BARYONS 2013 International Conference On The Structure of Baryons Glasgow, June 2013
Luciano L. Pappalardo University of Ferrara Selected TMD results from HERMES L.L. Pappalardo –...
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Transcript of Luciano L. Pappalardo University of Ferrara Selected TMD results from HERMES L.L. Pappalardo –...
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Luciano L. PappalardoUniversity of Ferrara
Selected TMD results from HERMES
L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-18 2013
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The full phase-space distribution of the partons encoded in the Wigner function
𝑊 (𝑥 ,𝑝𝑇 ,𝑟 )
2L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
The phase-space distribution of partons
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The full phase-space distribution of the partons encoded in the Wigner function
𝑊 (𝑥 ,𝑝𝑇 ,𝑟 )
𝑓 (𝑥 ,𝑝𝑇)
∫𝑑3𝑟TMDs H ( x , ξ ,𝑡)
∫𝑑2𝑝𝑇
GPDs
...but no simultaneous knowledge of momentum and position
cannot be directly accessed experimentally integrated quantities
The phase-space distribution of partons
3L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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𝑊 (𝑥 ,𝑝𝑇 ,𝑟 )
𝑓 (𝑥 ,𝑝𝑇)
∫𝑑3𝑟TMDs
The non-collinear structure of the nucleon
P
q
Tp
Pxp
• TMDs depend on and • Describe correlations between
and quark or nucleon spin (spin-orbit correlations)
• Provide a 3-dim picture of the nucleon in momentum space (nucleon tomography) Sivers worm-gears
Boer-Mulders
pretzelosity
helicity
transversity
momentum
Sivers worm-gears
H ( x , ξ ,𝑡)
∫𝑑2𝑝𝑇
GPDs
The full phase-space distribution of the partons encoded in the Wigner function...but no simultaneous knowledge of momentum and position
cannot be directly accessed experimentally integrated quantities
4L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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The non-collinear structure of the nucleon
• TMDs depend on and • Describe correlations between
and quark or nucleon spin (spin-orbit correlations)
• Provide a 3-dim picture of the nucleon in momentum space (nucleon tomography) Sivers worm-gears
Boer-Mulders
pretzelosity
helicity
transversity
momentum
Sivers worm-gears
DF
FF
Mostly investigated in SIDIS: detection of transverse momentum of produced hadrons gives access to
1D1H
LG1LH1
TD1 TG1 1H
TH1
Fragmentation Functions (FF)
hadron
Collins FF chiral-odd
unpol. FFchiral-even
5L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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The SIDIS cross-section
}6L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
DF
FF
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The SIDIS cross-section
}
beam polarization
unpolarized
beam and target polarization
target polarization
7L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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The SIDIS cross-section
}8L.L. Pappalardo - SPIN2012 – JINR, Dubna, Russia – September 17-22 2012
18 Structure FunctionsLeading twist Sub-leading Twist
𝑭 𝑿𝒀∝𝑫𝑭⊗ 𝑭𝑭
Distribution Functions
1D 1H
Fragmentation Functions
h1H
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Selected twist-2 and twist-3 1-hadron SIDIS results
9L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Distribution Functions
1D1H
Fragmentation Functions
h}
Sivers function
Describes correlation between quark transverse momentum and nucleon transverse polarization
10L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Sivers amplitudes
significantly positive
slightly positive
consistent with zero
consistent with Sivers func. of opposite sign for u and d quarks
(isospin-symmetry)
[An
se
lmin
o e
t al.,Eu
r.Ph
ys.J
.A3
,20
09]
11 Df T
[Airapetian et al., Phys. Rev. Lett. 103 (2009) 152002]
11L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Sivers amplitudes
significantly positive
slightly positive
consistent with zero
(isospin-symmetry)
[An
se
lmin
o e
t al.,Eu
r.Ph
ys.J
.A3
,20
09]
consistent with Sivers func. of opposite sign for u and d quarks
[Airapetian et al., Phys. Rev. Lett. 103 (2009) 152002]
12L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
Similar kinematic dependence of
significantly positive
slightly positive
11 Df T
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Sivers kaons amplitudes: open questions +/K+ production dominated by u-quarks,
but:
13L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Sivers kaons amplitudes: open questions +/K+ production dominated by u-quarks,
but:
14L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
different role of various sea quarks ?
suKdu ,?
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no effect for pions, but hint of a systematic shifts for kaons
Sivers kaons amplitudes: open questions
different role of various sea quarks ?
suKdu ,?
