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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)
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 4
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)
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 5
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 7
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)
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 8
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 9
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
2=10 GeV2SIDIS+DIS, Q
!
"u = "d = "s = "s
"u = #"d
symmetric
asymmetric
scenario
!
g1(x,Q
2) = 1
2"e2# Cq
s[ $%& + Cq
NS $%qNS + 2n fCG $%G ]
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 10
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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)
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 11
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 12
Idea: tag γ*g➝➝ccbar via open-charm production mechanism
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
• 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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 13
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
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 14
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 15
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 16
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 17
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Δs from charged Kaon’s asymmetry
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 18
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
• 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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 19
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
New: Proton data 2007, flavour separation
Q2 = (3 GeV/c)2
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 20
ΔG/G from high-pT hadron pairs
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 21
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.
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Extraction formula for ΔG/G
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 22
• 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
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Data selection
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 23
2 variables o1 and o2 are used (R’s sum up to 1)
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
NN parameterization of fractions R
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 24
Comparison: MC/data for high pT sample; x,y and Q2
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Data/MC comparison
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 25
Comparison: MC/data for high pT sample; transverse momenta of leading and sub-leading hadrons Impact of MC tuning
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Data/MC comparison
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 26
Plot has statistical errors only
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
Results
Systematic error dominated by MC
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 27
ΔG/G from open-charm channel
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 28
nD0: 37400 nD*: 8675
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
D0 and D* meson reconstruction,2002-2004 and 2006 data
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 29
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!
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
D0 and D* meson reconstruction,2002-2004 and 2006 data
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 30
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
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
D0 and D* meson reconstruction,2002-2004 and 2006 data
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 31
- 82% correlation NN/MC- very large dispersion of values, even change of sign: weighting essential
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
aLL parameterization with NN
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 32
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
New channels from D*
NN S/(S+B) parameterization method
Σ =
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 33
Open charm : D0 + D* Result
published: PLB676(2009)31
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
ΔG/G results
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 34
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!
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS
−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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS
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)
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 38
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 39
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
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
2=10 GeV2SIDIS+DIS, Q
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 40
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
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
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 41
• 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
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
MC simulations
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 42
Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
New channels from D*
Σ =
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 43
Open charm : D0 + D* Result Introduction Helicity distributions High-pT hadrons ΔG/G from open-charm
ΔG/G results
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 44
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 45
EPS HEP 2009, 16- 22 July, Krakow, Poland Krzysztof Kurek
New results on quark helicity distributions and gluon polarization from COMPASS 46