The first evidence for off-shell Higgs boson production is reported in the final state with two Z... more The first evidence for off-shell Higgs boson production is reported in the final state with two Z bosons decaying into either four charged leptons (muons or electrons), or two charged leptons and two neutrinos, and a measurement of the Higgs boson width is performed. Results are based on data from the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of up to 140 fb -1 . The total rate of off-shell Higgs boson production beyond the Z boson pair production threshold, relative to its standard model expectation, is constrained to the interval [0.0061, 2.0] at 95% confidence level. The scenario with no off-shell production is excluded at 99.97% confidence level (3.6 standard deviations). The width of the Higgs boson is extracted as Γ H = 3.2 +2.4 -1.7 MeV, in agreement with the standard model expectation of 4.1 MeV. The data are also used to set new constraints on anomalous Higgs boson couplings to W and Z boson pairs.
The B 0 s and B + production yields are measured in PbPb collisions at a center-of-mass energy pe... more The B 0 s and B + production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb -1 . The mesons are reconstructed in the exclusive decay channels B 0 s → J/ψ(µ + µ -) φ(K + K -) and B + → J/ψ(µ + µ -) K + , in the transverse momentum range 7-50 GeV/c and absolute rapidity 0-2.4. The B 0 s meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of B 0 s and B + is measured and compared to theoretical models that include quark recombination effects.
Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets or... more Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets originating from bottom (b) or charm (c) quarks. An overview of the algorithms used to identify c jets is described and a novel method to calibrate them is presented. This new method adjusts the entire distributions of the outputs obtained when the algorithms are applied to jets of different flavours. It is based on an iterative approach exploiting three distinct control regions that are enriched with either b jets, c jets, or light-flavour and gluon jets. Results are presented in the form of correction factors evaluated using proton-proton collision data with an integrated luminosity of 41.5 fb-1 at √s = 13 TeV, collected by the CMS experiment in 2017. The closure of the method is tested by applying the measured correction factors on simulated data sets and checking the agreement between the adjusted simulation and collision data. Furthermore, a validation is performed by testing the met...
Measurements of prompt $\psi$(2S) meson production cross sections in proton-lead (pPb) and proton... more Measurements of prompt $\psi$(2S) meson production cross sections in proton-lead (pPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{_\mathrm{NN}}}=$ 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb$^{-1}$ and 28.0 pb$^{-1}$, respectively. The nuclear modification factor $R_\mathrm{pPb}$ is measured for prompt $\psi$(2S) in the transverse momentum range 4 $
A measurement of the top quark mass is performed using a data sample enriched with single top qua... more A measurement of the top quark mass is performed using a data sample enriched with single top quark events produced in the t channel. The study is based on proton- proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at $$ \sqrt{s} $$ s = 13 TeV by the CMS experiment at the LHC in 2016. Candidate events are selected by requiring an isolated high-momentum lepton (muon or electron) and exactly two jets, of which one is identified as originating from a bottom quark. Multivariate discriminants are designed to separate the signal from the background. Optimized thresholds are placed on the discriminant outputs to obtain an event sample with high signal purity. The top quark mass is found to be $$ {172.13}_{-0.77}^{+0.76} $$ 172.13 − 0.77 + 0.76 GeV, where the uncertainty includes both the statistical and systematic components, reaching sub-GeV precision for the first time in this event topology. The masses of the top quark and antiquark are also determin...
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 ...
The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X... more The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (PbPb) collisions at a center-of-mass energy of √ s NN = 5.02 TeV per nucleon pair, using the decay chain X(3872) → J/ψ π + π -→ µ + µ -π + π -. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb -1 . The measurement is performed in the rapidity and transverse momentum ranges |y| < 1.6 and 15 < p T < 50 GeV/c. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to ψ(2S) yield ratio is found to be ρ PbPb = 1.08 ± 0.49 (stat) ± 0.52 (syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.
