Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 53

Progress of the polarized Drell-Yan experiment at Fermilab,
SpinQuest (E1039)
Y. Miyachi,∗1 Y. Goto,∗2 K. Nagai,∗2,∗3 K. Nakano,∗2,∗4 G. Nukazuka,∗1 S. Sawada,∗2,∗5 and T. -A. Shibata∗1,∗6for the SpinQuest Collaboration
SpinQuest is a polarized fixed-target Drell-Yan experiment using a 120 GeV proton beam from Main
Injector at Fermilab. The primary goal of SpinQuest
is to measure the Sivers asymmetries, aiming to obtain a hint for the following fundamental question:“Do the light sea quarks contribute to the intrinsic spinof the nucleon via their orbital angular momentum?”
The Sivers asymmetry was first introduced to explain
the unexpected, large, transverse, single-spin asymmetries observed in hadron scattering. Non-zero valuesof the Sivers asymmetry have been measured in theSemi-Inclusive Deep-Inelastic Scattering (SIDIS) experiments. The correlation between the transverse momentum of a quark and the spin of the parent nucleon,represented by the Sivers function, is a source of theasymmetry. The Sivers functions for u and d quarks
were determined to be similar in size but with the opposite signs.2,3) As no results for the Sivers functions
for sea quarks are available, SpinQuest can help deter¯ through the measurement ofmine them for ū and d,
the Sivers asymmetries in the Drell-Yan process using
the transversely polarized proton and deuteron targets,for the first time.
NH3 and ND3 are used as the polarized proton anddeuteron target material. The target polarization isobtained with dynamic nuclear polarization, which requires a low temperature of 1 K, strong magnetic fieldof 5 T, and 140 GHz microwave radiation. Under
the greatest instantaneous luminosity of any previous
evaporation refrigerator system, with a beam intensity of 3 ×1012 protons/s for 5 s, a high-cooling-power4
He evaporation refrigerator connected to a large pumpsystem (14,000 m3 /h) successfully maintains the target
material temperature at 1 K. The longest (along withthe beam-line) target cell to date for an evaporation
refrigerator requires a unique microwave distributing
horn. Three NMR coils installed for the target cell reduce systematic uncertainties in the polarization measurement.
The SpinQuest experiment inherits the spectrometerfrom the SeaQuest experiments,1) which measured the¯flavor asymmetry in the light quark sea, d/ū.
It covers
the kinematic region where target sea quarks dominate
the Drell-Yan process: u or d quarks in the beam areannihilated with ū or d¯ anti-quarks in the target, re∗1
∗2
∗3
∗4
∗5
∗6Fig. 1. Projected sensitivities of the single spin asymmetries at SpinQuest.

spectively. Because SpinQuest probes a lower xtarget
than SeaQuest, the target position has been moved
further upstream of the beam dump to increase acceptance in the low xtarget range, as well as to improveseparation for target and dump events. At present,
the commissioning of the target and spectrometer isongoing. The beam time is expected to begin in early2020.
Figure 1 shows the expected sensitivities of SpinQuest on the single spin asymmetries, AN , after twoyears of combined operation on the NH3 and ND3targets. The error bars are statistical only. A relative systematic uncertainty of 0.04 is expected. The
bands represent theoretical predictions based on theSivers functions2,3) extracted from the present available SIDIS data. A comparison between the NH3 andND3 results could also be sensitive to the flavor dependence of the sea-quark Sivers function.
References

Faculty of Science, Yamagata University
RIKEN Nishina Center
Institute of Physics, Academia Sinica, Taiwan
School of Science, Tokyo Institute of Technology
Institute of Particle and Nuclear Studies, KEK
College of Science and Technology, Nihon University

1) C. A. Aidala et al., [SeaQuest Collaboration], Nucl. Instrum. Methods Phys. Res. A 930, 49 (2019).
2) M. Anselmino et al., Eur. Phys. J. A 39, 89 (2009).
3) P. Sun, F. Yuan, Phys. Rev. D 88, 034016 (2013).

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