1. Massachusetts Institute of Technology
Parity Violation in Deep Inelastic Region at JLab 6 GeV — Experiment
Xiaochao Zheng
Massachusetts Institute of Technology
May 19, 2006
Motivation, PVDIS, Implication on EW standard model and hadronic physics;
Requirement on Instrumentation and Status
Summary and Outlook

2. Parity Violation in Electron Scattering
Observables — parity violating asymmetries (APV)
(polarized beam + unpolarized target)
study nuclear matter (neutron skin) PREx
study hadron structure
elastic scattering: strange form factors A4, G0, HAPPEX, SAMPLE
DIS: non-perturbative higher twist effects, etc PVDIS
test EW standard model E158, Atomic PV, Qweak
𝐴 𝐿𝑅 ≡  𝑟 −  𝑙  𝑟   𝑙 ≈ 𝑄 2 𝑀 𝑍 2 ≈120𝑝𝑝𝑚𝑎𝑡 𝑄 2 =1  𝐺𝑒𝑉 𝑐  2

3. Electro-Weak Standard Model
SM works well at present energy range, however:
Data exist: cannot be explained by the SM ( mn? NuTeV anomaly?..);
Conceptual reasons: What happens in the “high-energy desert” (250GeV ~ 5 x GeV ~ 2.4 x 1018 GeV)?
Search for Physics beyond the Standard Model
Direct: LEP, LHC
Indirect: E158, Atomic PV, NuTeV, Qweak, PVDIS

4. PV DIS Asymmetries Rc,Rs,Rv: nucleon PDF; Y: kinematic factor
For a deuterium target
𝐴 𝑑 =540𝑝𝑝𝑚 𝑄 2 2 𝐶 1u 1 𝑅 𝐶 𝑥 − 𝐶 1d 1 𝑅 𝑆 𝑥 𝑌2 𝐶 2u − 𝐶 2d  𝑅 𝑉 𝑥 5 𝑅 𝑆 𝑥4 𝑅 𝐶 𝑥
Rc,Rs,Rv: nucleon PDF; Y: kinematic factor
𝐶 1u = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑢 =− 1 2  4 3 sin 2   𝑊 
𝐶 2u = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑢 =− 1 2 2 sin 2   𝑊 
𝐶 1d = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑑 = 1 2 − 2 3 sin 2   𝑊 
𝐶 2d = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑑 = 1 2 −2 sin 2   𝑊 
In the SM, tree level
From Ad can extract C1,2q and sin2qW.

5. DIS Parity Experiment – History and Future
1970's, result from SLAC E122 consistent with sin2qW=1/4, confirmed the Standard Model prediction;
C.Y. Prescott, et al., Phys. Lett. B77, 347 (1978)
Development in experimental technique allows to search for new physics
If all hadronic effects are small or can be understood, then any deviation of sin2qW or Ciq from their SM predictions would be a hint of new physics.
P. Bosted, et al., SLAC E149 (1993), LOI2003-1;

6. Current Knowledge on Weak Coupling Coeffecients
𝐶 1q = 𝑔 𝐴 𝑒 𝑔 𝑉 𝑞
𝐶 2q = 𝑔 𝑉 𝑒 𝑔 𝐴 𝑞
𝐶 3q = 𝑔 𝐴 𝑒 𝑔 𝐴 𝑞
J. Erler, M.J. Ramsey-Musolf, hep-ph/ or Prog. Part. Nucl. Phys. 54, 351 (2005)

7. JLab Experiment
Co-spokesperson & contact: X. Zheng (MIT)
Co-spokesperson: P.E. Reimer (ANL), R. Michaels (JLab)
(Hall-A Collaboration Experiment, approved by PAC27, rated A-)
Use 85mA, 6 GeV, 80% polarized beam on a 25-cm LD2 target;
Two Hall A High Resolution Spectrometers (HRS) detect scattered electrons;
Measure Ad at Q2=1.10 and 1.90 GeV2 to about 2% (stat.);
ANL, Calstate, FIU, Jlab, Kentucky, U. of Ljubljana (Slovenia), MIT, UMD, UMass, UNH, Universidad Nacional Autonoma de Mexico, Rutgers, Smith C., Syracuse, UVa, W&M

