Diana Parno d 2 n and A 1 n : Recent Results and Outlook CENPA, University of Washington 2013 Users’ Group Meeting, Jefferson Lab
Diana Parno
d2n and A1
n: Recent Results and Outlook
CENPA, University of Washington
2013 Users’ Group Meeting, Jefferson Lab
Diana Parno - May 29, 2013 2
• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
Outline
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Deep Inelastic Scattering
• Start with a polarized electron and a polarized nucleon
• They exchange a virtual photon
• Virtual photon-nucleon vertex contains nucleon structure information
• Inclusive measurement: only detect scattered electrons
Incident electron
k
Incident nucleon
k’Scattered electron
q Virtual photon
p
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• Scattering from a point particle is straightforward:
Nucleon Structure Functions
• To describe scattering from a complex structure – like a nucleon – you need structure functions:
k
k’θ
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Polarized Structure Functions
• Now add relative spin orientations to the picture
• F1(x, Q2) and g1(x, Q2) have simple meanings in the quark-parton model:
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• From g1 and g2, we form the quantity d2 for the nucleon:
d2
• Clean probe of twist-3 physics (quark-gluon correlations)
Proton
Neutron
d2
Predictions and Data
Bag Model QCD Sum Rules
Lattice QCD
Chiral Soliton
Data
• 2σ discrepancy between lattice prediction and measurement of neutron d2
We need precise data at large x
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• Picture the polarizations at the hadron vertex:
A1
Same helicities: Opposite helicities:
Photon spin Photon spinNucleon spin Nucleon spin
• Flavor decomposition of spin structure from A1n and A1
p combined
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More Neutron DIS Data Needed
• ... at Q2 ≈ 5 GeV2 and large x.
d2n
Q2 (GeV2)
• ... at large x. pQCD predicts
Leader, Sidorov and Stamenov, PRD 75: 074027 (2007)
Avakian et al, PRL 99: 082001 (2007)
x
A1n
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• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
Outline
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E06-014 in Hall A
BigBite spectrometer
Left high-resolution spectrometer
ComptonPolarimeter
Beam direction• Feb-Mar 2009
• Ee = 4.7 and 5.9 GeV
• Inclusive asymmetries• Inclusive cross
sections
Polarized electron beam
Polarized 3He target
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Polarized 3He Target• 87% of the time, the neutron
carries the 3He nuclear spin• Polarized 3He target ≈
polarized neutron target
Ameya Kolarkar, PhD thesis, 2008
• Hybrid spin-exchange optical pumping
1. Polarize Rb via optical pumping
2. Rb-K interactions polarize K
3. K-3He interactions polarize 3He
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E06-014 Kinematics
DIS region
Resonance region
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• What you will see accounted for:– Beam polarization– Target polarization
– N2 dilution in target cell
– Dilution from e+/e- pairs produced in π0 decay– Basic nuclear corrections (effective polarization model)
Preliminary E06-014 Results
• What you won’t see accounted for:– Radiative corrections (nearly complete)– Asymmetries from e+/e- pairs– Some systematics (cut selection, kinematics)– More sophisticated nuclear corrections
Deconvolution method in progress – Melnitchouk et al.
