# Presentation: 885370

## Update on flow studies with PHOBOS

**Update on flow studies with PHOBOS**

**S. Manly**
**University of Rochester**
***Representing the PHOBOS collaboration***

**Flow Workshop**
**BNL, November 2003**

## The Phobos Collaboration

- Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,
- Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll,
-  Zhengwei Chai, Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George,
- Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington,
- Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova,
- Erik Johnson, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly,
- Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak,
-  Inkyu Park, Heinz Pernegger, Corey Reed, Michael Ricci, Christof Roland, Gunther Roland,
- Joe Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans,
- Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Siarhei Vaurynovich,
- Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs,  Barbara Wosiek,
- Krzysztof Wožniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang
- 	**ARGONNE NATIONAL LABORATORY****	****	****BROOKHAVEN NATIONAL LABORATORY**
**	****INSTITUTE OF NUCLEAR PHYSICS, KRAKOW****	****	****MASSACHUSETTS INSTITUTE OF TECHNOLOGY**
**	****NATIONAL CENTRAL UNIVERSITY, TAIWAN****	****	****UNIVERSITY OF ILLINOIS AT CHICAGO**
**	****UNIVERSITY OF MARYLAND****	****	****UNIVERSITY OF ROCHESTER**

## Flow in PHOBOS

**Flow in PHOBOS**

##   coverage

** ****Data at 19.6, 130 and 200 GeV**

##  Pixelized detector

**Hit saturation, grows with occupancy**
**Sensitivity to flow reduced **

**Can correct using analogue energy deposition **
**–****or- **
**measure of occupied and unoccupied pads in local region assuming Poisson statistics**

**Poisson occupancy ****correction**

## Poisson occupancy weighting

## Acceptance (phase space) weighting

**Relative phase space weight in annular rings = <Nocc>****-1 **

##  Non-flow Backgrounds

**Dilutes the flow signal**

** ****Remove Background**
** ****Estimate from MC and correct**

**flow signal**

** ****Non-flow Backgrounds**

## Background suppression

**Works well in Octagon **

**Technique does not work in rings because angle of incidence is ~90******

**Demand energy deposition be consistent with angle**

## Slide 10

## Determining the collision point

**extrapolate spectrometer tracks**

**octagon hit density peaks at vertex z position**

## Detector symmetry issues where SPEC vertex efficiency highest

**Detector symmetry issues where SPEC vertex efficiency highest**

**Most data taken with trigger in place to enhance tracking efficiency**

## Strategies:

** ****Avoid the holes – Offset vtx method**

**PHOBOS flow analyses based on subevent technique**
**Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671.**
**Azimuthal symmetry is critical**

** ****Use the holes – Full acceptance method**

** ****Use a different type of analysis, such as cumulants **

**Track-based analysis:**
**Avoids holes for reaction plane determination**
**Uses tracks passing into spectrometer**

**Hit-based analyses**

## Offset vtx method

**Offset vtx method**

**Subevents for reaction plane evaluation**

** ****Good azimuthal symmetry**
** ****Fewer events, no 19.6 GeV data**
** ****Gap between subevents relatively small **

## Full acceptance method

**Full acceptance method**

**Subevents for reaction plane evaluation vary with analysis**

** ****Good statistics, 19.6 GeV data in hand**
** ****Gap between subevents large**
** ****Requires “hole filling” **

## Dealing with the holes

## Dealing with the holes

**Fill spectrometer holes by extrapolating hit density from adjoining detectors onto a virtual Si layer.  (Actual spec layer 1 is much smaller than the hole in the octagon.)**

## Track-based method

**Track-based method**

**Subevents for reaction plane**

** ****Momentum analysis**
** ****200 GeV data**
** ****Gap between subevents large**
** ****Gap between tracks and subevents large **

## Track-based method

** ****Momentum analysis**
** ****200 GeV data**
** ****Gap between subevents large**
** ****Gap between tracks and subevents large **

## Track-based method – detector space

**Track-based method – detector space**

## Track-based method – detector space

**Track-based method – detector space**

## Are there non-flow correlations that stretch across 3-6 units of ?

**Are there non-flow correlations that stretch across 3-6 units of ********?**

**Full acceptance v****1****:  ********sep****=6**
**Full acceptance v****2****:  ********sep****=5.2**
**Offset vertex v****2****: ********sep****=0.2-1.0**
**Track-based analysis**

## v2 vs. centrality and energy

**v****2 *****vs.***** centrality and energy**

***PHOBOS Au-Au***

***130 GeV result: PRL 89:222301, 2002***

**|********|<1**

**200**

**130**

**v****2**

**<N****part****>**

## v2 vs. centrality, method comparison

**v****2****200 ****(hit)**

**v****2****200 ****(track)**

***PHOBOS Preliminary***
***200 GeV Au-Au***

**v****2 *****vs.***** ****centrality****, method comparison**

**|********|<1**

**track**

**hit**

**v****2**

**<N****part****>**

## v2

***PHOBOS preliminary***
**h****+**** + h****-**
***200 GeV Au-Au***

***track-weighted  centrality averaging***

**0<********<1.5**

***(top 55%)***

**v****2**

***17% scale error***

**v****2 *****vs.***** ********p****T**

## 130 GeV result: PRL 89:222301, 2002

***130 GeV result: PRL 89:222301, 2002***

## dN/dPT 

**BRAHMS Collaboration, Phys. Rev. Lett 91 (2003) 072305**

**dN/dP****T **

## V2 vs pT

**STAR Collaboration, Phys.Rev.Lett. 90 (2003) 032301 **

**V****2**** vs p****T**

******0, three centrality bins**

## Need data at 2.2 not 3.3

**Need data at ********2.2 not 3.3**
**At ********0, V****2****(p****T****)=0.1p****T****.   At ********3.3, V****2****(p****T****)=0.08p****T****.  **
** ****Assume v****2****(p****T****)=0.085p****T**** at ********2.2.**

## Parametrize slope as function of centrality at low pT and scale values at 2.2 by (0.085/0.1)value at 0

**Parametrize slope as function of centrality at low p****T ****and scale values at ********2.2 by (0.085/0.1)value at ********0**

**Then choose coefficients corresponding to PHOBOS centrality bins and convolute with dN/dp****T ****with a 200 MeV momentum cutoff.**

**Finally, integrate.**

## Plausible that change in slope of v2(pT) leads to drop in v2()

**PHOBOS result overlayed with plausible expectation given Brahms dN/dp****T**** and STAR FTPC v****2****(p****T****)**

## Directed flow:  MC analysis, resolution and background corrected, used event plane from 1st harmonic 

**A little Quark Matter preview**

## Preliminary directed flow sensitivity

**Preliminary directed flow sensitivity**

***PHOBOS preliminary***
**h****+**** + h****-****    *****Au-Au data***

**A little Quark Matter preview**

## Flow at PHOBOS:  What’s new?

**200 GeV analyses**
**  ****Finalizing systematics **
**  ****Plan to release soon final results in 3 bins of centrality**

**Directed flow (v1)**
**  ****Still optimizing analysis and working to understand fine ****	****points of data analysis using mid-z technique**
**  ****Goal is to release preliminary v****1****(********) at 19.6, 130 and 200 GeV ****	****	****for Quark Matter**