Transcript Transverse neutron spin structure using BigBite and

Semi-Inclusive DIS Experiments
Using BigBite and Super BigBite
Spectrometers in Hall A
Andrew Puckett
University of Connecticut and Jefferson Lab
On behalf of the Super BigBite Spectrometer and
E12-09-018 Collaborations
2014 Joint Hall A/C Summer Meeting
6/5/2014
Outline
• Introduction—Semi-Inclusive DIS, TMDs, flavor tagging
• SIDIS studies using BigBite and Super BigBite in Hall A
• Unique advantages of using two independent spectrometers for
electron and hadron detection—systematics control
• Emphasis on large scattering angles, high luminosity to reach highQ2, high-x
• High-performance hadron PID using RICH
• Approved experiment E12-09-018 (neutron transversity):
Collins/Sivers effects in SIDIS on transversely polarized 3He
• New Hall A Collaboration Proposal to PAC42—SIDIS on
longitudinally polarized 3He, high-statistics measurements of
A1nh in n(e,e’h)X
• Expected results and impact on nucleon spin-flavor decomposition
• Summary and conclusions
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Semi-Inclusive Deep Inelastic Scattering
• Detecting leading (high-energy) hadrons in DIS, N(e,e’h)X provides sensitivity to additional
aspects of the nucleon’s partonic structure not accessible in inclusive DIS:
• quark flavor
• quark transverse motion
• quark transverse spin
• Goal of SIDIS studies is (spin-correlated) 3D imaging of nucleon’s quark structure in
momentum space.
• Transverse Momentum Dependent (TMD) PDF formalism: Bacchetta et al. JHEP 02 (2007)
093, Boer and Mulders, PRD 57, 5780 (1998), etc, etc...
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SIDIS Kinematics—Notation and Definitions
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General Expression for SIDIS Cross Section:
Bacchetta et al. JHEP 02, 093 (2007)
• SIDIS structure functions
F depend on x, Q2, z, pT
• U, L, T subscripts indicate
unpolarized, longitudinally
and transversely polarized
beam, target, respectively
• S = nucleon spin
• λ = lepton helicity
• Sivers
• Eight terms survive at
• Collins
• “Pretzelosity” leading twist; the rest are
M/Q suppressed
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Quark-parton Model Interpretation of SIDIS:
Transverse Momentum Dependent PDFs (TMDs)
Quark polarization
Unpolarized
(U)
Longitudinally Polarized
(L)
Transversely Polarized
(T)
Nucleon Polarization
U
L
T
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SIDIS Structure Functions in Terms of TMDs
• Only f1, g1, h1 survive integration
over quark kT
• All eight leading-twist TMDs are
accessible in SIDIS with polarized
beams/targets via azimuthal angular
dependence of the SIDIS cross section
• Physical observables are
convolutions over two (unobserved)
transverse momenta:
• Initial quark kT
• Hadron pT relative to recoiling quark,
generated during fragmentation
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JLab 11/8.8 GeV SIDIS Kinematics
W > 2 GeV
• Optimal orientation of hadron arm is
along virtual photon direction—qdirection varies linearly with x for fixed
electron scattering angle
• Need forward-angle hadron detection
capability!
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• To reach high x in the DIS regime,
need large scattering angles/high-Q2
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SIDIS Using BigBite and SBS in Hall A
SIDIS w/BB 30
deg, SBS 14 deg.
•
•
•
• Above: Schematic of SIDIS
experiment(s)
• Independent electron and
hadron arms:
• Large momentum bite
• Moderate solid angle
• High-rate capability
• Excellent PID
• h+/h- symmetric acceptance
60 cm polarized 3He
10.5 atm
Ibeam ≥ 40 μA
SIDIS w/BB 30
deg, SBS 10 deg.
BigBite (SBS) as electron (hadron) arm
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SIDIS Kinematic Coverage
• Distributions of SIDIS kinematic variables—normalized to 10 (5) days
at each SBS angle setting for E = 11 (8.8) GeV
• θSBS = 10 deg; θSBS = 14 deg
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Acceptances weakly correlated (except Q2, x)
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SBS+BB Resolution—Charged Hadrons
• SBS+BB resolution more than adequate for SIDIS on 3He—kinematic
bin migration/resolution dominated by Fermi-smearing.
