Systematic study of nuclear effects in p+Al, p+Au, d+Au , and He3+Au collisions at sNN=200 GeV using π0 production

Le résumé fourni par la source

The PHENIX Collaboration presents a systematic study of inclusive ${\ensuremath{\pi}}^{0}$ production from $p+p, p+\mathrm{Al}, p\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}, d\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}$, and $^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. Measurements were performed with different centrality selections as well as the total inelastic, 0--100%, selection for all collision systems. For 0--100% collisions, the nuclear-modification factors, ${R}_{xA}$, are consistent with unity for ${p}_{T}$ above $8\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-${p}_{T}\text{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ production, the nucleons in the $d$ and $^{3}\mathrm{He}$ interact mostly independently with the Au nucleus and that the counterintuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower ${p}_{T}$ resemble the Cronin effect---an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}\phantom{\rule{4pt}{0ex}}>\phantom{\rule{4pt}{0ex}}d\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}\phantom{\rule{4pt}{0ex}}>\phantom{\rule{4pt}{0ex}}^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}\phantom{\rule{4pt}{0ex}}>p+\mathrm{Al}$. For collisions with Au ions, current calculations based on initial-state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower ${p}_{T}$.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.