jparc dy workshop, april 7 ralf seidl (rbrc) r.seidl: transverse spin 1riken, april 7 in jparc drell...
TRANSCRIPT
JPARC DY Workshop, April 7
Ralf Seidl (RBRC)
R.Seidl: Transverse Spin 1RIKEN, April 7
In JPARC Drell Yan accessible with: UU (unpolarized beam, unpolarized target)UT (unpolarized beam, transversely polarized target)TU (transversely polarized beam, unpolarized target)TT (transversely polarized beam, transversely
polarized target)
Outline
Introduction of TMDs and TransversityBoer-Mulders Function
Existing DY resultsCOMPASS , RHIC(?), FAIR(??)
Sivers FunctionSIDIS results and global analysisCurrent inclusive RHIC SSAs, future DY , COMPASS,
FAIR(??)Transversity
SIDIS results , global analysisComparison to Lattice predictions Evolution of
Collins FF(?) other measurements at RHIC(Collins, IFF) , SIDIS
(IFF, )R.Seidl: Transverse Spin RIKEN, April 7 2
In DY: UU
In DY: TUor UT
In DY: TT
Unpol. DF
Helicity
Transversity
Transversity and friends
Sivers function
Boer-Mulders function
q(x)
q(x)
q(x)
Tf1
1h
Lh1
Th1
Tg1
R.Seidl: Transverse Spin 3RIKEN, April 7
Boer Mulders measurements
Lam Tung relation: in leading order term should be zero Experiments see large cos asymmetries in +nuclear Drell Yanpossible explanationsvacuum polarization
(Nachtmann, Brandenburg) Boer Mulders function:
R.Seidl: Transverse Spin RIKEN, April 7 4
2cossin
2cos2sincos1
1 22
d
d
a
aaa
at
at
aa
xfxfe
kxhkxhe
)()(
),(),(
2 11112
11112
In DY: UU
Boer Mulders
E866 sees vanishing asymmetries on p+d DY
R.Seidl: Transverse Spin RIKEN, April 7 5
In DY: UU
Is it the isoscalar target? Or maybe the valence like antiquark in
Models and Lattice suggest, that u and d Boer Mulders function have similar sign
Unless the sea has opposite signs for u and d then this cannot explain smallness
However valence Boer mulders function in pion could
Gluon radiative effect becomes dominant at higher QT
Does that effect behave differently?
R.Seidl: Transverse Spin RIKEN, April 7 6
In DY: UU
Boer Mulders in SIDIS and future DYDifficult AUU
Asymmetrywhich contains convolution of Boer-Mulders function and Collins fragmentation function
Concurrent with Cahn-effect
For unpolarized asymmety acceptance effects in non 2 detectors
Analysis ongoing in HERMES, COMPASS and CLAS
In DY: COMPASS DY measurements (again large asymmetries?)
PANDA (FAIR) :only one they can do , some day
R.Seidl: Transverse Spin RIKEN, April 7 7
In DY: UU
RIKEN, April 7 8
Sivers function measurements I asymmetries clearly
positive First evidence of a
nonzero TMD K- asymmetries
consistent with zeroK+ asymmetries 2.3 times
larger than hard to explain
Consistent sign of Sivers functions as from M.Burkhardt’s chromodynamic lensing
R.Seidl: Transverse Spin
In DY: TUor UT
RIKEN, April 7 9
R.Seidl: Transver
se Spin
Sivers function measurements II
Results for all 3 pion states consistent with isospin symmetry
In DY: TUor UT
10
R.Seidl: Transver
se Spin
deuteron target transversely polarisedcharged hadrons (mostly pions)• 2004: results from 2002 data PRL94(2005)202002 confirmed by• 2006: results from 2002-2004 data NPB765(2007)31
Sivers asymmetry III
asymmetries compatible with zero within the statistical errors
(systematic errors much smaller)RIKEN, April 7
In DY: TUor UT
RIKEN, April 7 11
R.Seidl: Transver
se Spin
Sivers measurements IVAgain, 2003-
2004 data for identified hadrons
In DY: TUor UT
RIKEN, April 7 12
R.Seidl: Transver
