New results on quark helicity distributions and gluon ... fileKrzysztof Kurek SINS, Warsaw New results on quark helicity distributions and gluon polarization from the COMPASS experiment

Krzysztof KurekSINS, Warsaw

New results on quark helicity distributions and gluon polarization from the COMPASS experiment at CERN

16-22 July, Krakow, Poland

EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek

New results on quark helicity distributions and gluon polarization from COMPASS 2

COMPASS

SPS

LHC

Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Luminosity ~5 . 1032 cm-2 s-1 Beam polarization: -80%Beam momentum: 160 GeV/c Target polarization: PT = 50%, f ~ 40 % for 6LiD (2002 -2006)


New results on quark helicity distributions and gluon polarization from COMPASS

COMPASS Collaboration at CERNCommon Muon and Proton Apparatus for Structure and Spectroscopy

Bielefeld, Bochum, Bonn, Burdwan and Calcutta, CERN, Dubna, Erlangen, Freiburg, Lisbon, Mainz, Moscow, Munich, Prague, Protvino, Saclay,

Tel Aviv, Torino, Trieste, Warsaw, Yamagata

Czech Rep., France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia and CERN

~240 physicists, 30 institutes

3



160 Ge

V µSciFiveto

6LiD target

Si Micromegas

Drift Chambers

GEMs

Straws

SM1

RICH

ECALs & HCALs

µ Filters/ Walls

Trigger Hodoscopes

MWPCs

50 mSM2

COMPASS in muon run NIM A 577(2007) 455

• ~ 350 planes• 180 mrad acceptance • π, K, p separation (from 2, 9, 17 GeV up to ~ 50 GeV)



Target material: 6LiDPolarisation: >50%Dilution factor: ~0.4Dynamic Nuclear Polarisation

2006 - new solenoid with acceptance 180 mrad 3 target cells (reduce false asymmetries)

The COMPASS polarised target

!!""#

!""!"!""$

RICH 2006 upgrade : better PID

MAPMTs in central region

APV electronics in periphery

Identification of π, K and protonsCherenkov thresholds: π ≈ 3 GeV/c K ≈ 9 GeV/c p ≈ 17 GeV/c



Contents• Introduction • New results on quark helicity distributions• Gluon polarization from high-pT hadron pairs• New result on gluon polarization from open-charm

measurement• Summary

6



Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm

Polarized Deep Inelastic scattering

Inclusive asymmetry:

semi-nclusive asymmetry:

3 years of deuteron data taking in COMPASS: years 2002-2004 : 89*106 events for Q2 >1 (GeV/c)2 Phys.Lett.B 647 (2007)8

!

"1

NQ2( ) =

1

91#

$s(Q

2)

%+O($

s

2)

&

' (

)

* + a0(Q

2) +1

4a8

&

' (

)

* +

!

("s + "s ) =1

3( ˆ a

0# a

8) = #0.08 ± 0.01(stat) ± 0.02(syst)




First moment of g1

from Y. Goto et al., PRD62 (2000) 034017: (SU(3)f

assumed for weak decays)a8 = 0.585 ± 0.025

Phys.Lett.B 647 (2007)8 Compass only

QCD NLO

beyond NLO

!

A+"

=(#$%

h+

"#$%

h"

) " (#$$

h+

"#$$

h"

)

(#$%

h+

"#$%

h"

) + (#$$

h+

"#$$

h"

)

Fragmentation functions cancell out in LO and

under the assuption of independent fragmentation.

Idea: Phys.Lett.B230(1989)141, SMC:Phys.Lett.B369(1996)93, COMPASS: Phys.Lett.B660(2008)458




Difference asymmetries

!

Ad

" +#" #

(x) = Ad

K+#K

#

(x) =$u

v(x) + $d

v(x)

uv(x) + d

v(x)

Only valence quarks!

x-210 -110 1

0

0.1

0.2

0.3

0.4

0.5

0.6

2=10 GeV2SIDIS+DIS, Q

s!s=!=d!=u!

d!=-u!

unmeasured

0.7

0.006" 0.06±0.07±)dx=0.40vd!+vu!(

"x0.7

)dxvd!+vu!(

COMPASS


!

"u = "d = "s = "s

"u = #"d

symmetric

asymmetric

scenario

!

g1(x,Q

2) = 1

2"e2# Cq

s[ $%& + Cq

NS $%qNS + 2n fCG $%G ]




Gluon polarization

✦QCD evolution

✦“Direct” measurement: idea - tag photon-gluon fusion (PGF) process• Observation of the two hadrons with high-pT

• Observation of the charmed mesons produced via open-charm mechanism

✦Semi-inclusive asymmetries compared to theory predictions based on gluon polarization “model” (method used in RHIC)




high-pT hadron pairs

R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988)Revisited by A.Bravar,D.von Harrach and A.Kotzinian, Phys.Lett.B 421, 349 (1998) Applied by SMC, HERMES and COMPASS

