Transcript Neutron Transversity with BigBite & SBS Andrew Puckett, Jefferson Lab SBS Collaboration Meeting June 4, 2013

Neutron Transversity with BigBite &
SBS
Andrew Puckett, Jefferson Lab
SBS Collaboration Meeting
June 4, 2013
Outline
• Introduction: Semi-inclusive DIS and TMDs
• Transverse nucleon spin structure
– Collins and Sivers effects
• Existing data
– HERMES + COMPASS
– JLab E06-010
• Challenges of polarized SIDIS experiments
• Experiment E12-09-018
– Experiment goals and choice of kinematics
– Apparatus:
• BigBite: electron arm
• SBS: hadron arm
– GEM tracking
– HCAL
– HERMES RICH for PID
– Projected physics results
• Summary and Conclusions
11/6/2015
SBS Summer 2013 Collaboration Meeting
2
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 quarks 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...
11/6/2015
SBS Summer 2013 Collaboration Meeting
3
SIDIS Kinematics: Definitions
Coordinate system for SIDIS
(Trento convention)
11/6/2015
SBS Summer 2013 Collaboration Meeting
• SIDIS studies the
distribution of hadrons in
the “debris” of the struck
quark
• Kinematic regime of
interest for SIDIS:
• “current
fragmentation”—large z
and low-moderate pT
• Large Q2 and W—DIS
regime
• Large W’—avoid
exclusive and resonant
electroproduction
4
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
11/6/2015
SBS Summer 2013 Collaboration Meeting
5
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)
11/6/2015
SBS Summer 2013 Collaboration Meeting
6
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!
11/6/2015
SBS Summer 2013 Collaboration Meeting
7
Sivers effect as a probe of quark OAM
x = 0.2
• Proton spin is
along +y axis (up)
• Proton momentum
into screen
• Regions of
higher/lower quark
density in
transverse
momentum space
A. Prokudin
• Sivers effect: a left-right asymmetry in the transverse
momentum distribution of unpolarized quarks in a
transversely polarized nucleon
11/6/2015
SBS Summer 2013 Collaboration Meeting
8
The Sivers effect, time reversal and gauge invariance
• Sivers, PRD 41, 83 (1990):
– Left-right asymmetry in the kT distribution of unpolarized quarks in a transversely polarized
nucleon could lead to observable single-spin asymmetry (SSA).
• Collins, NPB 396, 161 (1993):
– Left-right asymmetry in the fragmentation of a transversely polarized quark leads to
observable SSA.
– Sivers effect forbidden due to time-reversal invariance of QCD
• Brodsky, Hwang and Schmidt, PLB 530, 99 (2002):
– Sivers effect allowed in the presence of QCD final-state interaction phases
– Corresponds to imaginary part of the interference between quark wavefunction
components differing by one unit of orbital angular momentum, coupling to the same
final state
• Collins, PLB 536, 43 (2002):
– Attractive final-state interaction in SIDIS mirrored by repulsive initial-state interaction in
Drell-Yan reaction ppμ+μ-X
– Application of time-reversal and gauge invariance in QCD leads to a fundamental
prediction (needs experimental verification):
11/6/2015
SBS Summer 2013 Collaboration Meeting
9
The Collins effect and transversity
General properties of transversity:
• h1 = g1 for non-relativistic quarks (boosts and
rotations commute);  h1 ≠ g1 signifies
relativistic effects
• Helicity conservation  gluon transversity =
0. quark transversity is “valence-like”, simpler
Q2 evolution.
• h1 is chiral-odd, inaccessible in DIS.
Accessible in SIDIS when coupled to chiralodd Collins fragmentation function.
• Soffer, PRL 74, 1292 (1995): Positivity,
unitarity & parity conservation  Soffer
bound: |h1| ≤ ½(f1 + g1)
• Doubt has been cast on validity of Soffer
bound: Ralston, arxiv:0810.0871
• Not experimentally verified in the valence
region (x >~ 0.3)
• First x moment of transversity = tensor
charge, calculated on the lattice:
QCDSF/UKQCD collaboration, PLB 627, 113
(2005)
11/6/2015
What is known about transversity?