8. E Physics Goals
𝐴 𝑑 = 3 𝐺 𝐹 𝑄 2 2 2  2 𝐶 1u 1 𝑅 𝐶 𝑥 − 𝐶 1d 1 𝑅 𝑆 𝑥 𝑌2 𝐶 2u − 𝐶 2d  𝑅 𝑉 𝑥 5 𝑅 𝑆 𝑥4 𝑅 𝐶 𝑥
From Ad at Q2=1.90 (GeV/c)2, can extract (2C2u-C2d) to ±0.03 — order of magnitude improvement compared to world data (PDG);
provide constraints on new physics up to 1 TeV mass limit (complementary to Qweak, E158);
Z' Searches; Compositeness; Leptoquarks.
help to extract C3q = gAegAq from CERN m±- DIS data SM
(for review of new physics from PVES:J. Ramsey-Musolf, et al., hep- ph/ ; hep-ph/ ; nucl-th/ ;

9. E Physics Goals
To cleanly separate higher-twist (HT) from New Physics will require precision measurement at various kinematics, and we are making the first step now;
Existing models show negligible HT effects;
Ad at Q2=1.10 (GeV/c)2 will help to investigate if there are significant HT effects:
Will help to investigate the HT contribution to the NuTeV anomaly:
May provide “clean” extraction of HT, and help with DIS analysis:
extract aS at low Q2 from DIS data — test pQCD and understand confinement.
Will provide important guidance for the future PVDIS program;

10. The NuTeV Anomaly and Higher Twist
sin2qW reported by NuTeV is 3s away from SM;
Possible hadronic causes: CSV, strange sea asymmetry, HT, etc.
G.P. Zeller et al, PRL88,091802(2002)
T. Londergan, PAVI06
E158: P.L. Anthoney et al., PRL95, (2005)
Cs-APV: S.C. Bennett, C.E. Wieman, PRL82,2484(1999)
If 80% of this deviation is from HT, it would imply a 6% HT contribution to our Ad at Q2 = 1.9 and 10% at Q2 = 1.1 (GeV/c)2, way larger than our expected error bar;
M. Gluck and E. Reya, Phys. Rev. Lett. 47, 1104 (1981);
also: G.A. Miller & A.W. thomas, hep-ex/

11. Extraction of aS at Low Q2 and Higher Twist
aS extracted from Bjorken sum rule at low Q includes HT;
HT from DIS (F2, g1...) — difficult to separate from higher order effects;
HT from PVDIS:
Leading Twist unambiguously determined by the SM;
More precise than polDIS;
If can use PVDIS HT for low Q DIS analysis, then may correct HT and compare aS with pQCD predictions ® Test standard model of strong interaction.
𝐴 𝑑 = 𝐴 𝑑 𝑆𝑀 1 𝐶 4 𝐻𝑇 𝑄 2 
A. Deur, V. Burkert, J.P. Chen, W. Korsch, hep-ph/
Perhaps PVDIS can serve as a (powerful?) tool to study some long-lasting problem in hadronic physics — HT, d/u, anything else???

12. The Accelerator at Jefferson Lab, Virginia, USA
“parity-quality”
beam since 1998
K. Paschke, PAVI06
NORTH
LINAC
SOUTH
LINAC
INJECTOR
RECIRCULATION
ARCs (Magnets) A C B
EXPERIMENTAL
HALLS

13. Experimental Hall A

14. PV-DIS (E05-007) Requirements and Status

15. PV-DIS (E05-007) Requirements and Status
upgrade from IR to green laser to provide 1% precision
upgrade to flash-ADC based DAQ to count 1MHz rate

16. Compton Polarimetry
Compton polarimeter: measure asymmetry of Compton scattering of electron beam and high power laser (Fabry-Pérot cavity);
Non-invasive, high current capacity;
Currently using: 200mW 1064nm laser;
Difficult for < 2GeV beam;
Providing 2-3% precision for 4 GeV beam, larger for <4 GeV;
see also: J. Diefenbach, PAVI06

