1. Transverse Momentum-Dependent Structure of Neutron
Yi Qiang
Duke University
Nov 25, 2009
Good day, everyone…
My name is Yi Qiang. I’m from Duke University …
Today, I will talk about the Transverse momentum-dependent structure of the nucleon.
11/25/2009
Transverse Momentum-dependent Structure of Neutron

2. Transverse Momentum-dependent Structure of Neutron
Outline
Introduction to TMDs
Recent Physics Results
Jefferson Lab Experiment E06-010
First 3He SIDIS
Experimental configuration
Polarized 3He target
Detector Performance
Analysis Status
Future Transversity with 12 GeV in Jefferson Lab
In this talk, I will first go through the background of the nucleon transverse momentum distributions.
Next, I will talk about discoveries from recent experiments.
Then I will focus on a experiment we just finished early this year in Thomas Jefferson Lab Hall A. In this session I will show you the details of the experiment including it’s setup, it’s polarized 3He target, the detectors and the analysis status.
At the end, I will talk about the great opportunity to further explore our knowledge of TMDs with future JLab 12 GeV upgrade.
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Transverse Momentum-dependent Structure of Neutron

3. Nucleon Structure through DIS
Phys. Lett. B652, 292 (2007)
Nucleon Structure through DIS
Nucleon is composite system with many degrees of freedom.
DIS: an important tool to understand nucleon structure.
Bjorken scaling in unpolarized DIS revealed the point-like structure inside nucleons.
f1(x,Q2), the unpolarized parton distribution function (PDF), describes the parton momentum distributions of the nucleon: k k’ p X q
Q2 = - q2: inverse of the momentum transfer square
x = Q2/2Mn : fraction of momentum carried by the struck quark
As we now know, nucleon is a composite systems with many internal degrees of freedom and have quarks and gluons as the constituents.
Deep inelastic lepton-hadron scattering (DIS) has played a seminal role in the development of our present understanding of the sub-structure of nucleons.
While scattered from the target nucleus, the electron can probe the structure of the nucleon by exchanging a virtual photon.
There are two quantities that we need to keep in mind and they are Q2 and x.
As we learn from the uncertainty principle, the greater the momentum transfer, more details in space will be probed. As we increase the Q2, at some point, what we are looking at in the inelastic scatterings is no more the properties of the whole nucleons but the substructure inside them. And usually, people define the inelastic scattering with Q2>2 GeV is region of DIS.
The discovery of Bjorken scaling in the late nineteen-sixties provided the critical impetus for the idea that nucleons contain point-like constituents and for the subsequent invention of the Parton Model.
Then, DIS continued to help us to further explore the nucleon sub-structure, such as the discovery of the gluons and the establishment of QCD.
What unpolarized DIS measures is the unpolarized structure function f1 which describe the momentum distributions of quarks inside the nucleon.
After 4 decades, people have measured f1 with excellent precision over a large range of kinematics.
The plot shows our current knowledge of the unpolarized momentum distributions: the valence quarks dominate the region with large x, on the other hand the sea quarks and gluons show up as x getting closer to 0.
f1 =
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Transverse Momentum-dependent Structure of Neutron