Anselmino et al., NPB 191, 98
(2009)
• Transversity and Collins functions from
global fit to HERMES+COMPASS SIDIS and
BELLE e+ e- h1h2 X data.
• Notably, Soffer bound, enforced in the fit, is
saturated at high x, particularly for d quark.
SBS Summer 2013 Collaboration Meeting
10
Experimental data on the Sivers function
Anselmino et al., EPJ A 39, 89 (2009)
• Fit to AUTSivers data from SIDIS experiments:
• HERMES proton: PRL 103, 152002 (2009)
• COMPASS deuteron: PLB 673, 127 (2010)
• Clear signal seen in π+/K+ production on the
proton
11/6/2015
SBS Summer 2013 Collaboration Meeting
11
Experimental data on the Collins effect
• SIDIS data:
• HERMES, PLB 693, 11 (2010): e± SIDIS on
transversely polarized protons
• COMPASS, PLB 673, 127 (2009): muon SIDIS on
transversely polarized deuterons
• e+e- annihilation data:
• BELLE, PRD 78, 032011 (2008)
• Directly access the Collins Fragmentation Function
11/6/2015
SBS Summer 2013 Collaboration Meeting
12
JLab E06-010: PRL 107, 072003 (2011)
Helium-3 results:
• Helium-3
asymmetries < 5% in
magnitude
• Collins π+
asymmetry at x = 0.35
is negative by 2.3σ
• π- asymmetries
mostly consistent with
zero
• π+ Sivers moments
favor negative values
Neutron results:
• Obtained from 3He
using effective
polarization
approximation
• Largely consistent
with global fit and
model predictions
• Precision is
statistics-limited
• Still best neutron
data at high x
• Higher precision
needed for progress
11/6/2015
Comparison to world data
SBS Summer 2013 Collaboration Meeting
13
New COMPASS proton data
Sivers asymmetries: Phys. Lett. B 717 (2012)
383
Collins asymmetries: Phys. Lett. B 717
(2012) 376
• Collins results largely consistent with HERMES proton data
• Sivers results qualitatively in agreement with HERMES data, but
smaller in magnitude (for positive hadrons)
• Suggest significant Q2 dependence
11/6/2015
SBS Summer 2013 Collaboration Meeting
14
Challenges of SIDIS spin asymmetry
measurements
•
•
•
•
•
First-generation experiments (HERMES/COMPASS/E06-010) are limited by statistics to onedimensional projections of data.
– physics depends on all four dimensions (x,z,Q2,pT) of the kinematic phase space
– small cross sections
– “small” asymmetries—polarized target dilution, kinematic suppression of Collins
asymmetry, etc...
– luminosity limitations of polarized targets
How to increase statistics and accuracy?
– Acceptance and complete azimuthal coverage
– Luminosity
– Target polarization
– Beam energy
Hadron PID
Quark-parton interpretation requires large Q2, moderate pT: ΛQCD ~< pT << Q2, ~ 0.3-1.0 GeV
High-z: 0.2 < z < 0.7 (low-z cutoff: current fragmentation region, high-z cutoff: stay above
the resonance/exclusive region)
11/6/2015
SBS Summer 2013 Collaboration Meeting
15
What experiment is needed?
 Phase space : full coverage of Sivers and Collins angles
 Neutral and both charged pions
 Kaons
 As large as possible Q2 range: DIS regime, factorization
 Intermediate pT: ΛQCD ~< pT << Q
 Wide range of xBj
Below: Zhongbo Kang seminar,
 Wide range of z = p/n: factorization
LANL, 4/2011
 Large x -> 0.5-0.7 when possible:
Experimental challenges are:
• A high performance polarized target
• The event rates at high Q2 and high xBj
• A high performance PID
11/6/2015
SBS Summer 2013 Collaboration Meeting
16
E12-09-018: SIDIS on polarized 3He @ 12 GeV
E12-09-018, 11 GeV
E12-09-018, 8.8 GeV
E06-010, 5.9 GeV
11/6/2015
Experiment E12-09-018
• Approved by JLab PAC38 (August
2011), 64 days, A- rating
• Spokespersons:
• G. Cates (UVA)
• E. Cisbani (INFN)
• G. Franklin (CMU)
• A. Puckett (LANL—currently
JLab, near future UConn)
• B. Wojtsekhowski (JLab)
• In two-months production run, E1209-018 will reach ~1000X statistical
FOM of E06-010 n, ~100X
HERMES p
• Electron arm: BigBite at 30 deg as
in E06-010 + A1n detector upgrades
• Hadron arm: Super BigBite (SBS)
at 14 deg.
