Is a physical quantity or just a parameter? and other unanswered questions in high-pT physics

10th International Workshop on High-pT Physics in the RHIC/LHC Era

Tannenbaum, M.J.^1

Physics Department, Brookhaven National Laboratory, Upton

NY

11973-5000, United States^1

关键词: Azimuthal correlations;    Forward energy;    Parton energy loss;    Per unit length;    Physical quantities;    Theoretical study;    Total energy loss;    Transport coefficient;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/805/1/012005/pdf
DOI  :  10.1088/1742-6596/805/1/012005

来源: IOP

【 摘 要 】

The many different theoretical studies of energy loss of a quark or gluon traversing a medium have one thing in common: the transport coefficient of a gluon in the medium, denoted q, which is defined as the mean 4-momentum transfer-square, q2, by a gluon to the medium per gluon mean free path, λmfp. In the original BDMPSZ formalism, the energy loss of an outgoing parton, -dE/dx, per unit length (x) of a medium with total length L, due to coherent gluon bremsstrahlung is proportional to the q2and takes the form: where μ, is the mean momentum transfer per collision. Thus, the total energy loss in the medium goes like L2. Additionally, the accumulated momentum-square, , transverse to a gluon traversing a length L in the medium is well approximated by . A simple estimate shows that the should be observable at RHIC at via the broadening of di-hadron azimuthal correlations resulting in an azimuthal width larger in Au+Au than in p + p collisions. Measurements relevant to this issue will be discussed as well as recent STAR jet results presented at QM2014 [1]. Other topics to be discussed include the danger of using forward energy to define centrality in p(d)+A collisions for high pTmeasurements, the danger of not using comparison p + p data at the same in the same detector for RAAor lately for RpAmeasurements. Also, based on a comment at last year's 9th workshop that the parton energy loss is proportional to dNch/dη [2], new results on the dependence of the shift in the pTspectra in A+A collisions from the TAA-scaled p + p spectrum (to be discussed in detail in another presentation [3]) will be shown.