+/K+ production dominated by u-quarks, but:
15L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
? Higher-twist contrib. for Kaons
only in low-Q2 region significant deviation
each x-bin divided into two Q2 bins
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Distribution Functions
1D1H
Fragmentation Functions
h}
Pretzelosity
Describes correlation between quark transverse momentum and transverse spin in a transversely pol. nucleon
Sensitive to non-spherical shape of the nucleon
16L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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…suppressed by two powers of Ph
w.r.t. Sivers amplitudes
All amplitudes consistent with zero
11 Hh T
17L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
The amplitudes
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Distribution Functions
1D1H
Fragmentation Functions
h}
Worm-gear
Describes the probability to find longitudinally polarized quarks in a transversely polarized nucleon!
Can be accessed in LT DSAs
18L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
}
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19L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
S. Boffi et al. (2009) Phys. Rev. D 79 094012Light-cone constituent quark modeldashed line: interf. L=0, L=1dotted line: interf L=1, L=2
Worm-gear
The only TMD that is both chiral-even and naïve-T-even
requires interference between wave function components that differ by 1 unit of OAM quark orbital motion inside nucleons
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The only TMD that is both chiral-even and naïve-T-even
requires interference between wave function components that differ by 1 unit of OAM quark orbital motion inside nucleons
Accessible in LT DSAs:
20L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
S. Boffi et al. (2009) Phys. Rev. D 79 094012Light-cone constituent quark modeldashed line: interf. L=0, L=1dotted line: interf L=1, L=2
Worm-gear
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21L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
S. Boffi et al. (2009) Phys. Rev. D 79 094012Light-cone constituent quark modeldashed line: interf. L=0, L=1dotted line: interf L=1, L=2
Simplest way to probe Tg1
Worm-gear
The only TMD that is both chiral-even and naïve-T-even
requires interference between wave function components that differ by 1 unit of OAM quark orbital motion inside nucleons
Accessible in LT DSAs:
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The amplitudes
similar observations from Hall-A and COMPASS
slightly positive ?
slightly positive ?
consistent with zero
consistent with zero
positive!!
11 Dg T
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23L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
The and amplitudes
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Distribution Functions
1D1H
Fragmentation Functions
h}
Worm-gear
Describes the probability to find transversely polarized quarks in a longitudinally polarized nucleon
24L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
some models support the simple relation
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The sin(2 amplitude 11 Hh L
Amplitudes consistent with zero for all mesons and for both H and D targets
Deuterium target Hydrogen target
A. Airapetian et al, Phys. Lett. B562 (2003)
A. Airapetian et al, Phys. Rev. Lett. 84 (2000)
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A. Airapetian et al, Phys. Lett. B562 (2003)
𝜋+¿¿
𝜋 0
𝜋−
𝐾 +¿ ¿
26L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
sin( amplitude
Positive: Hydrogen results larger than Deuteron (u-quark dominance)
Positive: Hydrogen and Deuteron of same size
Deuteron positive, Hydrogen 0
Positive and consistent with (u-quark dominance)
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Distribution Functions
}
Subleading twist
L.L. Pappalardo – Structure of Nucleons and Nuclei – Como – June 10-14 2013
Sensitive to worm-gear , sivers, transversity + higher-twist DF and FF
Tg1
27L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Subleading-twist sin(S) Fourier component• sensitive to worm-gear , Sivers function, Transversity, etc
• significant non-zero signal for - and K- !
Tg1
Large and
negative
negative
28L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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Subleading-twist sin(S) Fourier component• sensitive to worm-gear , Sivers function, Transversity, etc
• significant non-zero signal for - and K- !
Tg1
low-Q2 amplitude larger
hint of Q2 dependence for -
Large and
negative
negative
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2-hadron SIDIS results
Following formalism developed by Steve Gliske
Find details inTransverse Target Moments of Dihadron Production in Semi-inclusive Deep Inelastic Scattering at HERMES
S. Gliske, PhD thesis, University of Michigan, 2011
30L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
http://www-personal.umich.edu/~lorenzon/research/HERMES/PHDs/Gliske-PhD.pdf
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A short digression on di-hadron fragmentation functions
In the new formalism there are only two di-hadron FFs. Names and symbols are entirely associated with the quark spin, whereas the partial waves of the produced hadrons are associated with partial waves of FFs.