4. Nucleon Spin Structure
Polarized DIS measures g1,2(x,Q2) and probe directly the nucleon spin structure
Where does the nucleon spin come from?
Quark Polarization DS: ~ 30% (spin crisis!)
Gluon Polarization DG: not large
Orbital angular momentum: ?
g1 =
Nucleon Spin
Quark Spin
In the process of the DIS, the electron preserves its helicity in the high energy limit. Therefore polarized electron beam brings the polarized virtual photon. With the angular momentum conservation, quarks with spin opposite to the virtual photon spin will interact with the virtual photon. So the double polarized DIS directly probes the nucleon spin structure.
g1, and g2 are two structure function we measured. While g2 has no simple interpretation, g1 has a very straightforward meaning: The longitudinal polarization of quarks inside a longitudinally polarized nucleon. Some time we call it helicity for short.
After EMC experiment was carried out in 1980s, people found out that the total spin contributed by quarks is only a small part of the proton spin. That is what we called “proton spin crisis”
Since then, the g1 function has been determined over certain kinematic range. And current data showed that only 30% of the proton spin comes from quarks.
and people start to wonder where else the spin can come from. They can be either from the gluon and the orbital angular motion!
The plot here shows the latest flavor decomposition of the proton quark spin. We can clearly see that the u quark tends to be parallel to the proton spin while the d quark is anti-parallel.
And how about gluon, recent measurements from HERMES, COMPASS and RHIC shows that Delta G seems small and unlikely to solve the puzzle.
With the two aspects mentioned above, we are expecting non-zero orbital angular momentum inside the nucleon.
note: Another characteristic of the gluon box diagram is that it tends to be dominated by quark-anti-quark pairs with transverse momentum equal to or larger than Q. Thus, one can search directly for the existence of polarized gluons by making semi inclusive measurements that explicitly look for high-pT hadrons in a deep-inelastic event.
At RHIC both PHENIX 25,26 and STAR 27,28 have measured asymmetries in polarized proton-proton collisions, either looking for asymmetries (i.e. differences in the cross sections for helicities anti-parallel and parallel) in either jet or π0
production. The preliminary analysis of the latest PHENIX data prefers a value of G between -0.5 and zero. For STAR the preliminary analysis of Run 6 yielded a limit for |G| below 0.3 (at 90% confidence level) and again consistent with zero.
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Transverse Momentum-dependent Structure of Neutron

5. Transverse Spin Structure
Transversity:
Quark transverse polarization in a transversely polarized nucleon:
Probes the relativistic nature of the nucleon by comparing h1(x,Q2) to g1(x,Q2).
Can be probed in Semi-Inclusive DIS, Drell-Yan processes and perhaps others.
Does no mix with gluons, has valence like behavior.
Nucleon tensor charge can be extracted from the lowest moment of h1 and compared to LQCD calculation:
Nucleon Spin
h1T =
Quark Spin
If we look at a nucleon from a more realistic 3D point of view, transversity is the least known distribution function compared to f1 and g1, .
Transversity describes the quark transverse polarization in a transversely polarized nucleon
In the non-relativistic condition, the transversity should be equal to helicity. However, because the Lorentz boost does not commute with rotation, and bound quarks are highly relativistic, transversity is not equal to helicity and their difference reveal the relativistic nature of the quarks inside the nucleon.
Then how to measure this interesting quantity? Transversity is Chirally-odd, which means it can not be measured directly through inclusive DIS. One way we can do is to probe transversity through semi-inclusive DIS processes in which transversity is convoluted with a Chirally-odd fragmentation function so called Collins function. Drell-Yan process is another method since it involves two transversity distributions.
Tansversity has two interseting properties.
Transversity has no gluon component which makes it to have valence like behavior and has different Q2 evolution than g1.
The lowest moment of h1 measures “tensor charge”, which is a fundamental property of the nucleon and has been calculated by LQCD and various models. Due to the valence like nature of transversity, it’s crucial to measure transversity in x region.
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Transverse Momentum-dependent Structure of Neutron

