Engineering topics

Van Parijs, Isis

Publications and source records attributed to Van Parijs, Isis.

At least 19 records

DOE OSTI2020

Measurement of single-diffractive dijet production in proton-proton collisions at $\sqrt{s} =$ 8 TeV with the CMS and TOTEM experiments

Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss $\xi $ and the four-momentum transfer squared t. Both processes ${\text{ p }{}{}} {\text{ p }{}{}} \rightarrow {\text{ p }{}{}} {\text{ X }} $ and ${\text{ p }{}{}} {\text{ p }{}{}} \rightarrow {\text{ X }} {\text{ p }{}{}} $, i.e. with the proton scattering to either side of the interaction point, are measured, where ${\text{ X }} $ includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton–proton collisions at $\sqrt{s} = 8\,\text {Te}\text {V} $ during a dedicated run with $\beta ^{*} = 90\,\text {m} $ at low instantaneous luminosity and correspond to an integrated luminosity of $37.5{\,\text {nb}^{-1}} $. The single-diffractive dijet cross section $\sigma ^{{\text{ p }{}{}} {\text{ X }}}_{\mathrm {jj}}$, in the kinematic region $\xi < 0.1$, $0.03< |t | < 1\,\text {Ge}\text {V} ^2$, with at least two jets with transverse momentum $p_{\mathrm {T}} > 40\,\text {Ge}\text {V} $, and pseudorapidity $|\eta | < 4.4$, is $21.7 \pm 0.9\,\text {(stat)} \,^{+3.0}_{-3.3}\,\text {(syst)} \pm 0.9\,\text {(lumi)} \,\text {nb} $. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of $\xi $, is presented as a function of x, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for x values in the range $-2.9 \le \log _{10} x \le -1.6$, is $R = (\sigma ^{{\text{ p }{}{}} {\text{ X }}}_{\mathrm {jj}}/\Delta \xi )/\sigma _{\mathrm {jj}} = 0.025 \pm 0.001\,\text {(stat)} \pm 0.003\,\text {(syst)} $, where $\sigma ^{{\text{ p }{}{}} {\text{ X }}}_{\mathrm {jj}}$ and $\sigma _{\mathrm {jj}}$ are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Study of central exclusive $\pi^+\pi^-$ production in proton-proton collisions at $\sqrt{s} =$ 5.02 and 13 TeV

Central exclusive and semiexclusive production of pairs is measured with the CMS detector in proton-proton collisions at the LHC at center-of-mass energies of 5.02 and 13TeV. The theoretical description of these nonperturbative processes, which have not yet been measured in detail at the LHC, poses a significant challenge to models. The two pions are measured and identified in the CMS silicon tracker based on specific energy loss, whereas the absence of other particles is ensured by calorimeter information. The total and differential cross sections of exclusive and semiexclusive central production are measured as functions of invariant mass, transverse momentum, and rapidity of the system in the fiducial region defined as transverse momentum and pseudorapidity . The production cross sections for the four resonant channels [inline-graphic not available: see fulltext], , [inline-graphic not available: see fulltext], and [inline-graphic not available: see fulltext]are extracted using a simple model. These results represent the first measurement of this process at the LHC collision energies of 5.02 and 13TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles in $\mathrm {PbPb}$ collisions at $\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 2.76$ and 5.02$\,\text {TeV}$

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 $\mathrm {PbPb}$ collisions at nucleon-nucleon center-of-mass energies $\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 2.76$ and 5.02$\,\text {TeV}$ with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at $ \sqrt{s} $ = 13 TeV, corresponding to an integrated luminosity of 77.4 fb$^{−1}$. The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date.[graphic not available: see fulltext]

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DOE OSTI2020

Search for lepton flavour violating decays of a neutral heavy Higgs boson to $\mu\tau$ and e$\tau$ in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search for lepton flavour violating decays of a neutral non-standard-model Higgs boson in the μτ and eτ decay modes is presented. The search is based on proton-proton collisions at a center of mass energy $ \sqrt{s} $ = 13 TeV collected with the CMS detector in 2016, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. The τ leptons are reconstructed in the leptonic and hadronic decay modes. No signal is observed in the mass range 200–900 GeV. At 95% confidence level, the observed (expected) upper limits on the production cross section multiplied by the branching fraction vary from 51.9 (57.4) fb to 1.6 (2.1) fb for the μτ and from 94.1 (91.6) fb to 2.3 (2.3) fb for the eτ decay modes.[graphic not available: see fulltext]

