Nov 1-2, 2001 High PT Phenomena at RHIC 1STAR

High PT Identified Particles at STARB. Lasiuk (YALE) for the STAR collaboration

•Hard Processes at RHIC

•STAR Measurements–Detectors–Methods–Physics Implication

•Some Results and Beyond… at STAR...

Nov 1-2, 2001 High PT Phenomena at RHIC 2STAR

Hard Process Observables• Jets are the Most Direct Observable

– 30% of particle production at RHIC energies– In pp, e+e-, light ions

• Event Backgrounds Favorable

• Difficult in Au+Au

• What Can We See in Au+Au?– Leading Particles– Azimuthal Correlations– High Mass Objects

OPAL qq jet

Nov 1-2, 2001 High PT Phenomena at RHIC 3STAR

Models and Physics Implications• Parton Propagation Affects Spectral Shape

– dE/dx softens spectra

– color screening (high density)

– Where does the onset occur?

• Identified Particle Production Rates– Medium Effects on Fragmentation Functions

– Asymmetries in Coupling Between Quarks and Gluons

• Measured PT Anisotropy– Sensitive to Propagation Through Matter

Nov 1-2, 2001 High PT Phenomena at RHIC 4STAR

Charged Multiplicity

• Spectrum Softens with– Energy Loss– Increasing Multiplicity– Gluon Density

• Onset of Hard Scattering

M. Gyulassy, I. Vitev, X.N. Wang PRL 86 (2001) 2537

Where Does it Affect “MEASURED” Spectrum?

Nov 1-2, 2001 High PT Phenomena at RHIC 5STAR

STAR Detector

• Year 1 Detectors Shown– TPC

– RICH • Extensions in Year 2…

– Calorimeter

ZDC

Magnet

ZDC

Central Trigger Barrel

Time Projection Chamber

RICH

• Hadronic Observables:

• PID by Several Detectors

• Focus on Central Region

Nov 1-2, 2001 High PT Phenomena at RHIC 6STAR

STAR TPC• Large Acceptance

– |y|<1.6• High Efficiency Tracking• Azimuthally Symmetric• B Field = 2.5 kG

– Limits Momentum Resolution

– For 2001: 5.0 kG

• PID via Ionization– Below 1 GeV/c– Other Detectors Augment

Capabilities

PT (GeV/c)

Fra

ctio

nal

Mom

entu

m R

esol

uti

on •From Embedding

•“Primaries”

Nov 1-2, 2001 High PT Phenomena at RHIC 7STAR

Identification of Particles

•Specific Ionization

•Secondary Vertices (Topology)

•Ko

•RICH•TOF and Calorimetry …

Nov 1-2, 2001 High PT Phenomena at RHIC 8STAR

STAR-RICH Detector

• Radiator– C6F14 Liquid

• Photo Converter– CsI

– < 210 (nm)

• Ionization Detector– MWPC pad chamber

– CH4 Gas

80 mm

STAR-RICH Collaboration Headed by F. Piuz, E. Nappi, G. Paic, G.J. Kunde

Developed by CERN RD-26 in ALICE framework

Nov 1-2, 2001 High PT Phenomena at RHIC 9STAR

Identification with RICH• Direct Ray Tracing

– Hough Transform– D. Elia et al., NIM A433 (1999) 262.

• Momentum Range1 < p < 3

2 < p < 5 p

Nov 1-2, 2001 High PT Phenomena at RHIC 10STAR

Identification with RICH• Geometrical Patterns

– Statistical Basis

D

p

K

Ring

C

oun

ts

Nov 1-2, 2001 High PT Phenomena at RHIC 11STAR

15% Central

Triggering Capabilities• Symmetric Zero Degree Calorimeters

• Central Trigger Barrel

5% central

Au AuZDC ZDC

Nov 1-2, 2001 High PT Phenomena at RHIC 12STAR

Indications from Inclusive Spectra...

• Indication of:– JET QUENCHING?

STAR preliminary

• Turn over at PT > 2 GeV/c• Large Systematic ~30%• Double the PT Reach this YearX-N Wang

Nov 1-2, 2001 High PT Phenomena at RHIC 13STAR

Identified Particle Yields

• Most Striking for Protons– ~30% for STAR-RICH Range

– effect slight for , K…

• Species/Flavor Dependence– Asymmetry of Leading Particle

– Propagation in Medium

– Coupling to Medium

• Not Restricted to Protons…

• Reference Spectra Importance– Need for PID at RHIC

X.N.Wang, Phys.Rev.C 58 (1998) 2321

RICH Range

Rat

io

Nov 1-2, 2001 High PT Phenomena at RHIC 14STAR

• Constant Yields with PT

* Slight Difference in Centrality

• NO DECREASE with PT

– Compared to Inclusive Spectra

– Compared to v2…???

– Significant in Comparison with Other Observables?

