# Presentation: 405302

## Energy dependence of elliptic flow over a large pseudorapidity

**Energy dependence of elliptic flow over a large pseudorapidity**
**range in Au+Au collisions at RHIC**

**Steven Manly**
**University of Rochester**
**Representing the PHOBOS Collaboration**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Collaboration meeting, BNL October 2002

***Collaboration meeting, BNL October 2002***

**Birger Back,**** ****Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, ****Abigail Bickley****, **
**Richard Bindel****, ****Wit**** Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, **
**Edmundo Garc****í****a, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, **
**Joshua Hamblen****, ****Adam Harrington****, ****Michael Hauer****, ****Conor Henderson****, David Hofman, **
**Richard Hollis****, Roman Hołyński, Burt Holzman, ****Aneta Iordanova****, ****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****, Christof Roland, Gunther Roland, ****Joe Sagerer****, ****Helen Seals****, **
**Iouri Sedykh, Wojtek Skulski, Chadd Smith, ****Maciej Stankiewicz****, Peter Steinberg, **
**George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale,**** **
**Sergei Vaurynovich****, Robin Verdier, Gábor Veres, ****Peter Walters****, ****Edward Wenger****, **
**Frank Wolfs,  Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch**
- 	**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**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

**Notes:**
Here is a sampling of Phobos members who have gotten together for a collaboration meeting.

## “Flow” = patterns in the energy, momentum, or particle density distributions that we use to ferret out clues as to the nature of the collision/matter 

**To what extent is the initial geometric asymmetry mapped into the final state?**

- View along beamline

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow as an experimental probe

-  Sensitive to interaction strength

-  Sensitive to very early times and particle velocities since asymmetry disappears with time

-  With sufficient  coverage, it probes longitudinal uniformity of system

- View along beamline

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow quantified

**Flow quantified**

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + *****2V******2******cos (2(************R******)***** + ... ) **

- View along beamline

- Fourier decomposition of the azimuthal multiplicity distribution

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow quantified

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + *****2V******2******cos (2(************R******)***** + ... ) **

**Flow quantified**

- View from above

- View along beamline

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow quantified

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + *****2V******2******cos (2(************R******)***** + ... ) **

**Flow quantified**

- View along beamline

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow quantified

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + *****2V******2******cos (2(************R******)***** + ... ) **

**Flow quantified**

- View along beamline

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## n=2, elliptic flow

- View along beamline

**n=2, elliptic flow**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

**V****2****(p****T****) saturates at high p****T**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

**V****2****(p****T****) saturates at high p****T**

**Xhangbu Xu, Quark Matter 2004**

**nucl-ex/0306007**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

**V****2****(p****T****) saturates at high p****T**

**Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference**

**Elliptic flow falls off sharply as a function of |********|**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

**V****2****(p****T****) saturates at high p****T**

**Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference**

**Elliptic flow falls off sharply as a function of |********|**

**n********2 terms observed**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow at RHIC to date (a few highlights)

**Elliptic flow is large near ********=0 (relative to hydro limit)**

**V****2****(p****T****) grows with p****T**** at low p****T****, consistent with hydro**

**V****2****(p****T****) saturates at high p****T**

**Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference**

**Elliptic flow falls off sharply as a function of |********|**

**n********2 terms observed**

**Systematic study of v2(E,********) probes the longitudinal dynamics of the collision**

**This work ******

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow in PHOBOS

**Flow in PHOBOS**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Large  coverage

** ****Data at 19.6, 62.4, 130 and 200 GeV**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: basic method

** ****Correct for imperfect reaction plane resolution **

****** ****dependence of the multiplicity**

**Flow: basic method**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

##  Pixelized detector

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

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

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

##  Azimuthally symmetric backgrounds

**Dilutes the flow signal**

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

**flow signal**

** ****Azimuthally symmetric backgrounds**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## 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**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Slide 23

