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D. Kharzeev

Publications and source records attributed to D. Kharzeev.

At least 37 records · Page 2Linked to original sources
arXiv2003

Hard probes in heavy ion collisions at the LHC: heavy flavour physics

We present the results from the heavy quarks and quarkonia working group. This report gives benchmark heavy quark and quarkonium cross sections for $pp$ and $pA$ collisions at the LHC against which the $AA$ rates can be compared in the study of the quark-gluon plasma. We also provide an assessment of the theoretical uncertainties in these benchmarks. We then discuss some of the cold matter effects on quarkonia production, including nuclear absorption, scattering by produced hadrons, and energy loss in the medium. Hot matter effects that could reduce the observed quarkonium rates such as color screening and thermal activation are then discussed. Possible quarkonium enhancement through coalescence of uncorrelated heavy quarks and antiquarks is also described. Finally, we discuss the capabilities of the LHC detectors to measure heavy quarks and quarkonia as well as the Monte Carlo generators used in the data analysis.

hep-ph↗
arXiv2003

Open charm production in heavy ion collisions and the Color Glass Condensate

We consider the production of open charm in heavy ion collisions in the framework of the Color Glass Condensate. In the central rapidity region at RHIC, for the charm quark yield we expect N(coll) (number of collisions) scaling in the absence of final-state effects. At higher energies, or forward rapidities at RHIC, the saturation scale exceeds the charm quark mass; we find that this results in the approximate N(part) (number of participants) scaling of charm production in AA collisions and N(part)^A scaling in p(d)A collisions, similarly to the production of high pT gluons discussed earlier. We also show that the saturation phenomenon makes spectra harder as compared to the naive parton model approach. We then discuss the energy loss of charm quarks in hot and cold media and argue that the hardness of the spectrum implies very slow dependence of the quenching factor on pT.

hep-ph↗
arXiv2002

Parton saturation and N_part scaling of semi--hard processes in QCD

We argue that the suppression of high p_t hadrons discovered recently in heavy ion collisions at RHIC may be a consequence of saturation in the Color Glass Condensate. We qualitatively and semi-quantitatively describe the data, in particular, the dependence upon the number of nucleon participants. We show that if parton saturation sets in at sufficiently small energy, then in nucleus-nucleus collisions at RHIC and LHC energies the cross sections of semi-hard processes should scale approximately with the number of participants, N_{part}. Our results provide a possible explanation of both the absence of apparent jet quenching at SPS energies and its presence at RHIC. Under the same assumption we predict that in semi--central and central pA (dA) collisions at collider energies the dependence of semi--hard processes on the number of participating nucleons of the nucleus will change to \sim (N_{part}^A)^{1/2}. The forthcoming data on dA collisions will provide a crucial test of this description.

hep-ph↗
arXiv2002

Important experimental observables at RHIC

In this talk I discuss the significance of the first RHIC measurements for establishing the properties of hot and dense QCD matter and for understanding the dynamics of the theory at the high parton density, strong color field frontier. Hopes and expectations for the future are discussed as well.

nucl-th↗
arXiv2002

What are we learning from RHIC?

This talk is an attempt to summarize some of the first results obtained at RHIC. I discuss the significance of these measurements for establishing the properties of hot and dense QCD matter and for understanding the dynamics of the theory at the high parton density, strong color field frontier.

hep-ph↗
arXiv2002

Classical gluodynamics in curved space--time and the soft Pomeron

QCD at the classical level possesses scale invariance which is broken by quantum effects. This ``dimensional transmutation'' phenomenon can be mathematically described by formulating classical gluodynamics in a curved, conformally flat, space-time with non-vanishing cosmological constant. We study QCD high-energy scattering in this theory. We find that the properties of the scattering amplitude at small momentum transfer are determined by the energy density of vacuum fluctuations. The approach gives rise to the power growth of the total hadron-hadron cross section with energy, i.e. the Pomeron. The intercept of the Pomeron and the multiplicity of produced particles are evaluated. We also speculate about a possible link between conformal anomaly and TeV scale quantum gravity.

hep-ph↗
arXiv2002

Classical chromo-dynamics of relativistic heavy ion collisions

Relativistic heavy ion collisions produce thousands of particles, and it is sometimes difficult to believe that these processes allow for a theoretical description directly in terms of the underlying theory - QCD. However once the parton densities are sufficiently large, an essential simplification occurs - the dynamics becomes semi-classical. As a result, a simple ab initio approach to the nucleus--nucleus collision dynamics may be justified. In these lectures, we describe the application of these ideas to the description of multi--particle production in relativistic heavy ion collisions. We also discuss the role of semi-classical fields in the QCD vacuum in hadron interactions at low and high energies.

hep-ph↗
arXiv2001

Buckyballs and gluon junction networks on the femtometer scale

We explore the possibility that novel geometrical structures analogous to carbon Fullerenes may exist in Nature on the femtometer scale. QCD predicts the existence of special topological gluon field configurations called baryon junctions and anti-junctions. Here we show that femto-scale structures, networks or closed (gluon field) cages, can be constructed in the theory of QCD as tiny cousins of familiar nano-scale structures such as carbonic Fullerenes C_{60}, C_{70}. The most symmetric polyhedra of QCD junctions (J-balls) are characterized by the magic numbers 8, 24, 48, and 120, and zero net baryon number. Tubes, prisms, tori and other topological structures can also be created. In addition, special configurations can be constructed that are odd under charge and parity conjugation (CP), although the QCD Lagrangian is CP even. We provide a semi-classical estimate for the expected mass range of QCD Buckyballs and discuss the possible conditions under which such novel topological excitations of the QCD vacuum may be produced in experiments of high energy physics.