• Extend Reach with 2001 Data– Normalized Spectra

Protons in the Central Region

Nov 1-2, 2001 High PT Phenomena at RHIC 15STAR

Other Hadrons in Central Region• Less Sensitivity to Energy Loss than Protons

• Constant Ratio with PT

• More Statistics in 2001…

• Normalized Spectra

Nov 1-2, 2001 High PT Phenomena at RHIC 16STAR

Spectra

p = pe- + pe+

v

p

Primary Vertex

Photon Momentum Vector

e+

e-

Photon Conversion Vector

z (cm)

r (c

m)

0100200 2001000

100

200

TPC

Fit Mass ~ 131 MeV/ c2

FWHM ~ 20 MeV/c2

Minv (GeV/c2)

Nov 1-2, 2001 High PT Phenomena at RHIC 17STAR

o Spectrum• Small Reconstruction

Efficiency…BUT

• Continuous Kinematic Range

• 2nd

PHENIX pt range

0 - Top 10% most central0 – Minimum Bias data0 – 20% - 50%

1/pt

dN

/dp t (

a.u.

)X.N.Wang, Phys.Rev.C 58 (1998) 2321

• <PT> Consistent with

• Central To Min Bias ~2-3

• …Still Large Errors…

• EMC Extension to 6-10 GeV/c...

Nov 1-2, 2001 High PT Phenomena at RHIC 18STAR

• Anisotropy in geometry:

• Anisotropy in jet quenching:

– hydro valid up to some p t

– without dE/dx

v2 0

– with finite dE/dx

anisotropy in geometry

v2 > 0

Azimuthal Anisotropy

path

leng

th

X-N. Wang PRC 63 (2001) 054902

•A Pathlength Effect

•Sensitive to In Medium Effects

•Energy Loss Increases with Distance

•Difference in Hydrodynamic and Hard Scattering Evolution

Nov 1-2, 2001 High PT Phenomena at RHIC 19STAR

Elliptic Flow…What is it?

2cos2 v

v2: 2nd Harmonic Fourier Coefficient in Azimuthal Distribution of Particles with Respect to the Impact Parameter Vector

Origin: Spatial Anisotropy is created in Non-Central Collisions. Subsequent Rescattering in Evolving System Translates to Dynamics spatial anisotropy momentum anisotropy

Nov 1-2, 2001 High PT Phenomena at RHIC 20STAR

Physics From Anisotropy

• Sensitive to Energy Loss

• Saturation at PT=2 GeV/c

Gyulassy, Vitev and Wang,

Phys. Rev. Lett. 86, 2537(2001).

Nov 1-2, 2001 High PT Phenomena at RHIC 21STAR

Mass Dependence of v2

• Low PT Follow Hydro Predictions

• High PT Region Access:

– and K0S

– RICH in Future

Calculations: P. Huovinen, P. Kolb and U. Heinz

STAR Preliminary

• Minimum Bias Comparison

– K0S K±

consistent

– and K0S increase to PT =1.5 GeV/c

• “Saturation” of v2 independent of mass

Nov 1-2, 2001 High PT Phenomena at RHIC 22STAR

Conclusions

• STAR Capabilities to Measure Complimentary Observables

– v2 Measured for Kos and o

• Saturation of v2 Appears Independent of Particle Type

• Hydrodynamics Does NOT Describe v2 at PT > 2 GeV/c

– Possibility of Jet Quenching at PT > 2 GeV/c? BUT...

– = 0.6 to PT 2.5 GeV/c

• NO FALL OFF with increasing PT

• Why is Ratio NOT Decreasing if Partonic dE/dx Present?– Flow Effects Strongly Affecting Central Baryons?

– Information Regarding Fragmentation Functions?

/pp

Nov 1-2, 2001 High PT Phenomena at RHIC 23STAR

The

Collaboration

The STAR Collaboration

> 400 collaborators34 institutions8 countries

Brazil: Sao Paolo China: IHEP - Beijing, IPP - Wuhan

England: Birmingham France: IReS - Strasbourg, SUBATECH-Nantes

Germany: Frankfurt, MPI - Munich Poland: Warsaw University, Warsaw U. of TechnologyRussia: MEPHI - Moscow, JINR - Dubna, IHEP - Protvino

U.S.: Argonne, Berkeley, Brookhaven National Laboratories, UC Berkeley, UC Davis, UCLA, Creighton, Carnegie-Mellon, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas, Texas A&M, Washington, Wayne, Yale University

STARSTAR

Nov 1-2, 2001 High PT Phenomena at RHIC 24STAR

STAR-RICH Collaboration(Baria-CERNb-Yalec)

Y. Andresa, A. Braemb, D. Cozzaa. M. Davenportb,

G. De Cataldoa, L. Dell Oliaa, D. DiBaria, A. DiMaurob,

J.C. Dunlopc, E. Finchc, D.Fraissardb, A. Francoa, J. Gansc,

B. Ghidinia, J.W Harrisc, M. Horsleyc, G.J. Kundec, B. Lasiukc,

Y. Lesenechalb, R.D. Majkac, P. Martinengob, A. Morschb,

E. Nappia, G. Paicb, F. Piuzb, B. Posaa, J.Raynaudb, S. Salurc,

J. Sandweissc, J.C. Santinardb, J. Satinoverc, E.Schynsb,

N. Smirnovc, J. Van Beelenb, T.D Williamsb, Z. Xuc