Gluon contribution to open heavy-meson production in heavy-ion collisions

A sizable contribution to heavy quark production in high-energy hadronic and nuclear collisions comes from heavy quark-antiquark pair production from gluon splitting during the parton shower evolution. We investigate the effect of gluon-medium interaction on open heavy flavor spectra in ultra-relativistic heavy-ion collisions. The interaction of hard gluons and heavy quarks with the hot QCD medium is simulated by utilizing a Langevin transport model that simultaneously incorporates contributions from collisional and radiative processes. It is found that while the gluon splitting channel has quite an important contribution to the single $D$ meson production cross section, its influence on the final heavy meson nuclear modification turns out to be quite modest because the average lifetime of hard gluons is short before splitting into heavy quark-antiquark pairs during the evolution and propagation of the parton shower.Comment: 5 pages, 6 figure

A FRESH PERSPECTIVE ON U.S. MUTUAL FUNDS’ PERFORMANCE ATTRIBUTION, FACTOR MODEL AND QMJ

In this paper we evaluate the performance of the US mutual fund industry over the past 15 years, using a novel methodology developed by AQR Management’s Quality Minus Junk paper (2013). We augment the standard regression models of Fama-French used in the literatures with a new factor, the Quality Minus Junk factor, which is a quality-ranking factor developed by the AQR Management. (Quality Minus Junk) 2013 Previously, conflicting evidence was recorded with regard to the merits of the mutual fund industry, and we believe this could be a result of the preceding researches were constructed based on the Fama–French three-factor model (FFM) and its various variations. Despite the FFM’s prominent position in the asset-pricing field, it is subject to one critical limitation when it comes to evaluating active returns; no meaningful factor to directly quantify and evaluate the effects of active returns, as all existing factors are systematic in nature while active returns are idiosyncratic in nature largely. By incorporating the QMJ factor in the FFM framework, we hope to help investors better understanding their actively managed portfolios, as this unique factor is constructed based on four profoundly used fundamental metrics by the investment industry. We are still unable to use this factor to underpin the mutual industry as our results exhibit inconsistencies in the QMJ loadings despite QMJ’s strong statistic and theatrical supports. Adding the Market-Factor results in the QMJ factor insignificant 70% of the time, adding more of the standard-factors we see that only 50% of the time the QMJ loadings are significant, around 40% of the time the QMJ loadings are in the negative zone. Therefore, we believe this shows inconsistence in QMJ’s factor loadings. Furthermore, we identified consistent alphas (intercepts) in our regressions and we believe that combining Fama-French and QMJ factor still cannot explain all returns variations

Parton Energy Loss and the Generalized Jet Transport Coefficient

We revisit radiative parton energy loss in deeply inelastic scattering (DIS) off a large nucleus within the perturbative QCD approach. We calculate the gluon radiation spectra induced by double parton scattering in DIS without collinear expansion in the transverse momentum of initial gluons as in the original high-twist approach. The final radiative gluon spectrum can be expressed in terms of the convolution of hard partonic parts and unintegrated or transverse momentum dependent (TMD) quark-gluon correlations. The TMD quark-gluon correlation can be factorized approximately as a product of initial quark distribution and TMD gluon distribution which can be used to define the generalized or TMD jet transport coefficient. Under the static scattering center and soft radiative gluon approximation, we recover the result by Gylassy-Levai-Vitev (GLV) in the first order of the opacity expansion. The difference as a result of the soft radiative gluon approximation is investigated numerically under the static scattering center approximation.Comment: 33 pages in RevTeX with 30 figures, final version appeared in PRD with additional typos correcte