Methods are presented for calibrating the hadron calorimeter system of the CMS detector at the LH... more Methods are presented for calibrating the hadron calorimeter system of the CMS detector at the LHC. The hadron calorimeters of the CMS experiment are sampling calorimeters of brass and scintillator, and are in the form of one central detector and two endcaps. These calorimeters cover pseudorapidities |η| < 3 and are positioned inside the solenoidal magnet. An outer calorimeter, outside the magnet coil, covers |η| < 1.26, and a steel and quartz-fiber Cherenkov forward calorimeter extends the coverage to |η| < 5.19. The initial calibration of the calorimeters was based on results from test beams, augmented with the use of radioactive sources and lasers. The calibration was improved substantially using proton-proton collision data collected at √ s = 7, 8, and 13 TeV, as well as cosmic ray muon data collected during the periods when the LHC beams were not present. The present calibration is performed using the 13 TeV data collected during 2016 corresponding to an integrated luminosity of 35.9 fb -1 . The intercalibration of channels exploits the approximate uniformity of energy collection over the azimuthal angle. The absolute energy scale of the central and endcap calorimeters is set using isolated charged hadrons. The energy scale for the electromagnetic portion of the forward calorimeters is set using Z → ee data. The energy scale of the outer calorimeters has been determined with test beam data and is confirmed through data with high transverse momentum jets. In this paper, we present the details of the calibration methods and accuracy.
A search for narrow and broad resonances with masses greater than 1.8 TeV decaying to a pair of j... more A search for narrow and broad resonances with masses greater than 1.8 TeV decaying to a pair of jets is presented. The search uses proton-proton collision data at √ s = 13 TeV collected at the LHC, corresponding to an integrated luminosity of 137 fb -1 . The background arising from standard model processes is predicted with the fit method used in previous publications and with a new method. The dijet invariant mass spectrum is well described by both data-driven methods, and no significant evidence for the production of new particles is observed. Model independent upper limits are reported on the production cross sections of narrow resonances, and broad resonances with widths up to 55% of the resonance mass. Limits are presented on the masses of narrow resonances from various models: string resonances, scalar diquarks, axigluons, colorons, excited quarks, color-octet scalars, W and Z bosons, Randall-Sundrum gravitons, and dark matter mediators. The limits on narrow resonances are improved by 200 to 800 GeV relative to those reported in previous CMS dijet resonance searches. The limits on dark matter mediators are presented as a function of the resonance mass and width, and on the associated coupling strength as a function of the mediator mass. These limits exclude at 95% confidence level a dark matter mediator with a mass of 1.8 TeV and width 1% of its mass or higher, up to one with a mass of 4.8 TeV and a width 45% of its mass or higher.
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}}$$yt, yiel...
The average total energy as well as its hadronic and electromagnetic components are measured with... more The average total energy as well as its hadronic and electromagnetic components are measured with the CMS detector at pseudorapidities $$-6.6<\eta <-5.2$$-6.6<η<-5.2 in proton-proton collisions at a centre-of-mass energy $$\sqrt{s}=13\,\text {TeV} $$s=13TeV. The results are presented as a function of the charged particle multiplicity in the region $$|\eta |<2$$|η|<2. This measurement is sensitive to correlations induced by the underlying event structure over a very wide pseudorapidity region. The predictions of Monte Carlo event generators commonly used in collider experiments and ultra-high energy cosmic ray physics are compared to the data. All generators considered overestimate the fraction of energy going into hadrons.
Measurements of the cross sections for the production of single top quarks and antiquarks in the ... more Measurements of the cross sections for the production of single top quarks and antiquarks in the t channel, and their ratio, are presented for proton-proton collisions at a center-of-mass energy of 13 TeV. The data set used was recorded in 2016 by the CMS detector at the LHC and corresponds to an integrated luminosity of 35.9 fb -1 . Events with one muon or electron are selected, and different categories of jet and b jet multiplicity and multivariate discriminators are applied to separate the signal from the background. The cross sections for the t-channel production of single top quarks and antiquarks are measured to be 130 ±1(stat) ±19(syst) pb and 77 ±1(stat) ±12(syst) pb, respectively, and their ratio is 1.68 ±0.02(stat) ± 0.05(syst). The results are in agreement with the predictions from the standard model.