6. Longitudinally Polarized Transversely Polarized
Leading Twist TMDs
Nucleon Spin
Quark Spin
Quark polarization
Un-Polarized
Longitudinally Polarized
Transversely Polarized
Nucleon Polarization U L T
h1 =
f1 =
Boer-Mulder
g1 =
h1L =
Helicity
Beside the three parton distribution functions which survive the integration over the quark transverse momentum there are five more transverse momentum dependent distribution functions at leading twist.
Here is a table of all the 8 leading twist TMDs, the cartoons on the right hand side of each name tell you the meaning of each TMDs. Again, the virtual photon is supposed to go out of the paper and that’s our longitudinal direction. The red circle and arrow are the quark and it’s spin, and black circle and arrow are the nucleon and it’s spin. The blue arrow shows the momentum direction of the quark.
An important information these 5 new TMDs will tell you is the quark oribtal angular motion. They will vanish without orbital angular momentum.
In particular, the Sivers function directly tells you the quark orbital angular momentum in a transverse polarized target, Boer-Mulder tells you the correlation of the quark orbital momentum and it’s spin inside a unpolarized nucleon and Pretzelosity, in certain model context, direct measures the relativistic nature of the nucleon.
Blue: no kt dependence and T-even
Red: T-odd with kt dependence
Other: kt dependence and T-even
h1T =
f 1T =
Transversity
g1T  =
h1T =
Sivers
Pretzelosity
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7. Fermi Lab E704: p↑p→pX at 400 GeV
Huge single-spin asymmetry!
Opposite sign for and
Naïve T-odd: , can not be explained by QCD without orbital angular motion.
Either in fragmentation or parton distribution.
Confirmed by RHIC at much higher energies.
There is a very famous experiment whose result strongly encouged the study of the TMDs. And it is Fermi lab E704 in 1991.
The experiment used a 400 GeV transversely poalrized proton to hit a fixed proton target. And people saw a huge left and right asymmtry in the pion production.
And the asymmetry has oppsitve sigh for pi+ and p-.
The SSA observables J. (p1xp2) is odd under naive time-reversal and such large asymmetry can not be explained with leading order QCD amplitude without considering the orbital angular motion.
Since the process is a convolution of distribution function and fragmentation function, there must be spin-orbital structure in the fragmentation process or with the proton itself.
note: Since QCD amplitudes are T-even, the SSA must arise from interference between spin-flip and non-flip amplitudes with different phases. And suppressed in pQCD hard-scattering (perturbative subprocess cross sections):
a. q helicity flip suppressed by mq/sqrt(s)
b. need alpha_s-suppressed loop-diagram to generate necessary phase
So, at hard (enough) scales, SSA’s must arise from soft physics: T-odd distribution or fragmentation functions
must be a spin-orbit structure either in the fragmentation process or within the proton itself.
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8. Collins Effect (fragmentation H1 (z,pt))
Spin-orbit in fragmentation (naïve T-odd): H1 (z,pt)
Needs “transversity” distribution function: h1T(x) d -
pair
L = 1, S = 1 -> JP = 0+ p+ d - u
L=1 u d p u
One of the well recognized explanation is the naïve T-odd Collins fragmentation function.
It describes the correlation of the spin of the fragmenting quarks and the orbital angular momentum of the final hadrons.
The Collins fragmentation function when convoluted with transversity distribution function will raise a left and right asymmetry and here is how things work.
Here is transversely polarized proton, let say this u quark is parallel to the proton spin pointing up, when in the fragmentation process, it needs a d bar quark with spin opposite to it. In the vacuum, we have these qq_bar pairs with total spin_parity to be 0+. If it’s an S state then we will see no asymmetry, however, if the qq_bar is in P state with L=1 and S =1, the u quark will select the quark pair orientated in the following way, both the quark spin pointing down and the orbital momentum pointing up. In this case, after the u and d_bar quark will tend to go into the page due to the positive orbital angular momentum. And we call this favored transition.
The pi- production is alike the pi+ production and heads out of the page.
Please bare in mind that the name “fav” and “disfav” is just because that the proton has more u quarks then d quark. The experimental data showed shat they are equally important, actually they are about same amplitude with opposite sign.
note: Lund String Model + 3P0 hypothesis
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9. Sivers Effect (distribution f1T (x,kT))
Quark orbital motion in distribution (T-odd): f1T (x,kT)
Need ordinary fragmentation function: D1(z)
Correlation between pT and proton spin + FSI: Chromodynamic Lensing
FSI kick p+ d - u d u p d -
The next mechanism is the Sivers effect, which represents the quark orbital motion in the proton parton distribution. The Sivers function together with ordinary fragmentation function will create a left/right asymmetry.
Let assume that the active u quark is orbiting around the proton spin. Because the proton is moving to the right at the same time, the u quark will have a better chance to stay in front of the page. Then the u quark hadronizes with a d_bar quark. Due to the attractive final state interaction between the pion and the remaining spectators, outgoing pi+ will head into the page.
note: Phenomenological model of Meng, Boros, Liang
Correlation between the quark transverse momentum and transverse spin of the proton + FSI
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Transverse Momentum-dependent Structure of Neutron

