Initial-state energy loss in cold QCD matter and the Drell-Yan process

Abstract

The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and πA collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from J/ψ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and J/ψ data. Predictions for the COMPASS future measurements in πA collisions at √ s = 18.9 GeV are also performed. At higher collision energy ( √ s = 38.7 GeV), Drell-Yan measurements are only slightly affected by energy loss effects. On the contrary, the E906 results turn out in clear disagreement with nuclear PDF effects alone. The comparison of E772, E866, and E906 measurements indicates for the first time a clear violation of QCD factorization in Drell-Yan production in pA collisions.

Fully coherent energy loss effects on light hadron production in pA collisions

“…Finally, for the transport coefficient we useq 0 = 0.07 ± 0.02 GeV 2 /fm, which is consistent with phenomenological estimates from a variety of processes and reactions, for instance radiative energy loss in quarkonium production [41], Drell-Yan production [75] and hadron production in semi-inclusive DIS [76], nuclear p ⊥ -broadening of Drell-Yan and J/ψ from fixed-target to collider energies [77], and phenomenological extractions of the saturation scale in a proton from global fits to DIS data [15]. 16 In order to estimate the theoretical uncertainties, these quantities are varied around their central value, S 0 ≡ {n,ξ, z,q 0 }.…”

The study of the incoming parton energy loss effect on the NLO nuclear Drell–Yan ratios

“…Using the transport coefficientˆ=  q 0.34 0.03 q GeV 2 fm −1 , at next-to-leading order, the calculated results about the nuclear Drell-Yan production ratio modified by the effects of the nuclear parton distributions together with the incoming quark energy loss effect are shown as the dashed lines in figures 1-3. It is found that the obtained calculations by the HKM nPDF corrections together with the incoming quark energy loss (ˆ=  q 0.34 0.03 q GeV 2 fm −1 ) agree well with the experimental data, and particularly the obtained result for E906 data which is better than the model calculations obtained by EPS16 nPDF together with the fully coherent regimeˆ-= q 0.07 0.09 q GeV 2 fm −1 in [21]. In addition, from figures 1, 2, we can see that the theoretical results predict that the Drell-Yan suppression becomes more obvious with the increase of x F , which is consistent with the E906 and E866 measurements.…”

“…In our calculation we do not consider the corrections from isospin effects, because here we compare Drell-Yan yields on nuclei with similar Z/A ratios, which makes isospin effects are rather small. In [21], the calculations modified only by isospin effects display the small role of this effect on the nuclear Drell-Yan rations from E866 and E906 measurements.…”

“…The reason may be that the initial-state energy loss is only sensitive to the Landau-Pomeranchuk-Migdal (LPM) regime [33]. As discussed in [21], based on the LPM regime, the average incoming quark energy loss ⟨ ⟩μ  C q L R q 2 [33] where C R is the color charge of the incoming particle (C R =4/3 for quark), from which it can be inferred that ⟨ ⟩μ  C q A R q 2 3 . This indicates that the correction ⟨ ⟩  E h due to incoming quark energy loss would become important with the increase of the nuclear mass number A and vanish in the high energy limit, which coincides with the measured nuclear Drell-Yan data.…”

Nuclear p⊥-broadening of Drell-Yan and quarkonium production from SPS to LHC

“…Unlike quarkonium production, no FCEL is expected in the Drell-Yan channel [36], which may nonetheless be sensitive to initial-state energy loss. These effects, however, prove tiny either when x F is not too large or at high collision energies [37].…”