Nucleon Structure and Quark-Gluon-Plasma: HERMES and ALICE/STAR

T. Peitzmann, NUPECC Groningen, Nov. 18, 2005

Nucleon Structure and Quark-Gluon-Plasma:

HERMES and ALICE/STAR

Thomas PeitzmannUtrecht University/NIKHEF


Outline

• HERMES– fragmentation in nuclei

• STAR – elliptic flow– jet physics

• ALICE– silicon strip detector– analysis preparations


NIKHEF Research programs

LHCb& Babar

ATLAS& D0

ALICE& STAR

Antares

Theory

R&D

GRID

OutreachLEP

HERA ~16 M€ per annum excluding investments

2005


HERMES• HERA/DESY• investigate spin structure of the nucleon– DIS with polarized leptons on polarized hydrogen target

• fragmentation in the nucleus– lepto-production of hadrons off nuclei

hardware contribution from NIKHEF: Lambda wheels


HERMESspin decomposition

Analysis highlights:

• N spin decomposition• hyperon production• transversity

PhDs:

• 10 completed• 7 now @ institutes abroad

• +5 in preparation

Publications:

• expect ~100 by 2007


Absorption/Energy Loss in Nuclei?

• production of hadrons in nuclei vs deuterium

• significant suppression of large z hadrons in heavy nuclei– absorption?– energy loss?

RM

h z,n( ) =Nh z,n( ) Ne n( )( )

A

Nh z,n( ) Ne n( )( )D

n>7GeV


Fragmentation in the Nucleus?

• ratio of di-hadron to single hadron for different nuclei

• very little dependence on mass of nucleus

• important reference measurement for heavy ion collisions

R2h z2( ) =

N2h z2,z1( ) N1h z1( )( )A

N2h z2,z1( ) N1h z1( )( )D

z1 > 0.5


ALICE/STAR

• 7 PhD – 4 STAR, 3 ALICE

• 45 publications – STAR from 2002 up to now

• group will shift completely to ALICE in the near future

• part of one FOM programme

• ALICE at LHC/CERN– hardware contribution: silicon strip detector

– data taking from 2007

• STAR at RHIC/BNL– joined in 2002– data taking and analysis


QCD phase diagram• QCD predicts transition from hadronic phase to a quark-gluon-plasma– Tc ≈ 160-170 MeV– order of transition unknown (but much larger number of d.o.f.)

– deconfinement and chiral symmetry restoration

• studied in high-energy heavy ion collisions


The focus of our group• The properties of the QCD Equation of State

above Tc – dp/d calculable in lattice QCD – observables: collective motion of low transverse momentum particles as function of mass

• The color density of hot and dense QCD matter– induced soft gluon radiation by partons traversing the medium

– observables: medium modifications of jets and heavy particle production


The STAR DetectorMagnetMagnet

CoilsCoils

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

ZCalZCal

Time Time Projection Projection

ChamberChamber(TPC)(TPC)

Year 2000Year 2000

Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)

Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)

FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD

TOFp, TOFrTOFp, TOFr

FPDFPD

Year 2001+Year 2001+

PMD


Elliptic flow


Collective motion: velocity of sound

• buildup of collective flow depends on the magnitude of the velocity of sound and the relative time spend in various phases

• sensitive to difference in equation of state (EoS)

P.F. Kolb and U. Heinz, in Quark Gluon Plasma, nucl-th/0305084


Self-quenching of elliptic flow

• the driving force of elliptic flow (anisotropy of pressure gradient) dominates at “early” times

• elliptic flow “monitors” early collective (i.e. equilibrated) behaviour

P.F. Kolb and U. Heinz, in Quark Gluon Plasma, nucl-th/0305084

Measurement of elliptic flow

• asymmetry of number distribution of particles with respect to the reaction plane

• Fourier-decomposition:

strong 2. order (v2)

• early result from STAR: strength of elliptic flow reaches predictions of ideal hydrodynamics at RHIC

STARcharged hadrons

ideal hydrodynamics


Identified particle flow• hierarchy of momentum dependent flow for different hadrons– onset of v2 shifts to larger pT for heavier particles

– consistent with ideal hydrodynamics

– magnitude of difference not consistent with hadron gas, but with QGP

parallel talk by Bai Yuting


Jets and jet quenching


Parton energy loss: current understanding

• collisional energy loss– original idea by Bjorken

– very small effect

• more important:induced gluon radiation

• interference leads to non-linearity

• dominant feature:– energy loss determined by density of color charges• parameterized by transport coefficient

DE ª

CR

4aS ◊q ◊L2

q =

kT2

lµ r glue


p+p dijet+X

Au+Au ???

Measuring jets in AA?

