Muon Arm Physics Program Past, Present + Future Patrick L. McGaughey Los Alamos National Laboratory Santa Fe June 17, 2003

Outline Past - Muon Physics Program in PHENIX CDR. Spin Physics Program with Muon Arm. Present – Run II and III Dimuon Data. Future – RHIC II, Trigger and Silicon Vertex Upgrades.

PHENIX CDR, Jan One Muon Arm with Drift Chambers and Concrete Absorbers. Design adapted from Dimuon Proposal.

CDR Muon Physics Program

CDR Muon Arm Event Yields Yields were computed for 10X RHIC Blue Book Luminosity, per 37 week RHIC Year. Essentially a 10 year program J/  ! Charm dominates the continuum below 5 GeV.

Backgrounds large below 4 GeV, requiring accurate like sign correction. v region has bad S/N! ORNL S/N Simulation

Muon Spin Physics Program Quark Polarization / Flavor Decomposition via Parity Violating W +  - > μ + or μ  + X Gluon Polarization via J/  - > μ + μ  or D or B - > μ + or μ  + X Transversity Program requires high luminosity, good polarization, 500 GeV, and identification of heavy quark decays! Polarized p-p collisions at 200, 500 GeV

Quark Spin Asymmetries from W decays

Progress Toward Muon Physics PHENIX Conceptual Design approved and funded by DOE, but muon spectrometer was initially deferred. RHIC Spin Proposal approved, RIKEN funds first muon arm. DOE AEE funds approved for second muon arm. South Arm is completed for Run II, Au+Au and polarized p+p collisions at  S=200 GeV. North Arm is completed for Run III, d+Au and polarized p+p at  S=200 GeV. First J/  - > μ + μ  PRL written for Run II p-p data.

Muon Arms Completed in 2002! Largest Detectors at RHIC South Muon ArmNorth Muon Arm 9 Years from CDR to Completion 2 to 3 X Larger acceptance than CDR

Run II Measurements, South Arm p+p -> J/  -> μ + μ , 66 counts and -> μ + or μ , p T to ~6 GeV Au+Au -> J/  -> μ + μ , ? counts and -> μ + or μ  Limitations – Startup run for South muon spectrometer. Low beam intensity (5%, 8% of expected) High background rates in MuID. BLT trigger commissioning. Large decay contribution to single μ’s

p+p run II

p+p -> J/  -> μ + μ 

, K decays dominate spectrum

Run III Measurements d+Au -> J/  -> μ + μ , expect ~ 2000 counts ->  ’ -> μ + μ , expect ~ 40 counts -> μ + or μ  p+p -> J/  -> μ + μ , expect ~1000 counts ->  ’ -> μ + μ , expect ~ 20 counts -> μ + or μ  -> e  μ + or e + μ , expect ~ 2500 counts Limitations – Low integrated luminosity (27%, 12% of expected) High MuID rates. No local level I trigger. S/N for  ’ ?

J/  ->  +   signal in d-Au Collisions ~ 232 J/  ’s  = 164 MeV ~ 356 J/  ’s  = 145 MeV South Muon Arm North Muon Arm Dimuon Mass(GeV/c) ~1/4 of all data Good mass resolution! Theoretical ~110 MeV

Summary of Recorded Data from Runs II and III,  S=200 GeV North and South spectrometers and trigger are working well. Few thousand J/  ->  +   from p+p and d+Au  d  /dy, d  /dp T, measurement of sea quark shadowing and baseline for future Au-Au data. Large yield of single  from p+p and d+Au  charm cross section (e  coinc. Possible.) Potential measurement of  ’ and  +   (M>4 GeV) with < 50 counts each in Run III data, large yield of continuum pairs below the J/  with low S/N. Potential measurement of J/  with < 30 counts in Au+Au Run II data.

Upgrades and Future Physics RHIC II – 10X or more increase in luminosity. Haven’t reached RHIC I average luminosity yet! Rare muon signals require high luminosity and long running time. Muon Trigger Upgrade and Shielding – Will add shielding to reduce trigger rates. Local level I needed for low mass pairs. Plan to add detectors for track momentum selection, vital for W decays. Level II processor to use tracking chamber information for mass and p T cuts. Silicon Vertex Endcap Tracker Upgrade – Detection of secondary decay vertices. Rejection of hadron decays. Improved mass resolution.