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Neutral pion detection—Acceptance comparison
• π0 detected in HCAL via two high-energy
hits separated by at least one pixel
• Apertures of GEM/RICH limit useful area
of HCAL for π0 detection
• Pixel size 15 x 15 cm2 limits coord.
resolution for EM showers to 15
cm/sqrt(12) = 4.3 cm
• Estimated HCAL resolution for EM
showers is dE/E ~ 14%/sqrt(E in GeV)
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SBS+BB Resolution—Neutral Pions
• π0 kinematic resolution dominated by HCAL coordinate/energy
resolution—two-photon invariant mass resolution ~21 MeV
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Charged Hadron PID—SBS RICH Detector
• Re-use HERMES dual-radiator
RICH detector
• Aerogel n=1.0304
• C4F10 gas n=1.00137
“True”
• NIM A 479, 511 (2002)
• Above: RICH schematic
• Top right: HERMES RICH
implemented in SBS GEANT4
• Bottom right: actual and
reconstructed θC from
GEANT4
Reconstructed
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Expected PID performance (IRT algorithm)
5 GeV pion
5 GeV kaon
• PID results include acceptance effects—showing RICH geometry is well-matched to
SBS magnet/tracker acceptance
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Transverse target spin effects in SIDIS
Transverse target spin-dependent cross
section for SIDIS
• Collins effect—chiral-odd quark transversity DF; chiralodd Collins FF
• Sivers effect—access to quark OAM and QCD FSI
mechanism
• “Transversal helicity” g1T—real part of S wave-P wave
interference (Sivers = imaginary part) (requires polarized
beam)
• “Pretzelosity” or Mulders-Tangerman function—
interference of wavefunction components differing by 2 units
of OAM
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JLab Experiment E12-09-018
•
E12-09-018, E=11 GeV
•
E12-09-018,
E=8.8 GeV
•
E06-010,
E=5.9 GeV
7/6/2015
Primary physics goal: measure transverse target
SSA in 3He(e, e’h)X in SIDIS kinematics in the
valence region
• Extract neutron SSAs from Helium-3 using
effective polarization approximation—
relatively small theoretical uncertainty
• Wide, multi-dimensional kinematic coverage
• Detect π±/0 and K± simultaneously in
identical acceptance/kinematics (for charged
hadrons)
• First precision SSA data in a multidimensional phase space
Main experiment parameters:
• Electron-polarized neutron luminosity:
4.0 × 1036 𝑐𝑚−2 𝑠 −1
• Helium-3 target polarization: 65%
• Electron beam polarization: 80-85%
Approved by JLab PAC38 for 64 beam-days,
including:
• 40 beam-days production at Ebeam = 11 GeV
• 20 beam-days production at Ebeam = 8.8 GeV
• 4 beam-days for calibrations, configuration
changes
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Vast Improvement over Current Knowledge
1D binned neutron
precision ~0.2%
π± , K± Sivers compared to HERMES,
COMPASS, theory fit
FOM: Improvement on existing data by
2+ orders of magnitude
• E12-09-018 will achieve statistical FOM for the neutron ~100X better than HERMES
proton data and ~1000X better than E06-010 neutron data.
• Kaon and neutral pion data will aid flavor decomposition, and understanding of
reaction-mechanism effects.
