Upsilon production at Fermilab Tevatron and LHC energies

We update the theoretical predictions for direct Upsilon(nS) hadroproduction in the framework of nonrelativistic QCD. We show that the next-to-leading order corrections in alpha(S) to the color-singlet transition significantly raise the differential cross section at high p(T) and substantially affect the polarization of the Upsilon. Motivated by the remaining gap between the next-to-leading order yield and the cross-section measurements at the Fermilab Tevatron, we evaluate the leading part of the alpha(S)(5) contributions, namely, those coming from Upsilon(nS) associated with three light partons. The differential color-singlet cross section at alpha(S)(5) is in substantial agreement with the data, so that there is no evidence for the need of color-octet contributions. Furthermore, we find that the polarization of the Upsilon(nS) is longitudinal. We also present our predictions for Upsilon(nS) production at the LHC.     

Inclusive two-particle rapidity correlations at ISR energies and fireball production

ISR data on two-particle rapidity correlations in the region y₁ ≈ y₂ can be understood in terms of the multiperipheral fireball model and indicate an energy independent upper limit of the average fireball mass. The diffractive contribution to the fireball production leads to characteristic shapes of long range correlations. Data on long range rapidity correlations may be used to determine the fractions of non-diffractive and diffractive one- and two-fireball production.     

Inclusive particle production in π− n interactions at high energies

Results on inclusive particle production in π^? n interactions at 21, 205 and 360 GeV/c are presented. The invariant cross sections in both neutron fragmentation and central regions are found to be equal within errors to the corresponding cross sections for π^? p collisions and exhibit the same energy dependence. A strong energy dependence of the invariant cross section ratios of negative and positive pions is observed. There is also an indication of transverse momentum dependence of these ratios. The η^? correlations in the neutron fragmentation region show little variation with energy and are in agreement with the predictions of the naive quark recombination scheme.     

Inclusive lepton production from heavy hadron decay in pp collisions at the LHC

We present predictions for the inclusive production of leptons (e^±,μ^±$e^{\pm },{\mu }^{\pm }$) originating from charm and bottom hadrons at the CERN LHC in the general-mass variable-flavour-number scheme at next-to-leading order. Detailed numerical results are compared to data of the CMS, ATLAS and ALICE Collaborations.     

Jet shape modification at LHC energies by JEWEL

Jet shape measurements are employed to explore the microscopic evolution mechanisms of parton-medium interaction in ultra-relativistic heavy-ion collisions. In this study, jet shape modifications are quantified in terms of the fragmentation function F(z), relative momentum p_T~(rel), density of charged particles p(r), jet angularity girth, jet momentum dispersion p_T~(disp),and LeS ub for proton-proton(pp) collisions at 0.9, 2.76. 5.02, 7,and 13 TeV, as well as for lead-lead collisions at 2.76 TeV and 5.02 TeV by JEWEL. A differential jet shape parameter Dgirth is proposed and studied at a smaller jet radius r 0.3. The results indicate that the medium has the dominant effect on jet shape modification, which also has a weak dependence on the center-of-mass energy. Jet fragmentation is enhanced significantly at very low z 0.02, and fragmented jet constituents are linearly spread to larger jet-radii for p_T~(rel) 1. The waveform attenuation phenomena is observed in p_T~(rel),girth, and Dgirth distributions. The results obtained for D_(girth) from pp to Pb + Pb, where the wave-like distribution in pp collision is ahead of Pb + Pb collisions at small jetradii, indicates a strong medium effect.     

Description of pp collisions at LHC energies

The Monte Carlo version of quark-gluon string model is employed to study the multiplicity, rapidity and pr spectra of particles in pp collisions at energies from √s = 200 GeV to 14 TeV. A good quantitative agreement with the experimental data is found in a broad energy range. It means that the general features of ultrarelativistic pp interactions can be well understood in terms of soft- and hard-Pomeron exchanges. Predictions are made for the top LHC energy √s = 14TeV.     

Photon-photon luminosities in relativistic heavy ion collisions at LHC energies

Effective – luminosities are calculated for various realistic hadron collider scenarios. The main characteristics of photon-photon processes at relativistic heavy-ion colliders are established and compared to the corresponding –-luminosities ate ⁺-e ^– — and future photon linear colliders (PLC). Higher order corrections as well as inelastic processes are discussed. It is concluded that feasible high luminosity Ca–Ca collisions at the Large Hadron Collider (LHC) are an interesting option for – physics up to about 100 GeV – CM energy.     

Inclusive particle production at HERA

We calculate in next-to-leading order inclusive cross sections of single-particle production via both direct and resolved photons inep collisions at HERA. Transversemomentum and rapidity distributions are presented and the dependences on renormalization and factorization scales and subtraction schemes are investigated.Supported by the Bundesministerium für Forschung und Technologie under Contract 05 6 HH 93P (5), Bonn, Germany     

Inclusive particle production at HERA

We calculate in next-to-leading order inclusive cross sections of single-particle production via resolved photons inep collisions at HERA. Transverse-momentum and rapidity distributions are presented and the scale dependence is studied. The results are compared with first experimental data from the H1 Collaboration at HERA.     

