Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high... more Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in $$\mathrm {PbPb}$$PbPb collisions at nucleon-nucleon center-of-mass energies $$\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 2.76$$sNN=2.76 and 5.02$$\,\text {TeV}$$TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic ...
Search for high mass dijet resonances with a new background prediction method in proton-proton co... more Search for high mass dijet resonances with a new background prediction method in proton-proton collisions at √ s = 13 TeV The CMS collaboration
The standard model (SM) production of four top quarks ($$\text {t} {}{\overline{\text {t}}} \text... more The standard model (SM) production of four top quarks ($$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137$$\,\text {fb}^{-1}$$fb-1 at a center-of-mass energy of 13$$\,\text {TeV}$$TeV. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the $$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯ signal are respectively 2.6 and 2.7 standard deviations, and the $$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯ cross section is measured to be $$12.6^{+5.8}_{-5.2}\,\text {fb} $$12.6-5.2+5.8fb. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, $$y_{\text {t}}$$yt, yiel...
We present a measurement of the Z boson differential cross section in rapidity and transverse mom... more We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy √ s = 8 TeV, corresponding to an integrated luminosity of 19.7 fb −1. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the FEWZ program. The results are also compared to the commonly used leading-order MADGRAPH and next-to-leading-order POWHEG generators.
A search for the pair production of new light bosons, each decaying into a pair of muons, is perf... more A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 fb −1 collected in proton-proton collisions at center-of-mass energy of √ s = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-tominimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
View the article online for updates and enhancements. Related content Commissioning and performan... more View the article online for updates and enhancements. Related content Commissioning and performance of the CMS silicon strip tracker with cosmic ray muons CMS Collaboration-Commissioning and performance of the CMS pixel tracker with cosmic ray muons CMS Collaboration
The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmi... more The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmic ray data were taken with and without magnetic field at the surface hall and after installation in the experimental hall, hundred meters underground. Various measurements were also performed during the few days of beam in the LHC in September 2008. Calibration parameters were extracted, and the energy response of the HCAL determined from test beam data has been checked.
Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noi... more Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.
During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comp... more During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comprehensive test, in the presence of the 3.8 T magnetic field produced by the CMS superconducting solenoid. Cosmic ray muons were detected in the muon chambers and used to trigger the readout of all CMS sub-detectors. About 15 million events with a muon in the tracker were collected. The efficiency of hit and track reconstruction were measured to be higher than 99% and consistent with expectations from Monte Carlo simulation. This article details the commissioning and performance of the Silicon Strip Tracker with cosmic ray muons.
... The noise performance of the endcap detector is expected due to a different design of the sen... more ... The noise performance of the endcap detector is expected due to a different design of the sensors[11, 12] resulting in smaller pixel capacitance. These noise levels are well below operating thresholds, which must be set above crosstalk lev-els. ...
Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL... more Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL FUCaM. ...
The MIT Faculty has made this article openly available. Please share how this access benefits you... more The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation CMS Collaboration et al. "Alignment of the CMS muon system with cosmic-ray and beam-halo muons."
Journal of Physics G: Nuclear and Particle Physics, 2007
We report the first measurements of inclusive W and Z boson cross sections times the correspondin... more We report the first measurements of inclusive W and Z boson cross sections times the corresponding leptonic branching ratios for pp collisions at √ s = 1.96 TeV based on the decays of the W and Z bosons into electrons and muons. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 72.0 ± 4.3 pb −1. We test e-µ lepton universality in W decays by measuring the ratio of the W → µν to W → eν cross sections and determine a value of 0.991 ± 0.004(stat.) ± 0.011(syst.) for the ratio of W −ℓ−ν couplings (gµ/ge). Since there is no sign of non-universality, we combine our cross section measurements in the different lepton decay modes and obtain σW ×Br(pp → W → ℓν) = 2.749 ± 0.010(stat.) ± 0.053(syst.) ± 0.165(lum.) nb and σ γ * /Z × Br(pp → γ * /Z → ℓℓ) = 254.9 ± 3.3(stat.) ± 4.6(syst.) ± 15.2(lum.) pb for dilepton pairs in the mass range between 66 GeV/c 2 and 116 GeV/c 2. We compute the ratio R of the W → ℓν to Z → ℓℓ cross sections taking all correlations among channels into account and obtain R = 10.84 ± 0.15(stat.) ± 0.14(syst.) including a correction for the virtual photon exchange component in our measured γ * /Z → ℓℓ cross section. Based on the measured value of R, we extract values for the W leptonic branching ratio, Br(W → ℓν) = 0.1082 ± 0.0022; the total width of the W boson, Γ(W) = 2092 ± 42 MeV; and the ratio of W and Z boson total widths, Γ(W)/Γ(Z) = 0.838 ± 0.017. In addition, we use our extracted value of Γ(W) whose value depends on various electroweak parameters and certain CKM matrix elements to constrain the Vcs CKM matrix element, |Vcs| = 0.976± 0.030.
We report on the test beam results and calibration methods using high energy electrons, pions and... more We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region (3 ≤ |η| ≤ 5), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h ≈ 5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as a √ E ⊕ b. The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.
The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that... more The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that is not contained by the barrel (HCAL HB) and electromagnetic (ECAL EB) calorimeters. Due to space limitation the barrel calorimeters do not contain completely the hadronic shower and an outer calorimeter (HO) was designed, constructed and inserted in the muon system of CMS to measure the energy leakage. Testing and calibration of the HO was carried out in a 300 GeV/c test beam that improved the linearity and resolution. HO will provide a net improvement in missing E T measurements at LHC energies. Information from HO will also be used for the muon trigger in CMS.
Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high... more Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in $$\mathrm {PbPb}$$PbPb collisions at nucleon-nucleon center-of-mass energies $$\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 2.76$$sNN=2.76 and 5.02$$\,\text {TeV}$$TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic ...
Search for high mass dijet resonances with a new background prediction method in proton-proton co... more Search for high mass dijet resonances with a new background prediction method in proton-proton collisions at √ s = 13 TeV The CMS collaboration
The standard model (SM) production of four top quarks ($$\text {t} {}{\overline{\text {t}}} \text... more The standard model (SM) production of four top quarks ($$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137$$\,\text {fb}^{-1}$$fb-1 at a center-of-mass energy of 13$$\,\text {TeV}$$TeV. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the $$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯ signal are respectively 2.6 and 2.7 standard deviations, and the $$\text {t} {}{\overline{\text {t}}} \text {t} {}{\overline{\text {t}}} $$tt¯tt¯ cross section is measured to be $$12.6^{+5.8}_{-5.2}\,\text {fb} $$12.6-5.2+5.8fb. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, $$y_{\text {t}}$$yt, yiel...
We present a measurement of the Z boson differential cross section in rapidity and transverse mom... more We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy √ s = 8 TeV, corresponding to an integrated luminosity of 19.7 fb −1. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the FEWZ program. The results are also compared to the commonly used leading-order MADGRAPH and next-to-leading-order POWHEG generators.
A search for the pair production of new light bosons, each decaying into a pair of muons, is perf... more A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 fb −1 collected in proton-proton collisions at center-of-mass energy of √ s = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-tominimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
View the article online for updates and enhancements. Related content Commissioning and performan... more View the article online for updates and enhancements. Related content Commissioning and performance of the CMS silicon strip tracker with cosmic ray muons CMS Collaboration-Commissioning and performance of the CMS pixel tracker with cosmic ray muons CMS Collaboration
The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmi... more The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmic ray data were taken with and without magnetic field at the surface hall and after installation in the experimental hall, hundred meters underground. Various measurements were also performed during the few days of beam in the LHC in September 2008. Calibration parameters were extracted, and the energy response of the HCAL determined from test beam data has been checked.
Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noi... more Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.
During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comp... more During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comprehensive test, in the presence of the 3.8 T magnetic field produced by the CMS superconducting solenoid. Cosmic ray muons were detected in the muon chambers and used to trigger the readout of all CMS sub-detectors. About 15 million events with a muon in the tracker were collected. The efficiency of hit and track reconstruction were measured to be higher than 99% and consistent with expectations from Monte Carlo simulation. This article details the commissioning and performance of the Silicon Strip Tracker with cosmic ray muons.
... The noise performance of the endcap detector is expected due to a different design of the sen... more ... The noise performance of the endcap detector is expected due to a different design of the sensors[11, 12] resulting in smaller pixel capacitance. These noise levels are well below operating thresholds, which must be set above crosstalk lev-els. ...
Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL... more Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL FUCaM. ...
The MIT Faculty has made this article openly available. Please share how this access benefits you... more The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation CMS Collaboration et al. "Alignment of the CMS muon system with cosmic-ray and beam-halo muons."
Journal of Physics G: Nuclear and Particle Physics, 2007
We report the first measurements of inclusive W and Z boson cross sections times the correspondin... more We report the first measurements of inclusive W and Z boson cross sections times the corresponding leptonic branching ratios for pp collisions at √ s = 1.96 TeV based on the decays of the W and Z bosons into electrons and muons. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 72.0 ± 4.3 pb −1. We test e-µ lepton universality in W decays by measuring the ratio of the W → µν to W → eν cross sections and determine a value of 0.991 ± 0.004(stat.) ± 0.011(syst.) for the ratio of W −ℓ−ν couplings (gµ/ge). Since there is no sign of non-universality, we combine our cross section measurements in the different lepton decay modes and obtain σW ×Br(pp → W → ℓν) = 2.749 ± 0.010(stat.) ± 0.053(syst.) ± 0.165(lum.) nb and σ γ * /Z × Br(pp → γ * /Z → ℓℓ) = 254.9 ± 3.3(stat.) ± 4.6(syst.) ± 15.2(lum.) pb for dilepton pairs in the mass range between 66 GeV/c 2 and 116 GeV/c 2. We compute the ratio R of the W → ℓν to Z → ℓℓ cross sections taking all correlations among channels into account and obtain R = 10.84 ± 0.15(stat.) ± 0.14(syst.) including a correction for the virtual photon exchange component in our measured γ * /Z → ℓℓ cross section. Based on the measured value of R, we extract values for the W leptonic branching ratio, Br(W → ℓν) = 0.1082 ± 0.0022; the total width of the W boson, Γ(W) = 2092 ± 42 MeV; and the ratio of W and Z boson total widths, Γ(W)/Γ(Z) = 0.838 ± 0.017. In addition, we use our extracted value of Γ(W) whose value depends on various electroweak parameters and certain CKM matrix elements to constrain the Vcs CKM matrix element, |Vcs| = 0.976± 0.030.
We report on the test beam results and calibration methods using high energy electrons, pions and... more We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region (3 ≤ |η| ≤ 5), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h ≈ 5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as a √ E ⊕ b. The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.
The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that... more The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that is not contained by the barrel (HCAL HB) and electromagnetic (ECAL EB) calorimeters. Due to space limitation the barrel calorimeters do not contain completely the hadronic shower and an outer calorimeter (HO) was designed, constructed and inserted in the muon system of CMS to measure the energy leakage. Testing and calibration of the HO was carried out in a 300 GeV/c test beam that improved the linearity and resolution. HO will provide a net improvement in missing E T measurements at LHC energies. Information from HO will also be used for the muon trigger in CMS.
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