STAR Status of J/  Trigger Simulations for d+Au Running Trigger Board Meeting Dec5, 2002 MC & TU

STAR Simulations & Datasets Background Studies:  HIJING d+Au, min bias, plain GSTAR simulations: 90k events l Full BEMC was in but only ½ used J/  :  1 decay in e+e-/event + GSTAR: 100k events l flat in rapidity and p T l using simple generator for y and p T  Gaussian y distribution (  = 1) §Exponential in p T (slope 600 MeV/c) Use GSTAR data from BEMC, BBC only

STAR Assumptions for Run Conditions d+Au Collisions:  L = 1  cm -2 s -1   inel = 2.3 b  Interaction Rate = 23 kHz  5.3  J/  into e + e - in one unit at midrapidity  41  J/  into e + e - total  L2 runs with 1kHz l ADCs of all towers available l calibration ADC  E available l BBC timing info available  rough vertex z  L0 l one EMC patch > threshold § patch = 4x4 towers §available: patch sum and highest tower in patch l optional (?): count of patches above threshold

STAR L0 Simulation Results I BBC triggers fires in 93% of all min bias HIJING events BBC triggered events all HIJING events  21 kHz BBC rate

STAR J/  Acceptance Acceptance = Both Electrons with p MC >1 hit a BEMC tower. Accepted/Thrown = Accepted (in 0<  < 1) /Thrown (in 0 <  < 1 ) = Raw (input) Accepted

STAR L0 Simulation Results II How many patches in the event have high tower > 1 (1.5) GeV ? 1 high patch 2 high patches High tower 1 GeV GeV Sum of patch 1 GeV GeV Rejection power of non-J/  events J/  efficiency (wrt those in acceptance)

STAR L2 Trigger: Getting the invariant mass quickly p 1 = (E EMC-1 2 -m 2 ) ½  E EMC p 2 = (E EMC-2 2 -m 2 ) ½  E EMC cos  x1  x2/(|x1| |x2|) m 2  2 p 1 p 2 (1 – cos  ) Pro: simple, fast (no trig function) avoids ambiguity 

STAR L2 Energy Resolution Cluster 3 highest towers in a 3x3 patch 2 tower vs. 3 tower cluster: L2 Mass RMS changes from 668 to 311 MeV = 40 MeV RMS = 248 MeV Resolution ~ 17%/  E Conclusion: need clustering algorithm for L2 optimum: 3 tower cluster 3 tower cluster no clustering single tower 3 tower cluster

STAR cos  Resolution J/  flat in  and pt J/  realistic kinematics

STAR L2 Mass Resolution Several contributions:  Mass approximation l Negligible  Cluster Energy l RMS = 248 MeV  Cluster cos(  ) l ~tails Realistic simulations:  RMS mass = 311 MeV  99.9% contained in 3  1 GeV mass window Thrown mass L2 Mass, real E, real cos(  ) L2 Mass, cluster E, real cos(  ) L2 Mass, real E, cluster cos(  ) L2 Mass, cluster E and cos(  ) Here: MC z-vertex used (know from earlier studies that effect is small)

STAR L2 Simulation Results How many tower pairs in the event have mass > 1, 1.5, 2 GeV ? L0 High Tower Energy L2 Mass Threshold Rej., Eff. L0 & L2 Increase in S eff, or stat. Gain 1 GeV GeV2 GeV GeV GeV Rejection power of non-J/  events J/  efficiency (w.r.t. those in acceptance) Note: factors independent of 1 or 2 patch L0 trigger but NOT L0 rate

STAR L2 Mass & Cos(  ), Background L2 Mass cut reduces background, keeps efficiency at ~70%  Note correlation between mass and opening angle:  lowest mass pairs must come from cos (  ) ~ 1

STAR Next Step: Isolation Cuts? Try to exploit shower topology. Electromagnetic showers should deposit their energy mainly in one tower. All BG towers Photons PionsKaons Protons electrons background

STAR Trigger and Sample Rates Input:  41   21 kHz = 0.86 Hz  in acceptance: 0.86 Hz  = 44  Hz L0 with 1 GeV cut:  1 patch: 21 kHz/4.8 = 4.4 kHz event rate  2 patch: 21 kHz/24 = 0.9 kHz event rate L2 (1 kHz):  1kHz/2 (rejection) = 500 Hz L2 trigger rate  1 patch: 1kHz/4.4kHz  23%  2 patch: 100% J/  rate after L2:  1 patch: 44  Hz  0.23  0.7  50/500 = 0.7  Hz  2 patch: 44  Hz  0.7  50/500 = 3  Hz  for 10 6 sec  700 – 3000 J/  s

STAR Conclusions  Prospects for J/  Trigger look promising  Achieve reasonable efficiency at L0 and L2 l Tower Energy > 1 GeV, L2 Mass > 2 GeV gives §r ~ 24 at L0 (recall BBC rates is ~21 kHz) §r ~ 50 at L0 & L2, (simple Mass threshold increases r x 2) §L2 eff ~ 70% l Statistical gain of 25 over no trigger case.  Steps to finalize algorithm: l Isolation cuts (3x3 sum tested, 5x5 sum, 7x7 sum ?) l Test 2 Different Tower Thresholds, e.g. Tower1>1.5, Tower2>1 GeV  Implement trigger in L2 CPU’s next week l Note: Trigger fits in very nicely with Jeff’s proposed trigger scheme. l Worth reiterating: already a proof-of-principle would teach us a lot!!