University of Colorado, Boulder, Colorado 80309, USA.
Phys Rev Lett. 2013 Jul 19;111(3):032301. doi: 10.1103/PhysRevLett.111.032301. Epub 2013 Jul 16.
The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at √[s(NN)]=200 GeV. The p(T) of the photon is an excellent approximation to the initial p(T) of the jet and the ratio z(T)=p(T)(h)/p(T)(γ) is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I(AA), the ratio of hadron yield opposite the photon in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z(T). The associated hadron yield at low z(T) is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
采用直接光子-强子关联的方法，在质心能量为 √[s(NN)]=200GeV 的 p+p 和 Au+Au 碰撞中测量了喷注碎裂函数。光子的 p_T 非常近似于喷注的初始 p_T，比值 z_T=p_T(h)/p_T(γ) 被用作喷注碎裂函数的代理变量。在 Au+Au 碰撞中，采用统计减除方法提取直接光子-强子事例，而在 p+p 碰撞中采用光子隔离挑选。在 Au+Au 中相对于 p+p 光子横动量相反的强子事例的比度函数 I(AA) ，表明喷注碎裂函数发生了修正。在高 z_T 处观察到喷注碎裂函数的压低，这很可能是由于在介质中能量损失导致的。在大角度处，低 z_T 处的关联强子事例的产额增强。这种趋势是由于能量损失的再分布导致低动量粒子产生的增加。
