Centrality and pseudorapidity dependence of the transverse energy density in p Pb collisions at √{sN N}=5.02 TeV

The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, E_T, over 13.2 units of pseudorapidity, η , for p Pb collisions at a center-of-mass energy per nucleon pair of √{s_NN}=5.02TeV . The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 <η <-5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias p Pb collisions the maximum value of d E_T/d η is 22 GeV , which implies an E_T per participant nucleon pair comparable to that of peripheral PbPb collisions at √{s _NN}=2.76 TeV . The increase of d E_T/d η with centrality is much stronger for the lead-going side than for the proton-going side. The η dependence of d E_T/d η is sensitive to the η range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the η and centrality dependence of the data and the correlations observed between different η regions.