• Target: high-luminosity polarized
Helium-3
SBS Summer 2013 Collaboration Meeting
17
E12-09-018 Collaboration
G. Cates(spokesperson), H.
R. Kaiser, K. Livingston,
Baghdasaryan,
I. MacGregor, B. Seitz
D. Day, P. Dolph,
University of Glasgow, Glasgow,
N. Kalantarians, R. Lindgren, N.
Scotland
Liyanage, V. Nelyubin, Al Tobias
G. Rosner
University of Virginia,
FAIR, Darmstadt, Germany
Charlottesville, VA 22901
W. Boeglin, P. Markowitz, J.
E. Cisbani(spokesperson), A. Del
Reinhold
Dotto, F. Garibaldi, S. Frullani Florida International University, Fl
INFN Rome gruppo collegato
T. Averett
Sanita and Istituto Superiore di
College of William and Mary
Sanita, Rome, Italy
M. Khandaker, V. Punjabi
G.B. Franklin(spokesperson), V.
Norfolk State University
Mamyan, B. Quinn, R. Schumacher
S. Riordan
Carnegie Mellon University,
University of Massachusetts
Pittsburgh, PA 15213
Amherst, Amherst, MA 01003
A. Puckett (spokesperson), X. Jiang
D. Nikolenko, I. Rachek, Yu.
Los Alamos National Laboratory,
Shestakov
Los Alamos, NM 87545
Budker Institute, Novosibirsk,
B. Wojtsekhowski (contact and
Russia
spokesperson), K. Allada, A.
M. Capogni
Camsonne, E. Chudakov,
INFN Rome gruppo collegato
P. Degtyarenko, M. Jones, J.
Sanita and ENEA Casaccia, Rome,
Gomez, O. Hansen, D. W.
Italy
Higinbotham,
F. Meddi, G. Salme, G.M. Urciuoli
J. LeRose, R. Michaels, S. Nanda,
INFN Rome and “La Sapienza"
L.Pentchev
University, Rome, Italy
Thomas Jefferson National
S. Scopetta
Accelerator Facility, Newport News, University of Perugia and INFN
VA 23606
Perugia, Perugia, Italy
J. Annand, D. Hamilton, D. Ireland,
G. De Cataldo, R. De Leo, L.
11/6/2015
Lagamba, S. Marrone, E. Nappi
INFN Bari and University of Bari,
Bari, Italy
R. Perrino
INFN Lecce, Lecce, Italy
V. Bellini, F. Mammoliti, G. Russo,
M.L. Sperduto, C.M. Sutera
INFN Catania and University of
Catania, Catania, Italy
M. Aghasyan, E. De Sanctis, D.
Hasch, V. Lucherini, M. Mirazita,
S.A. Pereira, P. Rossi
INFN, Laboratori Nazionali di
Frascati, Frascati, Italy
A. D'Angelo, C. Schaerf, V. Vegna
INFN Rome2 and University \Tor
Vergata", Rome, Italy
M. Battaglieri, R. De Vita, M.
Osipenko, G. Ricco, M. Ripani, M.
Taiuti
INFN Genova and University of
Genova, Genoa, Italy
P.F. Dalpiaz, G. Ciullo, M.
Contalbrigo, P. Lenisa, L.