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DOE OSTI2020

Search for a heavy pseudoscalar Higgs boson decaying into a 125 GeV Higgs boson and a Z boson in final states with two tau and two light leptons at $\sqrt{s}=$ 13 TeV

A search is performed for a pseudoscalar Higgs boson, A, decaying into a 125 GeV Higgs boson h and a Z boson. The h boson is specifically targeted in its decay into a pair of tau leptons, while the Z boson decays into a pair of electrons or muons. A data sample of proton-proton collisions collected by the CMS experiment at the LHC at $ \sqrt{s} $ = 13 TeV is used, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. No excess above the standard model background expectations is observed in data. A model-independent upper limit is set on the product of the gluon fusion production cross section for the A boson and the branching fraction to Zh → ℓℓττ. The observed upper limit at 95% confidence level ranges from 27 to 5 fb for A boson masses from 220 to 400 GeV, respectively. The results are used to constrain the extended Higgs sector parameters for two benchmark scenarios of the minimal supersymmetric standard model.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Bose-Einstein correlations of charged hadrons in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Bose-Einstein correlations of charged hadrons are measured over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions at $ \sqrt{s} $ = 13 TeV. The results are based on data collected using the CMS detector at the LHC during runs with a special low-pileup configuration. Three analysis techniques with different degrees of dependence on simulations are used to remove the non-Bose-Einstein background from the correlation functions. All three methods give consistent results. The measured lengths of homogeneity are studied as functions of particle multiplicity as well as average pair transverse momentum and mass. The results are compared with data from both CMS and ATLAS at $ \sqrt{s} $ = 7 TeV, as well as with theoretical predictions.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Measurement of exclusive $\Upsilon$ photoproduction from protons in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The exclusive photoproduction of $\mathrm {\Upsilon }\mathrm {(nS)} $ meson states from protons, $\gamma \mathrm {p} \rightarrow \mathrm {\Upsilon }\mathrm {(nS)} \,\mathrm {p}$ (with $\mathrm {n}=1,2,3$ ), is studied in ultraperipheral $\mathrm {p}$ Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}} = 5.02\,\text {TeV} $ . The measurement is performed using the $\mathrm {\Upsilon }\mathrm {(nS)} \rightarrow \mu ^+\mu ^-$ decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 $\,\text {nb}^{-1}$ . Differential cross sections as functions of the $\mathrm {\Upsilon }\mathrm {(nS)} $ transverse momentum squared $p_{\mathrm {T}} ^2$ , and rapidity y, are presented. The $\mathrm {\Upsilon (1S)}$ photoproduction cross section is extracted in the rapidity range $|y |< 2.2$ , which corresponds to photon–proton centre-of-mass energies in the range $91

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Search for heavy resonances decaying into two Higgs bosons or into a Higgs boson and a W or Z boson in proton-proton collisions at 13 TeV

A search is presented for massive narrow resonances decaying either into two Higgs bosons, or into a Higgs boson and a W or Z boson. The decay channels considered are $ \mathrm{H}\mathrm{H}\to \mathrm{b}\overline{\mathrm{b}}{\tau}^{+}{\tau}^{-} $ and $ \mathrm{V}\mathrm{H}\to \mathrm{q}\overline{\mathrm{q}}{\tau}^{+}{\tau}^{-} $ , where H denotes the Higgs boson, and V denotes the W or Z boson. This analysis is based on a data sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV by the CMS Collaboration, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. For the TeV-scale mass resonances considered, substructure techniques provide ways to differentiate among the hadronization products from vector boson decays to quarks, Higgs boson decays to bottom quarks, and quark- or gluon-induced jets. Reconstruction techniques are used that have been specifically optimized to select events in which the tau lepton pair is highly boosted. The observed data are consistent with standard model expectations and upper limits are set at 95% confidence level on the product of cross section and branching fraction for resonance masses between 0.9 and 4.0 TeV. Exclusion limits are set in the context of bulk radion and graviton models:spin-0 radion resonances are excluded below a mass of 2.7 TeV at 95% confidence level. In the spin-1 heavy vector triplet framework, mass-degenerate W′ and Z′ resonances with dominant couplings to the standard model gauge bosons are excluded below a mass of 2.8 TeV at 95% confidence level. These are the first limits for massive resonances at the TeV scale with these decay channels at $ \sqrt{s}=13 $ TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at $\sqrt{s_{NN}}=$ 5.02 TeV Using Isolated Photon-Tagged Jets

Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with pTjet>30 GeV/c in events containing an isolated photon with pTγ>60 GeV/c, using charged tracks with transverse momentum pTtrk>1 GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial pT and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) pT particles, with a transition around 3 GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Measurements of Higgs boson properties in the diphoton decay channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Measurements of Higgs boson properties in the H → γγ decay channel are reported. The analysis is based on data collected by the CMS experiment in proton-proton collisions at $ \sqrt{s}=13 $ TeV during the 2016 LHC running period, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. Allowing the Higgs mass to float, the measurement yields a signal strength relative to the standard model prediction of 1.18$_{− 0.14}^{+ 0.17}$ = 1.18$_{− 0.11}^{+ 0.12}$ (stat)$_{− 0.07}^{+ 0.09}$ (syst)$_{− 0.06}^{+ 0.07}$ (theo), which is largely insensitive to the exact Higgs mass around 125 GeV. Signal strengths associated with the different Higgs boson production mechanisms, couplings to bosons and fermions, and effective couplings to photons and gluons are also measured.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos and b quarks at $ \sqrt{s}=13 $ TeV

A search for heavy resonances, decaying into the standard model vector bosons and the standard model Higgs boson, is presented. The final states considered contain a b quark-antiquark pair from the decay of the Higgs boson, along with electrons and muons and missing transverse momentum, due to undetected neutrinos, from the decay of the vector bosons. The mass spectra are used to search for a localized excess consistent with a resonant particle. The data sample corresponds to an integrated luminosity of 35.9 fb$^{−1}$ collected in 2016 by the CMS experiment at the CERN LHC from proton-proton collisions at a center-of-mass energy of 13 TeV. The data are found to be consistent with background expectations. Exclusion limits are set in the context of spin-0 two Higgs doublet models, some of which include the presence of dark matter. In the spin-1 heavy vector triplet framework, mass-degenerate W′ and Z′ resonances with dominant couplings to the standard model gauge bosons are excluded below a mass of 2.9 TeV at 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Measurement of differential cross sections for Z boson production in association with jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV

The production of a ${\text {Z}}$ boson, decaying to two charged leptons, in association with jets in proton-proton collisions at a centre-of-mass energy of 13 $\,\text {TeV}$ is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19 $\,\text {fb}^\text {-1}$ . The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the ${\text {Z}}$ boson, the jet kinematic variables (transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the ${\text {Z}}$ boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes one-loop corrections. The third is a fixed-order calculation with next-to-next-to-leading order accuracy for the process with a ${\text {Z}}$ boson and one parton in the final state. The fourth combines the fully differential next-to-next-to-leading order calculation of the process with no parton in the final state with next-to-next-to-leading logarithm resummation and parton showering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Search for Z$\gamma$ resonances using leptonic and hadronic final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is presented for resonances decaying to a Z boson and a photon. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{−1}$, and collected with the CMS detector at the LHC in 2016. Two decay modes of the Z boson are investigated. In the leptonic channels, the Z boson candidates are reconstructed using electron or muon pairs. In the hadronic channels, they are identified using a large-radius jet, containing either light-quark or b quark decay products of the Z boson, via jet substructure and advanced b quark tagging techniques. The results from these channels are combined and interpreted in terms of upper limits on the product of the production cross section and the branching fraction to Zγ for narrow and broad spin-0 resonances with masses between 0.35 and 4.0 TeV, providing thereby the most stringent limits on such resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Observation of proton-tagged, central (semi)exclusive production of high-mass lepton pairs in pp collisions at 13 TeV with the CMS-TOTEM precision proton spectrometer

