# Presentation: 285866

## Performance of the PHOBOS Trigger Detectors in 200 GeV pp Collisions at RHIC

**Joseph Sagerer**
**University of Illinois at Chicago**
- for the                     Collaboration
- DNP 2002: Michigan State University         October 12, 2002

- Trigger Hardware
- AuAu Trigger
- Concerns about pp

- pp Setup
- pp Data
- Performance of pp trigger

## Collaboration

- 	_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, KRAKOW_	Andrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski,
- 		Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak
- _	__MASSACHUSETTS INSTITUTE OF TECHNOLOGY_	Maartin 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, TAIWAN_	Chia Ming Kuo, Willis Lin, Jaw-Luen Tang
- 	_UNIVERSITY OF ILLINOIS AT CHICAGO_	Russell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
- 	_UNIVERSITY OF MARYLAND_	Abigail Bickley, Richard Bindel, Alice Mignerey,
- 		Marguerite Belt Tonjes
- 	_UNIVERSITY OF ROCHESTER_	Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly,
- 		Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

**Collaboration**

## Trigger Hardware:

**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)

- _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 collisions**

- Paddle Time Difference (ns)

- Events

## 200 GeV pp Environment, HiJing MC

- _200 GeV pp Environment, HiJing MC_

- _Additional concerns:_
- ZDCs not available for valid collision selection...Spectator neutrons not present for coincidence

- _Paddle Coverage:_
- Expect ~2 particles per paddle per event
- Multiplicity too low for AuAu trigger

## Change to 1-arm 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**

## Timing of Paddles:  PdlP-CC vs PdlN-CC

- Negative 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

_**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

- _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:

- _Effect of Trigger on dN/dEta:_

- dN/dη vs η for 200GeV pp MC                                        Black: 100k events       Red: Events with >0 hits in Paddles

## 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.