Thermal photons from fluctuating initial conditions

Event-by-event fluctuations of initial QCD-matter density produced in heavy-ion collisions at RHIC enhance the production of thermal photons significantly in the region $2 \le p_T \le 4$ GeV/$c$ compared to a smooth initial-state averaged profile in the ideal hydrodynamic calculation. This enhancement is a an early time effect due to the presence of hotspots or over-dense regions in the fluctuating initial state. The effect of fluctuations is found to be stronger in peripheral than in central collisions.Comment: 4 pages, 3 figures. Talk given at Quark Matter 2011, 22-28 May 2011, Annecy, Franc

Systematics of parton-medium interaction from RHIC to LHC

Despite a wealth of experimental data for high-P_T processes in heavy-ion collisions, discriminating between different models of hard parton-medium interactions has been difficult. A key reason is that the pQCD parton spectrum at RHIC is falling so steeply that distinguishing even a moderate shift in parton energy from complete parton absorption is essentially impossible. In essence, energy loss models are effectively only probed in the vicinity of zero energy loss and, as a result, at RHIC energies only the pathlength dependence of energy loss offers some discriminating power. At LHC however, this is no longer the case: Due to the much flatter shape of the parton p_T spectra originating from 2.76 AGeV collisions, the available data probe much deeper into the model dynamics. A simultaneous fit of the nuclear suppression at both RHIC and LHC energies thus has great potential for discriminating between various models that yield equally good descriptions of RHIC data alone.Comment: Talk given at Quark Matter 2011, 22-28 May 2011, Annecy, Franc

Elliptic flow from event-by-event hydrodynamics

We present an event-by-event hydrodynamical framework which takes into account the initial density fluctuations arising from a Monte Carlo Glauber model. The elliptic flow is calculated with the event plane method and a one-to-one comparison with the measured event plane $v_2$ is made. Both the centrality- and $p_T$-dependence of the $v_2$ are remarkably well reproduced. We also find that the participant plane is a quite good approximation for the event plane.Comment: 4 pages, 3 figures. Talk given at Quark Matter 2011, 22-28 May 2011, Annecy, Franc

Energy loss in a fluctuating hydrodynamical background

Recently it has become apparent that event-by-event fluctuations in the initial state of hydrodynamical modelling of ultrarelativistic heavy-ion collisions are crucial in order to understand the full centrality dependence of the elliptic flow coefficient v_2. In particular, in central collisions the density fluctuations play a major role in generating the spatial eccentricity in the initial state. This raises the question to what degree high P_T physics, in particular leading-parton energy loss, which takes place in the background of an evolving medium, is sensitive to the presence of the event-by-event density fluctuations in the background. In this work, we report results for the effects of fluctuations on the nuclear modification factor R_AA in both central and noncentral sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC. Two different types of energy-loss models, a radiative and an elastic, are considered. In particular, we study the dependence of the results on the assumed spatial size of the density fluctuations, and discuss the angular modulation of R_AA with respect to the event plane.Comment: 9 pages, 9 figure

Elliptic flow of thermal photons in heavy-ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

Peer reviewe

An 854-year tree-ring chronology of Scots pine for south-west Finland

A near-mil len nial tree-ring chro nol ogy (AD 1147–2000) is pre sented for south-west Fin land and an a lyzed us ing dendroclimatic meth ods. This is a com pos ite chro nol ogy com pris ing sam ples both from stand ing pine trees (Pinus sylvestris L.) and subfossil trunks as re cov ered from the lake sed i ments, with a to tal sam ple size of 189 tree-ring sample se ries. The se ries were dendrochronologically cross-dated to ex act cal en dar years to por tray vari abil ity in tree-ring widths on inter-an nual and lon ger scales. Al though the stud ied chro nol ogy cor re lates sta tis ti cally sig nif i cantly with other long tree-ring width chro nol o gies from Fin land over their com mon pe riod (AD 1520–1993), the south-west chro nol ogy did not ex hibit sim i larly strong mid-sum mer tem per a ture or spring/early-sum mer pre cip i ta tion sig nals in com par i son to pub lished chro nol o gies. On the other hand, the south-west chro nol ogy showed high est cor re la tions to the North At lan tic Os cil la tion in di ces in win ter/spring months, this as so ci a tion fol low ing a dendroclimatic fea ture com mon to pine chro nol o gies over the re gion and ad ja cent ar eas. Paleoclimatic com par i son showed that tree-rings had var ied sim i larly to cen tral Eu ro pean spring tem per a tures. It is pos tu lated that the col lected and dated tree-ring ma te rial could be stud ied for wood sur face reflectance (blue chan nel light in ten sity) and sta ble iso topes, which both have re - cently shown to cor re late notably well with sum mer tem per a tures