119237028
Jet Production in p-Pb Collisions
One of the major results from the study of high energy heavy ion collisions is the observation of jet quenching. The suppression of the number of jets observed in heavy ion collisions relative to pp collisions at the same energy scaled by the number of binary collisions, is attributed to partonic energy loss in the quark gluon plasma (QGP). However, cold nuclear matter effects due to the presence of a nucleus in the initial state could also influence this measurement. To disentangle these effects p-Pb collisions are studied, where QGP formation is not expected to occur and only cold nuclear matter effects are present. In addition to being an important baseline for understanding jet quenching, jets in p-Pb collisions may also be used to provide constraints on the nuclear parton distribution functions. Fully reconstructed jets measured using the ALICE tracking system and electro-magnetic calorimeter in p-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are reported. In addition to the spectra, studies of the jet fragmentation behavior in p-Pb collisions are also presented.
119653633
Jet-Hadron Correlations in pp and Pb-Pb Collisions with ALICE
Jet quenching has been observed at both RHIC and LHC energies, indicating that partons lose energy as they traverse the medium. To probe the effects of this partonic energy loss, measurements of the angular correlations between fully reconstructed jets and charged tracks in Pb-Pb collisions are studied. Fully reconstructing a jet provides access to the kinematics of the initial hard scattering while allowing us to study the distribution of hadrons on the away side from the modified recoil jet. Here we present first measurements of jet-hadron correlations in pp collisions at =2.76 TeV and an outlook for Pb-Pb collisions. The jets in this analysis are reconstructed from the 2011 data set using both charged tracks and neutral energy measured in the ALICE tracking system and the electromagnetic calorimeter respectively.
15012044
Direct Photon-Hadron Correlations Measured with PHENIX
Abstract Direct photon-hadron correlations greatly improve our ability to perform jet tomography in heavy-ion collisions because the momentum of the direct photon can be used to constrain the initial momentum of the opposing jet. By comparing the spectrum of away-side hadrons observed in heavy ion collisions to the spectrum seen in nucleon collisions we can quantify the medium modification to the fragmentation function due to energy loss of the away-side parton. High p T direct photon-hadron correlations have been measured with the PHENIX detector using a statistical subtraction method to remove the photon contribution from meson decays. The increased integrated luminosity in the most recent Au+Au RHIC run at s N N = 200 GeV provides substantially improved statistical precision and enhances the kinematic reach. These measurements are compared to PHENIX p+p results and several theoretical models of energy loss. In addition, we compare direct photon-hadron and π 0 -hadron correlations.
121607826
Direct photon-hadron correlations measured with the PHENIX detector
Photon tagged jets are an excellent probe of the hot dense matter created in heavy ion collisions at RHIC. Since photons interact weakly and are not modified by the strongly coupled medium, the measured photon momentum approximately balances that of the away-side parton. Therefore, the modification of the fragmentation function can be obtained by comparing the spectra of the away-side yields in direct photon-hadron correlations in Au+Au collisions to those in p+p. Direct photon-hadron correlations are measured with the PHENIX detector in p+p and Au+Au collisions at sNN=200GeV at RHIC. We employ a statistical subtraction method to remove the contribution of decay photons from the inclusive photon-hadron correlations. For the p+p analysis, we developed event by event techniques to improve the systematic uncertainty in the baseline measurement. Compared to previous measurements, this Au+Au result extends to higher ξ (lower zT) where a medium-induced modification of jet fragmentation is observed.
54937918
Evidence for a Color Dependence in the Size Distribution of Main-Belt Asteroids
We present the results of a project to detect small (~1 km) main-belt asteroids with the 3.6 m Canada-France-Hawaii Telescope. We observed in two filters (MegaPrime g' and r') in order to compare the results in each band. Owing to the observational cadence we did not observe the same asteroids through each filter and thus do not have true color information. However, strong differences in the size distributions as seen in the two filters point to a color dependence at these sizes, perhaps to be expected in this regime, in which asteroid cohesiveness begins to be dominated by physical strength and composition rather than by gravity. The best-fit slopes of the cumulative size distributions (CSDs) in both filters tend toward lower values for smaller asteroids, consistent with the results of previous studies. In addition to this trend, the size distributions seen in the two filters are distinctly different, with steeper slopes in r' than in g'. Breaking our sample up according to semimajor axis, the difference between the filters in the inner belt is found to be somewhat less pronounced than in the middle and outer belt, but the CSD of those asteroids seen in the r' filter is consistently and significantly steeper than in g' throughout. The CSD slopes also show variations with semimajor axis within a given filter, particularly in r'. We conclude that the size distribution of main-belt asteroids is likely to be color-dependent at kilometer sizes and that this dependence may vary across the belt.