Abstract
The pseudorapidity density of charged particles, dN_{ch}/dη, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02 TeV. For the 5% most central collisions, we measure a value of 1943±54. The rise in dN_{ch}/dη as a function of sqrt[s_{NN}] is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dN_{ch}/dη as a function of the average number of participant nucleons, ⟨N_{part}⟩, calculated in a Glauber model, is compared with the previous measurement at sqrt[s_{NN}]=2.76 TeV. A constant factor of about 1.2 describes the increase in dN_{ch}/dη from sqrt[s_{NN}]=2.76 to 5.02TeV for all centrality classes, within the measured range of 0%-80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.
Highlights
The pseudorapidity density measured at a center-of-mass collisions, we measure a value ooeffn1ec9rhg4ay3rgÆpeed5r p4na.urTtcihlceeloernsi,sepdaNinircdho=Nfdcηph,=ffisdaffiffiNtffiηffiNffimffias1⁄4idar5afu.p0ni2dcitTtiyoenVino. fPFpbo-ffisrPffiffiNffibtffiNhffiffifficeios5lsl%itseieompneosrshtthacasenbntethreaantl observed in proton-proton collisions and follows the trend established by measurements at lower energy
Its dependence on the impact parameter is sensitive to the interplay between particle production from hard and soft processes and coherence effects between individual nucleon-nucleon scatterings
Per in nucleon center-of-mass November 2015. This energy is the highest energy achieved in the laboratory to date and offers tmhoedeplossbsiybislittuydytiongfuthrtehirerpcffisffioffiNffiffinNffiffistdraeipnenpdaerntcicel.e production Collisions of extended objects such as nuclei can be classified according to their centrality, which is related to the overlap area of the nuclei
Summary
The pseudorapidity density measured at a center-of-mass collisions, we measure a value ooeffn1ec9rhg4ay3rgÆpeed5r p4na.urTtcihlceeloernsi,sepdaNinircdho=Nfdcηph,=ffisdaffiffiNtffiηffiNffimffias1⁄4idar5afu.p0ni2dcitTtiyoenVino. fPFpbo-ffisrPffiffiNffibtffiNhffiffifficeios5lsl%itseieompneosrshtthacasenbntethreaantl observed in proton-proton collisions and follows the trend established by measurements at lower energy. In this Letter, we present the measurement of the charged-particle pseudorapidity density averaged in the interval jηj < 0.5, hdNch=dηi, and its centrality dependence. The V0 detectors provide a signal proportional to the number of charged particles striking them which is used to classify the events into centrality classes, defined in terms of percentiles of the hadronic cross section.
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