se Spin
Sivers global analysisSimultaneous fit of
HERMES (02-04) and COMPASS (03-04) data on charged pions
u and d Sivers functions of nearly equal size and opposite sign
Vogelsang, Yuan
Anselmino et al
Collins et al
Anselmino et al
Also available:
Efremov,Goeke, Schweitzer
In DY: TUor UT
measurements in the near future
COMPASS proton targetImportant test of
the HERMES results in the overlap region
JLAB 6 and 12 GeVLow energies and
multiplicities
R.Seidl: Transverse Spin RIKEN, April 7 13
COMPASS, arXiv:0802.2160
In DY: TUor UT
Improvements in theoretical understanding will allow RHIC AN to be used
Fitting HERMES and COMPASS Sivers data,
Take Collins contribution into account and
Calculate phases to describe RHIC AN results
Pion asymmetries fairly well described
At least same sign for both K asymmetries as in data
Theoretical interpretations not yet consistent F.Yuan (Phys.Rev.Lett.100:032003,2008. )
R.Seidl: Transverse Spin RIKEN, April 7 14
Boglione, D’Alesia, Murgia e-Print: arXiv:0712.4240 [hep-ph]
STAR asymmetries:
Brahms asymmetries (200GeV):
In DY: TUor UT
Sivers back-to-back jet measurements
R.Seidl: Transverse Spin RIKEN, April 7 15
Emphasizes (50%+ ) quark Sivers
AN consistent with zero in central region Partial cancellation of SIDIS –like and DY –like
contributions from Sivers function
-VY 1, VY 2 are calculations by Vogelsang & Yuan, PRD 72 (2005) 054028-Bomhof et al PRD 75, (2007) 074019
STAR,PRL,99(2007)142003 In DY: TUor UT
RIKEN, April 7 16
R.Seidl: Transver
se Spin 0.1 0.2 0.3 x
Siv
ers
Am
plit
ude
0
Experiment SIDIS vs Drell Yan: Sivers|DIS= − Sivers|DY
*** Test QCD Prediction of Non-Universality ***HERMES Sivers
Results
Markus DiefenthalerDIS WorkshopMűnchen, April 2007
0RHIC II Drell Yan Projections
Feng YuanWerner Vogelsang
In DY: TUor UT
RIKEN, April 7 17R.Seidl: Transverse Spin
Transversity properties
Does not couple to gluons different QCD evolution than q(x)
Valence dominated Comparable to Lattice calculations, especially tensor charge:
Test relativistic nature of quarks in the nucleon
Positivity bound:
Soffer bound:
xqxδq
xqxqxδq 21
1
0
)()( xqxqdxgT
In DY: TT
RIKEN, April 7 18
R.Seidl: Transver
se Spin
How to access Transversity another chiral-odd function
Drell Yan: Combine two
Transversity distributions with each other
SIDIS: Combine
Transversity distributions with chiral-odd fragmentation function (FF)
Total process is chiral-even: OK
Possible Partners: Collins FF Interference FF Transverse L FF
Most require single spin asymmetries in the fragmentation
In DY: TT
RIKEN, April 7 19
R.Seidl: Transver
se Spin
First successful attempt at a global analysis for the transverse SIDIS and the BELLE Collins data
HERMES AUT p data
COMPASS AUT d data
Belle e+ e-
Collins dataKretzer FF
First extraction of transversity (up to a sign)
Anselmino et al: hep-ex 0701006
Tensor charges obtained from this fit (from Alexei Prokudin) at Q2= 2.4 GeV2:
0.340 +0.398 -
0.346 +0.392 -
189.0195.0
150.0203.0
0.236
0.569
166.0
403.0
du
du
d
u
In DY: TT
Current problems in the global transversity analysisUniversaliy? Is the Collins function from e+e-
the same in SIDIS, how about pp? According to Bacchetta et al.
and Gamberg et al, yesEvolution?
Is the evolution of transversity understood? YesIs the evolution of the Collins function understood?
Not really – is this the reason for low transversity in the global fit so far?