N

LO DISQCD-Compton+ +

The simple idea: three basic processes, PGF probes gluons

Two kinematical regions: • small Q2 - Q2<1 (GeV/c)2 - here pT is a perturbative scale, also resolved photon contribution important (~50%) - COMPASS 2002-2003 data PLB 633 (2006) 25-32• large Q2 - Q2>1 (GeV/c)2 - scale Q2 - 2002-2004 data, new method based on Neural Network approach used - this talk

Large statistics but Monte Carlo dependent analysis, limited to LO



Idea: tag γ*g➝➝ccbar via open-charm production mechanism


• Clean channel (less MC dependent) under the assumption that production mechanism is PGF only (true in LO pQCD)• Resolved photon and “intrinsic” charm production mechanism negligible in COMPASS kinematics• Limited statistics (no vertex detector - long polarized target)• Huge combinatorial background• NLO corrections potentially important

Open-charm analysis

COMPASS: PLB676(2009)31



Weighted method for open-charm analysis

PB, PT - are beam and target polarizations,f - dilution factor (~0.4 for 6LiD target)aLL is a partonic asymmetry (analysing power) for subprocess: µg ➝ ccbar µ




Helicity distributions

x -210 -110 1

d 1xg

-0.01

0

0.01

0.02

0.03

0.04SMCE143E155HERMESCLAS W>2.5COMPASS

COMPASSPRELIMINARY

x -210 -110 1

p 1xg

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08EMCSMCE143E155HERMESCLAS W>2.5COMPASS

COMPASSPRELIMINARY




New: Proton data 2007, g1

Very good agreement betweenexperiments

x-210 -110

NS 1

xg

0

0.02

0.04

0.06

0.08

0.1

Analysis ofCOMPASSdata alone




New: Proton data 2007

g1NS = g1p - g1n

QCD NLO fit allows estimate first moment and test Bjorken sum rule:

CNS = 0.89 Q2 = 3 (GeV/c)2




Δs from charged Kaon’s asymmetry




• RUF fixed at 0.14 from the DSS fragmentation functions• Large statistical uncertainty due to RSF, slight dependence on RUF

• If RSF>5 Δs(SIDIS)>Δs(DIS) and Δs <0 for x<0.004•If RSF<4: AK becomes insensitive to Δs

Δs from charged Kaon’s asymmetry

in LO pQCD

1,pA +!1,pA K+

1,pA

-!1,pA K-

1,pA

0

0.2

0.4

0.6

0.8

-210 -110

0

0.2

0.4

0.6

0.8

-210 -110 x-210 -110

COMPASS preliminary,proton data 2007

HERMES PRD71(2005)

u

!x

-0.10

0.10.2

0.30.4

COMPASS preliminary

DNS parametrization

d

!x

-0.25-0.2

-0.15-0.1

-0.050

0.05

u!x

-0.1

-0.05

0

0.05

0.1

d!x

-0.1

-0.05

0

0.05

0.1

x-210 -110

s

!x

-0.05-0.04-0.03-0.02-0.01

00.010.02




New: Proton data 2007, flavour separation

Q2 = (3 GeV/c)2



ΔG/G from high-pT hadron pairs



R’s are fractions of the sub-processes (LO,PGF, QCDC) in high-pT and inclusive samples, respectivelyaLL ‘s are so-called analysing powers for LO,PGF and QCDC (the ratio ofpartonic polarised and unpolarised cross sections for sub-processes)D is a depolarization factor.


Extraction formula for ΔG/G



• Cuts on inclusive variables: Q2 >1 (GeV/c)2 (Scale of the process) 0.1 < y < 0.9 • Cuts on hadronic variables: pT1 > 0.7 GeV/c and pT2 > 0.7 GeV/c xF1,2 >0, z1,2 >0, z1 + z2 <0.95 inv. mass of two hadrons > 1.5 (GeV/c)2

Total number of events in the selected sample: ~500 kevents2002-2004 data


Data selection



2 variables o1 and o2 are used (R’s sum up to 1)


NN parameterization of fractions R



Comparison: MC/data for high pT sample; x,y and Q2


Data/MC comparison



Comparison: MC/data for high pT sample; transverse momenta of leading and sub-leading hadrons Impact of MC tuning


Data/MC comparison



Plot has statistical errors only


Results

Systematic error dominated by MC



ΔG/G from open-charm channel



nD0: 37400 nD*: 8675


D0 and D* meson reconstruction,2002-2004 and 2006 data



Thick target - no D0 vertex reconstructionD0 reconstruction: Kπ invariant mass + cuts on D0 decay angle + zD + RICH particle identification (different likehoods)

nD0: 37400 nD*: 8675

Due to weighted method spectra are not optimized!





Thick target - no D0 vertex reconstructionD0 reconstruction: Kπ invariant mass + cuts on D0 decay angle + zD + RICH particle identification (different likehoods)

nD0: 37400 nD*: 8675



New!

