Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 51 (2018)

DAQ performances of the RHICf operation in 2017

The RHIC forward (RHICf) experiment,1) measuring very forward neutral particles, photons, neutrons,and π 0 s, produced in 510 GeV proton-proton collisions
at RHIC, has successfully completed a 4-day operation in June 2017. The data acquisition (DAQ) systemof the RHICf experiment was developed based on thesystem of the LHCf experiment2) as well as the detector. The RHICf detector consists of two sampling andimaging calorimeters. Each calorimeter is composed oftungsten plates, 16 layers of GSO scintillators and 4 XY hodoscopes of GSO bar bundles. Trigger signals aregenerated by a logic based on the energy deposit on thescintillator layers, which is implemented on a systemwith discriminator modules and a field programmablegate array (FPGA) board.3) In the logic, three trigger
modes were implemented as follows;• Shower trigger is implemented for detecting any
electromagnetic (EM) showers and hadronic showers induced by photons and neutrons. This trigger
is issued when each of any three successive layers
has an energy deposit greater than 45 MeV.
• π 0 trigger is specialized to detect photon pairs
from π 0 decays. This trigger is issued when EMshowers are detected in both the calorimeters simultaneously.
• High-EM trigger is newly introduced for theRHICf experiment to increase the statistics ofhigh-energy photon events (> 100 GeV). The trigger is issued when the 4th layer in either calorimeter has an energy deposit greater than 500 MeV.

Trigger Rate [Hz]

These trigger signals were mixed after being prescaled down by factors of 8–30 for shower triggers and
1–4 for high-EM triggers. The rate of π 0 triggers is1500

RHICf Run17 510GeV p+p
Fill 21142

Fill 21145

TotalShower

Fill 21148

Fill 21149

π0High EM
Fill 21150

10005000Jun-24 12:00 Jun-25 00:00 Jun-25 12:00 Jun-26 00:00 Jun-26 12:00 Jun-27 00:00
Time (EDT)

Fig. 1. Trigger rates of the RHICf operation in 2017. The
upper arrows indicate the physics operation periods.
∗1∗2∗3Graduate School of Science, Nagoya University
RIKEN Nishina Center
Institute for Space-Earth Environmental Research, Nagoya
University- 115 -#EventsH. Menjo∗1,∗2 and K. Sato∗2,∗3 for the RHICf collaboration
105AllShowerπ0High EM

410310102
1010

RHICf Preliminary
RHICf Run17 510 GeV p+p
RHICf Run2798 (TS center)
Small-Tower, Photon-like2468
Σ dE [GeV]

Fig. 2. Spectrum of total visible energy measured by theRHICf calorimeter. Colored lines correspond to spectra
obtained from the events triggered by the three modes.

the lowest among the three trigger modes and its prescaling factor was always set to 1 (no pre-scaling). Theevent rates of these triggers strongly depend on the operation conditions such as the detector position withrespect to the beam axis. The raw rate of shower triggers was 6–30 kHz, and it was scaled down to approximately 1 kHz after the pre-scaling. These pre-scaling
factors were optimized occasionally during the operation to keep the final trigger rate to approximately
1 kHz, which corresponds to the DAQ condition withapproximately 50% of the DAQ live fraction. Figure 1
shows the total trigger rate and rates of the three triggers. The rates decreased during an operation period
because of the decrease of beam intensity, while therate suddenly increased in some moments owing to reoptimizations of the pre-scaling factors.
Figure 2 shows the raw spectra of measured total
visible energy ΣdE obtained in the EM-shower events.
The number of EM showers in the π 0 trigger events
is mostly comparable with that in the shower trigger
events. The high-EM trigger successfully worked toenrich high-energy EM shower events in the recoded
data. The number of photon events in the high-EMtriggered events is larger than that in the shower triggered events by a factor of approximately 10 in theregion of ΣdE > 3 GeV, corresponding to photon energies greater than approximately 100 GeV.
References
1) RHICf Collaboration: Letter of Intent, arXiv:1401.1004;
RHICf proposal: arXiv:1409.4860.
2) LHCf Collaboration: TDR, CERN-LHCC-2006-004.
3) H. Menjo et al., RIKEN Accel. Prog. Rep. 50, 109(2017).