CERN Accelerating science

CMS Note
Report number	CMS-CR-2012-256
Title	Studies of the nuclear stopping power in PbPb collisions at 2.76 TeV with CMS
Author(s)	Wohrmann, Clemens (Karlsruhe U., EKP)
Publication	2012
Collaboration	CMS Collaboration
Imprint	05 Oct 2012
Number of pages	5
Presented at	23rd International Conference on Ultrarelativistic Nucleus-Nucleus Collisions, Washington, DC, USA, 13 - 18 Aug 2012
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LHC ; CMS
Keywords	General
Abstract	The energy flow at very high pseudorapidity in PbPb collisions is sensitive to the very low-x components of the nuclear wave-function. The CASTOR calorimeter extends the pseudorapidity coverage of CMS to -6.6, which is only 1.4 units away from the beam rapidity. A comparison of the centrality dependence of forward energy flow to that at lower pseudorapidities can shed light on the gluon saturation at low-x. This problem can also be approached by a direct comparison of PbPb and pp energy flow in the forward region. This analysis is based on data taken in 2010. The energy flow in the pseudorapidity range of -5.2 to -6.6 has been measured for 2.76 TeV PbPb collisions over a wide range of centrality and also for minium bias pp collisions. These data are compared to energy-flow measurements for pseudorapidities between -5.2 and +5.2. The very large angular coverage of the CMS detector allows for a test of limiting fragmentation of energy flow, and for an estimate of nuclear stopping. Finally, these data are compared to predictions of hydrodynamic models and microscopic event generators.
Copyright/License	Preprint: (License: CC-BY-4.0)