1. PHENIX RPC R&D EFFORT Beau Meredith
(University of Illinois at Urbana-Champaign)
for the PHENIX Collaboration
IX International Workshop on RPCs and Related Detectors
Mumbai, India

2. Long-term RPC Operation in PHENIX
RPC Technology in PHENIX
RPC R&D
This talk
PHENIX specific R&D
GSU
UIUC
CU Boulder
RPC Gap Production
See Byungsik Hong’s talk
Gap production at Korea University, Physics Motivation To
Have
Successful
Long-term RPC Operation
in PHENIX
RPC Assembly & QA
Rusty Towell’s Talk
Integration into PHENIX,
HPL testing
RPC FACTORY AT BNL

3. Outline Introduction PHENIX experiment Physics Motivation
RPC forward upgrade for muon spectrometer
Bakelite RPC R&D at PHENIX institutions
Gap construction
Using gaps to test PHENIX specific parameters
Basic R&D results

4. RHIC/PHENIX Two Muon Spectrometers, 1.2<|h|<2.4, Δφ=2π
STAR
PHENIX
PHOBOS
BRAHMS
RHIC, lenght: 3.83 km
Two Muon Spectrometers, 1.2<|h|<2.4, Δφ=2π
Tracking: Wire chambers with cathode strip readout, 3 stations/arm with multiple views (MuTr)
Identification: Iarocci streamer tubes, 5 detection planes (MuID)
Lampshade magnets produce radial magnetic field
Can obtain momentum from change in azimuthal angle Δφ

5. Motivation for RPC Forward Upgrade
orbital angular momentum
quark spin
gluon spin
Experiment
√s = 500 GeV polarized pp collisions
Probe the quark and anti-quark spin contributions via high momentum muons from the W bosons
Need to at least increase rejection factor of muon arms from ~500 to 6,000
Introduce RPC forward upgrade
We aim to have a rejection factor of ~ 10,000
For more details see Byungsik Hong’s Talk

6. PHENIX Muon Trigger Upgrade
RPC1: 32 RPC detector modules (768 read-out channels)
RPC2: 128 RPC detector modules (15392 read-out channels)
RPC3: 96 RPC detector modules (11488 read-out channels)
Strip Layout for RPCs, MuTr
RPC 3
RPC 3
RPC 2
RPC 1 (a,b)
RPC 2
RPC 3
Baseline trigger Consists of
RPC1 or MuTr1
MuTr2 (wire chamber with cathode strip readout)
RPC2
RPC3
Trigger makes momentum cut on muons
Draw line between RPC1,2 hit positions
Project this line onto MuTr2
Require hit position in MuTr2 to be within 3 strips of projection
CSC (MuTr2)

7. PHENIX Bakelite RPC R&D
Start from the CMS endcap design
Use Italian bakelite
Purpose of R&D is
to acquire experience and 1st hand knowledge of technology in group
to carry out R&D on PHENIX specific performance parameters
2 mm gas gaps
Gas mixture: 95% R134a, 4.5% Isobutane, 0.5% SF6
PHENIX RPC Detector Requirements
Efficiency
 95%
Time resolution
 3 ns
Average cluster size
 2 strips
Rate capability
0.5 kHz/cm2
Best Position Resolution
1 cm
Number of streamers
 10 %

8. Four RPC Test Stands
PHENIX has test stands at four different institutions. Each test stand is focused on different aspects of RPC R&D.
Georgia State University (GSU) – built and tested 5 generations of prototypes
University of Colorado at Boulder (CU) – conducted performance tests and integration studies for FEE and RPC detectors
University of Illinois at Urbana-Champaign (UIUC) – performed position resolution studies for small strip sizes, SF6 scan, non-uniform gap study
Brookhaven National Laboratory (BNL) – will carry out QA of prototypes and fully assembled detector modules
GSU
UIUC CU
BNL

9. GSU Prototype Generations
3rd generation
Generation
Number
of RPCs
Sizes
Notes
1st 2
46cmx46cm
2mm gaps
Initial effort
2nd
23cmx23cm
2,2.4 mm gaps
Signal study
3rd 8
30cmx30cm, 23x23cm
1.6, 2.0 mm gaps
Gaps sent to CU for study
4th 6
30cmx30cm
60cmx60cm
Added Cu wrap, high rb epoxy for edges
5th 4
2 glass, 2 bakelite
2 mm gaps
Add edge spacers protruding beyond bakelite edge, EVA glue
Gap Production
3rd generation
Double Gap Assembly

10. Example – GSU Design (Generation 3)
GSU gaps built for FEE tests at CU with different size strips
Use PCB sandwiched between two single gaps
Shown PCB consists of 5 x 4 cm x 20 cm strips and 11 x 0.5 cm x 20 cm strips; optional termination

11. Studying the CMS Design
Wrap top and bottom copper sheet together
TDC spectrum before wrap
After
Use polycarbonate spacers that protrude beyond the bakelite edges
Use EVA glue to keep the dark currents low
Use oiled gaps to keep noise rate low

