Impact of the LHCb p + 4He fixed-target D0/ over bar 0 data on the intrinisic cc over bar component in the nucleon

We discuss the impact of the new LHCb fixed-target p + 4He data for D0= over bar D0 production on the intrinsic cc over bar component in the nucleon wave function. Within the scenario presented here neither the traditional gluon-gluon fusion or quark-antiquark annihilation mechanisms calculated in the kT-factorization approach nor their counterparts from the collinear next-to-leading order collinear framework are sufficient to describe the transverse momentum and rapidity distributions of D0= over bar D0 mesons. First the cc over bar -pair production within the standard frameworks is considered. Here a crucial role of the c -D hadronization effects at low energies and low transverse momenta is found and discussed, which was not analyzed in previous studies. A contribution related to intrinsic cc over bar component in the nucleon wave function is included in addition. Two models of the symmetric (c(x) = c over bar (x)) intrinsic charm (IC) component are considered. The intrinsic charm g*c -gc (or g* c over bar -gc over bar ) contribution needs to be regularized in order to obtain a suppression of the minijet pT spectrum present in the phenomenological minijet model, commonly used in Monte Carlo generators. We show that in our model the regularization parameter can be obtained from the fit to the LHCb fixed-target data under consideration here. We discuss uncertainties of our calculations (scale, charm quark mass, fragmentation function) as well as set limits on the IC probability. According to our model the intrinsic charm probability PIC = 1.65% allows to significantly improve description of the LHCb data but the number is rather uncertain.

Automated summary

We discuss the impact of the new LHCb fixed-target p + 4He data on the cc over bar component in the nucleon wave function. We find that the traditional mechanisms calculated in the kT-factorization approach are not sufficient to describe the transverse momentum and rapidity distributions of D0= over bar D0 mesons. We also consider the contribution from the intrinsic cc over bar component and set limits on its probability.