Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1205.5759

Measurement of Direct Photons in Au+Au Collisions at sqrt(s_NN) = 200 GeV

S. Afanasiev·C. Aidala·N. N. Ajitanand·Y. Akiba·A. Al-Jamel·J. Alexander·K. Aoki·L. Aphecetche·R. Armendariz·S. H. Aronson·R. Averbeck·T. C. Awes·B. Azmoun·V. Babintsev·A. Baldisseri·K. N. Barish·P. D. Barnes·B. Bassalleck·S. Bathe·S. Batsouli·V. Baublis·F. Bauer·A. Bazilevsky·S. Belikov·R. Bennett·Y. Berdnikov·M. T. Bjorndal·J. G. Boissevain·H. Borel·K. Boyle·M. L. Brooks·D. S. Brown·D. Bucher·H. Buesching·V. Bumazhnov·G. Bunce·J. M. Burward-Hoy·S. Butsyk·S. Campbell·J. -S. Chai·S. Chernichenko·C. Y. Chi·J. Chiba·M. Chiu·I. J. Choi·T. Chujo·V. Cianciolo·C. R. Cleven·Y. Cobigo·B. A. Cole·M. P. Comets·M. Connors·P. Constantin·M. Csanád·T. Csörgő·T. Dahms·K. Das·G. David·H. Delagrange·A. Denisov·D. d'Enterria·A. Deshpande·E. J. Desmond·O. Dietzsch·A. Dion·J. L. Drachenberg·O. Drapier·A. Drees·A. K. Dubey·A. Durum·V. Dzhordzhadze·Y. V. Efremenko·J. Egdemir·A. Enokizono·H. En'yo·B. Espagnon·S. Esumi·D. E. Fields·F. Fleuret·S. L. Fokin·B. Forestier·Z. Fraenkel·J. E. Frantz·A. Franz·A. D. Frawley·Y. Fukao·S. -Y. Fung·S. Gadrat·F. Gastineau·M. Germain·A. Glenn·M. Gonin·J. Gosset·Y. Goto·R. Granier de Cassagnac·N. Grau·S. V. Greene·M. Grosse Perdekamp·T. Gunji·H. -Å. Gustafsson
View original source ↗Read source document ↗Export metadata ↓

Abstract

We report the measurement of direct photons at midrapidity in Au+Au collisions at sqrt{s_NN} = 200 GeV. The direct photon signal was extracted for the transverse-momentum range of 4 GeV/c < p_T < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive-photon sample. The direct-photon nuclear-modification factor R_AA was calculated as a function of p_T for different Au+Au collision centralities using the measured p+p direct-photon spectrum and compared to theoretical predictions. R_AA was found to be consistent with unity for all centralities over the entire measured p_T range. Theoretical models that account for modifications of initial-direct-photon production due to modified-parton-distribution functions in Au and the different isospin composition of the nuclei, predict a modest change of R_AA from unity and are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.

Explore related subjects

nucl-ex

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, A. Al-Jamel, J. Alexander, K. Aoki, L. Aphecetche, R. Armendariz, S. H. Aronson, R. Averbeck, T. C. Awes, B. Azmoun, V. Babintsev, A. Baldisseri, K. N. Barish, P. D. Barnes, B. Bassalleck, S. Bathe, S. Batsouli, V. Baublis, F. Bauer, A. Bazilevsky, S. Belikov, R. Bennett, Y. Berdnikov, M. T. Bjorndal, J. G. Boissevain, H. Borel, K. Boyle, M. L. Brooks, D. S. Brown, D. Bucher, H. Buesching, V. Bumazhnov, G. Bunce, J. M. Burward-Hoy, S. Butsyk, S. Campbell, J. -S. Chai, S. Chernichenko, C. Y. Chi, J. Chiba, M. Chiu, I. J. Choi, T. Chujo, V. Cianciolo, C. R. Cleven, Y. Cobigo, B. A. Cole, M. P. Comets, M. Connors, P. Constantin, M. Csanád, T. Csörgő, T. Dahms, K. Das, G. David, H. Delagrange, A. Denisov, D. d'Enterria, A. Deshpande, E. J. Desmond, O. Dietzsch, A. Dion, J. L. Drachenberg, O. Drapier, A. Drees, A. K. Dubey, A. Durum, V. Dzhordzhadze, Y. V. Efremenko, J. Egdemir, A. Enokizono, H. En'yo, B. Espagnon, S. Esumi, D. E. Fields, F. Fleuret, S. L. Fokin, B. Forestier, Z. Fraenkel, J. E. Frantz, A. Franz, A. D. Frawley, Y. Fukao, S. -Y. Fung, S. Gadrat, F. Gastineau, M. Germain, A. Glenn, M. Gonin, J. Gosset, Y. Goto, R. Granier de Cassagnac, N. Grau, S. V. Greene, M. Grosse Perdekamp, T. Gunji, H. -Å. Gustafsson. 2012-05-25. Measurement of Direct Photons in Au+Au Collisions at sqrt(s_NN) = 200 GeV. https://doi.org/10.1103/physrevlett.109.152302

