Simon Wicks

Influence of bottom quark jet quenching on single electron tomography of Au + Au

Influence of Bottom Quark Jet Quenching on Single Electron Tomography of Au+Au Magdalena Djordjevic, 1 Miklos Gyulassy, 1 Ramona Vogt, 2 and Simon Wicks 1 Department of Physics, Columbia University, 538 West 120-th Street, New York, NY 10027 Nuclear Science Division, LBNL, Berkeley, CA 94720 and Physics Department, University of California, Davis, California 95616 (Dated: July 21, 2005) High transverse momentum single (non-photonic) electrons are shown to be sensitive to the stop- ping power of both bottom, b, and charm, c, quarks in AA collisions. We apply the DGLV theory of radiative energy loss to predict c and b quark jet quenching and compare the FONLL and PYTHIA heavy flavor fragmentation and decay schemes. We show that single electrons in the p T = 5 − 10 GeV range are dominated by the decay of b quarks rather than the more strongly quenched c quarks in Au+Au collisions at s = 200 AGeV. The smaller b quark energy loss, even for extreme opacities with gluon rapidity densities up to 3500, is predicted to limit the nuclear modification factor, R AA , of single electrons to the range R AA ∼ 0.5−0.6, in contrast to previous predictions of R AA 3 GeV in pp collisions. In this letter, we show that jet quenching further amplifies the b contribution to the lepton spectrum and strongly limits the nuclear modification factor of electrons in AA collisions. The preliminary electron data [24]-[25] are so surpris- ing that novel jet energy loss mechanisms may have to be postulated [28]-[31]. The elliptic flow of high p T heavy quarks can be accounted for, e.g., if the elastic cross sec- tions of all partons, including bottom, are assumed to be anomalously enhanced to > 20 mb, far in excess of per- turbative QCD predictions, up to at least p T ∼ 10 GeV. While these enhanced cross sections could lead to heavy flavor elliptic flow at the pion level even at high p T , they may greatly overestimate the attenuation of light and heavy flavored hadrons [31]-[33]. Given the critical role that single electron tomography of the sQGP may play in the near future, it is especially important to scrutinize the theoretical uncertainties and robustness of current predictions. This is the aim of this letter. Theoretical framework. The calculation of the lepton spectrum includes initial

A theory of jet shapes and cross sections: from hadrons to nuclei

For jets, with great power comes great opportunity. The unprecedented center of mass energies available at the LHC open new windows on the QGP: we demonstrate that jet shape and jet cross section measurements become feasible as a new, differential and accurate test of the underlying QCD theory. We present a first step in understanding these shapes and cross sections in heavy ion reactions. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets in such high-multiplicity environment. It is demonstrated for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model-independent approach to determining the characteristics of the medium-induced bremsstrahlung spectrum. Surprisingly, in realistic simulations of parton propagation through the QGP we find a minimal increase in the mean jet radius even for large jet attenuation. Jet broadening is manifest in the tails of the energy distribution away from the jet axis and its quantification requires high statistics measurements that will be possible at the LHC.

Open Charm and Beauty at Ultrarelativistic Heavy Ion Colliders

Important goals of BNL RHIC and CERN LHC experiments with ion beams include the creation and study of new forms of matter, such as the quark gluon plasma. Heavy quark production and attenuation provide unique tomographic probes of that matter. We predict the suppression pattern of open charm and beauty in Au+Au collisions at RHIC and LHC energies based on the DGLV formalism of radiative energy loss. A cancellation between effects due to the sqrt[s] energy dependence of the high p(T) slope and heavy quark energy loss is predicted to lead to surprising similarity of heavy quark suppression at RHIC and LHC.

Heavy Quark Jet Quenching with Collisional plus Radiative Energy Loss and Path Length Fluctuations

Abstract With the QGP opacity computed perturbatively and with the global entropy constraints imposed by the observed d N c h / d y ≈ 1000 , radiative energy loss alone cannot account for the observed suppression of single non-photonic electrons. We show that collisional energy loss, which previously has been neglected, is comparable to radiative loss for both light and heavy jets and may in fact be the dominant mechanism for bottom quarks. Predictions taking into account both radiative and collisional losses significantly reduce the discrepancy with data. In addition to elastic energy loss, it is critical to include jet path length fluctuations to account for the observed pion suppression.

Improving a radiative plus collisional energy loss model for application to RHIC and LHC

With the QGP opacity computed perturbatively and with the global entropy constraints imposed by the observed dN ch /dy ≈ 1000, radiative energy loss alone cannot account for the observed suppression of single non-photonic electrons. Collisional energy loss is comparable in magnitude to radiative loss for both light and heavy jets. Two aspects that significantly affect the collisional energy loss are examined: the role of fluctuations and the effect of introducing a running QCD coupling as opposed to the fixed α S = 0.3 used previously.

The theory and phenomenology of jets in nuclear collisions

We report selected results from a recent in-depth study of jet shapes and jet cross sections in ultra-relativistic reactions with heavy nuclei at the LHC. We demonstrate that at the highest collider energies these observables become feasible as a new, differential and accurate test of the underlying QCD theory. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets emerging from a dense QGP. We show for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model-independent approach to determining the characteristics of the medium-induced bremsstrahlung spectrum. The connection between such cross section attenuation and the in-medium jet shapes is elucidated.