Standard definition of di-hadron FF assume no polarization of final state hadrons (pseudo-scalar mesons) or define mixtures of certain partial waves as new FFs
The cross-section is identical to the ones in literature, the only difference is the interpretation of the FFs:
31L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
’
’
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The di-hadron SIDIS cross-section
and correspond to angular momentum state of the hadron
Considering all terms () there are 144 non-zero structure functions at twist-3 level. The most known is
which for and reduces to the well known collinear related to transversity
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The di-hadron SIDIS cross-section
• independent way to access transversity
• Collinear no convolution integral
• significantly positive amplitudes
• evidence of non zero dihadron FF
• limited statistical power (v.r.t. 1 hadron)
33L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
JHEP 06 (2008) 017
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The di-hadron SIDIS cross-section
34L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
• New tracking, new PID, use of rather than • Different fitting procedure and function • Acceptance correction
JHEP 06 (2008) 017
• independent way to access transversity
• Collinear no convolution integral
• significantly positive amplitudes
• evidence of non zero dihadron FF
• limited statistical power (v.r.t. 1 hadron)
• signs are consistent for all species
• statistics much more limited for
• despite uncertainties may still help to constrain global fits and may assist in flavor separation
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ConclusionsA rich phenomenology and surprising effects arise when parton transverse momentum is not integrated out!
Transverse effects and orbital motion of partons are now established as key ingredients of the nucleon internal dynamics
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ConclusionsA rich phenomenology and surprising effects arise when parton transverse momentum is not integrated out!
Transverse effects and orbital motion of partons are now established as key ingredients of the nucleon internal dynamics
The HERMES experiment has played a pioneering role in these studies:
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Back-up
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Distribution Functions
1D1H
Fragmentation Functions
h}
Describes correlation between quark transverse momentum and transverse spin in unpolarized nucleon
Boer-Mulders function
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The cos2 amplitudes ),(),( 21
21 TT kzHpxh
negative
positive
A. Airapetian et al, Phys. Rev. D 87 (2013) 012010
- Amplitudes are significant clear evidence of BM effect
- similar results for H & D indicate
- Opposite sign for consistent with opposite signs of fav/unfav Collins
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The cos2 amplitudes
- Amplitudes are significant clear evidence of BM effect
- similar results for H & D indicate
- Opposite sign for consistent with opposite signs of fav/unfav Collins
),(),( 21
21 TT kzHpxh
negative
positive
Large and
negative
- amplitudes are larger than for pions , have different kinematic dependencies than pions and have same sign
- different role of Collins FF for pions and kaons?
- Significant contribution from scattering off strange quarks?
Large and
negative
A. Airapetian et al, Phys. Rev. D 87 (2013) 012010
http://www-hermes.desy.de/cosnphi/Analysis multi-dimensional in x, y, z,and PtCreate your own projections of results through:
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The cos amplitudes
negative
negative
Large and
negative
Consist. with
0
A. Airapetian et al, Phys. Rev. D 87 (2013) 012010
http://www-hermes.desy.de/cosnphi/Analysis multi-dimensional in x, y, z,and PtCreate your own projections of results through:
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Distribution Functions
1D1H
Fragmentation Functions
h}
Transversity
Describes probability to find transversely polarized quarks in a transversely polarized nucleon
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Consistent with Belle/BaBar measurements in e+e-
Collins amplitudes
positive
consistent with zero
large and negative!
(isospin-symmetry)
significantly positive
consistent with zero
[Airapetian et al., Phys. Lett. B 693 (2010) 11-16]
),(),( 21
21 TT kzHpxh
Soffer bound
xh1(x
)d
xh1(x
)u
xh1(x
, k )T
uxh
1(x, k
)T
d
Anselmino et al. Phys. Rev. D 75 (2007)
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}
𝐹 𝐿𝑈sin𝜙
Distribution Functions
Sensitive to , Boer-Mulders + higher-twist DF and FF
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}
𝐹 𝐿𝑈sin𝜙
open circles 0.2<z<0.5full circles 0.5<z<0.8open squares: 0.8<z<1.0
A. Airapetian et al, Phys. Lett. B 648 (2007)
1996-2000 data𝜋+¿¿
𝜋 0
𝜋−
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H target, 2000-2007 data 0.2<z<0.7
𝐹 𝐿𝑈sin𝜙
Released yesterday!!
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𝐹 𝐿𝑈sin𝜙
Released yesterday!!
D target, 2000-2007 data 0.2<z<0.7
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The sin(2+S) Fourier component
• arises solely from longitudinal (w.r.t. virtual photon direction) component of the target spin
• related to <sin(2)>UL Fourier comp:
• sensitive to worm-gear
• suppressed by one power of Ph w.r.t. Collins and Sivers amplitudes
• no significant signal observed (except maybe for K+)
Lh1
h
ULl
h
UTS )2sin(2)sin(2
1)2sin(2 *
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The subleading-twist sin(2-S) Fourier component• sensitive to worm-gear ,
Pretzelosity and Sivers function:
Tg1
• suppressed by one power of Ph w.r.t. Collins and Sivers amplitudes
• no significant non-zero signal observed
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1. Assume u quark and proton have (transverse) spin alligned in the direction . The model assumes that the struck quark is initially connected with the remnant via a gluon-flux tube (string)
2. When the string breaks, a pair is created with vacuum quantum numbers . The positive parity requires that the spins of and are aligned, thus an OAM has to compensate the spins
3. This OAM generates a transverse momentum of the produced pseudo-scalar meson (e.g. ) and deflects the meson to the left side w.r.t. the struck quark direction, generating left-righ azimuthal asymmetries
(a phenomenological explanation of the Collins effect)
In the cross-section the Collins FF is always paired withy a distrib. function involving a transv. pol. quark.