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x2g1n (d2
n integrand)
• Lacks radiative / pair-production corrections
• Systematic error bars will grow
• Preliminary nuclear-correction method
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x2g2n (d2
n integrand)
• Lacks radiative / pair-production corrections
• Systematic error bars will grow
• Preliminary nuclear-correction method
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A1He-3
• Lacks radiative / pair-production corrections
• Systematic error bars will grow
• No nuclear correction yet
E06014 (Ee = 5.89 GeV)
E06014 (Ee = 4.74 GeV)
E142
E99-117
E01-012 (resonance)
DIS Resonance
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• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
Outline
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• Ee=11 GeV, upgraded 3He target
• SHMS: large x range at nearly constant Q2
• HMS: fill in gaps at low x
E12-06-121: d2n at 12 GeV
Spokespeople:T. AverettW. KorschZ.-E. MezianiB. Sawatzky
Approved with A- rating29 days in Hall C
E06-014 kinematics
HMS
SHMS • Measure d2n at 4
constant Q2 values• Error at each point
will be comparable to E06-014
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• Ee=11 GeV, upgraded 3He target
• Simultaneous HMS, SHMS measurements improve statistics
E12-06-110: A1n at 12 GeV
Spokespeople:G. CatesJ.-P. ChenZ.-E. MezianiX. Zheng
Approved with A rating36 days in Hall C
Explore Q2 dependence
Push to high x
• Precise DIS A1n
measurements from 0.25 ≤ x ≤ 0.77
30°
12.5°
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• Ee=6.6, 8.8 GeV; upgraded 3He target
• BigBite: Primary measurement• Left HRS: Cross-check (lower statistics)
E12-06-122: A1n at 12 GeV
Spokespeople:T. AverettG. CatesN. LiyanageG. RosnerB. WojtsekhowskiX. Zheng
Approved with A- rating23 days in Hall A
• Third set of Q2 values for interpolation
• Test of open-geometry measurement technique
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• DIS measurements of d2n and A1
n at large x will
– test Lattice QCD and pQCD– probe higher-twist effects– explore nucleon spin structure
• E06-014 data will address these questions– Stay tuned for final results
• The 12-GeV program will improve the picture even further– Push to higher x– Explore Q2 evolution
Conclusions
The E06-014 Collaboration (Hall A)K. AlladaW. ArmstrongT. AverettF. BenmokhtarW. BertozziA. CamsonneM. CananG. D. CatesC. ChenJ.-P. ChenS. ChoiE. ChudakovF. CusannoM. M. DaltonW. DeconinckC. W. de JagerX. DengA. DeurC. DuttaL. El FassiD. Flay
G. B. FranklinM. FriendH. GaoF. GaribaldiS. GiladR. GilmanO. GlamazdinS. GolgeJ. GomezL. GuoO. HansenD. W. HiginbothamT. HolmstromJ. HuangC. HydeH. F. IbrahimX. JiangG. JinJ. KatichA. KelleherA. Kolarkar
W. KorschG. KumbartzkiJ. J. LeRoseR. LindgrenN. LiyanageE. LongA. LukhaninV. MamyanD. McNultyZ.-E. MezianiR. MichaelsM. MihovilovičB. MoffitN. MuangmaS. NandaA. NarayanV. NelyubinB. NorumNuruzzamanY. OhD. S. Parno
J. C. PengM. PosikX. QianY. QiangA. RakhmanR. D. RansomeS. RiordanA. SahaB. SawatzkyM. H. ShabestariA. ShahinyanS. ŠircaP. SolvignonR. SubediV. SulkoskyA. TobiasW. TrothD. WangY. WangB. WojtsekhowskiX. Yan
H. YaoY. YeZ. YeL. YuanX. ZhanY. ZhangY.-W. ZhangB. ZhaoX. Zheng
Co-spokesperson PhD (in progress) PhD (complete)
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• The DOE Office of Science
• The Accelerator Division
• The “Big Family” collaboration for setup help
Further Acknowledgments
Thank you!
• The Transversity collaboration for many of the pictures used in this talk
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Backup Slides
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DIS Vocabulary
• Let’s define some useful variables in the lab frame (nucleon rest frame)
kk’
θ
Four-momentum transfer
Electron energy loss (lab frame)
Bjorken x (momentum fraction)
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• Longitudinally polarized beam and target
Polarized Structure Functions
• Longitudinally polarized beam and transversely polarized target
k
k’θ
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Polarized Electron Beam
• The electrons on target are longitudinally polarized…but how well polarized are they?
• Two measurement methods for E06-014:
• Møller scattering (e-e- e-e-) • Destructive measurement
From Hall A Møller Group• Compton scattering (e-γ e-γ)
• Non-destructive measurement• Circularly polarized photons• Longitudinally polarized electrons
Photon energy
Asy
mm
etry
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• 3 multiwire drift chambers– Tracking– Momentum
BigBite
Adapted from Xin Qian, PhD thesis, 2010
Scatteredparticles
• Gas Čerenkov– Exclude pions from
trigger• 2 lead-glass calorimeters
– Energy– Particle identification
• Scintillator plane– Timing
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• Radiative corrections have not been applied
5.9-GeV Cross Sections
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• Radiative corrections have not been applied
4.7-GeV Cross Sections