# Presentation: 479641

## First performance results from Phobos at RHIC

- Heinz Pernegger for the PHOBOS collaboration
- Vertex 2000

## 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, JawLuen Tang**
_**UNIVERSITY OF ROCHESTER**_
**A. Hayes, Erik Johnson, Steven Manly, Robert Pak, Inkyu Park, Wojtech Skulski, Teng, Frank Wolfs**
_**UNIVERSITY OF ILLINOIS AT CHICAGO**_
**Russell Betts, Christopher Conner, Clive Halliwell, Rudi Ganz, Dave Hofman, 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**

## Relativistic Heavy Ion Collider

**RHIC environment:**
- Highest energy density ever produced in lab
- Au-Au collisions with total s= 25TeV
- About 4000 charged particle per central collision
**12 June**: 1st Collisions @ s = 56 AGeV
**24 June**: 1st Collisions @ s = 130 AGeV
**5 Sept**: end of first Au-Au physics run

## PHOBOS Detector

## What does Phobos measure ?

- Phobos searches for signs of Quark-Gluon Plasma at RHIC
- Measures multiplicity of charged particles over full solid angle
- Reconstruct tracks in mid-rapidity range with low Pt threshold and identifies them
- Measures particle ratio/spectra, particle correlation
- Phobos “lives” on analog signals of our silicon detectors
- Multiplicity measurement use dE/dx as multiplicity estimator
- Spectrometer uses dE/dx method for particle identification
- Analog information used to reject background
- Analog signals partially used in pattern recognition

## The Multiplicity detector

- 1 layer of large silicon pad detectors “everywhere”
- Count single hits or sum of analog signals in a detector area as measure of particle multiplicity
- Has to deal with high occupancy (>80%)

## The silicon spectrometer

**The silicon spectrometer**

- 16 layer of smaller silicon pad detectors near mid rapdity
- Tracks and Identifies particles (dE/dx) in 2T magnetic field
- All silicon readout with Viking VAHDR1 chips
- Very high dynamic range (>100MIPs), peaking time 1.1s

- 1x1mm to 0.7x19mm

## Our silicon detectors

- Double Metal, Single sided, AC coupled, polysilicon biased detectors
- produced by ERSO, Taiwan

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

## Before installation

## RHIC beams in Phobos

**Physics Run 2000**

- Luminosity estimated using coincidence of signals in the Zero Degree Calorimeters. =10.7barn used to convert counts to luminosity.

- PR00 Start6 Bunches

- Start 55 Bunches

**Integrated Luminosity****       ********B****-1**

**Date**

- _RHIC Integrated Luminosity 65+65 GeV _

- _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

## Performance of the Multiplicity Detector 

- phi

- Z (beam)

-  One high multiplicity event in the octagon
-  occupancy up to 80%
-  Color encodes pulse height

- Opening to Vtx

- Opening to Vtx

- Opening to Spec

- Opening to Spec

## Dealing with high occupancy

- Base line before and after
-  correction

## Signal dependence on occupancy

## Multiplicity sensor uniformity

- +/- 1%

- +/- 3%

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

**3.6 x 8.4 cm**

**8.3 cm x 6.5 cm**

- Smp= 93 keV

- Smp= 85keV

## Performance of tracking detectors

- Hits in VTX

- Hits in SPEC

- Tracks in SPEC

- 130 AGeV

- 56 AGeV

- 130 AGeV

## Signal uniformity in Spec/Vertex

- T1 Smp= 90
- T2 Smp=85

- T3 Smp= 85
- T4 Smp=85
- T5 Smp=85

- Inner Vtx Smp=87
- Outer Vtx Smp=85

## Uniformity within sensors

- Pad row (along readout lines accros sensor)

- Relative signal variation

- +/- 2%

- 1 x 1 mm2

- 0.4 x 6 mm2

- 0.7 x 7.5 mm2

- 0.7 x 15 mm2

- 0.7 x 19 mm2

- 0.3 x 23 mm2

- 0.3 x 46 mm2

## Signal/Noise vs sensor layout

**Signal/Noise vs sensor layout**

- Signal peak [e-]

- Noise [e-]

- Large pads
- Longs readout
- lines (high capacitance)

- Chip dominated base offset
- (ENC = 900 e-+5e-/pF @ 1.1s)

- =24000e-

- Closest to beam

## Focus on Si signal simulation

- Critical test of detector understanding
- Both distributions contain the same number of central events
- Points are for VTX data
- No correction for detector thickness
- Histogram is for simulated VTX signals
- GEANT
- Response from test-beam
- Electronics noise
- Shulek correction

- (CR setup)

## Optimizing our signal simulation

-   Data

-   Geant

-  
- 

## Measuring charged multiplicity

**Measuring charged multiplicity**

- VTX Tracklets
- Two hit combinations that point to the vertex
- d = 2 – 1
- Good tracklets have d<.1

## Results :PHOBOS Measurement of Charged Particle Multiplicitynear Mid-rapidity 

**Results**_ :PHOBOS Measurement of Charged Particle Multiplicitynear Mid-rapidity _

- hep-ex/0007036_ _Accepted for publication in PRL Oct 02 2000

- dNch/d (||<1) at  sNN=  56 GeV: 408±12±30

- dNch/d (||<1) at  sNN=130 GeV: 555±12±35

## Summary

## Next transparencies are backup + additions

## Readout & Calibration system

## Derivation of dN/d

- Extract  from correlation of
- Primaries in –1 <  < 1
- Measured number of tracklets

- dN/d

- Number of Tracklets

- 5<z<10

- SPEC

- VTX

## Measuring dN/d with tracklets

- Number of reconstructed tracklets is proportional to **dN/d******** | ********<1**
- To reconstruct tracklets
- Reconstruct vertex
- Define tracklets based on the vertex and hits in the front planes of SPEC and VTX
- Redundancy essentially eliminates feed-down, secondaries, random noise hits
- To determine 
- Run the same algorithm through the MC
- Folds in detector response and acceptance

## Measuring Vertex

**Measuring Vertex**

- Pointing accuracy describes how extrapolated tracks deviate from calculated vertex.
- Compares well with HIJING simulation

- Spectrometer sits very close to vertex
- High resolution tracking in 6 planes gives excellent vertex resolution