Momentum Selection Trigger Selects high momentum muons, which have small bend angles. Possible 10X suppression of singles rate. Place hodoscope in front of the muon tracker and correlate hits with MuId to make momentum cut. Hodoscope Positions Muon track through the radial magnetic field is bent in phi direction Main Issues – Hodoscope multiplicities. Segmentation of MuID.

Cherenkov Detector Trigger Proposed Cherenkov Detector 3.5 GeV Threshold for muons Main Issues – Large size, low electron threshold.

Purpose: (1) Calculate trigger primitives for Level-2 algorithms - sort data that spans individual DCM DSP’s - apply first calibrations and reduce data to x, E, t, … (2) Significant additional data buffering (3) Merge frames between DCM’s for SEB input Modification to data output stream DCMDCM DCMDCM DCMDCM DCMDCM DCMDCM DCMDCM DCMDCM PAR2PAR2 PPCPPC Frame I: Raw data from all DCM Frame II: Calibrated data (Q values) Frame III: Clustered data (x offsets) Smart Trigger Pre-Processor Partitioner II

DCM DSP needs to calculate quick calibrated values. e.g. MUTR – input  4 ADC values for each hit strip output  single Q value for each hit strip Q = gain x (ADC sample 2) PAR II is funded for Run-4 for the MUTR system only, but future includes processing for EMC, RICH, and possibly others. PAR II for MUTR case: Sorts strip data for each arm, station, plane, gap, halfoctant Finds clusters (2-3 contiguous hit strips above zero suppression) Fast x offset calculation using lookup table based on Q(peak)/Q(total) Output set of coordinate projections for use in fast tracking algorithm Pre-Processor Functionality

Silicon Vertex Upgrade ChannelsOccupancy (central Au+Au) barrel 1 st : pixels1.3 M<1% barrel 2 nd : strips92 K12% barrel 3 rd strips123 K7% barrel 4 th strips154 K5% endcaps; pixels2.8 M<3% Detects by displaced vertex : D -> μ + X B -> μ + X B -> J/  + X -> μ + μ  IP μ D

p T GeV/c Simulated Signal to Noise for Charm Decays with SVT p+p  S=200 GeV  L=10 36 Good S/N above 1 GeV/c 300K per day with RHIC II

Simulated Identification of B-> J/  with SVT Decay Distance (cm) 1mm vertex cut eliminates >99.95% of prompt J/  B decays Prompt J/  1mm cut Ratio of B decay to prompt J/  ~ 1%  =133u RHIC II - ~400 B-> J/  per day

Muon Physics Processes Summary  / ,  - Very difficult. Can only be detected at large pT in north arm. Requires high statistics background subtraction, improved tracking algorithms, upgraded trigger. May need SVT for background rejection. J/  - OK in p+p and d+Au. Au+Au backgrounds under study.  ’ – Should be OK with sufficient integrated luminosity. Good mass resolution important, can be improved by SVT. ,  ’,  ’’ – Requires RHIC II luminosity and trigger upgrade. Up to 10K  possible? μ + or μ  – Trigger upgrade required for highest p T. SVT needed for D decay identification at low p T, otherwise bad S/N. μ + μ   Continuum below 3 GeV - Requires high statistics background subtraction. S/N can be greatly improved by SVT.

Physics Processes Continued μ + μ   Continuum above 4 GeV - Requires RHIC II. S/N can be improved by SVT. e μ  – Should be OK after sufficient statistics for background subtraction. SVT upgrade would improve S/N. B -> J/  - Requires RHIC II, trigger upgrade and SVT upgrade. W +  - Requires RHIC II, 500 GeV beam and trigger upgrade.

Conclusions We’ve come a long way in the last 10 years! But we’re just beginning to scratch the surface of our physics program. With lots of high intensity beam and some upgrades to the trigger, I believe that we can accomplish much more than the physics program we proposed in ’93. The trigger upgrades are essential! If the Silicon Vertex Tracker is funded, high statistics heavy-quark physics is within reach. The SVT can also improve our S/N and mass resolution. Thanks to all of you who’ve worked hard for so many years to accomplish all of this.