GLUON POLARISATION

GLUON POLARISATION

introduction

ΔG from inclusive data analysis

direct measurements of ΔG/G

1) method and previous measurements

2) recent results from COMPASS

3) measurements at RHIC

outlook

Fulvio Tessarotto

INFN – Trieste

EINN 2005

Fulvio Tessarotto EINN 2005

Milos, 23 09 2005

In inclusive polarised DIS one can measure an asymmetry in the differential cross-section:

and extract the struture function g1.

In the QPM g1 has a simple interpretation:

In QCD at NLO g1 may depend explicitely

on G:

measuring Q2 variations of g1 we can try to

get G


Milos, 23 09 2005

The nucleon spin

½= ½ΔΣ + ΔG + Lq + Lg

quarks gluons orb. mom.

Ellis-Jaffe: ΔΣ = a0 ≈ 0.6

experimentally: a0 ≈ 0.25

ΔΣ = a0 + 3(s/2)

ΔG


Milos, 23 09 2005

0.43 0.80 ΔG

0.03 0.09 - Δs

0.04 0.43- Δd

0.03 0.84 Δu

0.06 0.32 ΔΣ

0.01 0.1 1

0.0

0.1

0.2

0.3

0.4

PD(g1

NLO/F1

NLO)

x

xG(x)

0.01 0.1 1

-0.4

-0.3

-0.2

-0.1

0.0

x

-x(d+d)

0.01 0.1 1

-0.2

-0.1

0.0

x

-x(s+s)

0.01 0.1 10.0

0.1

0.2

0.3

0.4

x

PD (g1

NLO + HT)

-x(u+u)

SLAC (E142, E143, E154, E155)CERN (EMC, SMC)DESY (HERMES)

185 exp. points

E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017

G not well constrained not extracted

dΔ ,uΔ

Spin-dependent PDFs

dp,1

dp,1

dn,p,1 /Fg ,A

1/2 = ½ + + Lz = 0.96 + Lz

Lz is negative

Two years ago …


Milos, 23 09 2005

g and q were largely unconstrained

Direct Direct g g measurementmeasurement

Is this still true?


Milos, 23 09 2005

final g1 data

- Very good statistics- Smearing (resolution and radiative corr.) →

correlation between x bins


Milos, 23 09 2005

g1n(x) at high x from JLAB

• pQCD + no Lz →

u/u= d/d=1 at high x

• Very accurate A1n at high x

A1n > 0 at x > 0.5

• + world A1p → d/d < 0

so Lz not negligible ?

u/u

d/d

PRL 92, 012004 (2004)


Milos, 23 09 2005

g1d(x) at low x

• new data : =0.202 (+0.042 -0.077) → 0.237 (+0.024 -0.029)

• COMPASS systematically > SMC at low x

PLB 612 (2005) 154

g1/F1


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NLO QCD fits with new data + new unpolarised PDFs


Milos, 23 09 2005

to know G we still need to measure it

possible trend toward smaller G but the results are scattered:

• Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988)……..and many more

•revisited by A.Bravar,D.von Harrach and A.Kotzinian,Phys.Lett.B 421, 349 (1998)

• Method used in HERMES for photoproductionHERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000)

• Applied for DIS region by SMC (data with Q2 >1GeV2) SMC, B.Adeva et al.., Phys. Rev. D 70, 012002 (2004).

History:

Direct Measurements:

polarised p p collision: RHIC

semi-inclusive deep inelastic scattering: DESY, CERN (Photon Gluon Fusion)


Milos, 23 09 2005

• Strategies to suppress background: 1) Open charm production: q = c unique, no background charm fragmentation, 1.2 D0 per event

D0 -> K- π+ (BR 4%), D*+(~20%) -> D0 π+

2) High-PT hadron pair production: q=u,d,s kT(intr) = 450 MeV/c

pT(frag) = 350 MeV/c

• pQCD scale set by: 1) ŝ > 4mc

2 or 2) ŝ > (pt1+pt2)2

ΔG/G from Photon-Gluon Fusion

Photon-Gluon Fusion


Milos, 23 09 2005

HERMES & DESY

• 27.5 GeV e • Pure atomic H or D targets• Spectrometer with complete hadron identification


Milos, 23 09 2005

Statistics decreases with pT

HERMES ALL from high pT hadron pairs

ehhXeNTeLL fAPP

NN

NNA

Proton target

Promising channel, but …

theoretical uncertainties

may be large

<xg> = 0.17

<Q2> = 0.06 (GeV/c)2

photoproduction


Milos, 23 09 2005

ΔG/G from SMC

µ+ 190 GeV Pµ= -0.78±0.03

DIS eventsQ2 > 1 GeV2, 0.4<y<0.9

xF > 0.1, pT2 > 2.5

(GeV/c)2

1% of inclusive sample

∆G/G = -0.200.290.11


Milos, 23 09 2005

COMPASS SPS

LHC

COMPASS EXPERIMENT

Beam: 2 . 108 µ+/ spill (4.8s / 16.2s)Luminosity: ~ 4 . 1032 cm-2 s-1 Beam polarisation: 76%Beam momentum: 160 GeV/c