Pappalardo
INFN Ferrara and University of
Ferrara, Ferrara, Italy
J. Lichtenstadt, I. Pomerantz, E.
Piasetzky
Tel Aviv University, Israel
G. Ron
SBS Summer 2013 Collaboration Meeting
Hebrew University of Jerusalem,
Jerusalem, Israel
A. Glamazdin
Kharkov Institute of Physics and
Technology, Kharkov 310077,
Ukraine
J. Calarco, K. Slifer
University of New Hampshire,
Durham, NH 03824
W. Bertozzi, S. Gilad, V. Sulkosky
Massachusetts Institute of
Technology, Cambridge, MA 02139
B. Vlahovic
North Carolina Central University,
Durham, NC 03824
A. Sarty
Saint Mary's University, Nova
Scotia, Canada B3H 3C3
K. Aniol and D. J. Magaziotis
Cal State University, Los Angeles,
CA 90032
S. Abrahamyan, S. Mayilyan, A.
Shahinyan, H. Voskanyan
Yerevan Physics Institute, Yerevan,
Armenia
18
Experiment Goals and Choice of Kinematics
• Measure the transverse single-spin asymmetries in SIDIS production of
charged pions/kaons and neutral pions on a neutron (3He) target in a broad
kinematic coverage at large x, Q2 and moderate pT (where the expected
asymmetries are largest)
• Provide timely data on transverse spin phenomena in SIDIS in the first few
years after the 12 GeV upgrade.
• First precision extraction of Collins and Sivers asymmetries in multidimensional kinematic phase space—x, z, pT, Q22nd-generation
experiment
• Excellent control of experimental systematics—advantages of two-arm
setup:
– Independent electron, hadron arms—independent polarity reversal:
• Measure pair production background in DIS electrons w/o changing hadron acceptance
• Hadron arm acceptance is nominally +/- symmetric—periodic polarity reversals can
cancel residual systematic differences.
– Detectors in field-free regions behind large dipole magnets
• Straight-line tracking and simple, reliable data analysis
– Fast target spin rotation period (change every ~120 s): limit uncertainties due to
slow variations in experiment conditions (e.g., luminosity, detection efficiency,
etc.)
11/6/2015
SBS Summer 2013 Collaboration Meeting
19
Super BigBite as Hadron Arm for SIDIS
• SBS main design goal—reach large solid-angle at forward angles
and high luminosity
• BigBite measures DIS electrons in a narrow range of polar angles,
wide range of momentum/azimuthal angle.
• SIDIS hadrons from current fragmentation emerge in a narrow
cone about the direction of q-vector:
– A large fraction of the relevant kinematic phase space for SIDIS can be
covered in a single setting of SBS+BB
– Freedom to orient target polarization in virtually any direction facilitates
full coverage of azimuthal angles.
• Planned SBS hardware for other approved expts. (upgraded 3He
target, magnetic field, tracking, calorimetry) is perfectly adequate
for SIDIS
• Additional hardware needed—Hadron PID!
– Low-cost solution: re-use RICH detector from HERMES experiment
11/6/2015
SBS Summer 2013 Collaboration Meeting
20
Charged Hadron PID in SBS
5.5 GeV K+
REAL DATA from NIMA 479 (2002) 511
1.5 GeV p-
• HERMES RICH geometry,
performance characteristics
well matched to SBS needs.
• π/K/p separation for p from
2-15 GeV based on dualradiator design.
