1,911 research outputs found

    Study of Bc+→J/ψDs+ and Bc+→J/ψDs∗+ decays in pp collisions at √s = 13 TeV with the ATLAS detector

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    A study of Bc+→J/ψDs+ and Bc+→J/ψDs∗+ decays using 139 fb−1 of integrated luminosity collected with the ATLAS detector from s = 13 TeV pp collisions at the LHC is presented. The ratios of the branching fractions of the two decays to the branching fraction of the Bc+→ J/ψπ+ decay are measured: B(Bc+→J/ψDs+)/B(Bc+→J/ψπ+) = 2.76 ± 0.47 and B(Bc+→J/ψDs∗+)/B(Bc+→J/ψπ+) = 5.33 ± 0.96. The ratio of the branching fractions of the two decays is found to be B(Bc+→J/ψDs∗+)/B(Bc+→J/ψDs∗+) = 1.93 ± 0.26. For the Bc+→J/ψDs∗+ decay, the transverse polarization fraction, Γ±±/Γ, is measured to be 0.70 ± 0.11. The reported uncertainties include both the statistical and systematic components added in quadrature. The precision of the measurements exceeds that in all previous studies of these decays. These results supersede those obtained in the earlier ATLAS study of the same decays with s = 7 and 8 TeV pp collision data. A comparison with available theoretical predictions for the measured quantities is presented. [Figure not available: see fulltext.]

    Exclusive electroproduction of rho0 and J / psi mesons at HERA

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    Exclusive production of rho(0) and J/psi mesons in e(+)p collisions has been studied with the ZEUS detector in the kinematic range 0.25 < Q(2) < 50 GeV2, 20 < W < 167 GeV for the rho(0) data and 2 < Q(2) < 40 GeV2, 50 < IS' < 150 GeV for the J/psi data. Cross sections for exclusive rho(0) and J/psi, production have been measured as a function of Q2, W and t. The spin-density matrix elements r(00)(04), r(1-1)(1) and Rer(10)(5) have been determined for exclusive rho(0) production as well as r(00)(04) and r(1-1)(04) for exclusive J/psi production. The results are discussed in the context of theoretical models invoking soft and hard phenomena

    Measurement of the cross-section ratio σψ(2S)/σJ/ψ(1S)\sigma_{\psi(2S )}/\sigma_{J/\psi(1S )} in exclusive photoproduction at HERA

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    The exclusive photoproduction reactions γpJ/ψ(1S)p\gamma p \to J/\psi(1S) p and γpψ(2S)p\gamma p \to \psi(2S) p have been measured at an epep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb1^{-1}. The measurement was made in the kinematic range 30<W<18030 < W < 180 GeV, Q2<1Q^2 < 1 GeV2^2 and t<1|t| < 1 GeV2^2, where WW is the photon--proton centre-of-mass energy, Q2Q^2 is the photon virtuality and tt is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ(1S)μ+μJ/\psi(1S) \to \mu^+ \mu^-, ψ(2S)μ+μ\psi(2S) \to \mu^+ \mu^- and ψ(2S)J/ψ(1S)π+π\psi(2S) \to J/\psi(1S) \pi^+ \pi^- with subsequent decay J/ψ(1S)μ+μJ/\psi(1S) \to \mu^+ \mu^-. The ratio of the production cross sections, R=σψ(2S)/σJ/ψ(1S)R = \sigma_{\psi(2S)} / \sigma_{J/\psi(1S)}, has been measured as a function of WW and t|t| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.Comment: 31 pages, 9 figures. Updated according to comments from journal referee including a new table. Added full collaboration author lis

    Exclusive photoproduction of J / psi mesons at HERA

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    The exclusive photoproduction of J/psi mesons, gammap → J/psip, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 lt W lt 290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the union and the electron decay channels using integrated luminosities of 38 pb(-1) and 55 pb(- 1), respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for \t\ lt 1.8 GeV2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b = 4.15 +/- 0.05(stat.)(-0.18)(+0.30)(syst.) GeV-2 at W = 90 GeV. The effective parameters of the Pomeron trajectory are alpha(P)(0) = 1.200 +/- 0.009(stat.)(-0.010)(+0.004) (syst.) and alpha(P)' = 0.115 +/- 0.018(stat.)(-0.015)(+0.008) (syst.) GeV-2

    Measurements of inelastic J / psi and psi-prime photoproduction at HERA

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    The cross sections for inelastic photoproduction of J/psi and psi' mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 38.0 pb(- 1). The events were required to have 0.1 lt z lt 0.9 and 50 lt W lt 180 GeV, where z is the fraction of the incident photon energy carried by the J/psi in the proton rest frame and W is the photon-proton centre-of-mass energy. The psi' to J/psi cross- section ratio was measured in the range 0.55 lt z lt 0.9. The J/psi data, for various ranges of transverse momentum, are compared to theoretical models incorporating colour-singlet and colour-octet matrix elements. Predictions of a next-to-leading- order colour-singlet model give a good description of the data, although there is a large normalisation uncertainty. The J/psi helicity distribution for z gt 0.4 is compared to leading-order QCD predictions

    Measurement of the production cross-section of J/ψ and ψ(2S) mesons in pp collisions at √s=13 TeV with the ATLAS detector

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    Measurements of the differential production cross-sections of prompt and non-prompt J/ψ and ψ(2S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range |y|<2 are reported. Furthermore, measurements of the non-prompt fractions of J/ψ and ψ(2S), and the prompt and non-prompt ψ(2S)-to-J/ψ production ratios, are presented. The analysis is performed using 140 fb-1 of s=13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018

    Measurement of J/psi helicity distributions in inelastic photoproduction at HERA

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    The J/ψ decay angular distributions have been measured in inelastic photo-production in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb-1. The range in photon-proton centre-of-mass energy, W, was 50 < W < 180 GeV. The J/ψ mesons were identified through their decay into muon pairs. The polar and azimuthal angles of the μ+ were measured in the J/ψ rest frame and compared to theoretical predictions at leading and next-to-leading order in QCD. © SISSA 2009

    Measurement of inelastic J / psi photoproduction at HERA

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    We present a measurement of the inelastic, non diffractive J/psi photoproduction cross section in the reaction e(+)p --> e(+)J/psi X with the ZEUS detector at HERA, The J/psi was identified using both the mu(+)mu(-) and e(+)e(-) decay channels and events were selected within the range 0.4 1 GeV(2), NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data, The predictions of a specific leading order colour-octet. model, as formulated to describe the CDP data on J/psi hadroproduction, are not consistent with the data

    Measurement of elastic J / psi photoproduction at HERA

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    The reaction a p --> J/psi p has been studied in epsilon p interactions using the ZEUS detector at HERA. The cross section for elastic J/psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 J/psi p), is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter delta in the form sigma(ap-->J/psi p) proportional to W-delta yields the value delta=0.92+/-0.14+/-0.10. The differential cross section d sigma/d\t\ is presented over the range \t\ < 1.0 GEV(2) where t is the square of the four-momentum exchanged at the proton vertex. d sigma/d\t\ falls exponentially with a slope parameter of 4.6+/-0.4(-0.6)(+0.4) GEV(-2). The measured decay angular distrubitions are consistent with 8-channel helicity conservation

    D* and J/psi inelastic photoproduction at HERA

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    Cross sections of D* and J/Psi inelastic photoproduction were measured by the ZEUS detector at HERA collider. Comparisons of the data with calculations in NLO pQCD and SHA QCD approaches were made
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