Milos, 23 09 2005

SM1 dipoleSM1 dipole

SM2 dipole

Polarised Target

HCAL1

Muon-filter1,MW1SPS 160 GeV 2.108/spill

Micromegas,DC,SciFi

Gems,SciFi,DCs,straws

MWPC Gems Scifi

trigger-hodoscopes

Silicon

Spectrometer 2002 -> 2004

RICH_1 Gem_11

ECAL2,HCAL2

straws,MWPC,Gems,SciFi

straws Muon-

filter2,MW2

DW45

SciFi

Veto

New detector technologies


Milos, 23 09 2005

ΔG/G from open charm

G

GaA LL

)s,x(G )s( sd

)s,x(G )s( sdccN

GPGF

GPGF

PGF at NLO:Bojak, Stratmann NPB 540 (1999) 345; A.P. Contogouris and G. Grispos, Phys. Rev. D 62 (2000). ŝ = m2

cc

D0 K- π+ (BR 4%)

D*+ D0 π+ + c.c.

Special trigger: quasi realphotoproduction

c

c


Milos, 23 09 2005

D* tagging: D* D0 π (Kπ)π

KD0MeV/c2)

sK

M

eV/c

2 )

Cuts:

zD > 0.2

|cos *| < 0.85 (Background)

10 < pK < 35 GeV/c(RICH PID)

D0 K π

D*

D

0 π

no vertex detector(solid target!)


Milos, 23 09 2005

ΔG/G from open charm

MC: Aroma + PolDis

ΔG/G = -1.08 ± 0.73

D0 (untagged, 2003) 4200 eventi

D*+→D0π+ (2003) 1100 eventi

<xg> ~0.15

0.73 0.43 with 2004 data

D0 → K π π0


Milos, 23 09 2005

Pairs of hadrons with high pt and Q2 > 1 GeV/c

Photon Gluon Fusion

h1

h2

• current fragmentation:

• event cuts:

xF > 0.1z > 0.1

pt > 0.7 GeV/cpt1

2+pt22 > 2.5 (GeV/c)2

m(h1h2) > 1.5 GeV/c2

• 2 high pt hadrons:

N

Q2 > 1 (GeV/c)2

xBj < 0.050.1 < y < 0.9


Milos, 23 09 2005

Result for high pt asymmetry

Aγ*d = -0.015 ± 0.080 (stat.) ± 0.013 (syst.)2002/03 data

Asymmetry for high-pt hadron pairs at Q2 > 1 (GeV/c)2:

Systematic uncertainty contains contributions from:• target and beam polarisation measurement (5% resp. 3%)• upper limit on false asymmetries (0.013)• determination of D and f (5% each)


Milos, 23 09 2005

determination of ΔG/G

Photon Gluon Fusion QCD-Compton Leading Order

DISLOq

q

D

a

G

G

D

a

D

AA

tot

ComComLL

tot

PGFPGFLL

hhNLLd

ˆˆ

Relative Fractions determined by Monte Carlo (LEPTO)

05.074.0DaPGFLL

0qq

DaComLL

cut on xBj < 0.05:

0Ad1


Milos, 23 09 2005

Data Monte Carlo comparision• Use LEPTO Monte Carlo for Q2>1 (GeV/c)2 including RADGEN

σPGF/σtot = 0.34 ± 0.07 (syst.)

Determination of thefraction of PGF eventsin LEPTO:

• Variation of the cut on pt2

• Standard and modified* set of fragmentation parameters

* SMC, B. Adeva et al., Phys. Rev. D70:012002, 2004


Milos, 23 09 2005

10% ofstatistics

COMPASS result for ΔG/G

ΔG/G = 0.06 ± 0.31stat. ± 0.06syst.2002/03 dataQ2 > 1 (GeV/c)2

at <xg> = 0.13 ± 0.08

GSA,B,C: T. Gehrmann and W. Sterling, Z. Phys. C65 (1994) 461.