10. SIDIS electroproduction of pions
Separate Sivers and Collins effects
Sivers angle, effect in distribution function:
(fh-fs) = angle of hadron relative to initial quark spin
Collins angle, effect in fragmentation function:
(fh+fs) = p+(fh-fs’) = angle of hadron relative to final quark spin
e-e’ plane q
target angle
hadron angle
Scattering Plane
No like the pp scattering, you have both Sivers and Collins effects mixed, we can clearly identify the Sivers and Collins effects in the SIDIS pion production based on their different azimuthal distributions.
Here is a figure for the SIDIS kinematics. We defined two important azimuthal angles about the Q-vector here, one is the target angle fs, which is the angle of the target spin to the scattering plane and another one is fs, which is the angle of produced hadron to the scattering plane. Here is the projection of the angles if we look into the virtual photon.
For the Sivers function, because it is an effect in the distribution function, it has a dependence on the angle between the produced hadron and the initial quark spin. And this angle is fh – fs.
For the Collins function, since it’s an effect in the fragmentation process, it will a dependence on the angle between the hadron and the final quark spin. So we got the Collins angle as fh + fs.
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Transverse Momentum-dependent Structure of Neutron

11. Access Leading Twist Parton Distributions through Semi-Inclusive DIS
SL, ST: Target Polarization; le: Beam Polarization
f1 =
f 1T =
g1 =
g1T  =
h1 =
h1L =
h1T =
h1T =
Unpolarized
Polarized
Target
Beam and
Boer-Mulder
Sivers
Transversity
Pretzelosity
Not just transversity and Sivers diftributions, we can actually access all the eight leading twist TMDs in semi-inclusive DIS by using different combinations of beam and target polarizations.
During the experiment we will cover in the later half of this talk, we used a transversely polarized 3He target and polarized electron beam. By forming single target spin asymmetry, we can measure Transversity, Sivers and Pretzelosity distribution functions through single target spin asymmetry.
The Pretzelosity shows the correletion of the quark transverse spin and it’s momentum inside a transversely polarized nucleon. And in certain model context, it directly measures the relativistic nature of the nucleon.
g1T tells us the chance that we find a longitudinally polarized quark inisde a transversely polarized nucleon due to the quark orbital angular momentum.
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Transverse Momentum-dependent Structure of Neutron

12. HERMES Hydrogen Results (2002-2005)
Sivers Moment
Collins Moment
Here I will show you some result before the Jlab 3He transversity.
HERMES took the hydrogen SIDIS data between 2002 – (with 27.6 GeV electron beam.)
In the Sivers moment, both the pi+ and K+ showed clear positive amplitudes which imply a non-vanishing orbital angular momentum of the quarks. And the facts that K+ asymmetry is larger than pi+ tells us that the see quark contribution to the Sivers mechanism appears to be important and the orbital angular momentum could be highly flavor dependent. For the negative particles, the Sivers moments are consistent with zero.
The Collins moment is positive for pi+ and negative for pi-. Also, the magnitude of two asymmetries are comparable which implies that the u and d quark transition of Collins effect are equally important. For charged kaons, there are no statistically significant non-zero Collins amplitudes.
X z Pt[GeV]
arXiv:
arXiv:
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Transverse Momentum-dependent Structure of Neutron

13. COMPASS Deuteron Results (2002-2004)
Sivers Moment
Collins Moment p+ p- K+ K- K0 p+ p- K+ K- K0
fC=(fh+fs)-p
At the about the same time , COMPASS took the data on the deuteron target. (with 160 GeV muon beam. )
As we can see from the plot, all the measured asymmetries are small, mostly compatible with zero within the measurement errors.
By taking into account the HERMES proton data, the most likely interpretation at this moment is that for the iso-scalar deuteron target there is a cancellation between the proton and the neutron asymmetries.
Phys. Lett. B 673 (2009) ?
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14. COMPASS Hydrogen Results (2007)
Sivers Moment
Collins Moment
fC=(fh+fs)-p
COMPASS took the hydrogen SIDIS data between 2007 with 160 GeV muon beam.
arXiv:
In the Sivers case the measured asymmetries are compatible with zero for both positive and negative hadrons, at variance with the HERMES result.
Collins asymmetries agree with the global fit with previous HERMES hydrogen, COMPASS deuteron and BELLE e+e- data.
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15. Summary of current datap d p
Transversity h1T :
h+: positive on proton
h-: negative on proton
Zero on deuteron
Sivers Distribution f 1T :
h+: positive? on proton
Zero on negative and deuteron
3He Data is crucial:
Independent neutron data from proton
More constraints on the flavor decomposition
Shed some light on the hypothesis Q2 dependence of Sivers u d
Here is a short summary of our current knowledge about the Transversity and Sivers distributions.
Why neutron data is important!
Quark-diquark model: Cloet, Bentz and Thomas PLB 659, 214 (2008), Q2 = 0.4 GeV2
CQSM: M. Wakamatsu, PLB B 653 (2007) 398. Q2 = 0.3 GeV2
Lattice QCD: M. Gockeler et al., Phys.Lett.B627: ,2005 , Q2 = GeV2
QCD sum rules: Han-xin He, Xiang-Dong Ji, PRD 52: ,1995, Q2 " 1 GeV2
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Transverse Momentum-dependent Structure of Neutron

