EIC Workshop, Hampton, VA

May 21

Ralf Seidl (RBRC)

EIC workshop, May 21th 1R.Seidl: Transversity measurements at EIC

Outline

TransversityChiral-odd PDFSIDIS results Belle resultsglobal analysis

First global analysis Comparison to Lattice predictions Evolution of Collins

FF(?)What will be important after these first measurements

Higher scales kt-Moments , lower x to get to tensor charge

other measurements (IFF, )

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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

Unpol. DF

Helicity

Transversity

Transversity and friends

Sivers function

Boer-Mulders function

q(x)

q(x)

q(x)

Tf1

1h

Lh1

Th1

Tg1

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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

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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

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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

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)

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Collins measurements IIK+ asymmetries

compatible with asymmetries (through u quark dominance)

K- asymmetries maybe slightly positive

Coming additions to global analysis

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arXiv:0802.2160

COMPASS full d data set,Charged , K and KS

In DY: TT

Further additionsBelle 547 fb-1 data set (submitted to PRD arXiv:0805.2975)

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New data to come

HERMES K data not yet used in fits

COMPASS K data not yet used

JLAB 6 and 12 GeVLow energies and

multiplicitiesHigher twist an issue?

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Very important Test: COMPASS proton data-

• Will it be consistent in the overlap with HERMES?

• Will they be different

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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

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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

What is needed at EIC?

Larger x range measured b y existing experimentsCOMPASS ends at ~

0.01, go lower by almost one order of magnitude, but asymmetries become small

Have some overlap at intermediate x to test evolution of Collins function and higher twist but at higher Q2

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What is needed at EIC IIDetect SIDIS hadrons at z range 0.1 – 0.9 Have to be able to reject exclusive VMs

nearly hermetic detector, reasonable momentum resolution

Good e/h separation needed everywhere, good hadron PID needed in hadron acceptance

So far: No Ph moments measured yet, why?

Acceptance effects are very difficult to correctMake sure we have very good and uniform Ph

coverage , say cone of Ph

< 3 GeV Need generator capable to produce kT

dependent asymmetries Generalize gmc_trans

Other channels: IFFHERMES,COMPASS,pp, BELLE

COMPASS: zero on deuteron target proton date will be interesting

Possibility to measure IFF also at RHIC

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Other channels II: polarization

Measurements available from COMPASS on deuteron target,

Plan to measure it at Belle

IFF and polarimetry can also be probed with great precision at EIC

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SummaryTransversity:

First global analysis available, errors still huge, evolution of Collins function?Newer data not yet included in global analysis

from HERMES (K), COMPASS (K, proton data), JLAB

Large Belle Collins data now finalNew accesses over IFF, polarimetry soon

EIC needs to cover intermediate x range, z>0.2, Ph

< 3 GeV , good e/h separation and PID

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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)