Kaluza-Klein gravitons below 855 (1079) GeV.
A measurement of the angular correlations between beauty and anti-beauty hadrons (BB) produced in... more A measurement of the angular correlations between beauty and anti-beauty hadrons (BB) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential BB production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 pb −1 , shows that a sizable fraction of the BB pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of bb production.
A search is presented for physics beyond the standard model (SM) in final states with opposite-si... more A search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 pb −1. No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.
A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into... more A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into a final state containing two quark jets and two leptons, H → ZZ(*) → q $ \overline {\text{q}} $ ℓ − ℓ + is presented. Results are based on data corresponding to an integrated luminosity of 4.6 fb−1 of proton-proton collisions at $ \sqrt {s} = 7 $ TeV, collected with the CMS detector at the LHC. In order to discriminate between signal and background events, kinematic and topological quantities, including the angular spin correlations of the decay products, are employed. Events are further classified according to the probability of the jets to originate from quarks of light or heavy flavor or from gluons. No evidence for the Higgs boson is found, and upper limits on its production cross section are determined for a Higgs boson of mass between 130 and 600 GeV.
Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data ... more Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 pb -1 . Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
A search for pair-produced bottom-like quarks in pp collisions at √ s = 7 TeV is conducted with t... more A search for pair-produced bottom-like quarks in pp collisions at √ s = 7 TeV is conducted with the CMS experiment at the LHC. The decay b → tW is considered in this search. The b b → tW − tW + process can be identified by the distinctive signature of trileptons and same-sign dileptons. With a data sample corresponding to an integrated luminosity of 34 pb −1 , no excess above the standard model background predictions is observed and a b quark with a mass between 255 and 361 GeV/c 2 is excluded at the 95% confidence level.
A new heavy gauge boson, W , decaying to a muon and a neutrino, is searched for in pp collisions ... more A new heavy gauge boson, W , decaying to a muon and a neutrino, is searched for in pp collisions at a centre-of-mass energy of 7 TeV. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 36 pb −1. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the muon-neutrino system. Masses below 1.40 TeV are excluded at the 95% confidence level for a sequential standard-model-like W. The W mass lower limit increases to 1.58 TeV when the present analysis is combined with the CMS result for the electron channel.
A measurement of the double-differential inclusive dijet production cross section in proton-proto... more A measurement of the double-differential inclusive dijet production cross section in proton-proton collisions at √ s = 7 TeV is presented as a function of the dijet invariant mass and jet rapidity. The data correspond to an integrated luminosity of 36 pb −1 , recorded with the CMS detector at the LHC. The measurement covers the dijet mass range 0.2 TeV to 3.5 TeV and jet rapidities up to |y| = 2.5. It is found to be in good agreement with next-to-leading-order QCD predictions.
with typographical errors in an author name in Refs. [4] and [9]. Reference [4] should read as ''... more with typographical errors in an author name in Refs. [4] and [9]. Reference [4] should read as ''U. Baur, I. Hinchliffe.. .'' and Ref. [9] should read as ''E. Eichten, I Hinchliffe,.. ..'' The references have been corrected as of 6 January 2011. The references are incorrect in the printed version of the journal.
We present a search for the standard model Higgs boson produced in association with a W boson in ... more We present a search for the standard model Higgs boson produced in association with a W boson in ffiffi ffi s p ¼ 1:96 TeV p p collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of 9:45 fb À1 . In events consistent with the decay of the Higgs boson to a bottomquark pair and the W boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the WH production cross section times the H ! b b branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV=c 2 , we observe (expect) a limit of 4.9 (2.8) times the standard model value.
A study of events with missing transverse energy and an energetic jet is performed using pp colli... more A study of events with missing transverse energy and an energetic jet is performed using pp collision data at a centre-of-mass energy of 7 TeV. The data were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb −1. An excess of these events over standard model contributions is a signature of new physics such as large extra dimensions and unparticles. The number of observed events is in good agreement with the prediction of the standard model, and significant extension of the current limits on parameters of new physics benchmark models is achieved.
A search for quark compositeness in the form of quark contact interactions, based on hadronic jet... more A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at ffiffi ffi s p ¼ 7 TeV, is described. The data sample of the study corresponds to an integrated luminosity of 2:9 pb À1 collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the standard model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.
Evidence is presented for the associated production of a single top quark and W boson in pp colli... more Evidence is presented for the associated production of a single top quark and W boson in pp collisions at ffiffi ffi s p ¼ 7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4:9 fb À1. The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the t t background from the signal. The observed signal has a significance of 4:0 and corresponds to a cross section of 16 þ5 À4 pb, in agreement with the standard model expectation of 15:6 AE 0:4 þ1:0 À1:2 pb.
Measurements of dijet azimuthal decorrelations in pp collisions at ffiffi ffi s p ¼ 7 TeV using t... more Measurements of dijet azimuthal decorrelations in pp collisions at ffiffi ffi s p ¼ 7 TeV using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of 2:9 pb À1. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.
A search for Z bosons in the µ + µ − decay channel has been performed in PbPb collisions at √ s N... more A search for Z bosons in the µ + µ − decay channel has been performed in PbPb collisions at √ s NN = 2.76 TeV with the CMS detector at the LHC, in a 7.2 µb −1 data sample. The number of opposite-sign muon pairs observed in the 60-120 GeV/c 2 invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of (33.8 ± 5.5(stat) ± 4.4(syst)) × 10 −8 , in the |y| < 2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.
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Papers by Michael Tytgat