Error treatment, first suggestions to start a CTEQ-like transversity global analysis group with contributors from Theory (Torino), COMPASS(Trieste),HERMES(Ferrara), Belle(Illinois, RBRC)
R.Seidl: Transverse Spin RIKEN, April 7 20
In DY: TT
RIKEN, April 7 21
R.Seidl: Transver
se Spin
Collins measurements IIK+ asymmetries
compatible with asymmetries (through u quark dominance)
K- asymmetries maybe slightly positive
In DY: TT
Coming additions to global analysis
R.Seidl: Transverse Spin RIKEN, April 7 22
Very important Test: COMPASS proton data-•Will it be consistent in the overlap with HERMES?•Will they be different
arXiv:0802.2160
COMPASS full d data set,Charged , K and KS
In DY: TT
Further additions
Belle 547 fb-1 data setJLAB 6 and 12 GeV
Low energies and multiplicities
Higher twist an issue?
R.Seidl: Transverse Spin RIKEN, April 7 23
In DY: TT
Other channels: IFF, polarizationHERMES,COMPASS,pp, BELLE
R.Seidl: Transverse Spin RIKEN, April 7 24
RIKEN, April 7 25
R.Seidl: Transver
se Spin
DY transversity measurements at RHIC, JPARC and FAIR
DY transverse double spin asymmetries golden channel to Transversity:
Requires both (anti)- protons transversely polarized
For mostly sensitive to u-quark transversity
For pp smaller asymmetries due to sea transversity , but for tensor charge absolutely necessary
)()( xqxqATT
pp
Q= 8GeV
Q= 3GeV
Q= 5GeV
Q=15GeV
RHIC @ √s=200GeV
JPARC @ √s=10 GeV
Kawamura et. alNucl.Phys.B777:203-225,2007.
Assuming Soffer bound
In DY: TT
RIKEN, April 7 26
R.Seidl: Transver
se Spin
Transversity access over DY in single spin asymmetries
Instead of double spin asymmetries measure single spin asymmetries
Advantage: only one proton polarized better FOM at RHIC, earlier feasible at JPARC and GSI
Disadvantage: first have to measure Boer-Mulders function with good precision
Also planned at COMPASS with pion beam
)()(1 xqxhAT
Q=2GeV
Q=3GeV
Q=4GeV
Q=6GeVGSI (collider option) @ √s=15 GeV
Kawamura et. alNucl.Phys.B777:203-225,2007.
Theory for ATT fairly well understood even at very low scales,
if there will be PAX, it will measure mostly u2 – until then already relatively well known only consistency test
Transversity over pp DY in double spin asymmetries
In DY: TT
SummaryBoer Mulders function:
not at all well defined, hopefully some improvements until JPARC DY, but not much
Important JPARC DY measurement even w/o polarization (UU)
Sivers function: Fairly well known from SIDIS, but at low scalesInclusion of pp asymmetries possible, soon?Universality test will be absolutely crucial, then sea
Sivers functions measurements (UT)Transversity:
First global analysis available, errors still huge, evolution of Collins function?New accesses over IFF, polarimetry soonClean experiment, sensitive to sea transversity in (TT)
R.Seidl: Transverse Spin RIKEN, April 7 27
R.Seidl: Transverse Spin RIKEN, April 7 28
RIKEN, April 7 29
R.Seidl: Transver
se Spin
Transversity In helicity basis: helicity
distribution and momentum difference and sum of diagonal amplitudes
Transversity contains helicity flip and is not diagonal
Helicity is conserved quantity for (nearly) massless quarks
All interactions conserve helicity/chirality
Transversity cannot be observed in DIS
RIKEN, April 7 30
R.Seidl: Transver
se Spin
q(x), G(x)
Difference of quarks with parallel and antiparallel polarization relative to longitudinally polarized proton(known from fixed target (SI)DIS experiments)
q(x),G(x)Sum of quarks with parallel and antiparallel polarization relative to proton spin(well known from Collider DIS experiments)
q(x)
Quark distributions in spin bases
Difference of quarks with parallel and antiparallel polarization relative to transversely polarized proton(first results from HERMES and COMPASS – with the help of Belle)
Unpolarized distribution function q(x)
Helicity distribution function q(x)
Transversity distribution function q(x)