# Presentation: 404807

## Mark D. Baker (BNL)
for the PHOBOS collaboration
August 7, 2000
RHIC/AGS Users Meeting

- for the PHOBOS collaboration
- August 7, 2000
- RHIC/AGS Users Meeting

- dN/d (~0) for central events
- Full (1-arm) detector commissioning

- PHOBOS

## 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, 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**

## Min. Bias Trigger & Event Selection

- _We attempt to trigger on ALL collisions._
- Good paddle timing.
- Good ZDC timing **OR **Large paddle signal.

- Negative Paddles

- Positive Paddles

- ZDC N

- ZDC P

- Au

- Au

- PP

- PN

- 3<||<4.5

- 

## ZDC Sum vs. Paddle Sum

- 130 AGeV

- central

- peripheral

## Estimating Npart

- 6% most central events based on paddles gives

- Npart

- Events/bin

## What do we learn from dNch/d | <1 ?

- It’s a fundamental handle on the initial state
- Proportional to energy density
- Proportional to entropy density
- Proportional to initial gluon density
- It constrains models, especially when energy and centrality systematics are included.

## Commissioning Run Setup

- Commissioning Run Setup

## Tracklets

**2 hits + vertex**

**beampipe**

**Si**

**Si**

## dN/d for ||<1

**Submitted to PRL**
**hep-ex/0007036**

- 56  AGeV: 408±12±30

- 130 AGeV: 555±12±35

## Constraining the Models

- X.N.Wang et al.

**PHOBOS**

## Silicon Detectors

**Partially assembled **
**Octagon**

- Ring arrays

## More Silicon Detectors

- Spectrometer

## PHOBOS Apparatus

## Full Detector Event

**~100,000 channels**

## Octagon Unrolled

**VTX**

**VTX**

**Z**

****

## Plans & Conclusions

- dN/dmeasured for central events.
- Full detector installed.
- Looks healthy.
- Hit processing, alignment, tracking...
- Physics Plans
- dN/d
- Centrality dependence
- Shape over full  range.
- Spectrometer physics: (ratios, HBT, spectra...)