F'H' Heinsius Universitt FreiburgCERN - PowerPoint PPT Presentation

Title: F'H' Heinsius Universitt FreiburgCERN


1
Recent Spin Physics Results from the
Experiment

• F.-H. Heinsius (Universität Freiburg/CERN)
• Introduction
• Gluon polarization in the nucleon
• Transverse spin distribution

DESY, June 2006
2
Towards understanding nonperturbative QCD

• Nucleon is fundamental in understanding QCD
• confinement
• asymptotic freedom
• spontaneous chiral symmetry breaking
• Mass around us mostly due to nucleons
• quark mass accounts for only about 1
• mostly due to dynamics
• of gluons and quarks
• Do we understand the structure of baryons?

3
Structure Functions
x momentum fraction of the nucleon
carried by the parton
Q² negative momentum transfer squared
4
Parton Density Distributions

• 40 of the momentum carried by gluons

5
Towards understanding nonperturbative QCD

• Nucleon is fundamental in understanding QCD
• confinement
• asymptotic freedom
• spontaneous chiral symmetry breaking
• Mass around us mostly due to nucleons
• quark mass accounts for only about 1
• mostly due to dynamics
• of gluons and quarks
• Do we understand the structure of baryons?
• measurements
• unpolarized 40 of momentum gluons
• polarized 30 of helicity quarks
• cannot be calculated from QCD (yet)
• lattice gauge calculation
• Study of special bound states
• double charmed baryons 2 heavy 1 light quark

6
COMPASS A Facility to study QCD
230 physicists, 10 countries, 25 institutes
LHC

COMPASS
SPS
m, p, or p/K beam

7
COMPASS A Facility to study QCD

• Experiments with muon beam
• Gluon polarization DG/G in the nucleon
• Flavor dependent quark helicity density
  distributions Dq
• Transverse quark spin distribution functions
  h1(x)
• Spin transfer in L-hyperon production
• Vector meson production
• Generalised parton distributions

• Experiments with hadron beams
• Pion and kaon polarizabilities
• Diffractive production of exotic states
• Search for glueballs
• Light meson spectroscopy
• Production of double charmed baryons

• Application and test of
• perturbative QCD
• nonperturbative QCD
• effective theories
• chiral perturbation theory
• lattice QCD

8
The COMPASS Spectrometer
50 m
Two stage spectrometer
Polarized beam and target 80 50
SAT,
LAT,
PID
10-5ltxlt0.5, 10-3ltQ2lt100 (GeV/c)2
9
Many new technologies for tracking and PID
MicroMegas
GEM
Trigger-System

Straws
RICH readout
Scintillating fiber trackers
Readout electronics
10
The polarized 6LiD-Target
4 possible spin combinations
reversed every 8 hrs
or
reversed once a week
Polarization 50
11
Probing the Spin Structure of the Nucleon
m
m
Nukleon
x fraction of nucleon momentum
carried by quark
12
A1 of the deuteron
COMPASS 2002-2004
2002/2003 COMPASS, Phys. Lett. B 612 (2005) 154
13
g1 of the deuteron
COMPASS 2002-2004
14
QCD analysis of g1
Plots Böttcher
fit to world data DS0.22 0.03 stat. Q²3
(GeV/c)² incl. COMPASS DS0.25 0.02 stat. Q²3
(GeV/c)² 02/03 DG0.40.2 stat.

• Systematic uncertainties
• fit parametrisation
• extrapolation x?0

15
What makes up the Nucleons Spin?
Naive quark model valence quarks
CERN, SLAC, DESY, JLAB DS 0.30
16
Polarization of Gluons DG/G in the Nucleon

• q c cross section difference in charmed
  meson production
• ? cross section known to NLO
• ? experiment challenging
• q u,d,s cross section difference in 21 jet
  production.
• In COMPASS events with
• 2 hadrons with high pT
• ? experiment easy
• ? background difficult
• use two complementary measurements
• Q²gt1 (GeV/c)² and LEPTO MC
• Q²lt1 (GeV/c)² and PYTHIA MC

Photon gluon fusion
N
17
DG/G from Open Charm (D-mesons)
Photon gluon fusion
D
N

• zD gt 0.2 (0.25 for D0) cosq lt 0.85 (0.5 for
  D0)
• RICH identification for K 9 GeV/c lt p (K )
  lt 50 GeV/c

