1 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results from the PHOBOS experiment at RHIC Steve Manly (Univ. of Rochester) for the

1 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001

Results from the PHOBOS experiment at RHIC

Steve Manly (Univ. of Rochester)

for the PHOBOS

Collaboration


PHOBOS CollaborationARGONNE NATIONAL LABORATORY

Birger Back, Nigel George, Alan Wuosmaa

BROOKHAVEN NATIONAL LABORATORY

Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov

INSTITUTE OF NUCLEAR PHYSICS, KRAKOW

Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

Wit Busza, Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed, Christof Roland, 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

Willis Lin, JawLuen Tang

UNIVERSITY OF ROCHESTER

Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

UNIVERSITY OF ILLINOIS AT CHICAGO

Russell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter

UNIVERSITY OF MARYLAND

Richard Bindel, Edmundo Garcia-Solis, Alice Mignerey April 2001


PHOBOS Detector

Ring Counters

Paddle Trigger Counter

Spectrometer

TOF

Octagon+Vertex

• 96000 Silicon Pad channels• 4- Multiplicity Array • Mid-rapidity Spectrometer• Scintillator Paddles + Zero Degree Calorimeter for triggering• TOF wall for high-momentum PID




The first look - 2000 run

• Energy dependence (vs. AGS/SPS data)

• System size (p+p, Npart dependence )

• Angular dependence ( and )

• Energy density and Entropy Production

• Thermal Equilibration

• Hadro-Chemistry

Charged Particle Density

Event Anisotropy - Flow

Particle Ratios


Results to date - I

dN/d

Versus energy

Central, =0, sNN = 56 and 130 GeV PRL 85 (2000) 3100

Versus centrality

Varying centrality, =0, sNN = 130 GeV QM2001, to be submitted soon

Versus angle (and centrality)

Varying centrality, ||<5.4, sNN = 130 GeV QM2001, to be submitted soon


Results to date - II

p/p, K-/K+, -/+ ratios, central, sNN = 130 GeV QM2001, Submitted to PRL

hep-ex/0104032

Elliptic flow, sNN = 130 GeV, as function of centrality and ||<5.3 QM2001, to be submitted soon


Selecting Collisions

• Coincidence between Paddle counters• Paddle + ZDC timing reject background

• Sensitive to 97% of inelastic cross-section for Au+Au at sNN = 130 GeV

Negative

Paddles

Positive Paddles

ZDC N

ZDC PAu Au

x

z

PPPN


• HIJING +GEANT• Glauber Calculation• Model of Paddle trigger

Paddle signal (a.u.)

Determination of Npart

Npart

MC

Data


Vertex Determination with vertex detectorVertex Determination with vertex detectorVertex Determination with vertex detectorVertex Determination with vertex detector

cm

cm

coun

ts

+z

Si

Si

Tracklets


Vertex determination with spectrometer arms

form 3D vertex z

tracklets

100 MeV/c+

-

-


sNN = 56 GeV

sNN = 130 GeV

sNN = 130 GeV

dNch/dmeasurements• What is the density of particles near =0?• How does it compare to p+p and A+A @ SPS?• How does it vary with centrality?• How does the density of particles vary with angle?• Total multiplicity

• Energy density

• Entropy production

• Relative importance of hard and soft production processes


Tracklets and dNch/d@ =0

• Hundreds of tracklets per central event

• Corrections– Background subtraction

– Uncertainty due to model differences

– Feed-down from strange decays

See talk by Mike Reuter in Session J12 (Sunday 15:18)


PRL 85 (2000) 3100

dNch/d @ =0 vs Energy


dNch/d @ =0 vs Npart

Npart•Good agreement with previous PHOBOS point•Good agreement with recent PHENIX data•Neither HIJING nor EKRT describe data well

Yellow band: Systematic uncertainty

Preliminary

dNch

/d/

(0.5

*Npa

rt)


octagon

Ring counter

-1.1m

1.1m2.3m

-2.3m

5.0m

-5.0m

• || < 5.3 (, 0 (

Interaction Point

dNch/d for ||<5.4


• Count hits – remove much background by demanding energy deposition

consistency with angle

– Occupancy per hit pad determined as fn of via number of empty and hit pads

• Corrections– residual background corrected via MC simulations

RingsN Octagon RingsP

“Unroll” the octagon and rings

See talk by Carla Vale in Session J12 (14:30, Sunday afternoon


45-55% 35-45% 25-35%

15-25% 6-15% 0-6%

dNch

/d

dNch

/d

dNch/d vs Centrality Preliminary

The width of the distribution changes with centralityStatistical errors only - 10% systematical uncertainty


Evolution of dNch/d vs Npart

(dN

ch/d

)/(

½N

pa

rt)

Data

HIJING

Npart=356

Npart=215

Npart=103

(dN

ch/d

)/(

½N

pa

rt)

