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Systematic study of nuclear effects in $p$ $+$Al, $p$ $+$Au, $d$ $+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV using $\pi^0$ production

The PHENIX collaboration
549 authors from 81 institutions, 21 pages, 13 figures, and 3 tables. Data from 2008, 2014, and 2015. Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html, 2021.

Abstract (data abstract)
PHENIX presents a systematic study of $\pi^0$ production from p+p, p+Al, p+Au, d+Au, and $^{3}$He+Au collisions at $\sqrt{s}$=200GeV. Measurements were done 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 GeV/c, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are the same for all systems for the same centrality class. It is shown that for high $p_T$ $\pi^0$ production, the nucleons in the d and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive 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+Au > d+Au > $^{3}$He+Au > p+Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects obtain the reversed order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

  • Figure5

    10.17182/hepdata.115023.v1/t1

    Differential cross section of $\pi^0$ in p+p collisions at $\sqrt{s}$ = 200 GeV

  • Figure6

    10.17182/hepdata.115023.v1/t2

    Invariant yield of $\pi^0$ from (a) p+Al, (b) p+Au, (c) d+Au, and (d) $^{3}$HeAu in different centrality selections at $\sqrt{s}$...

  • Figure7

    10.17182/hepdata.115023.v1/t3

    Nuclear modification factors from inelastic (a) p+Al, (b) p+Au, (c) d+Au, and (d) $^{3}$HeAu collisions at $\sqrt{s}$ = 200 GeV....

  • Figure8

    10.17182/hepdata.115023.v1/t4

    Exponent according to the Eq. 5 as a function of transverse momenta extracted from p+Au/p+Al and $^{3}$HeAu/p+Au collision systems. The...

  • Figure9

    10.17182/hepdata.115023.v1/t5

    Nuclear modification factors in p+Al, p+Au, d+Au, and $^{3}$He+Au in five centrality bins and for inelastic collisions at $\sqrt{s}$ =...

  • Figure10a

    10.17182/hepdata.115023.v1/t6

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10a1

    10.17182/hepdata.115023.v1/t7

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10a2

    10.17182/hepdata.115023.v1/t8

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10b

    10.17182/hepdata.115023.v1/t9

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10b1

    10.17182/hepdata.115023.v1/t10

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10b2

    10.17182/hepdata.115023.v1/t11

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10c

    10.17182/hepdata.115023.v1/t12

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10c1

    10.17182/hepdata.115023.v1/t13

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10c2

    10.17182/hepdata.115023.v1/t14

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10d

    10.17182/hepdata.115023.v1/t15

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10d1

    10.17182/hepdata.115023.v1/t16

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure10d2

    10.17182/hepdata.115023.v1/t17

    Average $R_{xA}$ in two different $p_T$ regions versus the number of collisions (panels a,b) and the number of collisions per...

  • Figure11

    10.17182/hepdata.115023.v1/t18

    $R_{xA}$ for inelastic collisions compared to three different nuclear PDF calculations and their uncertainties. The data points include the statistical...

  • Figure12a

    10.17182/hepdata.115023.v1/t19

    The upper panel (a) shows the <$R_{xA}$> above $p_T$ =8 Gev/c as a function $N_{coll}$/$N_{proj}$. The data are compared to...

  • Figure12a1

    10.17182/hepdata.115023.v1/t20

    The upper panel (a) shows the <$R_{xA}$> above $p_T$ =8 Gev/c as a function $N_{coll}$/$N_{proj}$. The data are compared to...

  • Figure12a2

    10.17182/hepdata.115023.v1/t21

    The upper panel (a) shows the <$R_{xA}$> above $p_T$ =8 Gev/c as a function $N_{coll}$/$N_{proj}$. The data are compared to...

  • Figure12bc

    10.17182/hepdata.115023.v1/t22

    The upper panel (a) shows the <$R_{xA}$> above $p_T$ =8 Gev/c as a function $N_{coll}$/$N_{proj}$. The data are compared to...

  • Figure13a

    10.17182/hepdata.115023.v1/t23

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

  • Figure13a1

    10.17182/hepdata.115023.v1/t24

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

  • Figure13a2

    10.17182/hepdata.115023.v1/t25

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

  • Figure13b

    10.17182/hepdata.115023.v1/t26

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

  • Figure13b1

    10.17182/hepdata.115023.v1/t27

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

  • Figure13b2

    10.17182/hepdata.115023.v1/t28

    Integrated yields for 1--2 GeV/c in panel (a) and 2--3 GeV/c in panel (b) as a function of charged particle...

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