17. Green Compton Upgrade Upgrade required by: PVDIS, PRex, 12 GeV
Upgrade includes:
from IR to Green (532nm) laser, completely new optics including the Fabry-Pérot cavity, factor of 4 increase in FOM — JLab;
(PRex) R. Michaels, PAVI06
new electron detectors (narrower micro-strip) to improve resolution — Univ. of Clement-Ferrand;
Photon integration method — improve systematics (JLab);
Will provide 1% precision down to 1 GeV beam energy;

18. Green Compton Lab

19. Green Compton Optics Setup
Currently
In Progress

20. Green Compton Cavity Alignment

21. Green Compton Optics Setup
Green laser
with safty cover
FOI L1
QWP
PA510 L2
Aiming in cavity locking July/August 2006.

22. DAQ Upgrade Current Hall A HRS DAQ:
Max event rate 4KHz (VDC limited);
Previous Hall A PV Experiments (HAPPEX) used Integrating DAQ
Will not work for DIS (large pion background);
Flash ADC (FADC) based DAQ is required:
FADC: 250MHz main sampling rate with on-board processor (FPGA);
Provide on-board fast PID on a counting basis up to 1MHz;
Full event information sampled at lower rate for cross-check;
Can be used for other high rate experiments.

23. FADC DAQ on HRS Inputs: Scintillators (S1, S2, 12 channels each);
Gas cherenkov (GC,10CH);
Lead glass counter (“Pre-shower” 48CH, “Shower” 80CH);

24. FADC DAQ on HRS On-board Processing: Outputs: Regular DAQ Spectrum
S1+S2 for track quality evaluation;
sum GC, Lead glass for PID;
segments GC and Lead glass blocks for pile-up rejection;
pile-up separation (signal shape analysis);
Regular DAQ Spectrum
electrons
Pre-Shower sum
Shower sum
Outputs:
helicity-gated electron and pion counts (per ~second);
full event sampling at low rate for quality control, including pile-up events for further off-line evaluation;
cross check with regular DAQ at low event rate (<4KHz);
pions

25. FADC DAQ on HRS Status: Schedule of E05-007:
Preliminary test using a 100 MHz module (no processor built-in) completed — design algorithm, signal shape analysis (Oct.2005):
Specification/algorithm provided to JLab DAQ group — Dec 2005;
First prototype will be available in summer 2006, more tests will follow;
Expect to completely test the full system in late 2007.
Schedule of E05-007:
Phase I (13 days) approved, will run in late 2008 – early 2009;
Will re-propose phase II (33 days) soon, hopefully will complete both at the same time;

26. Future of PV-DIS at JLab
The approval of E started the PV-DIS JLab:
SM test, precision C2q and sin2qW
(complimentary to other HEP and Nuclear experiments)
Study of hadronic effects:
Higher-twist study (low Q2 aS , test pQCD);
Using a proton target: measure PDF ratio d/u at high x;
Measure Charge Symmetry Violation (CSV).
Leading 12 GeV upgrade (2012?~)
P.E. Reimer, PAVI06
JLab Hall A
pCDR

27. Summary
PV-DIS is a powerful tool to test the Standard Model and to study many interesting hadronic effects:
C2q's, sin qW;
low Q2 aS , d/u at high x, higher twist... Anything else?
This program will start soon at JLab (E05-007):
Two major instrumentation need to be upgraded, in progress;
Will run in late ;
extract (2C2u-C2d) to ±0.03, factor of 8 improvement w.r.t PDG;
first HT extraction from PVDIS.
Will be one of the leading experiments of JLab 12 GeV.