Strange prospects for LHC energies

Strange quark and hadron production will be studied at the large hadron collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb–Pb and pp data will be available. PACS 25.75.-q; 25.75.Dw     

Top-quark pair production near threshold at LHC

The next-to-leading order analysis for the cross section for hadroproduction of top-quark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed-order perturbation theory is observed which originates from the characteristic remnant of the 1S peak below production threshold of top-quark pairs. The analysis includes all color-singlet and color-octet configurations of top-quark pairs in S-wave states and, for the dominant configurations, it employs all-order soft-gluon resummation for the hard parton cross section. Numerical results for the Large Hadron Collider at TeV and TeV and also for the Tevatron are presented. The possibility of a top-quark mass measurement from the invariant-mass distribution of top-quark pairs is discussed.     

Multiple charm production at the LHC energy

Cross sections for J/ψ mesons produced in association with open charm and two charmed hadrons from different $c\bar c$ pairs under LHC conditions are predicted theoretically. The respective processes are considered both in single and in double parton interactions. Particular attention is given to kinematical limits of the LHCb detector, and a comparison with the most recent experimental data is performed for them.     

Proton–proton interaction in constituent quarks model at LHC energies

In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12 and small value of the slope α^′ _P≈0.08 GeV^-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV^-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron.     

Inclusive prompt $$\chi _{c,b}(1^{++})$$ production at the LHC

We study the prompt production of the \(\chi _c(1^+)\) and \(\chi _b(1^+)\) mesons at high energies. Unlike \(\chi (0^+,2^+)\) production, \(\chi (1^+)\) mesons cannot be created at LO via the fusion of two on-mass-shell gluons, that is, \(gg\rightarrow \chi _{c,b}(1^+)\) are not allowed. However, the available experimental data show that the cross sections for \(\chi _c(1^+)\) and \(\chi _c(2^+)\) are comparable. We therefore investigate four other \(\chi (1^+)\) production mechanisms: namely, (i) the standard NLO process \(gg\rightarrow \chi _{c,b}(1^+)+g\), (ii) via gluon virtuality, (iii) via gluon reggeisation and, finally, (iv) the possibility to form \(\chi _{c,b}(1^+)\) by the fusion of three gluons, where one extra gluon comes from another parton cascade, as in the Double Parton Scattering processes.     

Observing many-body effects on lepton pair production from low mass enhancement and flow at RHIC and LHC energies

The ρ spectral function at finite temperature calculated using the real-time formalism of thermal field theory is used to evaluate the low mass dilepton spectra. The analytic structure of the ρ propagator is studied and contributions to the dilepton yield in the region below the bare ρ peak from the different cuts in the spectral function are discussed. The space-time integrated yield shows significant enhancement in the region below the bare ρ peak in the invariant mass spectra. It is argued that the variation of the inverse slope of the transverse mass (M _T ) distribution can be used as an efficient tool to predict the presence of two different phases of the matter during the evolution of the system. The sensitivities of the effective temperature obtained from the slopes of the M _T spectra to the medium effects are studied.     

Dilepton production at SIS energies

In this short review the results of detailed studies for dilepton production from p+A andA+A reactions at SIS energies are presented. The calculations are based on a semi-classical BUU transport model that includes the off-shell propagation of vector mesons and evaluates the width of the vector mesons dynamically. Different scenarios of in-medium modifications of vector mesons, such as collisional broadening and dropping vector meson masses, are investigated and the possibilities for an experimental observation of in-medium effects in p+A reactions at 1–4 GeV are discussed for a variety of nuclear targets.     

Kaon production at subthreshold energies

We present a comprehensive investigation of subthreshold and threshold kaon production in the framework of the QMD model. The calculation shows that the kaon yield depends strongly on the nuclear equation of state (EOS) and subthreshold kaon experiments may therefore offer the up to now best possibility to determine this yet unknown property of nuclear matter. Whereas static equations of state are in quite good agreement with the data the more realistic momentum dependent EOS's underpredict the data by about a factor of three. Most kaons are produced in a two step process with an intermediate Δ, a process which is absent in NN collisions. Therefore the kaon yield is much higher than expected from the extrapolation of pp data. We discuss in detail the influence of the elementary kaon production cross section, the contribution of different production channels and the properties of the nuclear environment at the place where the kaon is produced. The decrease of the number of produced kaons per participant with decreasing participant number, which is also observed experimentally, has two sources: The nonmaxwellian momentum distribution for small participant numbers as well as a reduction of the ΔΔ channel. This finding is supported by the observed decrease of high momentum pions. We compare our results with other calculations and discuss in detail the theoretical and experimental uncertainties. They include the yet only vaguely known elementary kaon production cross section at the threshold, the lack of a quantum-mechanical treatment of the two step production process as well as the behaviour of the kaon (and therefore also of the kaon production threshold) in the nuclear environment.