# Presentation: 885814

## Robert Pak (BNL)
for the PHOBOS Collaboration
Quark Matter 2001
Jan. 16, 2001

*for the PHOBOS Collaboration*
- Quark Matter 2001
- Jan. 16, 2001

**The PHOBOS Detector at RHIC**

- Present Status and Future Plans

## PHOBOS Collaboration

_**ARGONNE NATIONAL LABORATORY**_
**Birger Back, Nigel George, Alan Wuosmaa**
_**BROOKHAVEN NATIONAL LABORATORY**_
**Mark Baker, Donald Barton, Mathew Ceglia, Alan Carroll, Stephen Gushue, George Heintzelman, Hobie Kraner, Robert Pak, Louis Remsberg, Joseph Scaduto, Peter Steinberg, Andrei Sukhanov**
_**INSTITUTE OF NUCLEAR PHYSICS, KRAKOW**_
**Wojciech Bogucki, Andrzej Budzanowski, Tomir Coghen, Bojdan Dabrowski, Marian Despet, Kazimierz Galuszka, Jan Godlewski, Jerzy Halik, Roman Holynski,  W. Kita, Jerzy Kotula, Marian Lemler, Jozef Ligocki, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki, Andrzej Straczek, Marek Stodulski, Mieczylsaw Strek, Z. Stopa, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak, Pawel Zychowski**
_**JAGELLONIAN UNIVERSITY, KRAKOW**_
**Andrzej Bialas, Wieslaw Czyz, Kacper Zalewski**
_**MASSACHUSETTS INSTITUTE OF TECHNOLOGY**_
**Wit Busza*, Patrick Decowski, Piotr Fita, J. Fitch, C. Gomes, Kristjan Gulbrandsen, P. Haridas, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Clyde Law, Johannes Muelmenstaedt, Marjory Neal, P. Patel,  Heinz Pernegger, Miro Plesko, Corey Reed, Christof Roland, Gunther Roland, Dale Ross, Leslie Rosenberg, John Ryan, Pradeep Sarin, Stephen Steadman, George Stephans, Katarzyna Surowiecka, Gerrit van Nieuwenhuizen,  Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch**
_**NATIONAL CENTRAL UNIVERSITY, TAIWAN**_
**Yuan-Hann Chang, Augustine Chen, Willis Lin, Jaw Luen Tang**
_**UNIVERSITY OF ROCHESTER**_
**Adam Hayes, Erik Johnson, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs**
_**UNIVERSITY OF ILLINOIS AT CHICAGO**_
**Russell Betts, Christopher Conner, Clive Halliwell, Rudi Ganz, Richard Hollis, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter**
_**UNIVERSITY OF MARYLAND**_
**Richard Baum, Richard Bindel, Jing Shea, Edmundo Garcia-Solis, Alice Mignerey**

## Primary Physics Objectives

- PHOBOS searches for signatures of QGP at RHIC
- Multiplicity of charged particles for **|**** **| **< 5.4
- Particles down to low pT near y = 0
- Particle ratios, spectra, and correlations
- PHOBOS “lives” on analog signals of our silicon detectors
- dE/dx as multiplicity estimator
- dE/dx method for particle identification
- Background rejection
- Pattern recognition

## PHOBOS Apparatus

- Ring Multiplicity Detectors
- (Silicon)

## Event Selection

**Event Selection**

- Paddle Counters

- Coincidence (38 ns) between paddle counters

## Centrality with Paddles

- 3<|**|<4.5

**

**Centrality with Paddles**

- Energy deposited in paddle counters

- e.g., top 6% most central collisions

- Events/Bin

- Entries

## Centrality with ZDCs

- peripheral

- central

- See J.M. Katzy in Parallel Session II for details

- ZDC sum vs. Paddle sum:
- Independent methods to determine centrality that
- correlate well

**ZDC**

- Paddle Sum (au)

- ZDC Sum (au)

## Silicon Pad Technology

- AC coupled pad (p-implant + metal 1 pad)
- polysilicon bias resistor
- metal 2 readout line
- contact hole metal 1- metal 2

**Silicon Pad Technology**

## Silicon Pad Sensors

- High dynamic range ( > 100 MIPs), peaking time 1.1 s
- Si latch-up system interlocks during single-event upset to protect against chip damage

- Typical pad layout

- IDE VA-HDR1
- Readout Chips

## Silicon Everywhere

**Octagon/Vertex**

**Spectrometer Arm**

**Silicon Everywhere**

**Ring**

**137,000 channels in total **

##  Si Signal Simulation

**Vertex signal response**

-   Full understanding of detector signal at the most basic level

- angle corrected @ 300 m of Si

**normalized hit energy   x****0**

_**dE**_
**dx**

**[keV]**

## Sensor Uniformity

**Sensor Uniformity**

- +/- 1%

- +/- 3%

- No substantial signal variation due to different layout
- (double metal line routing and/or varying pad size)