(reconstructed)LLa-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 1

(gen

erat

ed)

LLa

-1

-0.8

-0.6

-0.4

-0.2

-0

0.2

0.4

0.6

0.8

1



- 82% correlation NN/MC- very large dispersion of values, even change of sign: weighting essential


aLL parameterization with NN




New channels from D*

NN S/(S+B) parameterization method

Σ =



Open charm : D0 + D* Result

published: PLB676(2009)31


ΔG/G results



Open charm : D0 + D* Result Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm

ΔG/G results

ΔG/G = -0.39± 0.24 (stat)New preliminary result including all channels

published:

10% gain in statistical precision!



−210 −110−1

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

gx

g/g

!

COMPASS, open charm, prel., 02−06, prel., 02−042>1 (GeV/c)2, Q

TCOMPASS, high p

, prel., 02−042<1 (GeV/c)2, QT

COMPASS, high p2, all Q

THERMES, high p

, prel.2 hadrons, all QT

HERMES, single high p2>1 (GeV/c)2, Q

TSMC, high p

2=3(GeV/c)2µG>0, !fit with 2=3(GeV/c)2µG<0, !fit with

COMPASS, open charm, prel., 02−06, prel., 02−042>1 (GeV/c)2, Q

TCOMPASS, high p

, prel., 02−042<1 (GeV/c)2, QT

COMPASS, high p2, all Q

THERMES, high p

, prel.2 hadrons, all QT

HERMES, single high p2>1 (GeV/c)2, Q

TSMC, high p

2=3(GeV/c)2µG>0, !fit with 2=3(GeV/c)2µG<0, !fit with

35



Summary• New inclusive and semi-inclusive results (A1 and hadron asymmetries)

from COMPASS proton data have been presented• The evaluation of the first moment of non-singlet g1 structure function

confirms the validity of Bjorken sum rule• Proton data allows to perform a full flavour separation• Small value of ΔG/G is preferred - ΔG/G compatible with 0 within 2σ • Under study for ΔG/G:

- pure NN approach (fit independent) and NLO for open-charm - 2006 data for high-pT hadron pairs analysis

36



Spares

37

!

"1

NQ2( ) =

1

91#

$s(Q

2)

%+O($

s

2)

&

' (

)

* + a0(Q

2) +1

4a8

&

' (

)

* +

!

"1N

Q2( ) =

1

9C1

S(Q

2)! a 0 +

1

36C1

NS(Q

2)a8

!

("s + "s ) =1

3( ˆ a

0# a

8) = #0.08 ± 0.01(stat) ± 0.02(syst)




First moment of g1

from Y. Goto et al., PRD62 (2000) 034017: (SU(3)f

assumed for weak decays)a8 = 0.585 ± 0.025!

"1NQ0

2 = 3GeV 2( ) = g1Nx( )

0

1

# dx = 0.050 ± 0.003(stat) ± 0.003(evol) ± 0.005(syst)

Phys.Lett.B 647 (2007)8 Compass only

C1 calculated behind 3 loops app. S.A.Larin et al.,Phys.Lett.B404(1997)153

QCD NLO

beyond NLO




Inclusive DIS asymmetry A1 and g1

3 years of deuteron data taking 2002-2004 : 89*106 eventsPhys.Lett.B 647 (2007)8

Good agreement between experiments Compatible with 0 for x<0.05, large for large x Improved significantly statistics at low x (COMPASS) No tendency towards negative values at x < 0.03

Q2 >1 (GeV/c)2

x-210 -110 1

0

0.1

0.2

0.3

0.4

0.5

0.6


s!s=!=d!=u!

d!=-u!unmeasured

0.7

0.006" 0.06±0.07±)dx=0.40vd!+vu!(

"x0.7

)dxvd!+vu!(

COMPASS





Difference asymmetries

!

"v

= (#uv

0

1

$ (x) + #dv(x))dx

#u + #d = 3"1

N % 1

2"

v+ 1

12a8

= (#s + #s ) + 1

2(a

8%"

v)

!

"u = "d = "s = "s

"u = #"d

symmetric

asymmetric

scenario



• 2 MC samples were used in the analysis: high-pT and inclusive• Input: LEPTO generator and full simulation of the detector PDFs: MRST2004LO• Gluon radiations in final and initial states – simulation of the part of NLO corrections: - Parton Shower on were used for DG/G extraction (means NN training) - Parton Shower off were tested and included in the systematics• To improve data/MC agreement - LEPTO was tuned (kT and parameters of fragmentation) • Default MC parameters were used in systematics studies

PARJ21 PARJ23 PARJ214 PARJ41 PARJ42

Default 0.36 0.01 2.0 0 .3 0.58 Compass 0.3 0.02 3.5 0.6 0.1

Final MC

<aLO> 0.63< aC> 0.50<aPGF> -0.36 RL 0.40 RC 0.29 RPGF 0.31


MC simulations




New channels from D*

Σ =



Open charm : D0 + D* Result Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm

ΔG/G results







Documents

New results on quark helicity distributions and gluon ... fileKrzysztof Kurek SINS, Warsaw New results on quark helicity distributions and gluon polarization from the COMPASS experiment