Investigation of particle production in h–A collisions using statistical distributions

Study of the characteristic properties of charged particle production in hadron–nucleus collisions at high energies by utilizing the approaches from different statistical models is performed. Predictions from different approaches using the negative binomial distribution, shifted Gompertz distribution, Weibull distribution and the Krasznovszky–Wagner distribution are considered for a comparative study of the relative success of these models. These distributions derived from a variety of functional forms are based on either phenomenological parameterizations or some model of the underlying dynamics. Some of these have also been used to study the data at the Large Hadron Collider (LHC) for both proton–proton and nucleus–nucleus collisions. Various physical and derived observables have been used for the analysis.

Thermal photons at PHENIX experiment

Direct photons are a unique probe to study the properties of the medium created in heavy ion collisions. In particular low pT direct photons are of great importance since one expects that they are predominantly of thermal origin. In A+A systems PHENIX has observed a large yield of low pT direct photon that are emitted with a significant azimuthal anisotropy with respect to the reaction plane (v2). The mechanism responsible for the large yield and large v2 is not understood yet. Following recent evidence for collective behavior of charged particle production from small systems like p+A, d+Au, and 3He+Au, PHENIX has made systematic measurements of direct pho- tons with different collision energies and system configurations. It has been found that the low pT direct photon yield dNγ/dη is proportional to (dNch/dη)α. This behavior holds for beam energies measured both at RHIC and at the LHC in large-on-large systems, while data from small systems suggest an onset of QGP formation at low dNch/dα. In this talk, I will report recent measurements of thermal photon and related observables.

Charged-particle production as a function of multiplicity and transverse spherocity in pp collisions at $$ \sqrt{\mathbf{s}} =\mathbf{5.02}$$ and 13 TeV

We present a study of the inclusive charged-particle transverse momentum ($$p_{\mathrm{T}}$$pT) spectra as a function of charged-particle multiplicity density at mid-pseudorapidity, $$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta $$dNch/dη, in pp collisions at $$\sqrt{s}=5.02$$s=5.02 and 13 TeV covering the kinematic range $$|\eta |<0.8$$|η|<0.8 and $$0.15<p_{\mathrm{T}} <20$$0.15<pT<20 GeV/c. The results are presented for events with at least one charged particle in $$|\eta |<1$$|η|<1 (INEL$$\,>0$$>0). The $$p_\mathrm{T}$$pT spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The $$p_{\mathrm{T}}$$pT spectra normalized to that for INEL$$\,>0$$>0 show little energy dependence. Moreover, the high-$$p_{\mathrm{T}}$$pT yields of charged particles increase faster than the charged-particle multiplicity density. The average $${ p}_{\mathrm{T}}$$pT as a function of multiplicity and transverse spherocity is reported for pp collisions at $$\sqrt{s}=13$$s=13 TeV. For low- (high-) spherocity events, corresponding to jet-like (isotropic) events, the average $$p_\mathrm{T}$$pT is higher (smaller) than that measured in INEL$$\,>0$$>0 pp collisions. Within uncertainties, the functional form of $$\langle p_{\mathrm{T}} \rangle (N_{\mathrm{ch}})$$⟨pT⟩(Nch) is not affected by the spherocity selection. While EPOS LHC gives a good description of many features of data, PYTHIA overestimates the average $$p_{\mathrm{T}}$$pT in jet-like events.