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STAR
Status of J/ Trigger Simulations for
d+Au Running
Trigger Board MeetingDec5, 2002MC & TU
STAR
Simulations & Datasets
Background Studies: HIJING d+Au, min bias, plain GSTAR simulations: 90k events
Full BEMC was in but only ½ used
J/: 1 decay in e+e-/event + GSTAR: 100k events
flat in rapidity and pT
using simple generator for y and pT
Gaussian y distribution ( = 1) Exponential in pT (slope 600 MeV/c)
Use GSTAR data from BEMC, BBC only
STAR
Assumptions for Run Conditions
d+Au Collisions: L = 1 1028 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
ADCs of all towers available calibration ADC E available BBC timing info available rough vertex z
L0 one EMC patch > threshold
patch = 4x4 towers available: patch sum and highest tower in patch
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 pMC>1 hit a BEMC tower.
Accepted/Thrown = 0.051
Accepted (in 0< < 1) /Thrown (in 0 < < 1 ) = 0.114
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 4.8 24.2
0.75
1.5 GeV 13.9 195.6
0.18
Sum of patch
1 GeV 2.8 7.9
0.94
1.5 GeV 6.2 38.4
0.37
Rejection power of non-J/ eventsJ/ efficiency (wrt those in acceptance)
STAR
L2 Trigger: Getting the invariant mass quickly
• p1 = (EEMC-12-m2)½ EEMC
• p2 = (EEMC-22-m2)½ EEMC
• cos x1x2/(|x1| |x2|)
• m2 2 p1 p2 (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
<Ee - Ecl> = 40 MeVRMS = 248 MeV
Resolution ~ 17%/E
Conclusion: need clustering algorithm for L2optimum: 3 tower cluster
3 towercluster
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
Negligible Cluster Energy
RMS = 248 MeV Cluster cos()
~tails
Realistic simulations: RMSmass = 311 MeV 99.9% contained in 31
GeV mass window
Thrown massL2 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 Seff, or stat. Gain
1 GeV 1 GeV 32.4
0.699
15.8
1 GeV 2 GeV 50.7
0.698
24.7
1.5 GeV 1.5 GeV 299.6
0.18
9.4
2 3 GeV
0.008
Rejection power of non-J/ eventsJ/ 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 towersPhotonsPionsKaonsKaonsProtons
i high towertowers
itowers
E E
E
electrons background
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 106 sec 700 – 3000 J/ s
STAR
Conclusions Prospects for J/ Trigger look promising Achieve reasonable efficiency at L0 and L2
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%
Statistical gain of 25 over no trigger case.
Steps to finalize algorithm: Isolation cuts (3x3 sum tested, 5x5 sum, 7x7 sum ?) Test 2 Different Tower Thresholds, e.g. Tower1>1.5, Tower2>1 GeV
Implement trigger in L2 CPU’s next week Note: Trigger fits in very nicely with Jeff’s proposed trigger scheme. Worth reiterating: already a proof-of-principle would teach us a lot!!