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First Precision Multi-Dimensional Analysis
Uncertainty in this
x, z bin ~ 0.6%
Large neutron π+ asymmetry
expectation at high z, large
uncertainty
• 2D Extraction: Sivers AUT in n(e,e’π+)X, 6 x bins 0.1<x<0.7, 5 z bins 0.2<z<0.7
• Curves are theory predictions (Anselmino et al.) with central value and error band
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Extraction in Fully Differential Binning
 Increasing pT
Increasing z 
Sivers AUT, n(e,e’π+)X vs. x, 40 days @ 11 GeV
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• 6 (0.1 < x < 0.7) × 5 (0.2 <
z < 0.7) × 6 (0 < pT (GeV) <
1.2) 3D binning
• Q2 dependence with E = 11
and 8.8 GeV data gives
fully-differential analysis
• Typically 120 bins with
good stats per beam energy
• Statistical precision:
• 83% of 3D bins have
separated Collins/Sivers
neutron asymmetry error of
less than 5% (absolute)
• Average stat. err ~4%
• Most probable stat. err
~1.5%
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Polarized DIS and Nucleon Spin Structure
PDG2010 compilation of g1 data
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DSSV NLO global fit:
PRD 80, 034030 (2009)
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Proton Spin “Crisis”
“Crisis”: EMC collaboration, NPB
328, 1 (1989)
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• 1989: Fraction of proton spin carried by
quarks is “small”—“crisis” for the parton
model
• Modern (DSSV2008) value of ΔΣ ≈ 0.240.37, depending on (controversial) behavior of
strange sea polarization Δs
• Remaining ~70% of nucleon spin distributed
among gluon spin and orbital motion of
quarks/gluons; poorly known but much recent
progress both theoretically and experimentally
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New Proposal to PAC42—PR12-14-008
Measurements of Semi-Inclusive DIS Double-Spin Asymmetries
on a Longitudinally Polarized 3He Target
A Hall A Collaboration Proposal
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PR12-14-008 Collaboration—Author list as of 6-1-2014
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<Q2> of SBS+BB SIDIS: > HERMES, < COMPASS
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Projected Asymmetry Precision—1D for all hadrons
• Projected asymmetry
precisions (stat. only) in
A1nh vs x, integrated over
z, pT, compared to
prediction of “DSSV+”
NLO global fit:
http://arxiv.org/abs/1108.
3955
• Fit includes COMPASS
2010 p and d data:
http://arxiv.org/abs/1007.
4061
• <Q2> between HERMES
and COMPASS
• More details, numerical
tables available at:
https://userweb.jlab.org/~
puckett/PAC42_deltad/pr
ojections/
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Projected Asymmetry Precision, 2D (x,z), E = 11 GeV
• Relatively weak z dependence of DSSV+ curves is a NLO
QCD effect.
• Strong hadron dependence of A1nh clear indication of flavor
sensitivity of SIDIS
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• Left-right, top-bottom: π+,
π-, π0, K+, K-.
• Curves: “DSSV+”:
http://arxiv.org/abs/1108.39
55
• More details including
numerical tables at:
https://userweb.jlab.org/~p
uckett/PAC42_deltad/proje
ctions/
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Major Systematic Uncertainties
• See proposal for additional details:
https://userweb.jlab.org/~puckett/PAC42_deltad/submitted_Deltaq.pdf
Identical phase space for π+, π- leads to excellent systematic control of ratio r:
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Impacts on Nucleon Spin-Flavor Decomposition
•
•
Left: Projected precision of five-flavor Δq/q extraction
using LO “purity” method
• Excellent precision/sensitivity to d and dbar, as
expected.
Below: existing data, from DSSV2008 analysis:
http://journals.aps.org/prd/abstract/10.1103/PhysRevD.80
.034030
¬
quark
1
0.8
model
Ru
0.6
0.4
CLAS (W > 2 GeV)
HALL A
HERMES
0.2
0
-0.2
¬
quark
-0.4
model
-0.6
-0.8
-1
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DSSV
Avakian et al. (L z ¹ 0)
Rd
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
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0.9
x
1
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Impacts on Spin-Flavor decomposition, II
•
•
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Left: valence d polarization from
Helium-3 charge-difference
asymmetries using LO ChristovaLeader method.
Below: polarized sea asymmetry
assuming proton data of comparable
precision to this proposal
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Impact on Spin-Flavor Decomposition, III
Very Preliminary (“hot off the
presses”) results of DSSV impact
study—dramatic impact to dbar,
significant impacts to ubar, sbar
polarization
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Unique Advantages of SBS+BB for SIDIS Physics
• The combination of moderate solid angle, large momentum acceptance
and high-rate capability at forward angles is ideal for high-luminosity
experiments (e.g., polarized 3He), SIDIS at high Q2
• Independent electron and hadron arms—straight-line tracking in “fieldfree” regions behind dipole magnets
• Simple, reliable reconstruction and data analysis
• Change magnet polarity of e(h) arm without changing h(e) acceptance:
• Most accurate possible measurement of pair-production background in BigBite
(important background for 3He targets w/thick glass walls, especially at low x)
• SBS polarity reversals to increase ϕh coverage and make h+/h- acceptances identical
• Ability to measure K and π0 simultaneously in addition to charged pions
• Excellent systematics control for charge-sum and difference asymmetries used
to separate valence/sea quark polarizations
• Complementarity with CLAS12/SOLID/Hall C experiments—precise,
timely neutron data w/unique kinematic coverage; can run within first
five years of 12 GeV part of fully funded SBS program
• For polarized proton SIDIS at lower luminosity, competitiveness of
SBS+BB less clear; large acceptance detectors have a bigger advantage
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Summary and Conclusions
• The BigBite-SBS spectrometer pair in Hall A is ideally suited for
high-luminosity polarized (and unpolarized) SIDIS experiments:
• BigBite as electron arm as in several other 12 GeV expt’s.
