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Predictions for Sivers single spin asymmetries in one- and two-hadron electroproduction at CLAS12 and EIC

Hrayr H. Matevosyan, Aram Kotzinian, Elke-Caroline Aschenauer, Harut Avakian, and Anthony W. Thomas
Phys. Rev. D 92, 054028 – Published 23 September 2015
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  • INTRODUCTION
  • THE SIVERS EFFECT IN SIDIS
  • MONTE CARLO PREDICTIONS FOR ONE HADRON…
  • MONTE CARLO PREDICTIONS FOR TWO HADRON…
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    The study of the Sivers effect, describing correlations between the transverse polarization of the nucleon and its constituent (unpolarized) parton’s transverse momentum, has been the topic of a great deal of experimental, phenomenological and theoretical effort in recent years. Semi-inclusive deep inelastic scattering measurements of the corresponding single spin asymmetries (SSA) at the upcoming CLAS12 experiment at JLab and the proposed Electron-Ion Collider will help to pinpoint the flavor structure and the momentum dependence of the Sivers parton distribution function describing this effect. Here we describe a modified version of the pythia6 Monte Carlo event generator that includes the Sivers effect. Then we use it to estimate the size of these SSAs, in the kinematics of these experiments, for both one and two hadron final states of pions and kaons. For this purpose we utilize the existing Sivers parton distribution function (PDF) parametrization extracted from HERMES and COMPASS experiments. Using this modified version of pythia6, we also show that the leading order approximation commonly used in such extractions may provide significantly underestimated values of Sivers PDFs, as in our Monte Carlo simulations the omitted parton showers and non-DIS processes play an important role in these SSAs, for example in the COMPASS kinematics.

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    • Received 13 February 2015

    DOI:https://doi.org/10.1103/PhysRevD.92.054028

    © 2015 American Physical Society

    Authors & Affiliations

    Hrayr H. Matevosyan1, Aram Kotzinian2,3, Elke-Caroline Aschenauer4, Harut Avakian5, and Anthony W. Thomas1

    • 1ARC Centre of Excellence for Particle Physics at the Tera-scale, and CSSM, Department of Physics, The University of Adelaide, Adelaide, South Australia 5005, Australia
    • 2Yerevan Physics Institute, 2 Alikhanyan Brothers Street, 375036 Yerevan, Armenia
    • 3INFN, Sezione di Torino, 10125 Torino, Italy
    • 4Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA
    • 5Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue Suite 5, Newport News, Virginia 23606, USA

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    Issue

    Vol. 92, Iss. 5 — 1 September 2015

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    Images

    • Figure 1
      Figure 1

      The leading order diagram for one hadron production in the current fragmentation region of SIDIS.

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    • Figure 2
      Figure 2

      γ*−N center of mass frame.

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    • Figure 3
      Figure 3

      The leading order diagram for two hadron production in the current fragmentation region of SIDIS.

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    • Figure 4
      Figure 4

      Sivers SSAs versus (a) x, (b) y and (c) PT from COMPASS data, and calculated with mlepto and mpythia.

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    • Figure 5
      Figure 5

      EIC toy model SSAs versus (a) x and (b) z for 5×50 SIDIS kinematics for π+. Comparison of sea and valence quark contributions in pure DIS events.

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    • Figure 6
      Figure 6

      EIC toy model SSAs for π+ for a range of beam energies. Comparison of (a) the full, (b) valence-only and (c) sea-only Sivers effect induced SSAs are shown for various energies versus z, where we only allow for the DIS process.

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    • Figure 7
      Figure 7

      EIC toy model SSAs for 5×50 SIDIS kinematics for charged pions and kaons versus xF. The Sivers asymmetry is present both in the current and target fragmentation regions.

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    • Figure 8
      Figure 8

      COMPASS SSAs for h+ versus (a) x, (b) z and (c) PT when various contributions beyond the DIS process are included.

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    • Figure 9
      Figure 9

      EIC(5×50) SSAs for π+ versus (a) x, (b) z and (c) PT when various contributions beyond the DIS process are included.

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    • Figure 10
      Figure 10

      Ratios of full to DIS-only results for rates (N) and SSAs (ASiv) for EIC(5×50) and COMPASS versus (a) x, (b) z and (c) PT.

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    • Figure 11
      Figure 11

      EIC SSAs versus (a) x, (b) z and (c) PT for 5×50 SIDIS production of charged pseudoscalars.

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    • Figure 12
      Figure 12

      EIC SSAs versus (a) x, (b) z and (c) PT for 5×250 SIDIS production of charged pseudoscalars.

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    • Figure 13
      Figure 13

      EIC model SSAs for 5×50 SIDIS kinematics for charged pions and kaons versus xF. The Sivers asymmetry is present both in the current and target fragmentation regions.

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    • Figure 14
      Figure 14

      EIC rates for the struck quark flavor for the selected events in SIDIS productions of charged pions and kaons for (a) 5×50 and (b) 5×250 energies.

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    • Figure 15
      Figure 15

      Predictions for the Sivers asymmetry in charged hadron production at CLAS12 versus (a) x, (b) z and (c) PT.

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    • Figure 16
      Figure 16

      Predictions for the relative rates for the flavor of the struck quark that produces charged hadrons in MC events at CLAS12, with all the relevant kinematical cuts.

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    • Figure 17
      Figure 17

      Predictions for SSAs for charged pions and kaons versus xF at CLAS12. The Sivers asymmetry is present both in the current and target fragmentation regions.

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    • Figure 18
      Figure 18

      Predictions for Sivers SSA for charged (a) pion and (b) kaon-inclusive pair production off proton target at CLAS12 versus x.

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    • Figure 19
      Figure 19

      Predictions for Sivers SSA for charged (a) pion and (b) kaon-inclusive pair production off proton target at CLAS12 versus z.

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    • Figure 20
      Figure 20

      Predictions for Sivers SSA for charged (a) pion and (b) kaon-inclusive pair production off proton target at CLAS12 versus Mh1h2.

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    • Figure 21
      Figure 21

      Predictions for the relative rates for the flavor of the struck quark that produces charged (a) pion and (b) kaon-inclusive pair in MC events at CLAS12, with all the relevant kinematical cuts.

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    • Figure 22
      Figure 22

      EIC 5×50 results versus x for (a) “R” and (b) “T” type SSAs.

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    • Figure 23
      Figure 23

      EIC 5×250 results versus x for (a) “R” and (b) “T” type SSAs.

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    • Figure 24
      Figure 24

      EIC 5×50 results versus z for (a) “R” and (b) “T” type SSAs.

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    • Figure 25
      Figure 25

      EIC 5×250 results versus z for (a) “R” and (b) “T” type SSAs.

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    • Figure 26
      Figure 26

      EIC 5×50 predictions for the relative rates for the flavor of the struck quark that produces charged (a) pion and (b) kaon-inclusive pair in MC events with all the relevant kinematical cuts.

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    • Figure 27
      Figure 27

      EIC results for Sivers asymmetry versus (a) x and (b) z with asymmetric cuts applied to the momenta of the hadrons in the pair.

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