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Hit-based method

**Hit-based method**

**Subevents for reaction plane evaluation**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

- Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

**Determine event plane in each subevent, ********2****±**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

- Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

**Correlate ********2****±**** with hits outside of given subevent to get raw v****2 **

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

- Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

**Determine event plane resolution by correlating ********2****+**** and ********2****-**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

- Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

**Correct raw v****2**** by resolution (factor of 1.7 to 3 depending on energy and centrality, well understood)**
**Correction determined from data**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Flow: method continued

**Have agreement between:**
** ****Two hit-based analyses ******** one “holy”, one not**
** ****Track-based analysis with NO background**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## v2 vs.  (four energies)

**(0-40% central Au+Au data)**

**Bars are 1******** “statistical” errors, expect some correlation**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## v2 vs.  (four energies)

**(0-40% central Au+Au data)**

**Boxes are 90% C.L. systematic errors**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## v2 vs.  (four energies)

**(0-40% central Au+Au data)**

**Shape is triangular at all four energies, no evidence of plateau**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## v2 vs.  (four energies)

**(0-40% central Au+Au data)**

**Drop highest |********| points at 19.6 GeV in following results**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Systematic errors

**Systematic errors**

- Hit definition
- Beam orbit/alignment
- Subevent definition
- Transverse vertex position cut
- Bins for weighting matrix definition
- Dead channel correction algorithm
- Poisson occupancy correction algorithm
- Hole filling alogorithm
- Knowledge of azimuthally symmetric background
- dN/d shape
- Symmetry in 

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## v2 vs.  (four energy overlay)

**v****2 ****vs. ******** (four energy overlay)**

- Only statistical errors shown

**Preliminary**

**Au+Au data**

**(0-40% central)**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Evolution of v2 with energy

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Limiting fragmentation

**Look at ********’ scaling**

**Limiting fragmentation**

**PHOBOS Au+Au results**
**PRL 91, 052303 (2003)**

**“****limiting fragmentation” ******** energy independence in ********’=|********|-y****beam**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## y vs. 

**y vs. ******

- Boost invariant spectra transform as:

- Jacobian suppresses spectra at low , low pT, and for large mass

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## y vs. : effect on multiplicity

**y vs. ********: effect on multiplicity**

- dN/d

- dN/dy

- 0

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## y vs. : effect on v2

**Near mid-rapidity, integration over p****T**** weights flow to higher p****T**** due to suppression at low p****T ******** v****2****(********) larger than v****2****(y)**

***P. Kolb, Proc. of 17******th****** Winter Workshop on Nuclear Dynamics (2001)***

**y vs. ********: effect on v****2**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## y vs. : effect on v2

**y vs. ********: effect on v****2**

- 0

- V2()

- V2(y)

- No change in the qualitative features of the result (<15% at =0)

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Limiting fragmentation and elliptic flow

- Only statistical errors shown

**Preliminary**

**Au+Au data**

**(0-40% central)**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Limiting fragmentation and elliptic flow

- Only statistical errors shown

**Preliminary**

**Au+Au data**

**(0-40% central)**

******’****=|********|-ybeam**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Conclusions

**No boost invariant plateau over a broad region of |********|**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Conclusions

**No boost invariant plateau over a broad region of |********|**

**Linear logarithmic growth with center-of-mass energy in differing regions of |********|**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Conclusions

**Conclusions**

**No boost invariant plateau over a broad region of |********|**

**Linear logarithmic growth with center-of-mass energy in differing regions of |********|**

**No sharp changes in the dynamics of particle production in pseudorapidity or beam energy**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Conclusions

**No boost invariant plateau over a broad region of |********|**

**Linear logarithmic growth with center-of-mass energy in differing regions of |********|**

**Preliminary**

**Au+Au data**

**No sharp changes in the dynamics of particle production in pseudorapidity or beam energy**

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004

## Slide 49

- BNL - Elliptic Flow,  S. Manly

- June 18, 2004