(STAR@RHIC)

how to find this in here?

two observables: - high pT single hadron distributions- dihadron distributions


Inclusive Hadron Suppression

• nuclear modification factor

• suppression requires initial density 30x larger than cold nuclear matter– compare to HERMES results

• very close to maximum suppression– provides only lower bound on density

q 5

GeV2

fm

Eskola et al., hep-ph/0406319

q = 0 GeV2 fm

q = 1GeV2 fm

q = 5- 15 GeV2 fm

RAA ∫

d 2N AA dydpT

d 2N pp dydpT ◊ NcollAA


Surface emission

• large energy loss: opaque core– emissions from surface

• inclusive measurements insensitive above certain density– more information from correlation measurements?

?Eskola et al., hep-ph/0406319


Dihadrons in heavy ion collisions

• near-side correlation unchanged

• away-side peak suppressed in central Au+Au– consistent with surface emission

• distributions in d+Au similar to p+p– suppression is final state effect

• more intuitive hint for “jet” suppression, but quantitatively much more difficult


Emergence of away-side peak

pT(trig)

pT(assoc) > 2 GeV/c

STAR Preliminary

Au+Au, 0-5%

High statistics year 4 dataset allows increase in Q2

Emergence of the away side peak with increased trigger pT

Equivalent to year 2 analysis


Emergence of dijets

increase associated pT threshold also:

clear jet-like peaks seen on near and away side in central Au+Au collisions!

yields info on upper and lower limit of density!

8 < pT(trig) < 15 GeV/c

STAR Preliminary

pT(assoc)>6 GeV


Where does the energy go?

Leading hadrons

Medium

significant softening of associated hadrons!

mean pT of away-side associated hadrons= remaining jet fragments?


The perfect fluid at RHIC, the wQGP at the LHC?

wQGP = weakly-interacting plasma

less flow at higher energies?beware: remember the predictions for RHIC!


Elliptic flow at LHC energies from ideal

hydrodynamics

• Whatever the outcome will be, elliptic flow is a day-one measurement at the LHC with very likely similar impact as at RHIC

From Heinz, Kolb, Sollfrank


ALICE: the dedicated HI experiment

Solenoid magnet 0.5 T

Central tracking system:• ITS •TPC• TRD• TOF

MUON Spectrometer:• absorbers• tracking stations• trigger chambers• dipole

Specialized detectors:• HMPID• PHOS

Forward detectors:• PMD• FMD, T0, V0, ZDC

Cosmic rays trigger


The Alice ITS

•FE moduleFE module

•EndcapEndcap

•FEROMFEROM

•DAQDAQSSD

•Support Support and coolingand cooling

•Main vertex 15 µm in central PbPb

•Vertex charm, strange decays 50 µm

•Δp/p (pT>1 GeV, with TPC) 14%->3%

•Particle ID (dE/dx)

•Strong contribution to outer layers (SSD)

•project leader SSD (6 labs)


SSD: the first real ladder!


NIKHEF/UU ALICE hardware activities (SSD)

• Design of SSD support (with Turin)• Design ladder frames (with St. Petersburg)• Design of SSD cooling system (with CERN)• Design of front-end modules (with Kharkov and Strasbourg)• Design ladder cabling (with Kharkov)

• Design SSD cabling (industrial production)• Design and production of front-end module test equipment• Design and production of EndCap electronics• Design and production of read-out modules

• Ladder assembly (with Nantes)• Final SSD assembly

• Bottom line: ITS project on schedule and NIKHEF SSD contribution will finish on time (2006)


ALICE group: current manpower

• Utrecht and NIKHEF Amsterdam• Amsterdam manpower:

– Staff physicist: 3 – PhD students: 2

• Utrecht manpower:– Staff physicist: 4– Post-doc: 1– PhD students: 5– Students: 2

• Amsterdam infrastructure:– Mechanical and electronics workshop– Ladder assembly room

• Utrecht infrastructure:– Faculty mechanical and electronics workshop– Mechanical and electronic workshop of the SAP department (4

fte)– Assembly room


ALICE group: current physics activities• Have strong role in STAR EMC analysis

– 1 fte staff, 1 post-doc, 3 PhD's (until 2009) and 2 students

• Had a leading role in correlation analysis with the reaction plane in STAR– Effort is scaled down to 1 PhD (until 2007) and 0.2 fte staff

• Have a coordinating role in correlation analysis with the reaction plane in ALICE (Physics Performance Report)– Effort 4 fte staff and 2 PhD – Will increase further with 3 PhD’s and 1 post-doc


Summary

• important nuclear physics contributions from NIKHEF– HERMES with nuclear physics program in parallel to spin

– ALICE/STAR nuclear physics at the highest energies

• rich physics harvest from STAR– elliptic flow– jet quenching

• ALICE well under way for data taking in 2007– strong Dutch contribution to SSD

– prepare physics analysis• elliptic flow as day-one topic

Documents

Nucleon Structure and Quark-Gluon-Plasma: HERMES and ALICE/STAR