A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings fro... more A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings from events with two Z bosons and two jets are presented. The analysis is based on a data sample of proton-proton collisions at √ s = 13 TeV collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb -1 . The search is performed in the fully leptonic final state ZZ → , where , = e or µ. The electroweak production of two Z bosons in association with two jets is measured with an observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial cross section for the electroweak production is measured to be σ EW (pp → ZZjj → jj) = 0.40 +0.21 -0.16 (stat) +0.13 -0.09 (syst) fb, which is consistent with the standard model prediction. Limits on anomalous quartic gauge couplings are determined in terms of the effective field theory operators T0, T1, T2, T8, and T9. This is the first measurement of vector boson scattering in the ZZ channel at the LHC.
The mass of the top quark is measured using a sample of $${{\text {t}}\overline{{\text {t}}}}$$ t... more The mass of the top quark is measured using a sample of $${{\text {t}}\overline{{\text {t}}}}$$ t t ¯ events collected by the CMS detector using proton-proton collisions at $$\sqrt{s}=13$$ s = 13 $$\,\text {TeV}$$ TeV at the CERN LHC. Events are selected with one isolated muon or electron and at least four jets from data corresponding to an integrated luminosity of 35.9$$\,\text {fb}^{-1}$$ fb - 1 . For each event the mass is reconstructed from a kinematic fit of the decay products to a $${{\text {t}}\overline{{\text {t}}}}$$ t t ¯ hypothesis. Using the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in $${\text {q}} \overline{{\text {q}}} ^\prime $$ q q ¯ ′ decays. The measurement is calibrated on samples simulated at next-to-leading order matched to a leading-order parton shower. The top quark mass is found to be $$172.25 \pm 0.08\,\text {(stat+JSF)} \pm 0.62\,\text {(syst)} \,\t...
The U.S. Material Management and Minimization Reactor Conversion Program is developing low enrich... more The U.S. Material Management and Minimization Reactor Conversion Program is developing low enrichment fuel systems encased in Al-alloy for use in research and test reactors. Monolithic fuel plates have local regions where the U-Mo fuel plate may come into contact with the Al-alloy 6061 (AA6061) cladding. This results in the development of interdiffusion zones with complex microstructures with multiple phases. In this study, the microstructural development of diffusion couples, U-7wt.%Mo, U-10wt.%Mo, and U-12wt.%Mo vs. AA6061, annealed at 600°C for 24 hours and at 550°C for 1, 5 and 20 hours, were analyzed by scanning electron microscopy with x-ray energy dispersive spectroscopy. The microstructural development and kinetics were compared to diffusion couples U-Mo vs. high purity Al and binary Al-Si alloys. The diffusion couples developed complex interaction regions where phase development was influenced by the alloying additions of the AA6061.
A search is presented for quark contact interactions and extra spatial dimensions in proton-proto... more A search is presented for quark contact interactions and extra spatial dimensions in proton-proton collisions at √ s = 8 TeV using dijet angular distributions. The search is based on a data set corresponding to an integrated luminosity of 19.7 fb -1 collected by the CMS detector at the CERN LHC. Dijet angular distributions are found to be in agreement with the perturbative QCD predictions that include electroweak corrections. Limits on the contact interaction scale from a variety of models at next-toleading order in QCD corrections are obtained. A benchmark model in which only left-handed quarks participate is excluded up to a scale of 9.0 (11.7) TeV for destructive (constructive) interference at 95% confidence level. Lower limits between 5.9 and 8.4 TeV on the scale of virtual graviton exchange are extracted for the Arkani-Hamed-Dimopoulos-Dvali model of extra spatial dimensions.
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Papers by Emmanuel Perez