Performance of the Performance of the PHOBOS Trigger PHOBOS Trigger
Detectors in 200 GeV Detectors in 200 GeV pp Collisions at RHICpp Collisions at RHIC
Joseph SagererJoseph Sagerer
University of Illinois at ChicagoUniversity of Illinois at Chicago
for the Collaborationfor the Collaboration
DNP 2002: Michigan State University DNP 2002: Michigan State University October 12, 2002October 12, 2002
•Trigger Hardware
•AuAu Trigger
•Concerns about pp
•pp Setup
•pp Data
•Performance of pp trigger
ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa
BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov
INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak
MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin Ballintijn, Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres, Robin Verdier, Bernard Wadsworth, Bolek Wysłouch
NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang
UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey,
Marguerite Belt Tonjes
UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
Collaboration
Trigger Hardware:
Paddle Counters:• ±3.21m from Z=0
(Nominal Collision Point)
•Cover 3 < |η| < 4.5 for collision at Z=0
•16 diamond shaped Scintillators with individual PMTs (Called ‘Slats’)
•Used for L0 trigger
Z = 0
ZDCs (0° Calorimeters):
•± 18m
•Tungsten plates /w light guides to 3 PMTs
•Standard to RHIC experiments
•Observe neutrons (used in L1)
•Luminosity monitor
DX Magnet
Additional detectors used in L1 (AuAu runs) to create different trigger mixes:
Cerenkovs & T0s
AuAu Triggering (2000-2002)• Basic Trigger: Coincidence of two Paddles
with >1 of 16 Slats Hit Pdl N Pdl P
Case 1: |Δt| ~0ns. Nominal collision + fraction of case 2 between paddles (removed by requiring ZDC coincidence or large Paddle Sum)
Case 2: |Δt| offset >10ns Largely beam-gas collisionsPaddle Time Difference (ns)
Eve
nts
200 GeV pp Environment, HiJing MC
Additional concerns:
•ZDCs not available for valid collision selection…Spectator neutrons not present for coincidence
dη
dN
η
Paddle Coverage:
Expect ~2 particles per paddle per event
Multiplicity too low for AuAu trigger
Change to 1-arm Trigger
• Disadvantages:• Potential for more
background
• Possible Bias in Multiplicity and VTX
• Advantages:• Sensitive to lower Mult
events.• Background and Bias
Understood
•Implement single arm paddle trigger (Slats hit on one side >0)
•Single particle may now trigger
•And with Synchronizing signal from RHIC (Crossing-Clock Gate)
•Crossing-Clock Gate reduces background by allowing triggers only when beam buckets overlap in the PHOBOS IR
(Neg
ativ
e si
de ti
me
– C
ross
ing
Clo
ck)
ns
0200100 300 400
100
200
300
400
Blue and Yellow = Background collisionsGreen = Real collisions + reduced BG
0(Positive side time – Crossing Clock) ns
Timing of Paddles: PdlP-CC vs PdlN-CCNegative side fires
Positive side fires
Analogous to AuAu picture shown earlier
Both sides fire
Removal of Background Events Using Paddle Timing
• Smaller peak with shorter time indicates paddle was hit early relative to the crossing-clock gate
• Green lined data has been cut to remove this smaller peak
• Smaller peaks are due to particles passing through the paddle range striking them in sequence
• This is analogous to AuAu trigger
• Green is the same cut we applied to the plot on left
Negative Side Paddle Time – CC (ns) (Negative-Positive) Side Paddle Time (ns)
Trigger vs charged particle Multiplicity
in 200GeV HiJing MC:
Multiplicity of Event
Red line: events that have at least 1 hit in both paddles
Black line: events that have at least 1 hit in only 1 paddle
Red line: events that have at least 1 hit in both paddles
Black line: all MC events
Ratio of Red/Black in above plot
=> sensitive to 95% of collisions, better at higher multiplicity
20
Check of Possible Vertex Bias
Black: All Events Red: Events with Trigger
Ratio of two plots to left
200 GeV pp HiJing MC Vertex Range of +/- 80cm (Useful PHOBOS Range)
Effect of Trigger on dN/dEta:
dN/dη vs η for 200GeV pp MC Black: 100k events Red: Events with >0 hits in Paddles
η
dηdN
Summary• Implemented single-arm trigger for
PHOBOS
• Trigger bias in new setup is minimal in vertex position and multiplicity
• The vertexing algorithm efficiency (Richard’s talk before mine) is dominant over the trigger efficiency.
• The combined efficiencies should allow physics studies in PHOBOS down to the lowest multiplicity 200 GeV pp events.