• SBS as hadron arm, equipped with existing RICH for high-performance
PID
• Experiment E12-09-018 (transversity) already approved for 64
beam-days, A- rating by PAC38
• New proposal PR12-14-008 (A1nh SIDIS) submitted to PAC42 for
33 beam-days, high-impact data for nucleon spin-flavor
decomposition, relevant to future EIC program
• SBS+BB SIDIS, with unique kinematic coverage and excellent
systematics control is complementary to other approved polarized
SIDIS experiments such as CLAS12, SOLID, etc.
• Impact studies of proposed measurements to NLO global QCD
analysis are underway by Dr. R. Sassot of DSSV group.
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Acknowledgements
• Thanks to all who contributed to successful
development/submission of new proposal
• PR12-14-008 Spokespeople:
• X. Jiang, N. Liyanage
• Hall A Collaborators/reviewers
• SBS Collaborators
• R. Sassot for grid of DSSV+ predictions and
forthcoming impact studies.
• S. Riordan for development of GEANT4 framework
for SBS/BB MC simulations
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Backup Slides
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Comparison With Other Approved Experiments
• Naive FOM comparison from basic experiment parameters
• Generally: High-luminosity 3He in Hall A roughly 10-100X higher FOM for
neutron than CLAS12 ND3 (kinematics-dependent)
• At same kinematics, SBS+BB and SOLID FOM are of the same order-of-magnitude
• SBS+BB higher luminosity partially offsets SOLID advantage in solid-angle
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SBS+BB vs. SOLID: Complementarity of kinematic
coverages
• Left: Q2-x of SBS+BB vs. SOLID: SBS+BB reaches higher Q2 at
similar x due to larger electron scattering angles.
• Right: theta-vs.-phi coverage between SBS+BB and SOLID
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Detailed FOM comparison—SBS+BB vs. SOLID
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Experiment design considerations
 Azimuthal coverage: full coverage of Sivers and Collins angles 𝜙ℎ ± 𝜙𝑆
 Charged and neutral pions and kaonsFlavor decomposition of PDF and FF
 As large as possible Q2: DIS regime, factorization
 Low-to-moderate pT: ΛQCD ~< pT << Q  Applicability of TMD formalism
 Wide, independent coverage of xBj, z = p/n: factorization
 Reach high x ~ 0.5-0.7, where observable asymmetries are expected to be large
Challenges:
• A high performance polarized target
• Low event rates at high Q2 and high xBj—
high luminosity.
• High-performance particle ID—separate
different hadron species
• Proton and neutron targets—flavor
decomposition
• Non-SIDIS backgrounds:
• Radiative tails of exclusive and
resonant electroproduction
• Charge-symmetric (e+/e- pairproduction) background
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Below: Zhongbo Kang seminar,
LANL, 4/2011
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Electron Arm—BigBite Spectrometer
BigBite @ 6 GeV (E06010 transversity expt):
• Three MWDCs for
tracking (18 wire planes)
• Pre-shower/shower
calorimeter for trigger and
PID
• Scintillator hodoscope for
timing
• Dipole magnet:
𝐵𝑑𝑙 = 1.0 𝑇 ⋅ 𝑚
•
•
BigBite @ 12 GeV:
Detector upgrades including:
• GEM chambers for high-rate, high-resolution tracking
(resolve higher electron momenta at same field integral)
• Gas Cherenkov for higher-fidelity e/π separation
• New detector support frame
BigBite parameters in E12-09-018:
• Central angle = 30 deg.
• Target to magnet yoke distance = 1.5 m
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Hadron Arm—Super BigBite Spectrometer
•
•
•
•
•
•
•
•
•
SBS main parameters for E12-09-018:
Central angle = 14 deg.
Target to magnet yoke distance ~ 2.5 m
Solid angle ~40 msr
Momentum acceptance: p > 1 GeV
More info:
http://hallaweb.jlab.org/12GeV/SuperBigBite
Super BigBite Spectrometer
Originally designed for nucleon elastic form
factor measurements at large Q2.
