The semi-inclusive properties of the system of neutral and charged particles with net charge equal to zero are considered in the grand canonical, canonical and micro-canonical ensembles as well as in micro-canonical ensemble with scaling volume fluctuations. Distributions of neutral particle multiplicity and charged particle momentum are calculated as a function of the number of charged particles. Different statistical ensembles lead to qualitatively different dependencies. They are being compared with the corresponding experimental data on multi-hadron production in $p+p$ interactions at high energies.
Different kinematical regimes of semi-inclusive deeply inelastic scattering (SIDIS) processes correspond to different underlying partonic pictures, and it is important to understand the transition between them. This is particularly the case when there is sensitivity to intrinsic transverse momentum, in which case kinematical details can become especially important. We address the question of how to identify the current fragmentation region --- the kinematical regime where a factorization picture with fragmentation functions is appropriate. We distinguish this from soft and target fragmentation regimes. Our criteria are based on the kinematic regions used in derivations of factorization theorems. We argue that, when hard scales are of order a few GeVs, there is likely significant overlap between different rapidity regions that are normally understood to be distinct. We thus comment on the need to take this into account with more unified descriptions of SIDIS, which should span all rapidities for the produced hadron. Finally, we propose general criteria for estimating the proximity to the current region at large Q.
High energy inclusive hadron production in the central kinematical region is analyzed within the models of unitarized pomeron. It is shown that the sum of multipomeron exchanges with intercept $alpha_P(0)>1$ reproduce qualitatively contribution of the triple pole (at $t=0$) pomeron to inclusive cross section. Basing on this analogy we then suggest a general form of unitarized pomeron contributions (in particular the dipole or tripole pomeron) to inclusive cross section. They lead to a parabolic form of the rapidity distribution giving $<n>propto ln^3s$ (tripole) or $<n>propto ln^2s$ (dipole). The models considered with suggested parametrization of $p_t$-dependence for cross sections well describe the rapidity distributions data in $pp$ and $bar pp$ interactions at energy $sqrt{s}geq 200$ GeV. The predictions for one particle inclusive production at LHC energies are given.
It is shown that in semi-inclusive deep inelastic scattering (DIS) of electrons off a complex nucleus A, the detection, in coincidence with the scattered electron, of a nucleus (A-1) in the ground state, as well as of a nucleon and a nucleus (A-2), also in the ground state, may provide unique information on several long standing problems, such as : i) the nature and the relevance of the final state interaction in DIS; ii) validity of the spectator mechanism in DIS; iii) the medium induced modifications of the nucleon structure function; iv) the origin of the EMC effect.
Motivated by recently observed tension between $Oleft(alpha_s^2right)$ calculations of very large transverse momentum dependence in both semi-inclusive deep inelastic scattering and Drell-Yan scattering, we repeat the details of the calculation through $Oleft(alpha_s^2right)$ transversely differential cross section. The results confirm earlier calculations, and provide further support to the observation that tension exists with current parton distribution and fragmentation functions.
We study the single-transverse spin asymmetry for open charm production in the semi-inclusive lepton-hadron deep inelastic scattering. We calculate the asymmetry in terms of the QCD collinear factorization approach for $D$ mesons at high enough $P_{hperp}$, and find that the asymmetry is proportional to the twist-three tri-gluon correlation function in the proton. With a simple model for the tri-gluon correlation function, we estimate the asymmetry for both COMPASS and eRHIC kinematics, and discuss the possibilities of extracting the tri-gluon correlation function in these experiments.