811 research outputs found
Unified Description of Efficiency Correction and Error Estimation for Moments of Conserved Quantities in Heavy-Ion Collisions
We provide a unified description of efficiency correction and error
estimation for moments of conserved quantifies in heavy-ion collisions. Moments
and cumulants are expressed in terms of the factorial moments, which can be
easily corrected for the efficiency effect. By deriving the covariance between
factorial moments, one can obtain the general error formula for the efficiency
corrected moments based on the error propagation derived from the Delta
theorem. The skellam distribution based Monto Carlo simulation is used to test
the Delta theorem and Bootstrap error estimation methods. The statistical
errors calculated from the two methods can well reflect the statistical
fluctuations of the efficiency corrected moments.Comment: 23 pages, 5 figure
Proton Cumulants and Correlation Functions in Au + Au Collisions at =7.7-200 GeV from UrQMD Model
We studied the acceptance dependence of proton cumulants (up to fourth order)
and correlation functions in 0--5\% most central Au+Au collisions at
=7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV from UrQMD
model. We found that high order proton cumulants show suppressions at large
acceptance. By decomposing the proton cumulants into linear combination of
multi-proton correlation functions, we observed the two-proton correlation
functions always show negative values due to the effects of baryon number
conservations. The three and four-proton correlation functions are close to
zero and show negligible acceptance dependence. We further observed that the
proton cumulants and correlation functions follow similar trends and show a
scaling behavior when plotting the results versus mean number of protons. The
comparisons between experimental data and the UrQMD calculations show that the
non-monotonic energy dependence of proton correlation functions measured by
STAR experiment cannot be described by the UrQMD model. The UrQMD calculations
can provide us baselines for the experimental studies of the proton cumulants
and correlation functions. Finally, we propose to measure the rapidity
dependence of the reduced proton correlation functions to search for the QCD
critical point in heavy-ion collisions.Comment: 9 pages, 8 figures, Accepted by Physics Letters
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