The J/$\psi$$\to$$\mu^+\mu^-\mu^+\mu^-$ decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb${-1}$. Normalizing to the J/$\psi$$\to$$\mu^+\mu^-$ decay mode leads to a branching fraction [10.1$^{+3.3}_{-2.7}$ (stat) $\pm$ 0.4 (syst) ]$\times$ 10$^{-7}$, a value that is consistent with the standard model prediction.
$\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu\mu\mu$ branching fraction
$\mathcal{B}(\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu\mu\mu)$ / $\mathcal{B}(\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi \to \mu\mu)$ ratio
Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering - referred to as single-parton scattering - leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/$\psi$ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process - reconstructed through the decays of J/$\psi$ mesons into pairs of oppositely charged muons - with a statistical significance above five standard deviations. We measured the inclusive fiducial cross section to be 272 $^{+141}_{-104}$ (stat) $\pm$ 17 (syst) fb, and compared it to theoretical expectations for triple-J/$\psi$ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross sections, double- and triple-parton scattering are the dominant contributions for the measured process.
Kinematic properties of each one of the three \JPsi mesons selected in the 5? 6? signal events.
Dimuon invariant mass ($m$), proper decay-length ($L$), transverse momentum ($p_{T}$), rapidity ($y$), and azimuthal angle ($\phi$) of each of the three $J/\psi$ candidates measured in the six triple-$J/\psi$ events passing our selection criteria.
DPS effective cross section
Inclusive D* production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D* meson is investigated. The analysis covers values of photon virtuality 2< Q^2 <=100 GeV^2 and of inelasticity 0.05<= y <= 0.7. Differential cross sections are measured as a function of Q^2 and x and of various D* meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k_T-unintegrated gluon distribution of the proton.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production with two jets.
This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb$^{-1}$. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: $|\eta^\gamma|<1.37$ and $1.56<|\eta^\gamma|<2.37$. The measurement covers photon transverse energies $25 < E_\textrm{T}^\gamma<400$ GeV and $25 < E_\textrm{T}^\gamma<350$ GeV respectively for the two $|\eta^\gamma|$ regions. For each jet flavour, the ratio of the cross sections in the two $|\eta^\gamma|$ regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central $\gamma+b$ measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.
Measured fiducial integrated $\gamma+b$ and $\gamma+c$ cross sections for $|\eta^\gamma|<1.37$ and $1.56<|\eta^\gamma|<2.37$.
Measured $\gamma+b$ fiducial differential cross section as a function of $E_\text{T}^\gamma$ for $|\eta^\gamma|<1.37$.
Measured $\gamma+b$ fiducial differential cross section as a function of $E_\text{T}^\gamma$ for $1.56<|\eta^\gamma|<2.37$.
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INCLUDES THE FOLLOWING DECAYS: D*(2010)+- --> D0 PI+-, D0 --> K- PI+.
INCLUDES THE FOLLOWING DECAYS: D*(2010)+- --> D0 PI+-, D0 --> K- PI+, D0 --> K- 2PI+ PI-.
INCLUDES THE DECAYS: D+ --> K- 2PI+.
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ERROR DUE TO ERROR IN BRANCHING VALUE IS 0.008.
THESE TABULATED VALUES OF THE TOTAL CROSS SECTION RATIO R ARE INCLUDED IN THE RECORD OF P. A. RAPIDIS ET AL., PRL 39, 526 (1977) AND PRL 39, 974 (1977) (ERRATUM).
THE D MESON INCLUSIVE PRODUCTION CROSS SECTIONS AND DECAY BRANCHING FRACTIONS AT THE PSI(3772)0 RESONANCE ARE PUBLISHED IN I. PERUZZI ET AL., PRL 39, 1301 (1977).
THESE D AND K MESON INCLUSIVE PRODUCTION CROSS SECTIONS ARE PUBLISHED IN M. PICCOLO ET AL., PL 86B, 220 (1979).
A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.
Cross-sections in the fiducial region for associated production of a Z boson and a D meson.
The production of a W boson in association with a single charm quark is studied using 4.6 fb^-1 of pp collision data at sqrt(s)=7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96 +0.26 -0.30 at Q^2=1.9 GeV^2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio sigma(W^+ + bar{c})/sigma(W^- + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s-bar{s} quark asymmetry.
Measured integrated cross sections of the production of a W boson with a single c-jet, a D meson or a D* meson times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured integrated cross section ratios of the production of W+ and W- bosons associated with a single c-jet, a D meson or a D* meson in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. Jets are not required for the W+D/D* cross sections. The cross sections are defined for OS-SS events.
Measured differential cross sections as function of the lepton pseudo-rapidity of the production of a W boson with a single c-jet times the branching ratio W -> l nu in the fiducial regions together with the statistical and systematic uncertainties. For the W+c-jet cross sections events with more than one c-jet are discarded. The particle-level c-jet is defined as the one containing a weakly decaying c-hadron with pt>5 GeV, within DeltaR<0.3. Jets containing c-hadrons originating from b-hadron decays are not counted as c-jets. The cross sections are defined for OS-SS events.
The production of $D^{*\pm}$ mesons in deep inelastic $ep$ scattering has been measured for exchanged photon virtualities $ 5<Q^2<1000 \gev^2 $, using an integrated luminosity of 363 pb$^{-1}$ with the ZEUS detector at HERA. Differential cross sections have been measured and compared to next-to-leading-order QCD calculations. The cross-sections are used to extract the charm contribution to the proton structure functions, expressed in terms of the reduced charm cross section, $\sigma_{\rm red}^{c\bar{c}}$. Theoretical calculations based on fits to inclusive HERA data are compared to the results.
D(SIG)/DPT IN NB/GEV as a function of PT IN GEV.
D(SIG)/DETARAP IN NB as a function of ETARAP.
D(SIG)/DZ IN NB as a function of Z.
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