28. Experimental Hall A

29. The Collaboration
A. Afanasev, D.S. Armstrong, J. Arrington, T.D. Averett, E.J. Beise,
W. Bertozzi, P.E. Bosted, J.R. Calarco, G.D. Cates, J.-P. Chen,
E. Chudakov, P. Decowski, A. Deur, J. Erler, R. Feuerbach, J.M. Finn,
O. Gayou, S. Gilad, R. Gilman, C. Glashausser, K.A. Griffioen, K. Hafidi,
J.-O. Hansen, R. Holmes, R.J. Holt, T. Holmstrom, H.E. Jackson, X. Jiang,
W. Korsch, K. Kumar, N. Liyanage, D.J. Mack, D.J. Margoziotis,
P. Markowitz, R. Michaels (co-spokesperson), P. Monaghan,
V. Nelyubin, K. Paschke, D.H. Potterveld, A.J. Puckett, Y. Qiang,
R. Ransome, P.E. Reimer (co-spokesperson), B. Reitz, E.C. Schulte,
J. Singh, S. Sirca, R. Snyder, P. Souder, V. Sulkosky, W.A. Tobias,
B. Zeidman, X. Zhan, X. Zheng (spokesperon)
The Hall A Collaboration
ANL, Calstate, FIU, Jlab, Kentucky, U. of Ljubljana (Slovenia), MIT, UMD, Umass, UNH, Universidad Nacional Autonoma de Mexico, Rutgers, Smith C., Syracuse, Uva, W&M
We have strong support from theorists and experts of parity experiments.

30. Beam Time Allocation for Running In Two Phases
Phase I: 13 days
4 days of commissioning and systematic checks including:
Commissioning fast counting DAQ and Compton
9 days with the HRS-L at Q2=1.10 (GeV/c)2 and the HRS-R at Q2= (GeV/c)2
Approved (Jan.2005), rated A-
Phase II: 33 days
complete both Q2 measurements.

31. Data Analysis Electron asymmetries 3He asymmetries From 3He to Neutron
𝐴 𝑟𝑎𝑤 = 𝑁 𝑝 𝑄 𝑝 − 𝑁 𝑚 𝑄 𝑚 𝑁 𝑝 𝑄 𝑝  𝑁 𝑚 𝑄 𝑚
𝐴 p,p = 𝐴 𝑟𝑎𝑤 𝑓 𝑃 𝑏 𝑃 𝑡
3He asymmetries
From 3He to Neutron

32. Exploring Nucleon Structure Using EM Probe (cont.)
elastic
quasi-elastic
resonances
DIS
The nucleon changes its appearance with the way we study it, and we have developed different models/languages for each facet;
However, all of them shall form a coherent picture, and perhaps one day all these aspects can be unified within QCD.

33. Scaling Violation in QCD
Bjorken limit: , xBj fixed, (strict) one photon exchange
𝑄 2 ∞
no scale (Q2 )dependence,
scaling
High , soft gluon emission,
𝑄 2
logQ2 dependence
Low , hard gluon emission
𝑄 2 0
1/(Q2)(t-2) dependence “higher- twist effects”

34. Structure Functions in the Quark-Parton Model
𝐹 1 𝑥= 1 2  𝑒 𝑖 2 𝑞 𝑖 𝑥
in the infinite momentum frame (IMF)
(P ® ∞)
After 35 years of DIS experiments, the unpolarized structure of the nucleon is reasonably well understood (for moderate xBj region).

35. Jlab 6 GeV

36. Upgrade magnets and power supplies
Jlab 6 GeV 12
Add new hall
Upgrade magnets and power supplies
CHL-2
Enhance equipment in existing halls

37. First FADC Test and Design for Algorithm
Preliminary test using 100MHz module and 1-2 CH/detector (Oct.2005):
Gas cherenkov (10 ch sum)
Pre-shower (2ch sum)
Shower (1ch)
Design on-board algorithm;
Event pile-up at 3% level at 1MHz (e-e pileup <1%), on-board identification possible;

38. Extraction of aS at Low Q2 and Higher Twist
aS extracted from Bjorken sum rule at low Q includes HT;
HT from DIS (F2, g1...) — difficult to separate from higher order effects;
HT from PVDIS:
Leading Twist unambiguously determined by the SM;
More precise than polDIS;
If can use PVDIS HT for low Q DIS analysis, then may correct HT and compare aS with pQCD predictions ® Test standard model of strong interaction.
Preliminary!
A. Deur, V. Burkert, J.P. Chen, W. Korsch, hep-ph/
Perhaps PVDIS can serve as a (powerful?) tool to study some long-lasting problem in hadronic physics — HT, d/u, anything else???

39. The Accelerator at Jefferson Lab, Virginia, USA