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Register a new userRole of gluons in soft and semi-hard multiple hadron production in pp collisions at LHC
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Hadron inclusive spectra in pp collisions are analyzed within the modified quark-gluon string model including both the longitudinal and transverse motion of quarks in the proton in the wide region of initial energies. The self-consistent analysis shows that the experimental data on the inclusive spectra of light hadrons like pions and kaons at ISR energies can be satisfactorily described at transverse momenta not larger than 1-2 GeV/c. We discuss some difficulties to apply this model at energies above the ISR and suggest to include the distribution of gluons in the proton unintegrated over the internal transverse momentum. It leads to an increase in the inclusive spectra of hadrons and allows us to extend the satisfactory description of the data in the central rapidity region at energies higher than ISR.
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The hadron inclusive spectra in pp collisions at high energies are analyzed within a soft QCD model, namely the quark-gluon string model. In addition to the sea quark distribution in the incoming proton we consider also the unintegrated gluon distribution that has an increasing behaviour when the gluon transverse momentum grows. It leads to an increase of the inclusive spectra of hadrons and their multiplicity in the central rapidity region of pp collision at LHC energies.
We analyze the inclusive spectra of hadrons produced in $pp$ collisions at high energies in the mid-rapidity region within the soft QCD and perturbative QCD assuming the possible creation of the soft gluons at low intrinsic transverse momenta $k_t$. From the best description of the LHC data we found the parametrization of the unintegrated gluon distribution which at low $k_t$ is different from the one obtained within the perturbative QCD.
Phenomenological Tsallis fits to the CMS, ATLAS, and ALICE transverse momentum spectra of hadrons for pp collisions at LHC were recently found to extend over a large range of the transverse momentum. We investigate whether the few degrees of freedom in the Tsallis parametrization may arise from the relativistic parton-parton hard-scattering and related processes. The effects of the multiple hard-scattering and parton showering processes on the power law are discussed. We find empirically that whereas the transverse spectra of both hadrons and jets exhibit power-law behavior of 1/pT^n at high pT, the power indices n for hadrons are systematically greater than those for jets, for which n~4-5.
Prospects for strangeness production in pp collisions at the Large Hadron Collider (LHC) are discussed within the statistical model. Firstly, the system size and the energy dependence of the model parameters are extracted from existing data and extrapolated to LHC energy. Particular attention is paid to demonstrate that the chemical decoupling temperature is independent of the system size. In the energy regime investigated so far, strangeness production in pp interactions is strongly influenced by the canonical suppression effects. At LHC energies, this influence might be reduced. Particle ratios with particular sensitivity to canonical effects are indicated. Secondly, the relation between the strangeness production and the charged-particle multiplicity in pp interactions is investigated. In this context the multiplicity dependence studied at Tevatron is of particular interest. There, the trend in relative strangeness production known from centrality dependent heavy-ion collisions is not seen in multiplicity selected pp interactions. However, the conclusion from the Tevatron measurements is based on rather limited data samples with low statistics and number of observables. We argue, that there is an absolute need at LHC to measure strangeness production in events with different multiplicities to possibly disentangle relations and differences between particle production in pp and heavy-ion collisions.
We present a systematic analysis of transverse momentum $(p_{T})$ spectra of the strange hadrons in different multiplicity events produced in pp collision at $sqrt{s}$ = 7 TeV, pPb collision at $sqrt{s_{NN}}$ = 5.02 TeV and PbPb collision at $sqrt{s_{NN}}$ = 2.76 TeV. Both the single and differential freeze out scenarios of strange hadrons $K^0_s$, $Lambda$ and $Xi^-$ are considered while fitting using a Tsallis distribution which is modified to include transverse flow. The $p_{T}$ distributions of these hadrons in different systems are characterized in terms of the parameters namely, Tsallis temperature $(T)$, power $(n)$ and average transverse flow velocity $(beta)$. It is found that for all the systems, transverse flow increases as we move from lower to higher multiplicity events. In the case of the differential freeze-out scenario, the degree of thermalization remains similar for events of different multiplicity classes in all the three systems. The Tsallis temperature increases with the mass of the hadrons and also increases with the event multiplicity in pp and pPb system but shows little variation with the multiplicity in PbPb system. In the case of the single freeze-out scenario, the difference between small systems (pp, pPb) and PbPb system becomes more evident. The high multiplicity PbPb events show higher degree of thermalization as compared to the events of pp and pPb systems. The trend of variation of the temperature in PbPb system with event multiplicity is opposite to what is found in the pp and pPb systems.
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