EMCal Jet Trigger Analysis for ALICE* Christopher Anson Creighton University *Supported by the U.S. DOE Office of Science

Christopher Anson Introduction The goals of this study are to… Investigate trigger properties starting with event simulations + simple assumptions about detector. Compare conclusions with other results starting with advanced simulations of detector response. Investigate the underlying physics and behavior of triggers. By using… 2 million jet events with AliPythia 1000 background events with HIJING Pb+Pb

Christopher Anson Outline I.Jet Triggers with Pythia Jets a)Leading  0 trigger b)Cone trigger c)Patch trigger II.Patch Triggers with Pythia Jets and HIJING Background a)Jet vs. background energy in patches b)Centrality dependence III.Patch Triggers with Rate Requirement Introduced

Christopher Anson Trigger Requirements Reduce data rate into higher level trigger Efficient jet selection at lowest possible energy Use most efficient patch size

Christopher Anson An EMC for ALICE inclusive jets GeV few x 10 4 /year for E T >150 GeV From Peter Jacobs Interaction Rate ~ 4 kHz Into High Level Trigger ~100 Hz Data to tape rate ~ 100 Hz Need 100% efficiency above ~ 100 GeV And enhancement at 50 GeV Must reduce data rate by times Rates at ALICE

Christopher Anson Leading  0 Trigger Investigating efficiency for different cuts Conclusions: Increasing cut reduces efficiency for high energy jets. Some higher energy jets have a low energy leading  0. Cut Energy 2 GeV cut 4 GeV cut 6 GeV cut

Christopher Anson Cone is around Pythia jet axis 100% e +,e -,  energy 25% hadron energy Conclusions: Reduced efficiency for smaller cones Sometimes jet energy is not centralized near Pythia defined jet axis Cone Radius R = 0.05 R = 0.10 R = 0.20 R = 0.30 R = 0.40 Cone Trigger with Different Cone Radii

Christopher Anson  ~ 0.05  ~ 0.05 Patch Trigger Slides Across the Detector In reality the smallest 2x2 Tower units are ~ 0.028x0.028 Smallest patches I use are 0.05x0.05 Larger patches are built from summing the smaller patches The patches looked at in my study are: 0.05x0.05 = 1x1 0.10x0.10 = 2x2 0.15x0.15 = 3x3 0.20x0.20 = 4x4 0.25x0.25 = 5x5  x  ~ 0.15x0.15  

Christopher Anson 10 GeV cut  x  = 0.15x0.15 patch Cone has equal area Conclusions: Sometimes jet energy is not centralized near Pythia defined jet axis Cone trigger has poor efficiency Patch Trigger vs Cone Trigger Trigger Type 0.15x0.15 Patch Trigger Cone Trigger (Same Area)

Christopher Anson Patch Size Dependance Energy is summed in dηxdφ patches Cuts produce 50% efficiency at fixed 72 GeV to investigate behavior of trigger Conclusion: Patch trigger efficiency is independent of patch size

Christopher Anson Patch Size Dependance Pythia + assumption of 25% hadron energy detected Agrees with full GEANT simulation Cuts produce 50% efficiency at 72 GeV to investigate behavior of trigger Conclusion: Patch trigger efficiency is independent of patch size *Full GEANT simulation: Bill Mayes, Houston

Christopher Anson 1x1 patch trigger doesn’t reduce to leading π 0 trigger Turning off the energy deposited by hadrons… Trigger Type 0.05x0.05 Patch Trigger Leading π 0 Trigger Comparing Patch Trigger and Leading  0 Trigger

Christopher Anson With energy in patch only due to e +,e -, and  energy… Now the two curves are similar Conclusions: Hadronic energy is significant Efficiency increases as more hadron energy is deposited Trigger Type 0.05x0.05 Patch Trigger Leading π 0 Trigger Comparing Patch Trigger and Leading  0 Trigger

Christopher Anson Summary using just Pythia Leading  0 trigger efficiency decreases with larger cuts (6 GeV). Cone trigger is inefficient. - (Energy not always near jet axis). Patch trigger is most efficient. Small patches as efficient as large patches. Hadronic energy contribution enhances efficiency.

Christopher Anson Central HIJING Pb+Pb collisions Background increases monotonically with patch size Jet energy levels off with patch size Background decreases for peripheral collisions Conclusions: Background comparable to jet energy for central collisions Need centrality dependent trigger (Agrees with Peter Jacobs and Andre Mischke’s conclusion) Comparing Jet Energy to Background in Patches

Christopher Anson Patch Trigger with Rates The cuts here select 1/10 events (about what is needed in the Level 1 trigger) NOTE: This is with central HIJING and should be redone with min-bias HIJING. Central HIJING may give a worst case scenario. Conclusion: Only smaller patch is less efficient Larger patches make the trigger more robust against fluctuations This graph is also consistent with the Full GEANT simulation done by Bill Mayes.

Christopher Anson Summary Patch trigger is most efficient trigger for the EMCal. For p-p jets, efficiency is independent of patch size. For p-p + background + meeting required rate, larger patches are efficient. (smallest patch is not). Centrality dependent higher level trigger is required –(due to decreasing background with decreasing centrality). For more information refer to pages listed at

Christopher Anson Backup Slides

Christopher Anson Increasing the Cut on the Energy in a Cone shifts the efficiency curve downwards for smaller patch energies. Larger cuts eliminate more low energy AND high energy jets. Cone Radius R = 0.05 R = 0.10 R = 0.20 R = 0.30 R = 0.40 Cone Radius R = 0.05 R = 0.10 R = 0.20 R = 0.30 R = 0.40

Christopher Anson Patch Trigger with Rates Only Pythia Jets 25% Hadron Energy contributed The reduction in rate is estimated by dividing the integrated jet spectra with a cut by that without a cut The cuts here select 1/50 of the events Conclusion: Patch trigger is still efficient even for small patch sizes

Christopher Anson Calculation of Trigger Rate 1)Project jets above “cut Et” and count how many (integrate). 2)Project jets with higest patch Et above 0 gev and count how many. 3)Divide number in Step 1 by number in Step 2. 4)This give the number of events selected.

Christopher Anson Smallest towers  x  ~ 0.02x0.02