Parton recombination at all pTp_T

Hadron production at all $p_T$ in heavy-ion collisions in the framework of parton recombination is reviewed. It is shown that the recombination of thermal and shower partons dominates the hadron spectra in the intermediate $p_T$ region. In $d+Au$ collisions, the physics of particle production at any $\eta$ is basically the same as at $\eta=0$. The Cronin effect is described as a result of the final-state instead of the initial-state interaction. The suppression of $R_{CP}$ at high $\eta$ is due to the reduction of the soft parton density on the deuteron side, thus resulting in less pions produced by recombination, an explanation that requires no new physics. In $Au+Au$ collisions large $p/\pi$ ratio is obtained because the thermal partons can contribute to the formation of proton more than they do to the pion.Comment: 12 pages + 5 figures. Invited talk at Hard Probes 200

Correlations at intermediate pTp_T

Correlations among hadrons in jets produced in heavy-ion collisions are discussed in the framework of the recombination model. The basic correlation at the parton level is among the shower partons arising from kinematical constraint. The resultant correlation between hadrons at intermediate $p_T$ is amazingly rich in characteristics.Comment: 10 pages including 12 figures. Talk presented at the MIT Workshop on Correlations and Fluctuations in Relativistic Nuclear Collisions, April 200

Quark-hadron phase transition with surface fluctuation

The effect of surface fluctuation on the observables of quark-hadron phase transition is studied. The Ginzburg-Landau formalism is extended by the inclusion of an extra term in the free energy that depends on the vertical displacements from a flat surface. The probability that a bin has a particular net displacement is determined by lattice simulation, where the physics input is color confinement. The surface fluctuation from bin to bin is related to multiplicity fluctuation, which in turn is measured by the factorial moments. It is found that both the F-scaling behavior and the scaling exponent are essentially unaffected by the inclusion of surface fluctuation.Comment: 9 pages, LaTex, 7 figures in a single postscript file, submitted to Phys. Rev.

Fragmentation or Recombination at High p_T?

All hadronization processes, including fragmentation, are shown to proceed through recombination. The shower partons in a jet turn out to play an important role in describing the p_T spectra of hadrons produced in heavy-ion collisions. Due to the recombination of the shower partons with the soft thermal partons, the structure of jets produced in AA collisions is not the same as that of jets produced in pp collisions.Comment: Talk given at Quark Matter 200

Void Analysis of Hadronic Density Fluctuations at Phase Transition

The event-to-event fluctuations of hadron multiplicities are studied for a quark system undergoing second-order phase transition to hadrons. Emphasis is placed on the search for an observable signature that is realistic for heavy-ion collisions. It is suggested that in the 2-dimensional y-phi space the produced particles selected in a very narrow p_T window may exhibit clustering patterns even when integrated over the entire emission time. Using the Ising model to simulate the critical phenomenon and taking into account a p_T distribution that depends on the emission time, we study in the framework of the void analysis proposed earlier and find scaling behavior. The scaling exponents turn out to be larger than the ones found before for pure configurations without mixing. The signature is robust in that it is insensitive to the precise scheme of simulating time evolution. Thus it should reveal whether or not the dense matter created in heavy-ion collisions is a quark-gluon plasma before hadronization.Comment: 11 pages in LaTeX + 6 figures in p

Evolution of shower parton distributions in a jet from quark recombination model

The evolution of shower parton distributions in a jet is investigated in the framework of quark recombination model. The distributions are parameterized and the $Q^2$ dependence of the parameters is given by polynomials of $\ln Q^2$ for a wide range of $Q^2$.Comment: 5 pages in RevTeX, 3 figures in ep

Comparison of Nuclear Suppression Effects on Meson Production at High p_T and p_L

The medium effect on the pion distribution at high $p_T$ in $AA$ collisions is compared to that of the pion distribution at high $p_L$ in $pA$ collisions. Both the suppression of the spectra and the energy losses of the measured pions are studied. Although the medium effect on $p_T$ is larger than on $p_L$, the difference is found surprisingly to be not as big as one would naively expect.Comment: 8 RevTex pages with 5 figure

Ridge Formation Induced by Jets in pppp Collisions at 7 TeV

An interpretation of the ridge phenomenon found in pp collisions at 7 TeV is given in terms of enhancement of soft partons due to energy loss of semihard jets. A description of ridge formation in nuclear collisions can directly be extended to pp collisions, since hydrodynamics is not used, and azimuthal anisotropy is generated by semihard scattering. Both the p_T and multiplicity dependencies are well reproduced. Some suggestions are made about other observables.Comment: Expanded version to be published in Phys. Rev.