The process pp → pℓ$^{+}$ℓ$^{−}$p$^{(*)}$, with ℓ$^{+}$ℓ$^{−}$ a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at $ \sqrt{s}=13 $ TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first time in 2016. The second proton either remains intact or is excited and then dissociates into a low-mass state p$^{*}$, which is undetected. The measurement is based on an integrated luminosity of 9.4 fb$^{−1}$ collected during standard, high-luminosity LHC operation. A total of 12 μ$^{+}$μ$^{−}$ and 8 e$^{+}$e$^{−}$ pairs with m(ℓ$^{+}$ℓ$^{−}$) > 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1.49 ± 0.07 (stat) ± 0.53 (syst) and 2.36 ± 0.09 (stat) ± 0.47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged γγ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Electroweak production of two jets in association with a Z boson in proton–proton collisions at $\sqrt{s}= $ 13 $\,\text {TeV}$

A measurement of the electroweak (EW) production of two jets in association with a $\mathrm {Z} $ boson in proton-proton collisions at $\sqrt{s}=13\,\text {TeV} $ is presented, based on data recorded in 2016 by the CMS experiment at the LHC corresponding to an integrated luminosity of 35.9 $\,\text {fb}^{\text {--}1}$ . The measurement is performed in the $\ell \ell \mathrm {jj}$ final state with $\ell $ including electrons and muons, and the jets j corresponding to the quarks produced in the hard interaction. The measured cross section in a kinematic region defined by invariant masses $m_{\ell \ell } >50\,\text {GeV} $ , $m_{\mathrm {jj}} >120\,\text {GeV} $ , and transverse momenta $p_{\mathrm {T j}} > 25\,\text {GeV}$ is $\sigma _\mathrm {EW}(\ell \ell \mathrm {jj})= 534 \pm 20\,\text {(stat)} \pm 57\,\text {(syst) fb} $ , in agreement with leading-order standard model predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. No evidence is found and limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are $-2.6< c_{WWW}/\varLambda ^2 < 2.6\,\text {TeV}^{-2}$ and $-8.4< c_{W}/\varLambda ^2 < 10.1\,\text {TeV}^{-2}$ . The additional jet activity of events in a signal-enriched region is also studied, and the measurements are in agreement with predictions.

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DOE OSTI2018

Search for a heavy resonance decaying into a Z boson and a vector boson in the $ \nu \overline{\nu}\mathrm{q}\overline{\mathrm{q}} $ final state

A search is presented for a heavy resonance decaying into either a pair of Z bosons or a Z boson and a W boson (ZZ or WZ), with a Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into two collimated quarks that are reconstructed as a highly energetic large-cone jet. The search is performed using the data collected with the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb$^{−1}$. No excess is observed in data with regard to background expectations. Results are interpreted in scenarios of physics beyond the standard model. Limits at 95% confidence level on production cross sections are set at 0.9 fb (63 fb) for spin-1 W′ bosons, included in the heavy vector triplet model, with mass 4.0 TeV (1.0 TeV), and at 0.5 fb (40 fb) for spin-2 bulk gravitons with mass 4.0 TeV (1.0 TeV). Lower limits are set on the masses of W′ bosons in the context of two versions of the heavy vector triplet model of 3.1TeV and 3.4 TeV, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Azimuthal correlations for inclusive 2-jet, 3-jet, and 4-jet events in pp collisions at $\sqrt{s}= $ 13 TeV

Azimuthal correlations between the two jets with the largest transverse momenta $p_{\mathrm {T}}$ in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet $p_{\mathrm {T}}$ up to 4 $\,\text {Te}\text {V}$ . For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading $p_{\mathrm {T}}$ jets are also presented. The analysis is based on data from proton–proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13 $\,\text {Te}\text {V}$ , corresponding to an integrated luminosity of 35.9 $\,\text {fb}^{-1}$ . Calculations based on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in herwig 7, gives a better overall description of the measurements than the powheg method.

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