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تسجيل مستخدم جديدOn the kinematic limit of the charm production in fixed-target experiments with the intrinsic charm from the target
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In this note we provide a detailed derivation of the kinematic limit of the charm production in fixed-target experiments with the intrinsic charm coming from the target. In addition, we discuss the first measurement of charm quark production in the fixed-target configuration at the LHC.
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The first measurement of heavy-flavour production by the LHCb experiment in its fixed-target mode is presented. The production of $J/psi$ and $D^0$ mesons is studied with beams of protons of different energies colliding with gaseous targets of helium
and argon with nucleon-nucleon centre-of-mass energies of $sqrt{s_{NN}} = 86.6 $ and $ 110.4$ ${rm GeV}$, respectively. The $J/psi$ and $D^0$ (including charge conjugate) production cross sections in $p{rm He}$ collisions in the rapidity range $[2,4.6]$ are found to be $sigma_{J/psi} = 652 pm 33$ (stat) $pm 42$ (syst) nb$/$nucleon and $sigma_{D^0} = 80.8 pm 2.4$ (stat) $pm 6.3$ (syst) $mu$b$/$nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-$x$ region.
Background: A nonperturbative charm production contribution, known as intrinsic charm, has long been speculated but has never been satisfactorily proven. The SeaQuest experiment at FNAL is in an ideal kinematic region to provide evidence of $J/psi$ p
roduction by intrinsic charm. Purpose: $J/psi$ production in the SeaQuest kinematics is calculated with a combination of perturbative QCD and intrinsic charm to see whether the SeaQuest data can put limits on an intrinsic charm contribution. Methods: $J/psi$ production in perturbative QCD is calculated to next-to-leading order in the cross section. Cold nuclear matter effects include nuclear modification of the parton densities, absorption by nucleons, and $p_T$ broadening by multiple scattering. The $J/psi$ contribution from intrinsic charm is calculated assuming production from a $|uud c overline c rangle$ Fock state. Results: The nuclear modification factor, $R_{pA}$, is calculated as a function of $x_F$ and $p_T$ for $p+$C, $p+$Fe, and $p+$W interactions relative to $p+$d. Conclusions: The SeaQuest kinematic acceptance is ideal for testing the limits on intrinsic charm in the proton.
We present an analysis of the existing data on charmonium hadro-production based on non-relativistic QCD (NRQCD) calculations at the next-to-leading order (NLO). All the data on J/psi and psi production in fixed-target experiments and on pp collision
s at low energy are included. We find that the amount of color octet contribution needed to describe the data is about 1/10 of that found at the Tevatron.
We analyze the sensitivity of fixed-target experiments to sub-GeV thermal relic dark matter models, accounting for variations in both mediator and dark matter mass, and including dark matter production through both on- and off-shell mediators. It is
commonly thought that the sensitivity of such experiments is predicated on the existence of an on-shell mediator that is produced and then decays to dark matter. While accelerators do provide a unique opportunity to probe the mediator directly, our analysis demonstrates that their sensitivity extends beyond this commonly discussed regime. In particular, we provide sensitivity calculations that extend into both the effective field theory regime where the mediator is much heavier than the dark matter and the regime of an off-shell mediator lighter than a dark matter particle-antiparticle pair. Our calculations also elucidate the resonance regime, making it clear that all but a fine-tuned region of thermal freeze-out parameter space for a range of simple models is well covered.
We analyze the open charm production in the binary $pi p to bar{D} Lambda_c$ and $pi(rho) J/psi$ reactions within the Regge theory including the absorption corrections. The calculations show that the total cross section is about a few $mu$b for the f
irst processes and a few mb for the second reactions at energy close to the threshold. Then it decreases with increasing energy according to the true Regge asymptotics.
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