Parasitic Measurement of Single-Spin Asymmetry in Inclusive DIS for Neutron Target

1. A Parasitic Measurement During E03-004 for Target Single-Spin Asymmetry in Inclusive DIS n↑(e,e) Reaction on a Vertically Polarized 3He Target Tim Holmstrom with Xiaodong Jiang, Todd Averett, Ron Gilman Hall A Meeting December 6, 2005

2. Introduction • E03-004 plans to measure SIDIS n↑(e,p-e) asymmetry on a transversely polarized 3He target. • We seek to parasitically measure the inclusive DIS n↑(e,e) vertical single-spin asymmetry. • This will require a change to the BigBite detector package and DAQ. • One day of dedicated beam time for: • Detector tests and • Systematic studies

3. Theory • It was shown in the 60’s, by Christ and Lee, that an inclusive DIS target single-spin asymmetry would be T-violating under these assumptions: • One photon exchange. • No quark mass. • Other particle exchanges are ignored. Strong interactions can create T-odd effects in SIDIS, but they are still T-violating in inclusive DIS. gg exchange Non-strong interaction T-odd effects that are not T-violating.

4. Two-Photon Effects mq≠0 • For the neutron the net asymmetry due to mass effects must be zero for symmetric u- and d-quark distributions. Would require chiral symmetry breaking, through a previously unobserved interaction, beyond the leading twist QCD picture of DIS. If ATn ≠0

5. Previous Measurement • There is only one previous measurement of the vertical target single spin asymmetry by S. Rock et al. in 1970. • Using a vertically polarized butanol target and a 18 GeV electron beam. • The average for all DIS measurements gives the proton asymmetry is ATp = -1.6%±3.5%. • No new measurement has been published in 35 years.

6. Goals of this Proposal Measure the vertical target single-spin asymmetry on the neutron to 10-4 level. Two order of magnitude improvement First neutron measurement Control systematic uncertainty to the 10-4 level. Provide tight limits on target single spin asymmetries. DIS Parity Ay Search for new chiral symmetry breaking interactions.

7. Big Bite Spectrometer E03-004 plans to use the standard BigBite electron detector package: • Scintillator trigger plane • Three wire chambers • Lead glass calorimeter Better particle ID needed for SSA! We purpose to add a new Cherenkov Detector

8. Aerogel Cherenkov An Aerogel (n=1.03) Cherenkov detector can be placed between wire chambers 2 and 3. A tentative agreement has been reached with MIT-Bates and Arizona State to ship parts of the BLAST Aerogel Detector. Only good for low energy pions If analysis of the GeN data shows: center wire chamber is not needed by E03-004 Remove that chamber and build a gas cherenkov. Good for all momentum pions

9. Trigger DAQ Scintillator plane hit Single arm trigger Energy threshold in the calorimeter Number of photons in the Cherenkov Trigger rate of less then 5kHz Deadtime less then 5%. Aggressive in setting the calorimeter threshold If necessary prescalling the trigger.

10. Hall A Lumis • The HAPPEX experiments have built and installed luminosity monitors (Lumis) in the Hall A beam pipe. • These detectors worked very well at 30 Hz for HAPPEX. 1 Slug of HAPPEX data 14 minute time window A systematic bias of only 510-5

11. 3He Polarized Target • E03-004 will use the new potassium/ rubidium hybrid 3He target. • These cells will be used for the first time in GeN, and preliminary studies suggest that PT>50%. • The target will be flipped every 10~20 minutes. Target densities will need to be monitored. Spin Duality saw 810-4 differences

12. Expected Results • E= 6 GeV, target polarization = 42%. • f is the neutron dilution factor. • One Big Bite Setting gets all x bins at once.

13. Kinematics Bite

14. Results Compared to SLAC proton. Two order of magnitude improvement!

15. Systematic Uncertainties This measurement will be dominated by systematic uncertainty. • Relative luminosity • p background • Quasi-elastic background ½ of the E03-004 data will be taken with beam in the scattering plane AT=0 Clear measurement of our total systematic bias Random quad run structure of target polarization  or  Better control of Systematic drifts

16. Relative Luminosities Luminosity enters directly as an asymmetry systematic. The Hall A Lumis are accurate to 510-5 in our time scale. After neutron dilution d(Aphys)sys= 3.4 10-4

17. Backgrounds: Quasi-Elastic • The modified Regge GPD model predicts a quasi-elastic signal spin asymmetry Ay=510-3, with a 30% uncertainty. • The Ay experiment E05-015 will test this model giving us a better correction. For the highest x bin radaitive background is less then 1%. For the lowest x bin quasi-elastic background of 10%.

18. Backgrounds: Pions The p/e ratio: less then 10:1 for the two high x bins less then 100:1 for the lowest x. Lead glass calorimeter rejection 100 to 1. Aerogel Cherenkov rejection of 10 to 1 for lowest x Gas Cherenkov rejection of 10 to 1 for all x The large p background will give us the Apvery accurately. Reverse BigBite Polarity D Coincidence Special Run Change L-HRS momentum Clean p signal

19. Relation with other Experiments Jefferson Lab is unique + High luminosity polarized 3He target Large acceptance of the BigBite spectrometer = Unique Physics reach HERMES has data with the target spin normal to the scattering angle But few polarization flips a year leads to large systematic errors Systematic Check for these experiments: Ay, and 12 GeV target single-spin PV

20. Beam Time Request • Cherenkov Commissioning, Lumi Check Out, and PID Study. • Density tests, position measurements, and linearity studies.

21. Summary We intend to measure the target single-spin asymmetry ATn on the neutron. In a parasitic experiment to E03-004. Two order of magnitude improvement We ask for one day of dedicated beam time: Checkout of the Lumis Checkout of the Aerogel Detector Special systematic measurements 2 hour delta run to get a clean p in PID First neutron measurement A large asymmetry would be a signal for previously unseen chiral symmetry breaking beyond the leading twist QCD picture of DIS

22. Overall Systematic Cancellation • Half of the E03-004 beam time will be spent with target spin left and right of the beamline. Since: • A full analysis will be done of this data, which will give us a clean measure of our systematic bias. • The quad run structure of target polarization, the random sequence of or runs will also to better cancel slow drifts in the spectrometer or beam. • Periodic special runs will be done to understand the behavior of the Lumi and detectors such as: • Target density runs • Beam position off runs • Linearity studies.

23. Target Polarization Differences • Polarization differences do not cause asymmetries they only change the size of the asymmetry. • NMR and EPR will be used to measure the polarization to a relative 4%.