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Register a new userImpact of $J/psi$ pair production at the LHC and predictions in nonrelativistic QCD
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For $J/psi$ pair production at hadron colliders, we present the full next-to-leading order (NLO) calculations with the color-singlet channel in nonrelativistic QCD. We find that the NLO result can reasonably well describe the LHCb measured cross section, but exhibits very different behaviors from the CMS data in the transverse momentum distribution and mass distribution of $J/psi$ pair. Moreover, by adding contributions of gluon fragmentation and quark fragmentation, which occur at even higher order in $alpha_s$, it is still unable to reduce the big differences. In particular, the observed flat distribution in the large invariant mass region is hard to explain. New processes or mechanisms are needed to understand the CMS data for $J/psi$ pair production.
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The associated production of J/psi + gamma at the LHC is studied within the NRQCD framework. The signal we focus on is the production of a J/psi and an isolated photon produced back-to-back, with their transverse momenta balanced. It is shown that even for very large values of transverse momentum (pT of the order of 50 GeV) the dominant contribution to this process is not fragmentation. This is because of the fact that fragmentation-type contributions to the cross-section come from only a q q(bar) initial state, which is suppressed at the LHC. We identify gg-initiated diagrams higher-order in alpha(s) which do have fragmentation-type vertices. We find, however, that the contribution of these diagrams is negligibly small.
In this work, we investigate the prompt $J/psi$ production in associated with top quark pair to leading order in the nonrelativistic QCD factorization formalism at the LHC with $sqrt{s} =13$ TeV. In addition to the contribution from direct $J/psi$ production, we also include the indirect contribution from the directly produced heavier charmmonia $chi_{cJ}$ and $psi^prime$. We present the numerical results for the total and differential cross sections and find that the $sideset{^3}{^{(8)}_1}{mathop{{S}}}$ states give the dominant contributions. The prompt $tbar t J/psi$ signatures at the LHC are analyzed in the tetralepton channel $ppto (tto W^+(ell^+ u)b) (bar t to W^-(ell^- bar u)bar b) (J/psitomu^+mu^-)$ and trilepton channel $ppto (tto W(q q^prime)b) ( t to W(ell u) b) (J/psitomu^+mu^-)$, with the $J/psi$ mesons decaying into muon pair, and the top quarks decaying leptonically or hadronically. We find that $tbar t J/psi$ proudction can be potentially detected at the LHC, whose measurement is useful to test the heavy quarkonium production mechanism.
Double parton scattering (DPS) is studied at the example of $J/psi$ pair-production in the LHCb and ATLAS experiments of the Large Hadron Collider (LHC) at centre-of-mass energies of $sqrt{S}=$ 7, 8, and 13 TeV. We report theoretical predictions delivered to the LHCb and ATLAS collaborations adjusted for the fiducial volumes of the corresponding measurements during Run I and provide new predictions at 13 TeV collision energy. It is shown that DPS can lead to noticeable contributions in the distributions of longitudinal variables of the di-$J/psi$ system, especially at 13 TeV. The increased DPS rate in double $J/psi$ production at high energies will open up more possibilities for the separation of single parton scattering (SPS) and DPS contributions in future studies.
We study $J/psi$ and $eta_c$ inclusive production in $Upsilon$ decay within the framework of nonrelativistic-QCD (NRQCD) factorization. In the latter case, for which no experimental data exist so far, we also include the $h_c$ feed-down contribution. We calculate the short distance coefficients completely through $mathcal{O}(alpha_s^5)$. The NRQCD predictions for the branching fraction $mathcal{B}(Upsilonto J/psi+X)$ via direct production, evaluated with different sets of long-distance matrix elements (LDMEs), all agree with the experimental data in a reasonable range of renormalization scale. Using $eta_c$ and $h_c$ LDMEs obtained from $J/psi$ and $chi_c$ ones via heavy-quark spin symmetry, we find that the bulk of $mathcal{B}(Upsilontoeta_c+X)$ via prompt production arises from the $cbar{c}({}^3!S_1^{[8]})$ Fock state. The experimental study of this decay process would, therefore, provide a particularly clean probe of the color octet mechanism of heavy-quarkonium production.
We propose and study the inclusive production of a forward $J/psi$ and a very backward jet at the LHC as an observable to reveal high-energy resummation effects `a la BFKL. Our different predictions are based on the various existing mechanisms to describe the production of the $J/psi$, namely, NRQCD singlet and octet contributions, and the color evaporation model.
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