16. Transverse Momentum-dependent Structure of Neutron
E Collaboration
E06-010: Single Target-Spin Asymmetry in Semi-Inclusive
n↑(e, e’p±) Reaction on a Transversely Polarized 3He Target.
First measurement on 3He(n) Transversity ever!
Spokespersons:
Xiaodong Jiang (Rutgers/Los Alamos, Contact Person), Jian-ping Chen (JLab), Evaristo Cisbani (INFN-Rome), Haiyan Gao (Duke), Jen-Chieh Peng (UIUC)
7 Thesis Students:
C. Dutta (Kentucky), J. Huang (MIT), A. Kalyan (Kentucky), J. Katich (W&M), X. Qian (Duke), Y. Wang (UIUC), Y. Zhang (Lanzhou U)
Just finished in early February, 2009, after 3 months of successful data taking.
This experiment is supported by a world-wide collaboration and we have 7 PhD thesis student in total. In early February this year, we successfully finished the three months of data taking.
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Transverse Momentum-dependent Structure of Neutron

17. Transverse Momentum-dependent Structure of Neutron
E Setup
Electron beam: E = 5.9 GeV
40 cm polarized 3He target
BigBite at 30 degrees as electron arm:
Pe = 0.7 ~ 2.2 GeV/c
HRSL at 16 degrees as hadron arm:
Ph = 2.35 GeV/c
Measure Collins, Sivers and pretzelosity asymmetries in valence range:
xb = 0.1 ~ 0.4 p
HRSL
16o e g* e’
BigBite
30o
The experimental is configured as following. We have 5.9 GeV polarized electron beam incident on a 40 cm polarized 3He target.
The scattered electrons were detected by the BigBite spectrometer positioned 30 degrees to the beam right. And the momentum range is …
The produced hadrons were detected coincidently using the left high resolution spectrometer 16 degrees to the beam left. And the momentum setting is 2.35 GeV/c.
This setup allowed us to measure the … asymmetries in the valence range which is x from 0.1 to 0.4
Because of the
Polarized
3He Target
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Transverse Momentum-dependent Structure of Neutron

