Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 50 (2017)

DAQ system in RHICf experiment
H. Menjo,∗1,∗2 Q. Zhou,∗2,∗3 K. Sato∗2,∗3 for the RHICf collaboration
The data acquisition (DAQ) system of the RHICf experiment1) , which measures very forward neutral particles at RHIC, was set up in 2016, and it has beenreadied for data acquisition in an operation scheduledfor June 20172) . The RHICf uses one of the LHCfdetectors3) , which has 2 independent calorimeter towers composed of tungsten plates, 16 layers of GSO
scintillators and 4 X-Y hodoscopes of GSO bar bundles. Figure 1 shows the schematic of the detector.
The RHICf detector is located 18 m away from theSTAR interaction point, which is immediately in thefront of the STAR zero-degree calorimeter (ZDC). TheRHICf DAQ uses read-out electronics, power supplies,
and also the trigger system of the LHCf experiment.
These are installed in a rack located in the STAR experimental cabin to avoid the eﬀect of high radiationnear the detector. The PMT analog signals from thesampling layers are transmitted from the detector tothe rack via coaxial cables, and they are distributed
over two analog-to-digital conversion (ADC) modules,
CAEN V965, for charge measurement and two discriminator modules, CAEN V814B, for the trigger system
via analog fanout modules. The AD conversion of signals from MAPMTs connected to the 480 GSO bars is
performed in a radiation-hard front-end circuit locatedinside the detector. A VME board receives the digital
data and stores it. The total data size per event isabout 2.7 KB.
The trigger logic was designed for detecting eventswith electromagnetic and hadronic showers induced byincident photons and neutrons. A trigger is issued
when any three successive layers have an energy deposit over a certain threshold. This type of trigger iscalled as a shower trigger. The logic was implemented
on a ﬁeld-programable gate array (FPGA) board with
inputs from the discriminator boards. It was originally designed for the LHCf DAQ and optimized for
the RHICf DAQ to work under the beam conﬁguration of RHIC. Assuming discriminator threshold of 30
MeV energy-deposit equivalent signals, we estimatedthe trigger eﬃciencies of 100% for photons with energies over 30 GeV and about 70% for neutrons withenergies over 50 GeV. In addition to the shower trigger, another trigger mode, the so-called π 0 trigger, wasimplemented. We note that π 0 particles generated in
p-p collisions decay to photon pairs immediately. Aπ 0 trigger is issued when both the towers detect electromagnetic showers upon the condition that showertriggers are initiated in the ﬁrst seven layers of each
∗1
∗2
∗3

Graduate School of Science, Nagoya University
RIKEN Nishina Center
Institute for Space-Earth Environmental Research, Nagoya
University- 109 -Schematic view
view ofof thethe RHICf
RHICf detector.
detector
Fig. 1. SchematicSTAR

RHICfShower trigger
orπ 0 trigger

Final Trigger
TokenEventbuild

Recode(STAR+RHICf )Data
via TCP/IP
Recode(RHICf )Fig.
Fig. 2.
2. Common-DAQ
Common-DAQ scheme
scheme ofof STAR
STAR andand RHICf.
RHICf

tower. The expected shower trigger rate is 18 kHz
while the π 0 trigger rate is only about 60 HzHz.4)4). To enrich recoded π 0 trigger events within the readout rateof 1 kHz, the shower trigger rate is pre-scaled down to0.8 kHz.
A common operation with the STAR experiment isperformed. The RHICf ﬁnal trigger signals are sent tothe STAR trigger system to trigger the STAR DAQ.
In the common operation, the RHICf works as a subdetector of STAR. Figure 2 illustrates this commonDAQ scheme. STAR issues an event ID token for eachtriggered event and distributes it to all sub-detectors.
The RHICf receives the token and sends RHICf data
together with token via the network. The STAR DAQ
combines all data from the sub-detectors and dumps
it into a disk. This common operation increases thephysics potential of the RHICf experiment, for example, the energy resolution for neutrons is improved
upon combining the RHICf and STAR-ZDC data.
data5)5).
References
1) RHICf Collaboration: LOI, arXiv:1401.1004; RHICf
proposal: arXiv:1409.4860.;
2) T. Sako, et al.,: RIKEN Accel. Prog. Rep. 50, in press.
3) LHCf Collaboration: TDR, CERN-LHCC-2006- 004.
4) RHICf Collaboration: BUR 2017.
5) M. H. Kim for the RHICf Collab oration: RIKEN Accel.
Prog. Rep. 50, in press.