56119429
Centrality dependence of particle production in p-Pb collisions at $\sqrt{s_{\rm NN} }$= 5.02 TeV
We report measurements of the primary charged-particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at sNN=5.02TeV and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined by using different event-activity estimators, i.e., charged-particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero degree). The procedures to determine the centrality, quantified by the number of participants (Npart) or the number of nucleon-nucleon binary collisions (Ncoll) are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy-centrality classes, the Npart dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapidity of the number of participating nucleons is observed. Furthermore, at high-pT the p-Pb spectra are found to be consistent with the pp spectra scaled by Ncoll for all centrality classes. Our results represent valuable input for the study of the event-activity dependence of hard probes in p-Pb collisions and, hence, help to establish baselines for the interpretation of the Pb-Pb data.
124087711
Gluon number fluctuations with heavy quarks at HERA
We study the effect of gluon number fluctuations (Pomeron loops) on the proton structure function at HERA. It is shown that the description of charm and bottom quarks and longitudinal structure functions are improved, with χ2/d.o.f=0.803 (fluctuations) as compared with χ2/d.o.f=0.908 (without fluctuations), once the gluon number fluctuations are included. We find that in the gluon number fluctuation case the heavy quarks do not play an important role in the proton structure function as the saturation model. The successful description of the HERA data indicates that the gluon number fluctuation could be one of the key mechanisms to describe the proton structure function at HERA energies.
119431648
Recent results on strangeness production at STAR
We report on the measurements of strange hadrons (K±, K0S, Λ, Ξ, Ω and ) production at mid-rapidity in Au+Au collisions at = 7.7 - 39 GeV from the STAR beam energy scan (BES) program. The collision energy dependence of strange hadron yields are presented. The strange hadron related particle ratios are compared with calculations from statistical and hadronic cascade models. The nuclear modification factors and baryon to meson ratios (/K0S and Ω/) are presented. The physics implications for collision dynamics are discussed.
35833011
Effect of partonic "wind" on charm quark correlations in high-energy nuclear collisions.
In high-energy collisions, massive heavy quarks are produced back to back initially and they are sensitive to early dynamical conditions. The strong collective partonic wind from the fast expanding quark-gluon plasma created in high-energy nuclear collisions modifies the correlation pattern significantly. While the hot and dense medium in collisions at the BNL Relativistic Heavy Ion Collider (sqrt[_s{NN}]=200 GeV) can only smear the initial back-to-back D_D correlation, a clear and strong near side D_D correlation is expected at the CERN Large Hadron Collider (sqrt[_s{NN}]=5500 GeV). This is considered as a signature for the strongly coupled quark-gluon plasma.
119109800
Study on the production of the subpicosecond electron bunch
The production of the high brightness femtosecond electron bunch is now one of the hot research topics. This paper describes one electron linac facility used to produce the subpicosecond electron bunch. We analyze the main structure parameters, and study the beam dynamics of the facility. Finally, we discuss the application of this facility in Compton scattering.
118151735
Scaling Law of Beam Break-Up for the Single Ultrashort Bunch in RF Linac
Femtosecond bunch is a hot topic in the present world accelerator research community. The high peak current bunch will lead to the beam breakup phenomenon. In this paper, the scaling law with current for the single ultrashort bunch beam breakup in the radio frequency linear accelerator is proposed and obtained. The scaling power factor is roughly estimated to be 1/6, 1/6 and 1/3 for the geometry wake, the surface roughness wake and the resistance wake respectively.