Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Operation summary of the RHICf experimet
J.S. Park,∗1∗2 for the RHICf collaboration∗1∗2

Department of Physics and Astronomy, Seoul National University
RIKEN Nishina Center- 112 -

Number of Eventssis. Figure 2 shows the accumulated number of events
during the operation time.
The RHICf experiment was completed successfully
under a stable beam condition with STAR detectors
and the data showed a reasonable π 0 mass spectrumwith suﬃciet statistics and correlation with STARZDC as expected.

6000

RHICf Preliminary

RHIC Run17 510GeV p+p
RHICf Run2925
Type-I π0 sample

5000
4000
3000
2000
10000020 40 60 80 100 120 140 160 180 200
Mγ γ [MeV]Fig. 1. Reconstructed π 0 mass with data.
Number of recorded events

The RHICf forward (RHICf) experiment is an experiment that can provide information about soft QCD
physics. One of the measurements in the RHICf experiment is the measurement of energy spectra of forward neutral particles. Another measurement in theRHICf experiment is the measuerment of transeverse
single-spin asymmetry (AN ) of forward neutral particles. These measurements are expected to contibuteto the determination of Feyman scaling and the production mechanism of forward neutral particles.1) The
main detector in the RHICf experiment is the the LHCfdetector that is an electromagnetic calorimeter usedin LHCf experiment which is optimized for detecting
π 0 s.2) In addition to the RHICf detector, the datafrom the STAR ZDC, VPD, BBC, and Roman pot
were read-out so that a combined analysis could beperformed.
The RHICf experiment was performed from 21stJune to 26th June in 2017 at STAR IR in RHIC.
The RHICf detector was installed immediately in frontof the west ZDC.3) The RHICf detector consists of alarge tower and a small tower so that π 0 can be detected more eﬀectively. The RHICf experiment wasperformed using a horizontally polarized beam (radial polarized beam) and the detector location was adjusted at 3 diﬀerent heights to extend the transverse
momentum (PT ) measurement range:1) i) the heightof the large tower center is the same as the height ofthe collision point (6 hours), ii) the height of the small
tower center is the same as the height of the collision
point (12 hous) and iii) the height of the small tower
center is 24 mm greater than the height of the collision point (8 hours). The operation was completedwith 3 kinds of triggers which enhance single showers,
π 0 s. and high-energy electromagnetic (EM) showers4)
during 5 RHIC ﬁlls and the total run time was approximately 23 hours.√Proton-proton collisions proceededat β ∗ = 8 m and s = 510 GeV with the radial polarization P ∼ 0.5.
During the operation time, the monitoring systemachieved stable polarization measurement with satisfactory precision, with a reasonably reconstructed π 0invariant mass and correlation between STAR ZDC
and the RHICf detector.5) Figure 1 shows the reconstructed invariant mass of photon pair events showing
a peak at the rest mass of π 0 from quick oﬄine data
analysis in the operation time. The peak location isslightly diﬀerent from the true π 0 mass because theenergy calibration was not perfect in the quick analy-120 ×10

6RHICf Run17 Cumulative Statistics
RHICf All100

RHICf && STARL3T Shower80

L3T Special2 (High-energy EM)
L3T Special1 (Type-I π0)6040

20024-21h

25-09h25-21h26-09h26-21hUS Eastern Time (June-2017)

Fig. 2. Black: accumulated events recorded by 3 kinds oftriggers, Magenta: accumulated events recorded by coincidence among STAR detector triggers and LHCf triggers, Blue: accumulated events recorded by shower trigger only, Red: accumulated events recorded by π 0 trigger only, Green: accumulated events recorded by highEM trigger only.

References
1) J. S. Park for the RHICf Collaboration, RIKEN Accel.
Prog. Rep. 50, 108 (2017).
2) M.H. Kim for the RHICf Collaboration, RIKEN Accel.
Prog. Rep. 50, 107 (2017).
3) Y. Goto for the RHICf Collaboraccel, Prog. Rep. 48,
108 (2017).
4) H. Menjo, K. Sato for the RHICf Collaboration, In thisreport.
5) M. Ueno for the RHICf Collaboration, In this report.