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

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

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

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

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

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)

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 %

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

2D Efficiency 9.5 kV 2 mm 2.2 mm

2D Efficiency 9.7 kV 2 mm 2.2 mm

2D Efficiency 9.9 kV 2 mm 2.2 mm

2D Efficiency 10.1 kV 2 mm 2.2 mm

2D Efficiency 10.3 kV 2 mm 2.2 mm

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

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

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

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

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

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)