• Re-use one half of detector,
both aerogels
• Currently in storage at UVA
14.6 GeV e-
Pion ID results
from HERMES
11/6/2015
SBS Summer 2013 Collaboration Meeting
21
RICH Backgrounds in SBS
PMT windows
HCAL
GEM material
Target
SBS magnet,
2.0 Tm
Lead Shielding
Aerogel + Al and
Lucite Windows
GEANT3 layout for RICH
background simulation
11/6/2015
GEANT background simulations predict
0.1% average occupancy in E12-09-018
• Detectors in direct view of target
• Large soft photon flux produces charged secondaries in
aerogel from Compton scattering and pair-production
• Aerogel Cherenkov threshold relatively low for
electrons: Tmin = 1.5 MeV
• Also direct interaction with PMT windows
• High segmentation (~2000 PMTs) and TDC readout
(10 ns window offline) lead to very low occupancy: 10-3,
no problems for PID performance
SBS Summer 2013 Collaboration Meeting
22
Neutral Pion Detection
• In the planned configuration, HCAL has good
capability for detection and reconstruction of
π0s
• Mass resolution ~24 MeV
• Acceptance/efficiency: average of ~53% of
charged pion acceptance, max at z ~ 0.6
• High-z limited by HCAL pixel size—could
increase target-HCAL distance at expense of
Kaon detection efficiency
11/6/2015
SBS Summer 2013 Collaboration Meeting
23
Experiment Simulation and Projected Results
• Physics event generator based on naive leading-order, leading-twist parton
model for rate estimation and asymmetry extraction:
– CTEQ6 PDFs
– DSS2007 FFs
– Anselmino et al. Collins and Sivers effects
• Experiment apparatus:
– BigBite model: realistic acceptance/resolution calculations calibrated to E06-010
data
– SBS model: GEANT acceptance calculations, parametrized detector resolution
– Target: 60 cm 3He at L = 4 × 1036 cm-2 s-1 electron-neutron
– 8 spin directions: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°, always
perpendicular to beam direction
• Output: large-statistics pseudo-data set
– Optimize phase space coverage
– Analysis to the level of final physics output, statistical and systematic
uncertainties related to acceptance/resolution/bin centering/reconstruction
accuracy
11/6/2015
SBS Summer 2013 Collaboration Meeting
24
Kinematic Coverage: Q2, z, pT vs. x and pT vs. z
• Reach high x, Q2 via large angles, high luminosity
• Probe two different Q2 ranges at each x using 8.8 GeV data of similar precision
• Large, independent range of x, z, pT—minimal correlations of acceptance in different dimensions (except x,
Q2 which are strongly correlated).
11/6/2015
SBS Summer 2013 Collaboration Meeting
25
Azimuthal Angle Coverage
• Complete, uniform coverage of the Collins and Sivers angles
• ~50% hadron angle coverage—sufficient for systematics control
• Polar pT, ϕ plots, left to right = hadron angle, target angle, Collins angle, Sivers angle
• 8 target spin orientations: ±horizontal ±vertical, ±45°, ±135°.
11/6/2015
SBS Summer 2013 Collaboration Meeting
26
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
• C12-09-018 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.
11/6/2015
SBS Summer 2013 Collaboration Meeting
27
First Precision Multi-Dimensional Analysis
Uncertainty in this
x, z bin ~ 0.6%
Large neutron π+ asymmetry
prediction 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
11/6/2015
SBS Summer 2013 Collaboration Meeting
28
Fully Differential Binning
 Increasing pT
Increasing z 
• 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 fullydifferential 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%
Sivers AUT, n(e,e’π+)X vs. x, 40 days @ 11 GeV
11/6/2015
SBS Summer 2013 Collaboration Meeting
29
Shrinking the Error Corridor
>5X reduction in neutron AUTSivers
uncertainty corridor (Prokudin
model fit)
AUTCollins ~10σ precision for π±
• E12-09-018 will provide neutron TSSA/TDSA data of ~10X greater precision than the best
current proton (HERMES) data, for π±/K±/π0.
• First precision measurements in multi-dimensional kinematic coverage.
• Extension of Collins/Sivers measurements into the valence region, where no data currently exist
• Will run soon after the 12 GeV upgrade.
11/6/2015
SBS Summer 2013 Collaboration Meeting
30
Shrinking the Error Corridor
>5X reduction in neutron AUTSivers
uncertainty corridor (Prokudin
model fit)
AUTCollins ~10σ precision for π±
• E12-09-018 will provide neutron TSSA/TDSA data of ~10X greater precision than the best
current proton (HERMES) data, for π±/K±/π0.
• First precision measurements in multi-dimensional kinematic coverage.
