# Presentation: 885369

## Pseudorapidity Dependence of Elliptic 

**Pseudorapidity Dependence of Elliptic **
**Flow in Au+Au Collisions at 19.6, ****62.4****, 130, and 200  GeV Using the PHOBOS Experiment at RHIC**

**Joshua Hamblen**
**University of Rochester**
**For the PHOBOS Collaboration**

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Figure out title

## Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, 

- Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley,
- Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Vasundhara Chetluru,
- Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen,
- Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich,
- Chia Ming Kuo, Wei Li, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen,
- Rachid Nouicer, Andrzej Olszewski, Robert Pak, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, 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 PAN, KRAKOW	MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- 	NATIONAL CENTRAL UNIVERSITY, TAIWAN	UNIVERSITY OF ILLINOIS AT CHICAGO
- 	UNIVERSITY OF MARYLAND	UNIVERSITY OF ROCHESTER

- DNP 2004 - J. Hamblen

- October 29, 2004

## Flow as an experimental probe

-  Probes the thermalization of the system
-  Sensitive to very early times and particle velocities since asymmetry disappears with time
-  With sufficient  coverage, it probes longitudinal uniformity of system

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Flow, what is it good for? Strong collective behavior (No flow would mean no interaction in the final state; it interacts quickly) sensitive to interaction strength

## Flow quantified

- (reaction plane: ******R**)

**Flow quantified**

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

- View along beamline

- Fourier decomposition of the azimuthal multiplicity distribution:

**Basic Formula:**
**V****2**** = < cos (2(********2****)) > /********cos(2(********2****a**** ********2****b****))> )****1/2**

- Directed flow

- Elliptic flow

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
How do we measure flow? Move dN/d(phi – psiR) eq. to the top, start with it.

## Flow in PHOBOS

**Flow in PHOBOS**

- 137000 Silicon Pad Channels
- Nearly 4 coverage

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Describe detector.  Important detector elements for this analysis described on next slide.  Add # of Si channels like MBT. Mention VTX det’s ability to find fertex...in addition to the first 6 spec planes we use. (I can cut this discussion down. Say less about Spec and VTX)

## Large  coverage

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

**      ****Ability to study v2(E,********)**

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
V2 over a broad range of pseudorapidity and energy.  Another view of detector.  What to say here about large eta and many energies? V2(E,eta)?

## Slide 7

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Unrolled oct and ring hit map.  Event by event estimate R.P. and correlate hits to it.  Recall how much sensitivity we lose.

## Vertex range -10 cm <z<10 cm

**Vertex range -10 cm <z<10 cm**

**Subevents for reaction plane evaluation**
**-3 < ******** < -0.1 and 0.1 < ******** < 3**

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Get rid of hit-based method add centimeters, give eta coverage of subevents(?) 

## Flow: method continued

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

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

************

************

- DNP 2004 - J. Hamblen

- October 29, 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 **

**V****2**** = < cos (2(********2****)) > **

************

************

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Obs -> raw

## Flow: method continued

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

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

**Resolution = <cos(n********2****+,-********R********cos(2(********2****+**** ********2****-****))> )****1/2**

************

************

**V****2**** = < cos (2(********2****)) > /********cos(2(********2****+**** ********2****-****))> )****1/2**

- DNP 2004 - J. Hamblen

- October 29, 2004

## Flow: method continued

**Resolution-corrected v****2**** is further corrected by ~30%  **
** ****dilution due to azimuthally symmetric (“non-flow”) background **

**Correction derived from Monte Carlo **

************

************

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Is all the discussion about corrections necessary?

## v2 vs.  (four energies)

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

- Submitted to PRL (nucl-ex/0406021)

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

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
All charged particles.  Consistent with previous results.  Smaller statistics at 20 GeV give larger errors.  Non-boost invariant, roughly triangular shape at all 4 energies.  (Mention correlated stat. errors, and that we throw out the end pts. At 20 gev.   Don’t mention rise of v2 and lower en.)

## Limiting fragmentation and elliptic flow

**Limiting fragmentation and elliptic flow**

- Only statistical errors shown

**Take out differing beam boosts by going into approximate frame of reference of target**
**Look at ********’ scaling**

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

- (nucl-ex/0406021)

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Remember eta->y Jacobian discussion for dN/deta’ plot, as to why the curves peel off.  Mention systs. Are dropped.  You’re in the frame of one nucleaus (eta+ybeam), and then the other (eta-ybeam), and the behavior is approx. the same in these 2 different independent sides of eta.

## Limiting fragmentation and elliptic flow

**Limiting fragmentation and elliptic flow**

- Only statistical errors shown

******’****=|********|-ybeam**

- (nucl-ex/0406021)

- Average positive and negative v2(points together
- Then shift by ybeam

- DNP 2004 - J. Hamblen

- October 29, 2004

**Notes:**
Shows limiting fragmentation throughout the region of eta’ overlap

## Conclusions

**Triangular shape of v****2**** at all 4 energies**
**No boost invariant plateau over a broad region of |********|**

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

- DNP 2004 - J. Hamblen

- October 29, 2004

## End

- DNP 2004 - J. Hamblen

- October 29, 2004

## V1 from QM04

- DNP 2004 - J. Hamblen

- October 29, 2004