• <Nch> = 4100 +/- 410 for 3% most

central• Additional particle

production near =0• Wider + more particles

relative to HIJING

Preliminary

Statistical errors only


• Baryo-Chemical Potential• Baryon Stopping

• Determine ratio of -/+, K-/K+, p/p

• Compare to AGS/SPS results

Particle ratios: Hadro-chemistry

See talk by Conor Henderson - session Q12 (11 am Monday)


Tracking and Particle ID

• Particle ID– dE/dx in silicon

• Two B-field polarities– Many systematic effects

cancel in the ratio

pp

KK


Results for ratios

.)(06.0.)(04.060.0

.)(06.0.)(07.091.0

.)(02.0.)(01.000.1

syststat

syststat

syststat

p

p

K

K

• Higher values of K-/K+ and p/p than at lower energies

• Results consistent with B=45±5 MeV, which is much lower that that observed at SPS (~240-270 MeV)

Assumes freezeout temp ~170 MeV in statistical model of Redlich (QM01)


Elliptic flow

dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )

Determine to what extent is the initial state spatial/momentum anisotropy preserved in the final state.

b (reaction plane)

• Sensitive to the initial equation of state and the degree of thermalization.

• Affects other variables, such as HBT and spectra.


Elliptic Flow

-2.0 < < -0.1

RingPRingNSubE (a) SubE (b)

na n

b

0.1 < < 2.0

•Subevent technique: correlate reaction plane in one part of detector to asymmetry in hit pattern in other part of detector

•Correct for imperfect reaction plane resolution and hit saturation

(formalism given in A. M. Poskanzer,S. A. Voloshin Phys. Rev. C 58, 1671)


Centrality Dependence

Hydrodynamic model

V2

Normalized Paddle Signal

Systematic error ~ 0.007

|| < 1.0

SPS

AGS

Preliminary

Large V2 Signal compared to lower energy, closer to hydrodynamic limit implying substantial thermalization

Preliminary


V2 PHOBOS STAR (PRL)

V2 vs

• Averaged over centrality

• V2 drops for || > 1.5

Preliminary

Systematic error ~ 0.007


Conclusions from year 1

• dNch/d @=0 per participant– Substantially higher than SPS (Pb-Pb) and p+p – Npart evolution between HIJING and EKRT

• dNch/d in 4-– Additional particle production near =0 for central events– Distribution wider than HIJING

• Elliptic flow– V2– large, close to hydrodynamic limit– drops for || > 1.5

• Particle ratios ~ 45 MeV vs 270 MeV at SPS


Expectations for year 2 (starts mid-June!)

• 100x statistics• Both arms completed• Physics:

– low-pT physics– Spectra– HBT– Resonances (at low pT– Event-by-Event physics

• Energy systematics• [Species systematics if

enough running time]


BACKUP SLIDES FOLLOW



Comparison to SPS

•General features (rapid rise/flat top) similar

•Note that WA98 dNch/d measured in lab frame

WA98 Pb+Pb PHOBOS Au+Au`

NpartNpartdN

ch/d/

(0.5

*Npa

rt)

dNch

/d/

(0.5

*Npa

rt)

p+p

p+p


Spectrometer : Vertex Reconstruction

form 3D vertex z


Event Selectionvertex available Rings PRings N

• To cover pseudo-rapidity -2.0 to 2.0, only events with vertex -38cm to -30 cm are used

• Rings will cover 3.0 < || < 5.3

• 13K events are used finally for the analysis

-56cm -14cmOctagon

z


• If we know the reaction plane perfectly: Vn = < cos (n(R)) >

Flow Analysis* (Subevent correlation)

• In real experiment, R is unknown: use n

Vnobs = < cos (n(n)) >

<cos(nna,bRcos(n(n

a nb))> )1/2

• Finally, correct for event plane resolution

Vn= Vnobs / < cos (n(n R)) >

* Phys. Rev. C 58, 1671

A. M. Poskanzer,

S. A. Voloshin

-2.0 < < -0.1

RingPRingNSubE (a) SubE (b)

na n

b

0.1 < < 2.0


Subevent Plane Correlation

Normalized Paddle Signal


Kinematic Coverage

• Acceptance near y=0.5• Identical for positive particles in BPLUS/negative particles in BMINUS

P

K


Discriminating background with

E E

(“M

IP”)

20 64-2-6 -4

04

81

2

20 64-2-6 -4

E (

“MIP

”)0

48

12

Data Monte Carlo

Si

E vs. in the OctagonFrom vertex

Not from vertex


Future plans: 2003 + beyond

Micro-Vertex

Transition Radiation Detector

EM-Calorimeter

• Existing Spectrometer• High rate (> 0.5

kHz)• High Resolution

• Add • Micro-Vertex

Detector

• ALICE prototype TRD Electron-ID

• EM-Calorimeter

Discussing upgrade to focus on charm production at RHIC.

Measure single electrons from displaced vertices

Documents

1 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results from the PHOBOS experiment at RHIC Steve Manly (Univ. of Rochester) for the