Two components in charged particle production in heavy-ion collisions

Transverse momentum spectra of charged particle production in heavy-ion collisions are considered in terms of a recently introduced Two Component parameterization combining exponential (soft) and power-law (hard) functional forms. The charged hadron densities calculated separately for them are plotted versus number of participating nucleons, $N_{part}$. The obtained dependences are discussed and the possible link between the two component parameterization introduced by the authors and the two component model historically used for the case of heavy-ion collisions is established. Next, the variations of the parameters of the introduced approach with the center of mass energy and centrality are studied using the available data from RHIC and LHC experiments. The spectra shapes are found to show universal dependences on $N_{part}$ for all investigated collision energies.

Transverse momentum distributions of baryons at LHC energies

Transverse momentum spectra of protons and anti-protons from RHIC ($sqrt{s}$ = 62 and 200 GeV) and LHC experiments ($sqrt{s}$= 0.9 and 7 TeV) have been considered. The data are fitted in the low $p_T$ region with the universal formula that includes the value of exponent slope as a main parameter. It is seen that the slope of low-$p_T$ distributions is changing with energy. This effect impacts on the energy dependence of average transverse momenta, which behaves approximately as $s^{0.06}$ that is similar to the previously observed behavior for $Lambda^0$-baryon spectra. In addition, the available data on $Lambda_c$ production from LHCb at $sqrt{s}= 7$ TeV were also studied. The estimated average $<p_T>$ is bigger than this value for protons proportionally to masses. The preliminary dependence of hadron average transverse momenta on their masses at LHC energy is presented.

The origin of thermal component in the transverse momentum spectra in high energy hadronic processes

The transverse momentum spectra of hadrons produced in high energy collisions can be decomposed into two components: the exponential (thermal) and the power (hard) ones. Recently, the H1 Collaboration has discovered that the relative strength of these two components in Deep Inelastic Scattering depends drastically upon the global structure of the event - namely, the exponential component is absent in the diffractive events characterized by a rapidity gap. We discuss the possible origin of this effect, and speculate that it is linked to confinement. Specifically, we argue that the thermal component is due to the effective event horizon introduced by the confining string, in analogy to the Hawking-Unruh effect. In diffractive events, the $t$-channel exchange is color-singlet and there is no fragmenting string -- so the thermal component is absent. The slope of the soft component of the hadron spectrum in this picture is determined by the saturation momentum that drives the deceleration in the color field, and thus the Hawking-Unruh temperature. We analyze the data on non-diffractive $pp$ collisions and find that the slope of the thermal component of the hadron spectrum is indeed proportional to the saturation momentum.

Hydrodynamic extension of the two component model for hadroproduction in heavy-ion collisions

The dependence of the spectra shape of produced charged hadrons on the size of a colliding system is discussed using a two component model. As a result, the hierarchy by the system-size in the spectra shape is observed. Next, the hydrodynamic extension of the two component model for hadroproduction using recent theoretical calculations is suggested to describe the spectra of charged particles produced in heavy-ion collisions in the full range of transverse momenta, $p_T$. Data from heavy-ion collisions measured at RHIC and LHC are analyzed using the introduced approach and are combined in terms of energy density. The observed regularities might be explained by the formation of QGP during the collision.

Role of quarks in hadroproduction in high energy collisions

Qualitative model for hadroproduction in high energy collisions considering two components (thermal and hard) to hadroproduction is proposed. Inclusive pseudorapidity distributions, $dsigma/deta$, and transverse momentum spectra, $d^2sigma/(deta dp_T^2)$, measured by different collaborations are considered in terms of this model. The shapes of the pseudorapidity distributions agree with that one can expect from the qualitative picture introduced. Finally, the differences between charged particle spectra produced in inclusive and diffractive events are discussed and the absence of the thermal component in the latter is observed.

Secondary hadron distributions in two component model

Inclusive charged hadron cross sections, $dsigma/deta$, and the mean transverse momenta, $<p_T>$, are considered within the two component model, which combines the power-like and the exponential terms in $p_T$. The observed dependences of the spectra shape on energy and the event multiplicity qualitatively agree with that expected from the Regge theory with the perturbative QCD pomeron. Finally, the dependences observed are used to make predictions on the mean transverse momenta, $<p_T>$ as function of multiplicity at LHC-energies, which are tested on available experimental data.

Hadroproduction in heavy-ion collisions

The shapes of invariant differential cross section for charged particle production as function of transverse momentum measured in heavy-ion collisions are analyzed. The data measured at RHIC and LHC are treated as function of energy density according to a recent theoretical approach. The Boltzmann-like statistical distribution is extracted from the whole statistical ensemble of produced hadrons using the introduced model. Variation of the temperature, characterizing this exponential distribution, is studied as function of energy density.

A photon-proton marriage

The shapes of invariant differential cross section for charged hadron production as function of hadrons transverse momentum and rapidity in ep collisions at HERA machine are considered. The particle spectra shapes observed in pp and gamma-gamma collisions before have shown very different properties. This difference could be directly measured in the mixed type collisions of photon and proton at HERA experiments.

A variation of the charged particle spectrum shape as function of rapidity in high energy pp collisions

The shapes of invariant differential cross section for charged particle production as function of transverse momentum measured in pp collisions by the UA1 detector are analyzed. The spectra shape varies with the produced particles pseudorapidity changing. To describe this and several other recently observed effects a simple qualitative model for hadroproduction mechanism was proposed.

An analysis of charged particles spectra in events with different charged multiplicity

The shapes of invariant differential cross section for charged particle production as function of transverse momentum measured in $pp$ collisions by the STAR detector are analyzed. The spectra shape varies with the event charged multiplicity changing. To describe this and several other recently observed effects a simple qualitative model for hadroproduction mechanism was proposed.