18. Transverse Momentum-dependent Structure of Neutron
Separation of Collins, Sivers and Pretzelosity effects through angular dependence
Rotate target spin direction to increase fs coverage
Vertical
Horizontal
Transversity
The separation of the three single spin azimuthal asymmetries will be done based on their different angular dependences.
The transversity distribution is modulated by the sum of fs and fh, sivers distributions by the difference of fs and fh and the pretzelosity has the dependence on 3fh – fs.
Due to the small acceptance of the left HRS, in order to increase the angular coverage, we polarized the 3He spin in four directions around the beam and they are marked by the arrows: vertical up and down, horizontal left and right.
Sivers
Pretzelosity
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19. Transverse Momentum-dependent Structure of Neutron
Why 3He target?
aaa
Greater figure of merit than polarized Deuteron target
Nuclear Polarization: 40~60% vs 30~50%
Neutron Polarization: 90% vs 90%
Less uncertainty due to proton asymmetry
Polarized through spin exchange optical pumping(SEOP)
Compact size: No cryogenic support needed
Take higher beam current
~90% ~1.5% ~8%
Best effective polarized neutron target:
Due to the Pauli principle, the two proton will most likely form a pair with total spin equal to 0, and
The unpaired electrons are polarized to nearly 100% in the field, and this polarization is transferred to the hydrogen nuclei via the process of Dynamic Nuclear Polarization (DNP), by employing microwave radiation of the proper frequency to induce coupled electron nucleon spin transitions.
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20. Polarized 3He Target in Jefferson Lab Hall A
High luminosity: L(n) = 1036 cm-2 s-1
Fast spin exchange with K/Rb hybrid cells
Polarized Laser
795 nm
Oven
230 oC
F = 3”
Pumping Chamber
1o atm 3He
Some N2, Rb, K
The 3He target is widely used as an effective polarized neutron target. Because the two protons in the 3He nucleus will most likely form a pair, about 90% of the 3He spin is carried by the single neutron.
The 3He target we used is high pressure cell and was polarized through spin-exchange optical pumping. It has 10 atm 3He inside which allows the luminosity to be as high as 10 to the 36 level with 15 uA beam. We also put K and Rb alkali metal into the cell as the spin transfer medium.
Here is the picture of a 3He cell. It has two parts. The lower part is the 40 cm long target chamber and the electron passes through it. Top part is the 3 inch spherical pumping chamber where the optical pumping happens.
We put the pumping chamber into a oven and heat it up to 230 degrees so that we have some amount of alkali vapor in it.
The whole target was put in a uniform 25 G magnetic field, and a circular polarized high power laser was shot to the pumping chamber.
The wave length of the laser is chosen to be the D1 transition of the Rb atom, so with the existence of the external magnetic field, the Rb atom will be polarized by the laser. Then the spin of the Rb atoms will first be transferred to K and then to the 3He nuclei. Actually, the spin of the Rb atom can be directly transferred to 3He, but with K as a media, the spin exchange efficiency got greatly improved!
25 G Holding Field
40 cm Target Chamber
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21. Target Setup for Transversity
New COMET lasers
Narrow line with laser make more efficiency optical pumping.
3D Holding Field Control
New vertical coil together with existing horizontal coils create holding field in any direction and cancel out any residue field.
New Oven and Optics
Better insulation, lighter weight and all three pumping directions.
Transverse/Vertical for E
A Smart Target
Auto spin flip every 20 minutes using Adiabatic Fast Passage (AFP). Log and alarm.
For the Transversity experiment, the Hall A 3He target got upgraded mainly in the following ways
vertical coil and oven
comet lasers
spin direction
auto flip by 180 degree every 20 minutes though adiabatic fast passage to reduce the systematic error.
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22. 3He Target Polarimetries
NMR: Nuclear Magnetic Resonance
Measures the RF signal strength radiated by 3He nuclei while being flipped.
Relative measurement.
Free NMR at pumping chamber from every auto spin flip.
Calibrated by Water NMR measurement.
EPR: Electron Paramagnetic Resonance
Measures the frequency shift of Zeeman splitting of alkali atoms with 3He spin parallel and anti-parallel to the holding field.
Absolute measurement.
Got signal from both K and Rb.
Measures pumping chamber polarization.
Both worked very well!
Water NMR
EPR
We used two polarimetries to cross calibrate the target polarization
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Transverse Momentum-dependent Structure of Neutron

23. Transverse Momentum-dependent Structure of Neutron
Target Performance
Polarized 3He ran reliably smoothly through the experiments, and the following three.
Reached a steady 65% polarization with 15 mA beam and 20 minute spin flip! A NEW RECORD!
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Transverse Momentum-dependent Structure of Neutron

24. Transverse Momentum-dependent Structure of Neutron
BigBite Spectrometer
Single Dipole Magnet
Detects electrons
A big bite of acceptance
DW = 64 msr
P : 0.7 ~ 2.2 GeV/c
3 Wire Chambers: 18 planes for precise tracking and momentum reconstruction
Pre-Shower and Shower for electron PID
Scintillator for coincidence with Left HRS
Pre-Shower
Shower
Scintillators
3 Multi-wire
Drift Chambers
(18 planes)
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25. Transverse Momentum-dependent Structure of Neutron
BigBite Optics
BigBite Sieve Slit
Crucial for kinematics calculation and vertex coincidence.
Optics for both negative and positive charged particles have been done
Angular Resolution: < 10 mrad
Momentum Resolution: 1%
Vertex Resolution: 1 cm
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26. Pre-Shower/Shower in BigBite
Select electron from pion background
Provides good trigger for the electrons
Requires higher pre-shower output
Calibrated using H(e,e’)p elastic data:
resolution about 8%
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27. High Resolution Spectrometer
Left HRS to detect hadrons of ph = 2.35 GeV/c
QQDQ magnet configuration
Very high momentum resolution
Vertical Drift Chambers
Tracking and momentum
Scintillator trigger planes
Aerogel Cherenkov counter
n = 1.015
RICH detector
n = 1.30
Gas Cherenkov
Lead-glass blocks
Detector Hut D1 Q1 Q2 Q3
Detector
Package
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28. Hadron PID and Coincidence
Vertex Difference (m)
s=1.1cm
Clean e rejection with Gas Cherenkov and Lead-glass blocks
Vertex coincidence with BigBite
Reduce background by a factor of 6
Coincidence time/TOF by assuming particle mass
Reduce accidental background
PID: K/p 4 s separation
Kaon data can be further cleaned up by additional detectors:
A1: Pion rejection > 90 %
RICH: K/p separation ~ 4 s
Pion rejection ~ 99.9%
proton p+ K+
s=340ps
CT (ns)
Cherenkov Angle Ring Image
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Transverse Momentum-dependent Structure of Neutron

