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.