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Measurements of $γ_v p \to π^+ π^-p'$ Cross Sections with the CLAS12 Detector for $Q^2$ from 2.4-8.0 GeV$^2$ and $W$ from 1.4-2.1 GeV

This paper reports exclusive cross sections for the $ep \to e'π^+π^-p'$ reaction using the CLAS12 detector at Jefferson Laboratory. The extractions of fully integrated and nine single-differential cross sections are presented for the first time for photon virtualities $Q^2$ from 2.4 to 8.0 GeV$^2$ and center-of-mass energies $W$ from 1.4 to 2.1 GeV, which covers a large part of the nucleon resonance region. These data considerably extend the kinematic reach of previous measurements from CLAS that covered $Q^2$ up to 5.0 GeV$^2$. Exclusive $γ_v p \to π^+ π^-p'$ cross section measurements are of particular importance for the extraction of $γ_vpN^*$ resonance electrocouplings across the $N^*$ spectrum, especially in the mass range above 1.6 GeV where several resonances decay preferentially to the $ππN$ final states. The electrocouplings with extended $Q^2$ coverage expected from these new data will enable an improved understanding of the emergence of $N^*$ mass and structure in the transition from the strongly coupled toward the perturbative QCD regime.

nucl-ex↗
arXiv2026

Direct measurement of Enhanced octupole collectivity in 148Dy

Excited states in $^{148}_{~66}$Dy were populated via $β^+/EC$ decay of $^{148m}$Ho using the GRIFFIN spectrometer at the TRIUMF ISAC-I facility. A combined measurement of the mean lifetime of the $3_1^-$ level using the Generalized Centroid Difference (GCD) method and branching fraction of the $3_1^-\rightarrow0_1^+$ $γ$-ray decay has been performed. From these results, an enhanced electric octupole $B(E3;3_1^-\rightarrow0_1^+)$ transition strength of 46(3)~W.u. has been determined in $^{148}_{~66}$Dy. This is the largest measured value across the closed neutron shell at $N=82$ and provides direct evidence of enhanced octupole collectivity beyond $Z=64$. The evolution of the $B(E3; 3^-_1 \rightarrow 0^+_1)$ strength along the $N=82$ isotonic chain is compared with quasiparticle random-phase approximation (QRPA) calculations using the SkI3 and SkM$^*$ Skyrme energy-density functionals, as well as with large-scale shell-model (SM) calculations. This result extends the boundaries of enhanced octupole collectivity far from the so-called `octupole magic numbers' $Z=56$ and $N=88$.

nucl-ex↗
arXiv2026

First observation of the fine structure of the Pygmy Dipole Resonance in a nucleus away from stability via the $β^-$ decay of $^{92}$Rb to $^{92}$Sr

A comprehensive $γ$-ray spectroscopy study of excited states in $^{92}$Sr populated via $β^-$ decay of $^{92}$Rb ($J^π=0^-$, $Q_β=8095(6)$~keV) was performed with the GRIFFIN spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high $γ$-ray efficiency of the GRIFFIN spectrometer combined with the intense rubidium beams produced allowed for 864 $γ$-ray transitions to be placed in the level scheme with 190 excited levels populated, most of them identified for the first time. The excitation energies of low-spin states in $^{92}$Sr are well reproduced by large-scale Shell Model calculations up to 5~MeV. The $β$-feeding intensities are in very good agreement with results from a recent study employing Modular Total Absorption Spectroscopy, indicating a significant suppression of the Pandemonium effect. The experimental picture reveals the energy level dependence of log~$ft$ values in unprecedented detail. These log~$ft$ values are well reproduced by Multiple-Commutator Model calculations that identify the features in the excited levels' wavefunctions that enable the population of high-lying levels with a low effective Q-value that belong to the Pygmy Dipole Resonance.

nucl-ex↗