Milos, 23 09 2005

ALL/D = Rpgf G/G aLLpgf

+ Rqcdc q/q aLLqcdc

all Q²

Pairs of hadrons with high pt and Q2 < 1 GeV/c


Milos, 23 09 2005

+ Rqq q/q aLLqq q/q

Physical background


+ Rqcdc q/q aLLqcdc

Q² < 1

all Q²


Milos, 23 09 2005

+ Rqg G/G aLLqg q/q

Physical background


+ Rqcdc q/q aLLqcdc

+ Rqq q/q aLLqq q/q

all Q²

Q² < 1


Milos, 23 09 2005

+ Rgq q/q aLLgq (G/G)

Physical background


+ Rqcdc q/q aLLqcdc

+ Rqq q/q aLLqq q/q

+ Rqg G/G aLLqg q/q

all Q²

Q² < 1


Milos, 23 09 2005

+ Rgg G/G aLLgg (G/G)

Physical background


+ Rqcdc q/q aLLqcdc

+ Rqq q/q aLLqq q/q

+ Rqg G/G aLLqg q/q


all Q²

Q² < 1


Milos, 23 09 2005

Inputs:

-generation of Monte Carlo evts-parametrization (world data)-pQCD calculations

Physical background


+ Rqcdc q/q aLLqcdc

+ Rqq q/q aLLqq q/q

+ Rqg G/G aLLqg q/q


+ Rgg G/G aLLgg (G/G)


Milos, 23 09 2005

Resolved photon processes

polarised parton distribution functions of (virtual…) photon areunknown!

BUT:

-q(x,²) < q(x,²) < q(x,²)

leads to 2 extreme (min&max) scenarios

additional (theoretical) uncertainty

measured


Milos, 23 09 2005

MC/data comparison

Q²

PYTHIA generator is used for Q²<1GeV²GEANT is used for spectrometer simulation

.data

- MC

data/MC


Milos, 23 09 2005

MC/data comparison

pT

.data

- MC

.data

- MC

data/MC data/MC


Milos, 23 09 2005

Results from MC

The Monte Carlo describes our data quite well!

Rpgf ≈ 31%


Milos, 23 09 2005

Q2>1GeV2 :

Q2<1GeV2:

Gluon polarisation, high pT pairs 2002-2003

data


Milos, 23 09 2005

G = 2.48

G = 0.62

G = 0.16

Gluon polarisation results:

ΔG/G (xg ≈ 0.1) is small G>1 disfavoured

GRSV2000NLO fits to g1

2 = 3 Gev2


Milos, 23 09 2005


Milos, 23 09 2005

ΔG/G from two jet events

LLAˆ

Hard Scattering Process

2P2 2x P

j 2f x

i 1f x1P

1 1x P

zhqDs

1ps

2ps

gggg gqgq qqqq

qg+gq

qq

gg

0

Fraction

's produced

Pt [GeV/c]

Leading hadron used as jet tag

G

G

G

G

G

G

q

q

q

q

q

q


Milos, 23 09 2005

Prompt photon production asymmetry• Gluon Compton Dominates

• At LOLO no fragmentation function• Small contamination from annihilation

•

2i i 2

i u,d,s

2i i 2

i u,d,s

LL1

1LL

e f (xg(

)

e f (A

x )a (gq

x )

g(x )q )

A1


Milos, 23 09 2005

NSRL

2 superconducting rings3.8 km circumference


Milos, 23 09 2005

RHIC – first polarized hadron collider

BRAHMS

STAR

PHENIX

AGS

LINACBOOSTER

Pol. H- Source

Spin Rotators(longitudinal polarization)

Solenoid Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter Internal Polarimeter

Rf Dipole

pC PolarimetersAbsolute Polarimeter (H jet)

pC Polarimeter

25% Helical Partial Siberian Snake

5% Helical Partial Siberian Snake

PHOBOS

Spin Rotators(longitudinal polarization)

Spin flipper

Siberian Snakes

Achieved ~ 50% beam polarization at 100 GeVAchieved ~ 30% beam polarization at 205 GeV on first try!


Milos, 23 09 2005

New AGS helical snakes

2.6 m

2.6 m

25% s.c. helical snake build at BNL

Warm snake avoids polarization mismatch at AGS injection and extraction.

Cold strong snake eliminates all depolarizing resonances in AGS.

6 % helical snake build at Tokana Industries funded by RIKEN.


Milos, 23 09 2005

STAR spin physics program: ∆G, ∆q/∆q, δq

Large acceptance TPC and EMC -1<η<2


Milos, 23 09 2005

ΔG – Star: ALL for jets (2005)

STARSTAR

0 5 10 15 20 25 30

0.2

0.4

0.6

0.8

1.0

0.0

gg qq

qg

Inclusive Jets :LOW. Vogelsang

pT (GeV)

2005


Milos, 23 09 2005

PHENIX Detector

• Central Arms: ||<0.35, =2900

Charged particle ID and tracking; photon ID

• Muon Arm:1.2<||<2.4Muon ID and tracking

• Global Detectors Collision triggerCollision vertex characterizationRelative luminosityLocal Polarimetry

