Collisional Energy Loss of Non Asymptotic Jets in a QGP

We calculate the collisional energy loss suffered by a heavy (charm) quark created at a finite time within a Quark Gluon Plasma (QGP) in the classical linear response formalism as in Peigne {\it et al.} \cite{peigne}. We pay close attention to the problem of formulating a suitable current and the isolation of binding and radiative energy loss effects. We find that unrealistic large binding effects arising in previous formulations must be subtracted. The finite time correction is shown to be important only for very short length scales on the order of a Debye length. The overall energy loss is similar in magnitude to the energy loss suffered by a charge created in the asymptotic past. This result has significant implications for the relative contribution to energy loss from collisional and radiative sources and has important ramifications for the ``single electron puzzle'' at RHIC.Comment: 15 Pages, 11 figures, revte

Open heavy flavor production at RHIC

The study of heavy flavor production in relativistic heavy ion collisions is an extreme experimental challenge but provides important information on the properties of the Quark-Gluon Plasma (QGP) created in Au+Au collisions at RHIC. Heavy-quarks are believed to be produced in the initial stages of the collision, and are essential on the understanding of parton energy loss in the dense medium created in such environment. Moreover, heavy-quarks can help to investigate fundamental properties of QCD in elementary p+p collisions. In this work we review recent results on heavy flavor production and their interaction with the hot and dense medium at RHIC.Comment: Quark Matter 2006 proceedings, 8 pages, 5 figure

Diagnosing Energy Loss: PHENIX Results on High-pT Hadron Spectra

Measurements of inclusive spectra of hadrons at large transverse momentum over a broad range of energy in different collision systems have been performed with the PHENIX experiment at RHIC. The data allow to study the energy and system size dependence of the suppression observed in RAA of high-pT hadrons at sqrt(s_NN)= 200 GeV. Due to the large energy range from sqrt(s_NN)= 22 GeV to 200 GeV, the results can be compared to results from CERN SPS at a similar energy. The large Au+Au dataset from the 2004 run of RHIC also allows to constrain theoretical models that describe the hot and dense matter produced in such collisions. Investigation of particle ratios such as eta/pi0 helps understanding the mechanisms of energy loss.Comment: 4 pages, 6 figures. To appear in the proceedings of the 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006), Shanghai, China, November 14-20, 200

Scaling anisotropy of the power in parallel and perpendicular components of the solar wind magnetic field

Power spectra of the components of the magnetic field parallel (Pzz) and perpendicular (Pzz+Pyy) to the local mean magnetic field direction were determined by wavelet methods from Ulysses’ MAG instrument data during eighteen 10-day segments of its first North Polar pass at high latitude at solar minimum in 1995. The power depends on frequency f and the angle θ between the solar wind direction and the local mean field, and with distance from the Sun. This data includes the solar wind whose total power (Pxx + Pyy + Pzz) in magnetic fluctuations we previously reported depends on f and the angle θ nearly as predicted by the GS95 critical balance model of strong incompressible MHD turbulence. Results at much wider range of frequencies during six evenly-spaced 10-day periods are presented here to illustrate the variability and evolution with distance from the Sun. Here we investigate the aniso tropic scaling of Pzz(f,θ) in particular because it is a reduced form of the Poloidal (pseudo-Alfvenic) component of the (incompressible) fluctuations. We also report the much larger Pxx(f,θ)+Pyy(f,θ) which is (mostly) reduced from the Toroidal (Alfvenic, i.e., perpendicular to both B and k) fluctuations, and comprises most of the total power. These different components of the total power evolve and scale differently in the inertial range. We compare these elements of the magnetic power spectral tensor with “critical balance” model predictions

Energy Loss of a Heavy Quark Produced in a Finite Size Medium

We study the medium-induced energy loss $-\Delta E_0(L_p)$ suffered by a heavy quark produced at initial time in a quark-gluon plasma, and escaping the plasma after travelling the distance $L_p$. The heavy quark is treated classically, and within the same framework $-\Delta E_0(L_p)$ consistently includes: the loss from standard collisional processes, initial bremsstrahlung due to the sudden acceleration of the quark, and transition radiation. The radiative loss {\it induced by rescatterings} $-\Delta E_{rad}(L_p)$ is not included in our study. For a ultrarelativistic heavy quark with momentum p \gsim 10 {\rm GeV}, and for a finite plasma with L_p \lsim 5 {\rm fm}, the loss $-\Delta E_0(L_p)$ is strongly suppressed compared to the stationary collisional contribution $-\Delta E_{coll}(L_p) \propto L_p$. Our results support that $-\Delta E_{rad}$ is the dominant contribution to the heavy quark energy loss (at least for L_p \lsim 5 {\rm fm}), as indeed assumed in most of jet-quenching analyses. However they might raise some question concerning the RHIC data on large $p_{\perp}$ electron spectra.Comment: 18 pages, 3 figures. New version clarified and simplified. A critical discussion added in section 2, and previous sections 3 and 4 have been merged together. Main results are unchange

An Experimental Overview of Results Presented at SQM 2006

I have been asked to give an critical overview on the experimental results shown in the conference with a emphasis of what has been learned and the challenges that are ahead in trying to understand the physics of the strongly interacting quark-gluon plasma. I will not try to summarize all of the results presented, rather I will concentrate primarily on RHIC data from this conference. Throughout this summary, I will periodically review some of the previous results for those not familiar with the present state of the field.Comment: 15 pages, 12 Figure

Cascading Effects and Escalations in Wide Area Power Failures: A Summary for Emergency Planners

This special report is the result of a collaboration between academics and practitioners. It aims to provide a synthetic overview of the cascading effects caused by wide-area power failures, and to define the recurrent impacts and sources of escalation. It provides a reference for the training and the situational awareness of decision makers and emergency operators. The format uses bullet points and examples to facilitate reading in conditions of limited availability of time. The following topics have been developed:- ⚫ A definition of cascading effects. ⚫ An introduction for of wide area power failures (PF) policies and practices. ⚫ Illustrative examples. ⚫ A table listing cascading effects and escalations caused by wide area PF. ⚫ Resources for training and essential references for further reading