18
DG/G from Open Charm (D-mesons)
mD0 with D tagging
mD0 without D tagging
2002 - 2004
m213 (GeV/c)2
19
DG/G from high-pT meson pairs
Photon Gluon Fusion
h1
h2
N
Q2 gt 1 (GeV/c)2 LEPTO Monte Carlo
Q2 lt 1 (GeV/c)2 PYTHIA Monte Carlo
20
How to get ?G/G Q2gt1 (GeV/c) 2
fractions of cross section determined by Monte
Carlo
Leading Order
QCD-Compton
Photon Gluon Fusion
21
DG/G from high-pT meson pairs
Photon Gluon Fusion
h1
h2
N
Q2 gt 1 (GeV/c)2 LEPTO Monte Carlo
?G/G 0.06 0.31stat. 0.06syst.
at ltxggt 0.13 0.08
2002/2003
22
Background for Q2lt1 (GeV/c) 2
PYTHIA


23
Background for Q2lt1 (GeV/c) 2
PYTHIA


Uncertainty due to the unknown spin distribution
in the hadronic structure of the photon
24
Monte Carlo Tuning

• scrutinize systematic error 15 independent
  simulations
• map the parameter space, i.e.
• for kT in nucleon and photon
• Fragmentation functions
• parton shower on/off,
• renormalization scale

Nucleon
Photon
25
DG/G from high-pT meson pairs
Photon Gluon Fusion
h1
h2
N
Q2 gt 1 (GeV/c)2 LEPTO Monte Carlo
?G/G 0.06 0.31stat. 0.06syst.
at ltxggt 0.13 0.08
2002/2003
m23 (GeV/c)2
26
DG/G summary
DG2.5
DG0.6
DG0.2
GRSV Glück et al.,Phys. Rev. D63 (2001) 094005
NLO fits to g1 at m2 3 (Gev/c)2
27
Transverse Spin Distributions
3 independent structure functions are necessary
to describe the spin structure of the nucleon at
leading order

All of equal importance !
h1(x) decouples from leading twist DIS because
helicity of quark must flip No mixture with Gluon
28
Transverse Spin Physics

• 3 possible quark polarimeters suggested
• Azimuthal distribution of hadrons
• Azimuthal dependence of the plane containing 2
  hadrons
• Measure transverse polarization of L
• COMPASS studies all of them

transverse target polarisation
fS azimuthal angle of spin vector of
initial-state quark/nucleon fS' azimuthal angle
of spin vector of fragmenting quark
fS'p- fS fh azimuthal angle of hadron
momentum fColl fh - fS' AColl sin
fColl fSiv fh - fS ASiv sin fSiv


h
29
Transverse Spin Physics Collins
Azimuthal distribution of hadrons

Collins spin dependent fragmentation of
transversely polarised quarks into unpolarised
hadrons
30
Transverse Spin Physics Collins FF
Collins fragmentation function extracted from
HERMES / BELLE

From Efremov, Goeke, Schweitzer PRD 73 (2006)
094025
COMPASS 2002 data PRL 94 (2005) 202002 compatible
with fit deuteron essential to determine h1d
31
Transverse Spin Physics Collins
Azimuthal distribution of hadrons

Collins spin dependent fragmentation of
transversely polarised quarks into hadrons
Efremov, Goeke, Schweitzer PRD 73 (2006) 094025
compared to new COMPASS data
32
Transverse Spin Physics Sivers
Effect related to parton orbital momentum

Sivers modulation of transverse momentum of
unpolarised quarks in the transverse polarised
nucleon (intrinsic kT dependence of the quark
distribution)
Efremov, Goeke, Scheitzer, hep-ph/060354 (fit to
BELLE HERMES data)
Anselmino et. al PRD 72 (2005) 094007
33
Transverse Spin Physics Pions/Kaons
Asymmetries with pion and kaon identifications
by RICH
Pions
Kaons

• Collins and Sivers
• compatible with zero
• for pions and kaons
• interesting to see
• proton in 2006

34
Transverse Spin Physics
Azimuthal dependence of the plane containing 2
hadrons

all /- combinations per event
1 /- combination per event pt ordering
2002-2004 COMPASS data

• precise measurement of few
• systematics seems well under control
• also compatible with zero

35
Transverse Spin Physics
Measure transverse polarization of L

36
Results not covered

• semi-inclusive
• asymmetries, r
• single hadron high-pT
• r spin-density
• matrix elements
• L polarisation
• pentaquark search
• diffractive processes
• J/Y production

37
COMPASS upgrades for this year

• New solenoid magnet
• Larger acceptance
• 70 mrad ? 180 mrad
• RICH upgrade
• Central region MAPMT system
• Outer region new faster electronics
• Other upgrades
• Large Drift Chamber
• ECAL1

38
Summary / Outlook

• COMPASS results (2002-2004)
• polarisation of gluons in the nucleon
• transversity small asymmetries on deuteron
• Many more results not covered
• Major upgrade of spectrometer for this year
• Next year start spectroscopy
• hybrids, glueballs,
• Long term future (2010)
• generalised parton distributions (DVCS,)