Strangeness and Spin in Fundamental Physics

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Strangeness and Spin in Fundamental Physics
Varenna, June 19-29, 2007
Spin lectures
Mauro Anselmino The transverse spin structure of
the nucleon Delia Hasch The transverse spin
structure of the nucleon exp. Elliot Leader
The longitudinal spin structure of the
nucleon Werner Vogelsang QCD spin physics in
hadronic interactions Naohito Saito Spin Physics
at RHIC - experiment Raimondo Bertini
Spin physics with strangeness
Spin seminars
Robert Jaffe Gluon spin basics Harut Avakian
Spin Physics at JLab Mariaelena Boglione The
first way to transversity
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Why spin ? .
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Mauro Anselmino The transverse spin structure of
the nucleon - I
Central object of investigation the proton
transverse internal structure, that is the quark
transverse spin and transverse motion (with
respect to the direction of motion)
Why transverse? How? Single Spin
Asymmetries Transverse Momentum Dependent
distribution and fragmentation functions
(TMDs) Combining all together and learning
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How and what do we know about the longitudinal
proton structure? (E. Leader)
Naive parton model
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imaginary part of forward scattering amplitude
handbag diagram
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Longitudinally polarized DIS gives information on
the helicity distributions of quarks (and,
indirectly, of gluons)
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QCD interactions induce a well known Q2 dependence
factorization
universality same q(x,Q2) measured in DIS can be
used in other processes
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essentially x and Q2 degrees of freedom .
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The transverse structure is much more interesting
and less studied
orbiting quarks?
spin-k- correlations?
Space dependent distribution functions
Transverse Momentum Dependent distribution
functions
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Transversity distribution
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The correlator
at leading twist, in collinear configuration
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Does transversally polarized DIS give information
on the transversity distributions of quarks? No!
in helicity basis
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QED and QCD interations (and SM weak
interactions) conserve helicity h1
decouples from DIS
no h1 in DIS
odd numbers of gamma matrices
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Possible access transversity Drell-Yan processes
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What do we know about transversity? (E. Boglione
seminar)
No gluon contribution to h1, simple Q2 evolution
Soffer bound
tensor charge from lattice
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(The problem of) Single Spin Asymmetries
What are SSA? SSA in QED and QCD, helicity
conservation SSA at hadronic level, experiments
Transverse SSA related to intrinsic partonic
motion, new spin effects in distribution and
fragmentation functions .
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Transverse single spin asymmetries in elastic
scattering
Example
5 independent helicity amplitudes
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for a generic configuration
AN is zero for longitudinal spin
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QED and QCD interactions conserve helicity, up to
corrections
at quark level
but large SSA observed at hadron level!
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AN simple left-right asymmetry
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based on factorization theorem (in collinear
configuration)
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Latest PHENIX data on unpolarized cross section
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SSA?
was considered almost a theorem
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BNL-AGS vs 6.6 GeV 0.6 lt pT lt 1.2
E704 vs 20 GeV 0.7 lt pT lt 2.0
observed transverse Single Spin Asymmetries
E704 vs 20 GeV 0.7 lt pT lt 2.0
experimental data on SSA
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STAR-RHIC vs 200 GeV 1.2 lt pT lt 2.8
and AN stays at high energies .
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Transverse single spin asymmetries in SIDIS,
experimentally observed (D. Hasch)
in collinear configurations there cannot be (at
LO) any PT
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Transverse ? polarization in unpolarized p-Be
scattering at Fermilab
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And now ....... ?
Polarization data has often been the
graveyard of fashionable theories. If
theorists had their way, they might
just ban such measurements altogether
out of self-protection.
J.D. Bjorken St. Croix, 1987