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

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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

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STAR Assumptions for Run Conditions d+Au Collisions: L = 1 10 28 cm -2 s -1 inel = 2.3 b Interaction Rate = 23 kHz 5.3 10 -6 J/ into e + e - in one unit at midrapidity 41 10 -6 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

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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

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STAR J/ Acceptance Acceptance = Both Electrons with p MC >1 hit a BEMC tower. Accepted/Thrown = 0.051 Accepted (in 0< < 1) /Thrown (in 0 < < 1 ) = 0.114 Raw (input) Accepted

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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 GeV4.824.2 0.75 1.5 GeV13.9195.6 0.18 Sum of patch 1 GeV2.87.9 0.94 1.5 GeV6.238.4 0.37 Rejection power of non-J/ events J/ efficiency (wrt those in acceptance)

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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

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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

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STAR cos Resolution J/ flat in and pt J/ realistic kinematics

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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)

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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 32.4 0.699 15.8 1 GeV2 GeV50.7 0.698 24.7 1.5 GeV 299.6 0.18 9.4 23 GeV 0.008 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

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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

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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

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STAR Trigger and Sample Rates Input: 41 10 -6 21 kHz = 0.86 Hz in acceptance: 0.86 Hz 0.051 = 44 10 -3 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 10 -3 Hz 0.23 0.7 50/500 = 0.7 10 -3 Hz 2 patch: 44 10 -3 Hz 0.7 50/500 = 3 10 -3 Hz for 10 6 sec 700 – 3000 J/ s

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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!!

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