29. Transverse Momentum-dependent Structure of Neutron
Kinematics Coverage
Pretzelosity Angle: 3fh-fs
Sivers Angle: fh-fs
Collins Angle: fh+fs y
0.6 ~ 0.9
x<0.25
0.6 ~ 3 (GeV/c)2 Q2 Mm
Y: forwardness
Q2: momentum transfer
W’: missing mass, above main resonance region
Z: fraction of the energy transfer carried by the produced hadron, selecting leading hadron in the fragmentation
Pt: transverse momentum up to ~ 0.5 GeV
Have pretty much
1.5 ~ 2.3 (GeV/c2)
x>0.25
0.4 ~ 0.6 z
0.25
0.5 x
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30. Projections of Collins Asymmetries
Errors on neutron Collins moment is from 3% to 5%
Based on the QCD factorization approach, Vogelsong and Yuan considered Sivers and Collins contributions to the asymmetries. They fit simple parametrizations for the Sivers and Collins functions to the HERMES data, and compare to results with COMPASS. Using the fitted parametrizations for the Sivers functions
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Transverse Momentum-dependent Structure of Neutron

31. Projections of Sivers Asymmetries
Errors on Sivers are slightly worse due to more limited angular coverage
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32. Transverse Momentum-dependent Structure of Neutron
Projections of g1T xB
COMPASS
arXiv:
80% beam polarization.
Double spin asymmetry with fast beam helicity flip: 30Hz.
Existing result from COMPASS on Deuteron target.
Projected
Uncertainties
(Stat. Only):
2.3% at low x
3.4% at high x
Preliminary
The statics uncertainty of g1T is very similar to Sivers uncertainty except for the addition beam polarization term and this will make the error bars slightly larger.
The plotted g1T was estimated from g1 through Lorentz Invariance Relations and Wandzuraand Wilczek Relations.
A. Kotzinian, et. al. Phys. Rev. D 73 (2006)
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33. Transverse Momentum-dependent Structure of Neutron
Status of E06-010
The first 3He(neutron) transversity experiment was smoothly performed from Oct 2008 to Feb 2009 in Jefferson Lab Hall A.
Statistics reached the approved goal.
Detector calibrations, data quality check and target analysis are almost finished.
Will start to extract physical asymmetries afterwards. Very soon!
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Transverse Momentum-dependent Structure of Neutron

34. Transverse Momentum-dependent Structure of Neutron
12 GeV upgrade of JLab
A new hall, Hall-D:
Gluon-X collaboration: exotic meson spectroscopy, gluon-quark hybrid, confinement
Max beam energy upgraded to 12 GeV to Hall D, 11 GeV to Hall A, B and C.
Double cryogen capacity.
Hall A:
Dedicated devices + HRS
Polarized 3He target
Hall B
CLAS12
Polarized p/d target
Hall C
SHMS+HMS
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Transverse Momentum-dependent Structure of Neutron

35. Transverse Momentum-dependent Structure of Neutron
SIDIS with Solenoid
A solenoid with detector package (GEM, Shower counter, Gas Cherenkov …).
Larger acceptance
f : 2p coverage
q : 7-22 degrees
p: 1-7 GeV/c.
Better angular dependence decomposition.
Coil
Yoke GC HG A C
Collimator
Polarized 3He Target LC
GEMx4
GEMx5
TOF
LC: Large angle Calorimeter
GC: Gas Cherenkov
HG: Heavy Gas Cherenkov
A: Aerogel Detector
C: Calorimeter
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Transverse Momentum-dependent Structure of Neutron