12. Clustering Algorithm at Level 1?
Is a cluster algorithm needed in the level 1 trigger?
Full GEANT simulation of trigger performance confirms that the use of raw hit info leads to sufficiently high trigger rejection
No need for clustering algorithm
A prototype was tested by CU with 0.5 cm strips
The setup, cluster size, and efficiency curves are shown on the next slide
Generation 3 GSU gaps were used in the testing

13. CU Setup and Results Paddle Scintillator Finger Scintillators RPC
Notes:
Additional shower rejection paddle not shown
Use scope to view and analyze output pulses
Efficiency
Cluster Size
Fit cluster size data by assuming a hit-inducing Gaussian radius. Input resulting distribution into trigger simulation
0.5 cm strips used
HV (kV)

14. Trigger Simulation Results
997,710 pythia √s = 500 GeV pp events run through GEANT
Rejection factors are combined for both muon arms
Azimuthal angle cut between RPC1,2
Trigger Efficiency (25 GeV muons)
Rejection Factor
2 degree cut
95% N / 92% S
15,600
3 degree cut
98% N / 96% S
9,317
This meets our criteria of R >10,000

15. CU Timing Resolution Study
We need timing resolution of < 3 ns
Remove beam related and cosmic muon backgrounds
Use CMS amplifier/discriminator board
Will not terminating the strips affect the timing resolution, efficiency?
CMS amplifier discriminator
35.5cm (3.6ns) Ω
Center
End
Measure timing resolution and efficiency at two locations on strip with and without termination
Hit position
Center with Termination
End with Termination
End without Termination
FEE Efficiency (%)
98.6
96.1
99.6
Time resolution (ns)
1.34
1.32
1.49

16. UIUC R&D Setup Position Resolution Studies Non-uniform gap tests
SF6 Scan
Drift Chambers (resolution ~ 1 mm)
Timing Scintillators
Allows precise position measurements in x and y directions
2 mm teflon spacers
RPCs
Prototypes are small, open gap designs which can be easily modified
Flow gas through cylinders to immerse open gap RPCs
Signal Plane
2 mm thick Bakelite
Graphite

17. RPC Position Resolution
Use three methods to calculate position of muons incident on a RPC
Cluster Center Method
Strip with maximum charge – ADC Max Method
Mean of Gaussian fit to charge distribution on strips – Gaussian Method
Compare position to drift chamber position to calculate position resolution

18. Example Position Resolution Plots
Cluster Center
ADC Max
Gaussian
0.3 cm strips
s = 0.26 cm
s = 0.30 cm
s = 0.22 cm
1.0 cm strips
s = 0.46 cm
s = 0.64 cm
s = 0.45 cm

19. Gaussian Position Resolution vs Strip Width
Bad Fit
1.0 cm strips
0.6 cm strips
0.3 cm strips
1.0 cm
0.6 cm
0.3 cm

20. Performance Study: non-uniform Gap
Original uniform double gap design
19 cm
Top Gap
2 mm
2 mm
Readout Strips
Bottom Gap
17 cm
6 cm
1 cm
Strip # 1
0.2 cm strip separation

21. Performance Study: non-uniform Gap
Non-uniform double gap design
19 cm
Top Gap
2 mm
2.2 mm
Readout Strips
Bottom Gap
17 cm
6 cm
Strip # 1

22. 2D Efficiency
Tracking Problem on left hand side for this set of data
9.3 kV
Top Gap
2 mm
2.2 mm

23. 2D Efficiency
9.5 kV
2 mm
2.2 mm

24. 2D Efficiency
9.7 kV
2 mm
2.2 mm

25. 2D Efficiency
9.9 kV
2 mm
2.2 mm

26. 2D Efficiency
10.1 kV
2 mm
2.2 mm

27. 2D Efficiency
10.3 kV
2 mm
2.2 mm

28. RPC used for recent SF6 Scan
Polycarbonate (only on sides)
19 cm
2.09 mm
2.09 mm
17 cm
Strip # 15
6 cm
1 cm
0.2 cm strip separation

29. SF6 Scan 1.0 cm strips Note: Gap Size = 2.09 mm 95% 50% SF6 = 0.1%

30. Rate Capability Study
6 cm cylindrical 0.6 milliCi Fe55 sources placed between gas gaps
19 cm
2.09 mm
17 cm
6 cm
1 cm
0.2 cm strip separation

31. Rate Capability Study
~ 0.05 kHz
~ 0.5 kHz
~ 9 kHz
Source

32. Concluding Remarks
We use the CMS endcap RPC technology in the PHENIX forward trigger upgrade
PHENIX institutions have been involved in
Building prototype gaps
Testing PHENIX specific parameters
Performing basic R&D

33. Position Resolution 0.3 cm strips 1.0 cm strips 0.6 cm strips
ADC Max
Cluster Center
Gauss
1.0 cm strips
ADC Max
Cluster Center
Gauss
0.6 cm strips
ADC Max
Cluster Center
Gauss
Position Resolution (cm)
HV (-kv)