• Extension of Collins/Sivers measurements into the valence region, where no data currently exist
• Will run soon after the 12 GeV upgrade.
11/6/2015
SBS Summer 2013 Collaboration Meeting
31
To Do—Future Plans
• Begin work on RICH refurbishment project ASAP
– Define scope of project and determine cost
– Pursue funding/identify manpower
– New simulationsoptimize experiment design—quantify benefit to
physics impact vs. increased cost of using both aerogels side-by-side.
– Goal—RICH ready for in-beam testing in time for first SBS expts./e.g.
GMn
• Imagined schedule:
–
–
–
–
2014: First beam to Hall A
2015: A1n
2016: GEn-II and GMn
2017: GEp-V and SIDIS
• SBS with RICH detector would enable many other physics
opportunities, including but not limited to:
– Polarized/unpolarized SIDIS on p, d, (3H?) targets
– Dihadron SIDIS
– Vector meson production
11/6/2015
SBS Summer 2013 Collaboration Meeting
32
Conclusions
SIDIS: E12-09-018
• Transverse spin phenomena in SIDISwealth of
new fundamental information on nucleon structure
• Relevant to the nucleon spin puzzle
• Test fundamental predictions of QCD
• Theoretical groundwork ~1990s (still rapidly
evolving/maturing) experimental study has just begun
~2000s
• JLab 12 GeV upgrade is the first opportunity for
next-generation (precision) studies in the “valence”
quark region ( = high-x = fast quarks)
• Exclusive and semi-inclusive reactions form the core of the JLab 12 GeV “nucleon imaging”
program.
• Super BigBite Spectrometer = progress toward the “holy grail” of fixed-target electron
scattering experiments:
• Large acceptance
• High luminosity
• Forward angles
• JLab 12 GeV promises new discoveries and insights into QCD by comprehensive mapping of
nucleon structure with unprecedented precision!
11/6/2015
SBS Summer 2013 Collaboration Meeting
33
BACKUP SLIDES
11/6/2015
SBS Summer 2013 Collaboration Meeting
34
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
11/6/2015
SBS Summer 2013 Collaboration Meeting
35
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
11/6/2015
SBS Summer 2013 Collaboration Meeting
36
SIDIS Structure Functions in Terms of TMDs
• Only f1, g1, h1 survive 2D
integration over quark kT
• h1 is chiral-odd (related to a quark
helicity-flip amplitude), and
inaccessible in inclusive DIS
• All eight leading-twist TMDs are
accessible in SIDIS with polarized
beams/targets via characteristic
azimuthal modulations of the SIDIS
cross section
• In this talk we will focus on
transverse single-spin asymmetries
(SSAs); i.e., Collins/Sivers effects!
11/6/2015
SBS Summer 2013 Collaboration Meeting
37
Gas Electron Multipliers (GEMs) for High-Rate,
High Resolution Tracking
Recent technology: F. Sauli, NIM A 386, 531 (1997)
Stable gain up to very high rates
• High spatial granularity
• Ability to cascade several foils: higher gain at lower
voltage, reduced discharge risk
• Readout and amplification stages decoupled
• Excellent spatial resolution ~70 μm
• Fast signals: time resolution <10 ns
11/6/2015
SBS Summer 2013 Collaboration Meeting
38
High Luminosity Polarized 3He Target
• New design with convection-driven flow
• Fast replacement of polarized gas
• Tolerate higher beam currents—support up to
60 μA, 60 cm long cell
• 4 × 1036 cm-2 s-1 en luminosity @40 μA,
65% polarization
• Decouple location of target chamber and
pumping chamber; decouple magnetic field
directions.
• Fast spin reorientation with adiabatic
rotation—eliminate gradients, and enable 120 s
spin-flip period (similar to HERMES) to
control systematics with minimal polarization
loss
• Concept already demonstrated in bench tests
Details almost out of date—See G.
Cates talk later this mtg.
Bench test of convection-driven flow
Schematic of target chamber in vacuum and
double optical pumping chamber
11/6/2015
SBS Summer 2013 Collaboration Meeting
39