hep-ph↗
arXiv2001

Heavy quarks and QCD matter

I present recent results on the theory of QCD matter production in high energy heavy ion collisions and on the interactions of heavy quarks in such environment. The centrality and rapidity dependence of hadron production is evaluated in semi--classical approach. The energy loss of heavy quarks in matter is computed. The heavy--to--light meson ratio (e.g., D/pion) at moderate transverse momenta is demonstrated to be both sensitive to the density of color charges in the medium and infrared stable.

hep-ph↗
arXiv2001

The onset of classical QCD dynamics in relativistic heavy ion collisions

The experimental results on hadron production obtained recently at RHIC offer a new prospective on the energy dependence of the nuclear collision dynamics. In particular, it is possible that parton saturation -- the phenomenon likely providing initial conditions for the multi--particle production at RHIC energies -- may have started to set in central heavy ion collisions already around the highest SPS energy. We examine this scenario, and make predictions based on high density QCD for the forthcoming 22 GeV run at RHIC.

hep-ph↗
arXiv2001

Manifestations of high density QCD in the first RHIC data

We derive a simple analytical scaling function which embodies the predictions of high density QCD on the energy, centrality, rapidity, and atomic number dependences of hadron multiplicities in nuclear collisions. Both centrality and rapidity dependences of hadron multiplicity in $Au-Au$ collisions as measured at RHIC at $\sqrt{s}= 130 {GeV}$ are well described in this approach. The centrality and rapidity dependences of hadron multiplicity at $\sqrt{s}= 200 \ {GeV}$ run at RHIC are predicted; the variation of these dependences with energy appear different from other approaches, and can be used as an important test of the ideas based on parton saturation and classical Chromo-Dynamics.

nucl-th↗
arXiv2001

Anomalous chirality fluctuations in the initial stage of heavy ion collisions and parity odd bubbles

We compute numerically the topological charge distribution in the initial stage of a high energy heavy ion collision. This charge distribution is generated by Chern-Simons number fluctuations associated with the dynamics of strong classical fields in the initial state. The distribution is found to be quite narrow at RHIC and LHC energies reflecting a small value of the topological susceptibility. Thus the effective potential of classical fields is shallow in the $θ$-direction likely creating favorable conditions for the subsequent generation of P-odd bubbles.

hep-ph↗
arXiv2001

QCD and Heavy Ions

This short paper is an attempt to describe a theorist's view of the goals of relativistic heavy ion program which has just entered the collider era. These goals are centered around understanding the properties and the critical behavior of Quantum Chromo-Dynamics (QCD) in the non-linear regime of high color field strength and high parton density. Some of the current theoretical challenges are highlighted, and the place of heavy ion research in the broader context of modern particle and nuclear physics is discussed.

nucl-th↗
arXiv2001

Hadron production in nuclear collisions at RHIC and high density QCD

We analyze the first results on charged particle multiplicity at RHIC in the conventional eikonal approach and in the framework of high density QCD. We extract the fraction $F$ of the hadron multiplicity originating from ``hard'' (i.e. proportional to the number of binary collisions) processes; we find a strong growth of this fraction with energy: $F(\sqrt{s}=56 {\rm GeV}) \simeq 22%$, while $F(\sqrt{s}=130 {\rm GeV}) \simeq 37 %$. This indicates a rapid increase in the density of the produced particles. We outline the predictions of high density QCD for the centrality, energy, and atomic number dependence of hadron production. Surprisingly, the predictions of the conventional eikonal approach and of high density QCD for centrality dependence of hadron multiplicity at $\sqrt{s}=130 {\rm GeV}$ appear very similar.

nucl-th↗
arXiv2001

Buckyballs of QCD: gluon junction networks

We propose that femto scale QCD analogs of Fullerene type excitations may exist with ``magic numbers'' 8,24,48, and 120. These ``J-balls'' are the most symmetrical closed networks of gluonic baryon junctions and anti-junctions with zero net baryon number. CP odd J-Moebii and other femto-tubes and tori gluonic structures may also exist. We estimate the relative binding energies and discuss possible experimental signatures of the formation of these new topological gluonic states.

hep-ph↗
arXiv2000

Soft Double-Diffractive Higgs Production at Hadron Colliders

We evaluate the non-perturbative contribution to the double-diffractive production of the Higgs boson, which arises due to the QCD scale anomaly if the mass of the Higgs M_H is smaller than the mass of the top quark M_T, M_H < M_T. The cross section appears to be larger than expected from perturbative calculations; we find σ_H = 0.019 - 0.14 pbarn at the Tevatron energy, and σ_H = 0.01 - 0.27 pbarn at the energy of the LHC.

hep-ph↗
arXiv1999

Scale Anomaly and "Soft" Pomeron in QCD

We propose a new non-perturbative approach to hadronic interactions at high energies and small momentum transfer, which is based on the scale anomaly of QCD and emphasizes the role of semi-classical vacuum fields. We find that the hadron scattering amplitudes exhibit Regge behavior and evaluate the intercept alpha(0) of the corresponding trajectory. Both the intercept and the scale for the slope of the trajectory appear to be determined by the energy density of non-perturbative QCD vacuum (the gluon condensate). Numerically, we find Delta = alpha(0) - 1 = 0.08 -0.1, consistent with the values ascribed phenomenologically to the ``soft'' Pomeron. For arbitrary numbers of colors N_c and flavors N_f, Delta is found to be proportional to (N_f/N_c)^2; however, in the large N_c (N_f fixed) limit, Delta \sim N_c^0.

hep-ph↗