The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, ...AuAu-->Au*Au*rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrts(NN)=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes.
Performance of prototypes for the ALICE electromagnetic calorimeter Allen, J.; Awes, T.; Badalá, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2010, Letnik:
615, Številka:
1
Journal Article
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The performance of prototypes for the ALICE electromagnetic sampling calorimeter has been studied in test beam measurements at FNAL and CERN. A
4
×
4
array of final design modules showed an energy ...resolution of about
11
%
/
E
(
GeV
)
⊕
1.7
%
with a uniformity of the response to electrons of 1% and a good linearity in the energy range from 10 to 100
GeV. The electromagnetic shower position resolution was found to be described by
1.5
mm
⊕
5.3
mm
/
E
(
GeV
)
. For an electron identification efficiency of 90% a hadron rejection factor of
>
600
was obtained.
We report measurements of the nuclear modification factor R_{CP} for charged hadrons as well as identified π^{+(-)}, K^{+(-)}, and p(pover ¯) for Au+Au collision energies of sqrts_{NN}=7.7, 11.5, ...14.5, 19.6, 27, 39, and 62.4 GeV. We observe a clear high-p_{T} net suppression in central collisions at 62.4 GeV for charged hadrons which evolves smoothly to a large net enhancement at lower energies. This trend is driven by the evolution of the pion spectra but is also very similar for the kaon spectra. While the magnitude of the proton R_{CP} at high p_{T} does depend on the collision energy, neither the proton nor the antiproton R_{CP} at high p_{T} exhibit net suppression at any energy. A study of how the binary collision-scaled high-p_{T} yield evolves with centrality reveals a nonmonotonic shape that is consistent with the idea that jet quenching is increasing faster than the combined phenomena that lead to enhancement.
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