# Presentation: 890016

## THE PHOBOS EXPERIMENT AT RHIC

- Judith Katzy
- for the
- PHOBOS Collaboration

## PHOBOS Collaboration

**Birger Back, Russell Betts, Alan Wuosmaa**, **Nigel George**
**BROOKHAVEN NATIONAL LABORATORY**
**Mark D.Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Louis Remsberg, Andrei Sukhanov**
**INSTITUTE OF NUCLEAR PHYSICS, KRAKOW****Wojciech Bogucki , Andrzej Budzanowski, Tomir Coghen, Kazimierz Galuszka, Jan Godlewski ,Roman Holynski, **
**Jerzy Kotula, Marian Lemler, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki **
**Marek Stodulski, 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, Kristjan Gulbrandsen, P. Haridas, Piotr Kulinich, Heinz Pernegger, Miro Plesko, Gunther Roland†, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch‡**
**NATIONAL CENTRAL UNIVERSITY, TAIWAN****Yuan-Hann Chang, Augustine Chen, Willis Lin**
**UNIVERSITY OF ROCHESTER****Adam Hayes, Erik Johnson, Steven Manly, Robert Pak, Inkyu Park, Frank Wolfs**
**UNIVERSITY OF ILLINOIS AT CHICAGO****Russell Betts, Clive Halliwell, Burt Holzman, Judith Katzy, Wojtek Kucewicz, **
**Don McLeod, Rachid Nouicer, Michael Reuter**
**UNIVERSITY OF MARYLAND****Edmundo Garcia-Solis, Peter Stanskas, Alice Mignerey**

## Physics Goals of PHOBOS:

_**Study QCD Vacuum and Confinement**_

- Look for Excess Entropy
-  Multiplicity Distribution and Fluctuations
-  Source Size and Lifetime
- Look for Collective Phenomena over large V
-   Low Transverse Momentum
- Look for Unusual Medium Effects
-  Phi Mass and Width

## The Phobos detector

**first year :**
** ****full multiplicity and vertex detector**
** ****1 spectrometer arm**
** ****2 TOF elements**

**The Phobos detector**

-  multiplicity array:
- 
-  spectrometer:
- deg
-  vertex detector
-  tof
-  trigger detectors
-  magnet

## Triggering and data rates 

- _Simple, unbiased trigger_:
- paddle scintillators 3.7  || 4.5
- ring cerenkov          4.9  ****
- _Rates at nominal Luminosity _**L ****= **10**26** cm**2** s**1**
- R(Au+Au)              = 600 Hz (b  fm)
- R(Au+Au, central) = 60 Hz
- R(BeamGas)          = 100 Hz
- R(e+e+)                 = 10 Hz
- _data collection volume_
- 18 kb/ event
-  => 60 Tb raw - 430 Tb total / year

- Reduced by vertex timing
- cut

## Multiplicity array and Vertex detector

- octagon

- ring
- counter

**-1.1**m

**1.1**m

**2.3**m

**-2.3**m

**5.0**m

**-**5.0m

**Multiplicity array and Vertex detector**

- Multiplicity measurement:
- octagon and 6 ring counters
- acceptance: || < 5.4  0 ********
- bin width        

- vertex

- interaction
- point

## Vertex reconstruction

**z**

**11 cm**

**5.5 cm**

**Vertex reconstruction**

- 

- z

- = 60 m

- Vertex Resolution:

- Vertex Reconstruction in x,y:
- with tracks reconstructed in
- spectrometer

- z

- beam

- beam

- Vertex acceptance:
- -20cm ****** **z  **** 20 cm

## Multiplicity array

**Multiplicity array**

- Part of octagon

- 1 ring counter

## Silicon Detector modules used in the Multiplicity array

**Silicon Detector modules used in the Multiplicity array**

- Octagon module

- 8.5cm

- 6.5 cm

- 120 pads / sensor
- ~0.05 - 0.1
- =/16

- 64 pads / sensor
- ~0.05
- =/32

- Ring module

## Multiplicity Reconstruction

**Multiplicity Reconstruction**
** ****from Energy Loss**

- Reconstructed multiplicity in Pad i:
-    Mi = Edepi /  (Eisingle • Nitot/Niprim)

-   Edepi :   deposited Energy (angle corrected)
-   Eisingle:  mean energy loss for one particle
-              traversing pad

-    Nitot/Niprim** : **ratio of total/primary tracks

- 1.5 * 107  distributions in 1 month at 1% nominal luminosity

- Error on total Multiplicity: 2/3

## Event by Event Multiplicity 

**Average over 50 Events**

## Spectrometer and Tracking

**1 GeV/c**

- 

- -

- -

**100 MeV/c**

**100 MeV/c**

- 

- 

**+**

- Low field region
- for pattern recognition
- particle id via dE/dx

**High B-field**

**Spectrometer and Tracking**

## The Magnet

- conventional magnet
- maximal B-field: 2.1 Tesla

**The Magnet**

## Silicon Detectors mounted 

**on Spectrometer Frame**

## Response of Silicon Detector to  285MeV/c Pions  - Data!

**Response of Silicon Detector to  285MeV/c Pions  - Data!**

- without gaussian addition

- in collaboration with hephy in Vienna

## Spectrometer Acceptance

## Momentum Resolution

## Track Finding - very low P

**Track Finding - ****very low P**

- deg

- deg

- deg

- deg

- 7 Planes, E>800 keV

- 7 Planes, all Hits

- 80

- 60

- 20

- 40

- 20

- 40

- 60

- 80

- 0

- 0

- -8

- 8

- 8

- -8

- Stopping Kaon

## HBT Acceptance for  

**HBT Acceptance for ******

- Truth
- Resolution smeared

- Source Parameterization:
-   C2 = 1 + * exp(-Qi2 R**i****2**)      i = L, TO,TS

## HBT Capabilities

- “Standard” Scenario
- Extrapolate from AGS/Cern Energies

- Exotic Scenario I
- Very Large Source

## Phi measurement

-  results after 1 nominal week, 15% central cut,  Si  pid:
- 50000 
- Resolution: (Minv) = 1.6 MeV
- Dominated by momentum resolution
- Error on Width: 1.0 MeV

-     K+K-

## Summary - PHOBOS Highlights

-  Coverage for Charged Multiplicity in almost 4 
-   with the Multiplicity Array
-  Momentum Measurement and Particle Identification
-   at Mid-rapidity with Low pt Threshold with the
-   Spectrometer
-  Unbiased Taking Data Due to  High Data Rate Capability

**READY **
**FOR RHIC START-UP **
**IN NOVEMBER**