- signal (keV)

- Smp= 93 keV

- Smp= 85 keV

- counts

- counts

- signal (keV)

- Rings

- Octagon

##  Signal/Noise Ratios

- S/N ratios better than 10:1 design specification
- Larger pads & longer readouts           lower S/N ratio
- Ave. noise in entire detector setup stable over time

## Background Suppression 

**Background Suppression**** **

- E vs. ** in the Octagon

- Good agreement between data and simulation
- Powerful method to reject background

- Si

- from vertex

- not from
- vertex

**Notes:**
The next thing we have to do is contend with background.  In the octagon, this turns out to be not such a big deal, because we can get rid of it by noticing that the characteristics of secondary particles, ie their energy loss is very different from those of particles that come from the vertex.  The reason is that esp. at the ends of the octagon, where we expect the most background as we have a thick beam pipe and some magnet steel, particles from the vertex go through a lot of silicon and deposit more energy.  You can see this by looking at the plot here which shows energy loss vs eta.  We have a very clear “smiley face” picture from primary particles from the vertex. Particles not from the vertex have different trajectories and go through less silicon, and deposit less energy, so we eliminate a large fraction of the background just by cutting on de. On the right is the same plot only with monte-carlo “data” showing exactly the same features.  I’ve also drawn the decut.  In fact this deals with a very large fraction of the secondary particles produced both in the beam pipe and the other parts of the experiment near the octagon.

## Multiplicity & Vertex Array 

- Vertex

- Octagon

- Ring

- Multiplicity:

- Vertex:

-  Single layer of Si with large pads

-  Two layers of Si with “strip” pads

- Count single hits or sum of analog signals in a detector area as a measure of particle multiplicity

## Vertex Determination

- _Vertex Resolution:_
- x ~ 450 m
- y ~ z ~ 200 m**    **

- For this event:
- vertex @
- Z = -0.054 cm

- cm

- counts

## Multiplicity Array Unrolled

- 0

- +3

- -3

- +5.4

- -5.4

- Spec

- Spec

****

******

- Rings

- Rings

- Vertex

- Octagon

## Multiplicity Distribution

- Also Collective Effects: See I.C. Park in Parallel Session II

**Multiplicity Distribution**

## PHOBOS Magnet

- B Field Map

- By (T)

- cm

- Reproducibility of absolute field strength better than 1%

## Full Tracking

- Particle ID with the spectrometer
- See N.K. George in Parallel Session III  for details

****

**p**

**K**

**Full Tracking**

- protons

- Kaons

- pions

- _Run 5332 Event 35225 08/31/00 06:59:24__PHOBOS Online Event Display_

- Spectrometer Arm N

- Spectrometer Arm P

- Octagon Multiplicity
- detector

- Trigger
- Scintillators  N

- Trigger
- Scintillators  P

- Not to scale

- Not all sub-detectors shown

- Au-Au Beam Momentum = 65.12 GeV/c

## PHOBOS DAQ

_**Run 2000:**_
- Data taking rate: 15 ev/sec
- Sustained: 5 MB/sec
- 8 PowerPC’s
_**Run 2001:**_
- Goal: 100 ev/sec
- Sustained: 40 MB/sec
- _New features:_
- Direct VMEGigabit
- Multi-buffering
- Compression 2:1
- 22 PowerPC’s

**PHOBOS DAQ**

## Summary of 2000 Run

- RHIC delivered ~ 2.7 b-1 integrated luminosity to PHOBOS over 6 weeks of running in Summer 2000.
- PHOBOS captured ~ 3.5M events on tape: mixture of minimum bias and central triggers; 99% DAQ uptime.
- Silicon systems performed to specifications: Average S/N measured in the detector was 14 to 18 depending on sensor type; 98% channels fully functional.
- Front End Electronics were stable. Every instance of latch-up in the VA chips was detected successfully during adverse beam conditions.

## Future Plans: 2001 Run

- DAQ upgrade
- Complete installation of 2nd spectrometer arm
- Significantly improved 2-particle phase space
- HBT for small sources
- down to pT = 0
- Back-to-back high pT  particles
- Doubles the one-particle statistics
- Symmetric system improves systematics

## PHOBOS Charm Upgrade

- Open charm measurement is essential for understanding total charm production
- D      e_ + X is best suited for small acceptance near midrapidity** **

- Study single electrons at high pT from displaced vertices
- Suppress the hadronic background
- Upgrade PHOBOS with:
- microvertex detector
- ALICE Transition Radiation Detector prototypes
- Electromagnetic calorimeter

- TRD

- EMCal

- vertex

## Stay tuned to:     www.phobos.bnl.gov 
Drop by PHOBOS IR during your BNL Day Tour today 

- Stay tuned to:     www.phobos.bnl.gov
- Drop by PHOBOS IR during your BNL Day Tour today

**Conclusion**

**Robert Pak** for