Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 51 (2018)√RHICf-STAR common operation in s = 510 GeV proton-proton
collisions
M. Ueno∗1,∗2 for the RHICf collaboration
The RHIC forward (RHICf) experiment1,2) and theSTAR experiment4) had a joint operation in June
2017.3) During the RHICf operation, RHICf took
about 1.1 × 108 events in total, and 80% of theevents were common with STAR. At the RHICf-STAR
joint data taking, we recorded the data of the STARdetector, Zero Degree Calorimeter (ZDC),5) Beam
Beam Counter (BBC),6) and Vertex Position Detector (VPD)7) together. These common data are usefulfor the improvement of physics performance. In thisreport, the improvement of energy resolution for neutrons is discussed.
The RHICf detector has two independent calorimeter towers, which are composed of tungsten plates, 16
layers of GSO scintillators, and 4 X-Y hodoscopes ofGSO bar bundles.1) The thickness of the RHICf detector is 44 radiation length and 1.6 interaction length.
The STAR-ZDC detectors were installed on both sidesof the STAR IP. The detector was installed 18 m awayfrom the STAR interaction point in front of the westside STAR ZDC, as shown in Fig. 1. The particle
identiﬁcation between photons and neutrons is performed by using the diﬀerence in detector response.
The hadronic showers induced by neutrons develop
in deeper layers than the electromagnetic showers induced by photons. Because the RHICf detector thickness is not enough to contain hadronic showers, theseshower particles leak out from the detector and hit
the STAR-ZDC. An MC simulation study by Geant4
shows that the energy resolution for neutrons is expected to be improved from 40% to 20% by combining
the RHICf data and ZDC data.
The correlation between the RHICf detected energy
and the STAR-ZDC detected energy was conﬁrmed bythe data. Figure 2 shows the correlation between theRHICf raw energy and the STAR-ZDC ADC sum when
the beam center was set at the RHICf small calorimeter

Fig. 2. Correlation between RHICf detected energy andthe STAR-ZDC detected energy. The horizontal axis
shows the RHICf raw energy and the vertical axis shows
STAR-ZDC ADC sum. The RHICf detector, which
consists of two calorimeter towers, was installed at thewest side of the STAR interaction point. Only thewest side STAR-ZDC ADC sum shows correlation withRHICf raw energy.

tower (TS tower). The upper ﬁgures show the resultsof the west-side STAR ZDC and the lower ﬁgures show
the results of the east-side STAR ZDC. Figure 2 showsthat there is a correlation between the west side STARZDC and RHICf raw data. On the other hand, there
is no correlation between the east side STAR-ZDC andRHICf raw data. These results indicate that the event
matching between the RHICf and STAR data worked
correctly. Analysis of common operation data is ongoing.
ReferencesFig. 1. Schematic location view of the RHICf detector (left)
and the STAR-ZDC (right).
∗1∗2

RIKEN Nishina Center
Institute for Space-Earth Environmental Research, Nagoya
University- 113 -1) RHICf Collaboration, Letter of Intent, arXiv:1401.1004.
2) RHICf Collaboration, RHICf proposal, arXiv:1409.4860.
3) J. S. Park for the RHICf Collaboration, in this report.
4) K. H. Ackermann et al., Nucl. Instrum. Methods Phys.
Res. A 499, 624–632 (2003).
5) C. Adler et al., Nucl. Instrum. Methods Phys. Res. A470, 488–499 (2001).
6) C. A. Whitten for the STAR Collaboration, AIP Conference Proceedings, 980, 390–396, (2008).
7) W. J. Llope et al., Nucl. Instrum. Methods Phys. Res.
A 759, 23–28 (2014).