Overview of recent HERMES results on longitudinal spin asymmetries
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XXVIII International Workshop on Deep-Inelastic Scattering
and Related Subjects
Virtual Event @ Stony Brook University, April 12-16, 2021
Overview of recent HERMES results
on longitudinal spin asymmetries
D. Veretennikov on behalf of the HERMES collaboration
University of the
Basque Country
UPV/EHU
Introduction
Deep-inelastic scattering (DIS) with charged lepton beams is the key tool for probing the structure of the nucleon.
With polarized beams and targets the spin structure of the nucleon becomes accessible
What we need:
• polarized lepton beams
• polarized targets
• large-acceptance spectrometer
• good particle identification (PID) Cross-section
factorization
Parton
distributions fragmentation
functions
D. Veretennikov DIS2021 2
HERMES experiment
FIELD CLAMPS TRIGGER HODOSCOPE H1
m
FRONT DRIFT CHAMBERS 270 mrad
2 MUON
170 mrad
HODO
PRESHOWER (H2)
DRIFT 140 mrad
CHAMBERS
1
FC 1/2
PROP.
CHAMBERS 27.5 GeV
LUMINOSITY
0
TARGET MC 13
MONITOR
e+
CELL
SILICON DVC
1 HODOSCOPE H0
BC 1/2
BC 3/4 TRD CALORIMETER 140 mrad
STEEL PLATE
RICH IRON WALL
2 270 mrad 170 mrad
WIDE ANGLE
MUON HODOSCOPES
MUON HODOSCOPE
• Located at DESY, Hamburg
MAGNET
0 1 2 3 4 5 6 7 8 9 10 m
• 27.6 GeV longitudinally polarized (up to 60%) e+/e-
beam • Particle ID detectors allow for:
• Longitudinally polarized (up to 85%) pure H, D, 3He gas o - lepton/hadron separation
target, flip ~ 90 sec o - Ring Imaging Cherenkov detector (RICH):
• Transversely polarized H gas target pion/kaon/proton discrimination 2 GeV < p < 15 GeV
• Unpolarized H, D, Ne, … Xe gas target
• Data taking end at 2007
D. Veretennikov DIS2021 3
Longitudinal double-spin asymmetries
Cross-section excluding transverse polarization
λ - beam helicity
Λ - target helicity
U/L – unpolarized/longitudinally polarized
double-spin asymmetry
D. Veretennikov DIS2021 4
Longitudinal double-spin asymmetries
In experiment extract instead A|| which differs from ALL
in the way the target polarization is measured:
o ALL: along virtual-photon direction
o A||: along beam direction (results in small
admixture of transverse target polarization and
thus contributions from ALT)
A|| related to virtual-photon–nucleon asymmetry A1
D. Veretennikov DIS2021 5x dependence of A||
Phys.Rev.D99 (2019) 11, 112001
• Results are fully consistent with
previous analysis
(Phys.Rev.D71:012003,2005)
• slightly larger data set
• results for A|| and A1
• 2D and 3D dependences
• extracted twist-3 cosine
modulation
D. Veretennikov DIS2021 6x-z dependence of A||
Phys.Rev.D99 (2019) 11, 112001
• No strong z-dependence visible
• Asymmetries bigger for high x
value
• On deuteron A|| lower due to
neutron contribution
D. Veretennikov DIS2021 7x-Ph⊥ dependence of A||
Phys.Rev.D99 (2019) 11, 112001
• again, no strong dependence
D. Veretennikov DIS2021 8Charge-difference asymmetries
Phys.Rev.D99 (2019) 11, 112001
1/2(3/2) – denotes beam and target spins
antiparallel (parallel)
The advantage of the charge difference asymmetry is
that at leading order the fragmentation functions
cancel and one is mainly sensitive to the PDFs
no significant hadron-type dependence for deuterons
deuteron results (unidentified hadrons) consistent with
COMPASS
D. Veretennikov DIS2021 9Helicity distributions for valence quarks
(Phys.Rev.D71:012003,2005)
MC calculation
Two different methods and
model assumptions give
very consistent results.
