RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Trigger logic for the SπRIT experiments
C. Santamaria,∗1,∗2 P. Pawlowski,∗3,∗2 W. Lynch,∗1 K. Pelczar,∗3 J. Barney,∗1,∗2 G. Cerizza,∗1,∗2 J. Estee,∗1,∗2T. Isobe,∗2 M. Kaneko,∗4,∗2 M. Kurata-Nishimura,∗2 P. Lasko,∗3,∗2 J. Lukasik,∗3 A.B. McIntosh,∗5T. Murakami,∗4,∗2 M. B. Tsang,∗1 S.J. Yennello,∗5,∗6 Y. Zhang∗7,∗2 for the SπRIT collaboration
The SπRIT experiments1) require a trigger to selectcentral collisions in order to probe the nuclear equation of state at high densities using heavy ion collisions. Central collisions are studied via a Time Projection Chamber (TPC) surrounded by ancillary detectors. They are triggered by suitable multiplicities
of charged particles in the Kyoto plastic scintillators
located on the sides of the TPC and KATANA plastic
scintillator paddles located downstream of the TPC.
An extensive description of the KATANA array is provided in Ref.3)3.. The trigger was vetoed by the presenceof a projectile-like fragment in the three KATANA vetoscintillators, which are downstream of the TPC andcentered about the beam trajectory, or if there is a hit
in the active collimator that shadows the target framefrom the incident beam.
The ultimate trigger decision was made by an FPGA
in a ”trigger box”, shown in Fig. 1 in the shaded graybox. The internal trigger logic of this trigger box is notshown. It required a signal from the beam in a Start
Counter scintillator located upstream, a multiplicity
signal from the EASIROC module servicing the Kyoto
multiplicity array or a multiplicity in the KATANA
plastic that exceeds a threshold multiplicity selectedby user. For regular data runs, the trigger condition
required a multiplicity greater than four in the Kyoto
array and the multiplicity in KATANA was ignored.
Moreover, this trigger was vetoed in the trigger box
if heavy fragments hit any of the three KATANA vetoscintillators or if the beam hit the active collimator upstream. To obtain minimum bias events and to study
the trigger bias of this event selection, the values of theKyoto multiplicity, the KATANA trigger multiplicity,and the KATANA beam veto paddle thresholds werevaried in separate minimum bias runs for further analysis.
To avoid a loss of track information in the TPC,a Fast Trigger decision was made. This Fast Trigger
AND coincidence, shown in the ﬁgure, required theStart Counter, none of the three KATANA veto signals
and vetoed by a BUSY signal. This opened the gating
grid driver (GGD)2) via a TTL open signal generated
by the latch G&D 2. The TTL open is normally terminated by G&D 1 after 11 μsec but can be shortened
∗1
∗2
∗3
∗4∗5
∗6
∗7

NSCL and Department of Physics and Astronomy, Michigan
State UniversityRIKEN Nishina Center
Institute of Nuclear Physics, PAN
Department of Physics, Kyoto University
Cyclotron Institute, Texas A&M University
Department of Chemistry, Texas A&M University
Department of Physics, Tsinghua Universityby the arrival of a random beam particle in one of theKATANA veto paddles or the lack of a trigger signal
from the trigger box. The 11 μsec maximum lengthof the gate is calculated from the 9 μsec drift lengthof the TPC plus some safety margin to make sure all
the volume of the TPC is included in the accepted timewindow. The TTL close signal, generated by the G&D
4, starts on the trailing edge of the TTL open signal
and deﬁnes the closing of the GGD. The 5 μsec widthof the TTL close gate is calculated as the maximum
drift time in the TPC for a heavy fragment to avoid
these tracks from producing a signal in the next event.

Fig. 1. Schematic circuit diagram of the trigger logic usedduring the SπRIT experiments.

Three data acquisitions (DAQ) are coupled during
the experiment to write data from the TPC (SπRIT),
the beam tracking counters and Kyoto array (RIKEN)
and the KATANA array (KATANA). The BUSY signal is generated from an OR of the three DAQ BUSYsignals plus the TTL open and TTL close. The trigger
sent to the DAQ systems is a coincidence of the trigger from the trigger box, a NOT BUSY signal, and adelayed Start Counter signal in order to keep the Start
Counter as the reference time for the DAQ.
During the experiment, the data acquisition successfully selected heavy ion collisions with on average a 800
μs dead time. Analysis of data runs will quantitatively
determine the average impact parameter of the heavyion collisions in our setup and a further study of theminimum bias runs will constrain the bias of our experimental detection system.
References
1) R. Shane et al., Nucl. Instr. Meth. A 784, 513 (2015).
2) S. Tangwancharoen et al., Nucl. Instr. Meth. A 853, 44(2017).
3) P. Lasko et al., Nucl. Instr. Meth. A 856, 92 (2017).

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