36. Transverse Momentum-dependent Structure of Neutron
Kinematic Coverage
3-D (x, pT and z) mapping of Collins, Sivers and pretzelosity.
Coverage with 11GeV beam plotted here.
xB: 0.1 ~ 0.6
PT: 0 ~ 1.3 GeV/c
W: 2.3 ~ 4 GeV
z: 0.3 ~ 0.7
Mm: 1.6~ 3.3 GeV
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Transverse Momentum-dependent Structure of Neutron

37. From Exploration to Precision
z ranges from 0.3 ~ 0.7, only a sub-range of 11 GeV shown here.
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Transverse Momentum-dependent Structure of Neutron

38. Summary
Probing the transverse momentum-dependent nucleon structure is a very important step to further understand internal spin structure of the nucleon.
Single-spin asymmetry from SIDIS is a powerful tool to study TMDs.
First set of 3He neutron data has been collected in Jefferson Lab Hall A, analysis ongoing. Complementary to world data from proton, deuteron SIDIS and e+e- annihilation.
Precise measurement of neutron SIDIS is being developed with JLab 12 GeV upgrade.
Supported by U.S. Department of Energy DE-FG02-03ER41231
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Transverse Momentum-dependent Structure of Neutron

39. Transverse Momentum-dependent Structure of Neutron
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Transverse Momentum-dependent Structure of Neutron

40. Collaboration members
E Collaboration
Institutions
California State Univ., Duke Univ., Florida International. Univ., Univ. Illinois, JLab, Univ. Kentucky, LANL, Univ. Maryland, Univ. Massachusetts, MIT, Old Dominion Univ., Rutgers Univ., Temple Univ., Penn State Univ., Univ. Virginia, College of William & Mary, Univ. Sciences & Tech, China Inst. Of Atomic Energy, Beijing Univ., Seoul National Univ., Univ. Glasgow, INFN Roma and Univ. Bari, Univ. of Ljubljana, St. Mary’s Univ., Tel Aviv Univ.
Collaboration members
A.Afanasev, K. Allada, J. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, F. Butaru, G. Cates, C. Chang, J.-P. Chen (Co-SP), W. Chen, S. Choi, C. Chudakov, E. Cisbani(Co-SP), E. Cusanno, R. De Leo, A. Deur, C. Dutta, D. Dutta, R. Feuerbach, S. Frullani, L. Gamberg, H. Gao(Co-SP), F. Garibaldi, S. Gilad, R. Gilman, C. Glashausser, J. Gomez, M. Grosse-Perdekamp, D. Higinbotham, T. Holmstrom, D. Howell, J. Huang, M. Iodice, D. Ireland, J. Jansen, C. de Jager, X. Jiang (Co-SP), Y. Jiang, M. Jones, R. Kaiser, A. Kalyan, A. Kelleher, J. Kellie, J. Kelly, A. Kolarkar, W. Korsch, K. Kramer, E. Kuchina, G. Kumbartzki, L. Lagamba, J. LeRose, R. Lindgren, K. Livingston, N. Liyanage, H. Lu, B. Ma, M. Magliozzi, N. Makins, P. Markowitz, Y. Mao, S. Marrone, W. Melnitchouk, Z.-E. Meziani, R. Michaels, P. Monaghan, S. Nanda, E. Nappi, A. Nathan, V. Nelyubin, B. Norum, K. Paschke, J. C. Peng(Co-SP), E. Piasetzky, M. Potokar, D. Protopopescu, X. Qian, Y. Qiang, B. Reitz, R. Ransome, G. Rosner, A. Saha, A. Sarty, B. Sawatzky, E. Schulte, S. Sirca, K. Slifer, P. Solvignon, V. Sulkosky, P. Ulmer, G. Urciuoli, K. Wang, Y. Wang, D. Watts, L. Weinstein, B. Wojtsekhowski, H. Yao, H. Ye, Q. Ye, Y. Ye, J. Yuan, X. Zhan, Y. Zhang, X. Zheng, S. Zhou.
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Transverse Momentum-dependent Structure of Neutron

41. Transverse Momentum-dependent Structure of Neutron
Kinematics Coverage
HERMES: Proton
27.6 GeV e- beam
COMPASS: Proton
160 GeV m- beam
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Transverse Momentum-dependent Structure of Neutron