48D48 magnet: acquired from BNL by
JLab, Bdl ~ 2 Tm.
Flexible, modular design w/ basic detector
package consisting of:
HERMES RICH performance characteristics
• GEMs
• π/K/p separation from 2-15 GeV using dual• HCAL
radiator (aerogel + heavy gas) design
Suitable for SIDIS with modest addition:
• RICH details: NIM A 479 (2002) 511
• Re-use RICH detector from HERMES
for hadron PID
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High-luminosity polarized 3He target
•
•
•
•
•
Conceptual design of
SIDIS target w/metal end
windows
•
•
Basic Target Parameters in E12-09-018
Polarization: 60-65% based on alkali-hybrid spin-exchange
optical pumping technology
Beam current: 40 μA
Target cell length along beam-line: 60 cm
Electron-polarized neutron luminosity: 4 × 1036 𝑐𝑚−2 𝑠 −1
Luminosity * Pol.2 capability upgraded (relative to previous
targets) by using convection-driven circulation of gas between
“pumping chamber” and “target chamber” (already demonstrated
in bench tests) and metal end-windows to prevent cell rupture
(under development)
Spin orientation in “any” direction; holding field ~25 G
Fast spin rotation: Change spin orientation every ~120 s.
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Experiment status, future plans, conclusion
• Experiment E12-09-018 represents an exciting near-term
opportunity to elucidate neutron transverse spin structure.
• Super BigBite Spectrometer (SBS) recently funded by DOE,
construction underway, with contributions from INFN
(GEM), UVA (GEM), CMU (HCAL), JLab (Magnet,
infrastructure, program management, etc.) and others.
Exciting program of high-impact approved experiments:
• Nucleon elastic Form Factors at large Q2—GMn, GEn, GEp
• Neutron transversity in SIDIS on Helium-3
• Custody of half of HERMES RICH detector (and all aerogel)
transferred to JLab, currently in controlled storage at UVA,
plan to start refurbishment at UConn soon.
• Many exciting physics opportunities beyond initial approved
program (if beam time in Hall A is available)
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Acknowledgements
• E12-09-018 co-spokespeople:
• Gordon Cates (UVA), Evaristo Cisbani (INFN), Gregg
Franklin (CMU), Bodgan Wojtsekhowski (JLab)
• E12-09-018 collaboration
• SBS collaboration
• A. Prokudin (for phenomenological model fit results
and “theoretical” uncertainty projections)
• US DOE
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Electron-Nucleon Scattering: Kinematics
Incident electron four-momentum
Scattered electron four-momentum
Initial nucleon four-momentum
Squared Momentum
Transfer
Energy Transfer (nucleon rest frame)
Bjorken “x” variable
Fractional electron energy loss (nucleon rest frame)
Invariant mass of virtual-photon + initial nucleon system
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Kinematic coverage from simulation
BB+SBS solid angle
coverage
Above: azimuthal coverage vs pT, Below: Kinematic coverage
Direction of q vs Bjorken x
@ 11 GeV
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Transverse spin dynamics in eqeq
•
•
•
•
•
Magnitude of quark normal and in-plane transverse polarization components is reduced by a factor of
• Dnn = (1-y)/(1-y+y2/2), where y = (1 - cosθCM)/2 is invariant (y=(ν/E)LAB).
Direction of normal polarization is unchanged
In-plane transverse polarization component in the cms rotates with quark momentum vector—
corresponds to a spin flip in target rest frame (P, q collinear)
Simplified view—ang. mom. conservation requires spin flip for quark to absorb transverse
virtual photon
DNN, an inherent feature of the hard partonic subprocess, suppresses the observable SSA
corresponding to Collins effect, esp. at large y!
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Where do the azimuthal dependences come from?
• Sivers effect is due to the correlation between
unpolarized quark kT and nucleon transverse
polarization:
• Collins effect is due to the left-right
asymmetry in the fragmentation of a
transversely polarized quark.
• The observable asymmetry results from the
convolution of the transversity distribution and
the Collins fragmentation function.
• The modified azimuthal dependence of the
Collins SSA relative to Sivers is due to a spinflip of the in-plane component of the quark’s
transverse polarization component by the
virtual photon (ang. mom. conservation)
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