This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute ‘Heavy Ion Collisions at the LHC—Last Call for Predictions’, held from 14th May to 10th June 2007.

We report our recent work on conversions between gluon and quark jets as they traverse through a quarkgluon plasma (QGP) and their effects on the nuclear modification factors for quark and gluon jets as well as the ratios of p/π + andp/π − at high transverse momentum in ultra-relativistic heavy ion collisions.Keywords: Ultra-relativistic heavy ion collisions; Quark-gluon plasma; Jet quenching; Jet conversions One of the most interesting observations in central heavy ion collisions at Relativistic Heavy Ion Collider (RHIC) is suppressed production of hadrons with large transverse momentum [1]. This phenomenon has been attributed to the radiative energy loss of partonic jets, produced from initial hard scattering of incoming nucleons, as they traverse through the dense partonic matter created during these collisions [2][3][4]. Recent studies have shown that elastic scattering of jets in the produced quark-gluon plasma (QGP) also leads to an appreciable loss of their energies [5,6]. Because of its larger color charge, a gluon jet is expected to lose more energy than quark and antiquark jets [7]. Since the ratio of high momentum protons and antiprotons to pions produced from fragmentation of a gluon jet is much larger than that from a quark jet and there are more gluon than quark jets in proton-proton collisions, a larger energy loss of gluon jets than that of quark jets would lead to smaller p/π + andp/π − ratios at high transverse momentum in central heavy ion collisions than in proton-proton collisions at same energy [8]. This is in contrast to p/π + and p/π − ratios at intermediate transverse momentum where they are enhanced in central heavy ion collisions due to production via quark coalescence or recombination [9][10][11]. Experimentally, data from the STAR collaboration have indicated, however, that the p/π + andp/π − ratios at high transverse momentum in central Au+Au collisions [12] approach those in p+p and d+Au collisions [13], implying that the ratio of final quark and gluon jets at high transverse momentum is similar to that of initial ones. A possible mechanism for reducing the effect due to difference in quark and gluon jet energy losses in QGP is to allow a net conversion of quark jets to gluon jets via both elastic (q(q)g ↔ gq(q)) and inelastic (qq ↔ gg) scattering with thermal quarks and gluons in the QGP, an idea first considered in Refs. [14] for deeply inelastic scattering. In this talk, we report the results from our recent study [15].The conversion rate of a quark jet to a gluon jet or vice versa in a QGP is related to its collisional width due to conversion scattering , i.e., given by the thermal average Γ = ∑ i |M i | 2 of the sum of squared amplitudes for these scattering processes after averaging over the spins and colors of initial partons and summing over those of final partons. For the two-body processes q(q)g ↔ gq(q) and qq ↔ gg, their amplitudes are * On leave from Institute of Particle Physics, Huazhong Normal University, Wuhan 430079, China well-known. To ensure that a quark (gluon)...

The cross section for J/ absorption by nucleons is studied using a gauged SU͑4͒ hadronic Lagrangian but with empirical particle masses, which has been used previously to study the cross sections for J/ absorption by pion and meson. Including both two-body and three-body final states, we find that with a cutoff parameter of 1 GeV at interaction vertices involving charm hadrons, the J/-N absorption cross section is at most 5 mb and is consistent with that extracted from J/ production from both photonuclear and proton-nucleus reactions.

Using hadronic Lagrangians that include the interaction of pentaquark Θ + baryon with K and N , we evaluate the cross sections for its production from meson-proton, proton-proton, and photonproton reactions near threshold. With empirical coupling constants and form factors, the predicted cross sections are about 1.5 mb in kaon-proton reactions, 0.1 mb in rho-nucleon reactions, 0.05 mb in pion-nucleon reactions, 20 µb in proton-proton reactions, and 40 nb in photon-proton reactions.

The cross sections for production of pentaquark $\Xi^+_5$ from the reaction $\gamma p\to K^0K^0\Xi^+_5$ and $\Xi^{--}_5$ from the reaction $\gamma n\to K^+K^+\Xi^{--}_5$ are evaluated in a hadronic model that includes their couplings to both $\Sigma\bar K$ and $\Sigma\bar K^*$. With these coupling constants determined from the empirical $\pi NN(1710)$ and $\rho NN(1710)$ coupling constants by assuming that $\Xi^+_5$, $\Xi^{--}_5$, and N(1710) belong to the same antidecuplet of spin 1/2 and positive parity, and using form factors at strong interaction vertices similar to those for pentaquark $\Theta^+$ production in photonucleon reactions, we obtain a cross section of about 0.03-0.6 nb for the reaction $\gamma p\to K^0K^0\Xi^+_5$ and about 0.1-0.6 nb for the reaction $\gamma n\to K^+K^+\Xi^{--}_5$ at photon energy $E_\gamma=4.5$ GeV, depending on the value of the coupling constant $g_{K^*\Sigma\Xi_5}$.Comment: 14 pages, 5 figure