D. Veretennikov DIS2021 10Beam-helicity asymmetries
Cross-section excluding transverse polarization
λ - beam helicity
Λ - target helicity
U/L – unpolarized/longitudinally polarized
single-spin asymmetry
D. Veretennikov DIS2021 11Beam-helicity asymmetries
Describe intrinsic motion of quarks and gluons inside target nucleon due to correlations of pT and its spin
s with the spin of the target nucleon S
asymmetry amplitudes extracted by minimizing
where wi is event weight from hadron-ID, charge-symmetric background, etc.
D. Veretennikov DIS2021 12Beam-helicity asymmetry
Phys.Lett.B 797 (2019) 134886
Results also available in 3D (x, z, Ph⊥)
binning
D. Veretennikov DIS2021 13Beam-helicity asymmetry
Phys.Lett.B 797 (2019) 134886
Results also available in 3D (x, z, Ph⊥)
binning
D. Veretennikov DIS2021 143D beam-helicity asymmetry for π-
Phys.Lett.B 797 (2019) 134886
Mainly (non zero
contribution) coming from
lower x and lower Ph⊥
D. Veretennikov DIS2021 15HERMES - CLAS comparison
Phys.Lett.B 797 (2019) 134886
Opposite behavior of
negative pions in z projection
due to different x-range
D. Veretennikov DIS2021 16HERMES - COMPASS comparison
Phys.Lett.B 797 (2019) 134886
consistent behavior for charged
pions / hadrons at HERMES /
COMPASS
D. Veretennikov DIS2021 17Summary
Longitudinal double-spin asymmetries
several longitudinal double-spin asymmetries in SIDIS have been presented that:
o extend the analysis of previous HERMES publications to include also transverse-momentum dependence
o provide A|| in addition to A1, and in a 2D and 3D kinematic binning
the twist-3 cosine modulation of the double-spin asymmetry is found to
be consistent with zero
within precision of the measurements, the virtual-photon-nucleon asymmetries display no significant dependence on z and Ph⊥
hadron-charge difference asymmetries in agreement with COMPASS
Beam-helicity asymmetries
First 3D extraction for charge-separated pions, kaons, as well as for (anti)protons
clearly non-zero and rising as function of z beam-helicity asymmetries observed for charged pions
K+ asymmetries are slightly positive, but no kinematical dependencies
high-x behavior in HERMES - CLAS comparison might be driven by TMD e & Collins FF
COMPASS and HERMES in agreement despite different Q2 ranges probed
D. Veretennikov DIS2021 18Backup D. Veretennikov DIS2021 19
Longitudinal spin transfer DLL’ in SiDIS
r r
e + N → e′ + Λ + X Due to weak decay polarization of the Λ can be
extracted by measuring angular distribution of decay
proton
e'
PLΛ′ P=
= D
γ * LL ′
Pb D( y ) DLL ′
e
γ∗ q L – primary axis, along virtual photon
Λ L’ – secondary axis, along lambda momentum
hadronization
Pγ = Pb D ( y ) , virtual gamma polarization
q
*
D ( y ) , depolarization factor
X
p Longitudinal spin transfer coefficient give
us access to spin structure of Λ hyperon
D. Veretennikov DIS2021 20Comparison of HERMES data with other experiments
DΛLL
HERMES preliminary
0.5 (1996-2005)
More data (2006-2007) currently
being analysed for final
0.0 publication.
-0.5
-1.0
NOMAD (νµN → µΛX)
E665 (µN → µ'ΛX)
-1.5 COMPASS (µN → µ'ΛX)
HERMES (eN → e'ΛX)
-0.8 -0.4 0.0 0.4
xF
D. Veretennikov DIS2021 21You can also read
