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arXiv · 1805.04084

Beam-energy and centrality dependence of direct-photon emission from ultra-relativistic heavy-ion collisions

A. Adare·S. Afanasiev·C. Aidala·N. N. Ajitanand·Y. Akiba·R. Akimoto·H. Al-Bataineh·J. Alexander·M. Alfred·A. Al-Jamel·H. Al-Ta'ani·A. Angerami·K. Aoki·N. Apadula·L. Aphecetche·Y. Aramaki·R. Armendariz·S. H. Aronson·J. Asai·H. Asano·E. C. Aschenauer·E. T. Atomssa·R. Averbeck·T. C. Awes·B. Azmoun·V. Babintsev·A. Bagoly·M. Bai·G. Baksay·L. Baksay·A. Baldisseri·B. Bannier·K. N. Barish·P. D. Barnes·B. Bassalleck·A. T. Basye·S. Bathe·S. Batsouli·V. Baublis·F. Bauer·C. Baumann·S. Baumgart·A. Bazilevsky·S. Belikov·R. Belmont·R. Bennett·A. Berdnikov·Y. Berdnikov·J. H. Bhom·A. A. Bickley·M. T. Bjorndal·D. S. Blau·M. Boer·J. G. Boissevain·J. S. Bok·H. Borel·K. Boyle·M. L. Brooks·D. S. Brown·J. Bryslawskyj·D. Bucher·H. Buesching·V. Bumazhnov·G. Bunce·J. M. Burward-Hoy·S. Butsyk·C. M. Camacho·S. Campbell·V. Canoa Roman·A. Caringi·P. Castera·J. -S. Chai·B. S. Chang·W. C. Chang·J. -L. Charvet·C. -H. Chen·S. Chernichenko·C. Y. Chi·J. Chiba·M. Chiu·I. J. Choi·J. B. Choi·S. Choi·R. K. Choudhury·P. Christiansen·T. Chujo·P. Chung·A. Churyn·O. Chvala·V. Cianciolo·Z. Citron·C. R. Cleven·Y. Cobigo·B. A. Cole·M. P. Comets·Z. Conesa del Valle·M. Connors·P. Constantin·M. Csanád·T. Csörgö
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Abstract

The PHENIX collaboration presents first measurements of low-momentum ($0.4 $1\,GeV/$c$) direct-photon yield $dN_{\gamma}^{\rm dir}/d\eta$ is a smooth function of $dN_{\rm ch}/d\eta$ and can be well described as proportional to $(dN_{\rm ch}/d\eta)^\alpha$ with $\alpha{\approx}1.25$. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different, $A$$+$$A$ collision systems. At a given beam energy the scaling also holds for high $p_T$ ($>5$\,GeV/$c$) but when results from different collision energies are compared, an additional $\sqrt{s_{_{NN}}}$-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.

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A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Bataineh, J. Alexander, M. Alfred, A. Al-Jamel, H. Al-Ta'ani, A. Angerami, K. Aoki, N. Apadula, L. Aphecetche, Y. Aramaki, R. Armendariz, S. H. Aronson, J. Asai, H. Asano, E. C. Aschenauer, E. T. Atomssa, R. Averbeck, T. C. Awes, B. Azmoun, V. Babintsev, A. Bagoly, M. Bai, G. Baksay, L. Baksay, A. Baldisseri, B. Bannier, K. N. Barish, P. D. Barnes, B. Bassalleck, A. T. Basye, S. Bathe, S. Batsouli, V. Baublis, F. Bauer, C. Baumann, S. Baumgart, A. Bazilevsky, S. Belikov, R. Belmont, R. Bennett, A. Berdnikov, Y. Berdnikov, J. H. Bhom, A. A. Bickley, M. T. Bjorndal, D. S. Blau, M. Boer, J. G. Boissevain, J. S. Bok, H. Borel, K. Boyle, M. L. Brooks, D. S. Brown, J. Bryslawskyj, D. Bucher, H. Buesching, V. Bumazhnov, G. Bunce, J. M. Burward-Hoy, S. Butsyk, C. M. Camacho, S. Campbell, V. Canoa Roman, A. Caringi, P. Castera, J. -S. Chai, B. S. Chang, W. C. Chang, J. -L. Charvet, C. -H. Chen, S. Chernichenko, C. Y. Chi, J. Chiba, M. Chiu, I. J. Choi, J. B. Choi, S. Choi, R. K. Choudhury, P. Christiansen, T. Chujo, P. Chung, A. Churyn, O. Chvala, V. Cianciolo, Z. Citron, C. R. Cleven, Y. Cobigo, B. A. Cole, M. P. Comets, Z. Conesa del Valle, M. Connors, P. Constantin, M. Csanád, T. Csörgö. 2018-05-10. Beam-energy and centrality dependence of direct-photon emission from ultra-relativistic heavy-ion collisions. https://doi.org/10.1103/physrevlett.123.022301

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