Charged pions multiplicities at the NA 49 energy

The wounded quark-diquark model predictions for charged pions multiplicities in P bP b and pP b collisions in the central rapidity region at √ s = 17.3 GeV c.m. energy are presented. 1. The NA49 collaboration published precise results 1 on inclusive production of charged pions in pp collisions at √ s = 17.3 GeV [1]. This measurement allows to investigate the consequences of the wounded quark-diquark model [2] for particles production in the central rapidity region of pP b and P bP b collisions at the same energy. We conclude that the model provides rather precise predictions (at the level of 2 − 3%) for the production of charged pions in nuclear collisions. 2. We follow closely the Ref. [3] where the predictions of the model in pP b and P bP b collisions at the LHC energy are presented. Here we only list the parameter values used in the present calculation and show the final results. In our calculations for the nuclear density we take the standard Woods-Saxon formula with the nuclear radius R P b = 6.62 fm and the skin depth d = 0.546 fm [4]. For the total inelastic pp cross section at √ s = 17.3 GeV we take the value obtained by the NA49 collaboration σ in = 31.46 mb [1]. We assume the differential inelastic pp cross section σ in (s) to be in a Gaussian form with σ in (0) = 0.92 [5]. 2 The average number of wounded quarks and diquarks in a single pp collision w (q+d) p = 1.18 (per one colliding proton) 3. Finally we take p q = w (q+d) p /3 and p d = 2p q where p q * 1 Total systematic uncertainty of 2.0% (quadratic sum) and 4.8% (upper limit). 2 We checked that different values of σ in (0) hardly influence final results. 3 At √ s = 23 GeV w (q+d) p ≈ 1.182 and changes very slowly with energy [2]. 1 and p d are the probabilities for a quark and a diquark to interact in a single pp collision, respectively. 4 3. In Fig. 1 we present the predicted relation between R pA ≡ N pA (0)/N pp (0) and the number of wounded nucleons w [6]. N pA (0) and N pp (0) are the midrapidity particle densities measured in pP b and pp collisions, respectively. 2 …