A short digression on the Lund/Artru string fragmentation model
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Relative to the proton transv. spin, the fragmenting quark can have spin parallel or antiparallel to Then combining the spins of the formed di-quark systems one can get:
12⨂ 12=1⊕0⇒ { 1𝑠𝑝𝑖𝑛0𝑠𝑡𝑎𝑡𝑒|0 ,0 ⟩
3𝑠𝑝𝑖𝑛1𝑠𝑡𝑎𝑡𝑒𝑠 { |1 , 0 ⟩|1 , ±1 ⟩
1 pseudo-scalar meson (PSM) 1 Longitudinal VM2 transvrse VM
Lund/Artru prediction at the amplitude level: the asymmetry for PSM has opposite sign to that for transversely polarized VM (left vs. right side), and the amplitude for is 0
Lund/Artru model makes predictions for the individual di-hadrons, but the Collins function includes pairs of di-hadrons
® to make predictions for the Collins function one needs to consider the cross-section level, i.e. the sum of contributing amplitudes times their complex conjugate
Using the Clebsch-Gordan algebra one obtains:
Lund/Artru prediction at the cross-section level: the partial waves of the Collins func. for SIDIS VM production have the opposite sign as the respective PS Collins func.
A short digression on the Lund/Artru string fragmentation model
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“gluon radiaton model” vs. Lund/Artru model
The Lund/Artru model only accounts for favored Collins fragmentation. An extension of the model (the gluon radiation model), elaborated by S. Gliske accounts for the disfavored case
1. Struck quark emits a gluon in such a way that most of its momentum is transferred to the gluon2. The struck quark then becomes part of the remnant 3. The radiated gluon produces a pair that eventually converts into a meson4. For PSM the di-quark must interact further with the remnant to get the PSM quantum numbers. In
case of VM the di-quark directly forms the meson
Lund/Artu Gluon radiation
• Di-quark has q.n. of vacuum• Struck quark joins the anti-quark in the
final state favored fragment.
• Di-quark has q.n. of observed final state• Produced quark joins the anti-quark in the
final state disfavored fragment.
Prediction: the partial wave of the Collins funct. for SIDIS VM production have the opposite sign as the respective PS Collins function
Prediction: the disfavored Collins frag. also is expected to have opposite sign as the respective PS Collins function.
Models predict: fav = disfav for VM
Data say: fav disfav for PSM (Collins )52L.L. Pappalardo – Baryons 2013 – Glasgow – June 24-28 2013
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…and now let’s look at the results
Fragment. process Fav/disfav Deflection Sign of amplitude
fav PSM left > 0 (Collins )
disfav PSM ight < 0 (Collins )
fav VM right < 0
disfav VM right < 0
mixed VM right 0 or < 0
from data
from modelsu
dom
inan
ce
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…and now let’s look at the results
Fragment. process Fav/disfav Deflection Sign of amplitude
fav PSM left > 0 (Collins )
disfav PSM ight < 0 (Collins )
fav VM right < 0
disfav VM right < 0
mixed VM right 0 or < 0
from data
from models
consistent with zero for all flavors Not in contraddiction with models: if the transversity function causes the fragmenting quark to have positive polarization than Collins must be zero as this partial wave requires fragmenting quark with negative polarization
consistent with model expect:• No signal outside -mass bin no non-resonant pion-pairs in p-wave• Negative for (model predictions)• very small for (consistent with small
Collins )
u do
min
ance
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Aerogel n=1.03
C4F10 n=1.0014
hadron separation
lepton-hadron > 98%
TRD, Calorimeter, preshower, RICH:
~ 98%, K ~ 88% , P ~ 85%
The HERMES experiment at HERA
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Siver amplitudes: additional studies
No systematic shifts observed between high and low Q2 amplitudes for both + and K+
No indication of important contributions from exclusive VM
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The pion-difference asymmetry
Contribution from exclusive r0 largely cancels out!
• significantly positive Sivers and Collins amplitudes are obtained
• measured amplitudes are not generated by exclusive VM contribution
Contribution by decay of exclusively produced vector mesons (0,,) is not negligible (6-7% for pions and 2-3% for kaons), though substatially limited by the requirement z<0.7.
)()(
)()(1,
UUUU
UUUU
TSUT P
Aa new observable
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