Philosophy: High rate capability & granularity Good mass resolution and particle ID Sacrifice acceptance


Milos, 23 09 2005

ppπ0/prompt + X

prompt γπ0

Excellent agreement with NLO & NLL

calculation with collider data !

http://www.phenix.bnl.gov/


Milos, 23 09 2005

Outlook 2005/7

2003/4

PHENIX ALL for Inclusive 0 productionat √s=200 GeV, 2003 + 2004 data with about ∫Ldt~0.3pb-1 and <Pb>~0.3

Run 5 (April –June 2005):

absolute polarimeter: ∆Pb/Pb~7%

∫Ldt ~ 3pb-1, <Pb>~0.45

reduces statistical error by factor 7

pp -> 0 + X



Milos, 23 09 2005

B. Jaeger et al. Phys. Rev. D67, 054005 (2003)

Y. Fukao, spin2004



Milos, 23 09 2005

ΔG at RHIC – summary & outlook

• Various channels, large coverage in xg

- Jet/leading hadron production : First results of ALL pp 0 +X from PHENIX Very good perspective for +- at PHENIX and jets at STAR - Direct photon production: hard scale 100 GeV 2, xg reconstructed in STAR

- Heavy flavours, ...

• RHIC Spin program on track, major effort to reach performance

Run s1/2(GeV) Pbeam L(pb-1)

3 200 0.27 0.35

4 + 5 200 >0.40 10

>5 200 0.70 320

500 0.70 800


Milos, 23 09 2005

Physics vs Luminosity and Polarization at RHIC

2005 2006 2007 2008 2009 …. 2012 (RHIC II)

10 pb-1 …………………………………… 275pb-1 …….. 950pb-1

√s= ……………………….. 200 GeV …………………......... 500 GeV|

P= 0.5 0.6 0.7 ……………………………………

Inclusive hadrons + Jets ~ 25% Transverse Physics Charm Physics direct photons bottom physics W-physics

ALL(hadrons, Jets) ALL(charm)

ALL(γ) AL(W)

L= 1x1031cm-2s-1 6x1031cm-2s-1 1.6x1032cm-2s-1

see Spin report to DOE http://spin.riken.bnl.gov/rsc/

@ 200GeV @ 500GeV

eRHIC

ELIC

Outlook


Milos, 23 09 2005

PHENIX Forward Upgrade: W-physics and jet+photon

Muon Trigger Upgrade

RPC + FPGA based

trigger logic

Nose cone calorimeter

W-Si calorimeter

Trigger RPC Locations

RPC2

June 2005: $1.99M NSFMRI grant approved + $280k institutional support

UC Riverside, Abilene Christian, Iowa State, U. Illinois, U. Colorado, Columbia, Georgia Tech., RBRC, Kyoto, Peking U.,


Milos, 23 09 2005

Final results on ∆G will come from combined NLO analysis of RHIC and DIS

RHIC measurements will span broad range in x with good precision. Multiple channels with independent theo. and exp. uncertainties.

Uncertainty through extrapolation to small x

s=200 GeV incl. 0 prod’n s=500 GeV incl. jet prod’n

∆G Measurements by 2012 see Spin report to DOE http://spin.riken.bnl.gov/rsc/


Milos, 23 09 2005

COMPASS


Milos, 23 09 2005

COMPASS upgrade in 20065

m5

m

6 m6 m3 m3 m

Photon Photon Detectors:Detectors:CsI MWPCCsI MWPC

mirrormirrorwallwall

vesselvessel

radiatorradiator::

CC44FF1010


Milos, 23 09 2005

• 2002 – 2004 -> 2006• • FoM(G/G)

G/G)=1/FoM1/2

hard work to increase FoM

0

2

4

6

8

10

12

14

16

2002 2003 2004 2006

per year accumulated FoM

Figure of Merit for open charm

2006 will be a very important year


Milos, 23 09 2005


Milos, 23 09 2005

μ’

p’μ

DVCS μp μ’p’

Additional equipment to the COMPASS setup

At these energies (for μ, μ’, and ) the missing mass technique is not adapted

M2required = (mp+mπ)2-mp

2 = 0.25 GeV2

M2observed > 1 GeV2

ECal 1 or 2

12°

Nμ=2.108/SPS cycle(duration 5.2s, each 16.8s)

2.5m liquid H2 targetto be designed and built

L = 1.3 1032 cm-2 s-1

Recoil detector to insure exclusivityto be designed and built

+ additional calorimeter at larger angle


Milos, 23 09 2005

COMPASS far future:

GPD’s, transversity, G/G and hadron programwill benefit from a possible upgrade of the SPS:

a Superconducting SPS (1 TeV) is better suited to LHC needs;

A bright future for G both at short and long term

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