Presentation on theme: "Target Normal Single-Spin Asymmetry in Inclusive DIS n (e,e with a Polarized 3 He Target Tim Holmstrom with Xiaodong Jiang, Todd Averett, Ron Gilman Hall."— Presentation transcript:
Target Normal Single-Spin Asymmetry in Inclusive DIS n (e,e with a Polarized 3 He Target Tim Holmstrom with Xiaodong Jiang, Todd Averett, Ron Gilman Hall A Collaboration Meeting January 5, 2007
N x k k N x k k 1 -exchange A N =0 (Time-Reversal Invariance). A N 0 due to imaginary part of 1 2 interference Connected to 3-current correlation function At quark level requires Chiral Symmetry Breaking to generate A N Clean probe to 2 response to DIS q q1q1 q2q2 A N : A Direct 2 -exchange Measurement
Recent Surprises with 2 -Exchange Rosenbluth vs. polarization transfer in nucleon FF's –Disagreement solved by two- exchange –Elastic intermediate state (Blunden et al.) –General Parton Distribution Functions (Afanasev et al.) ep e p with transversely polarized beam –Contribution of inelastic intermediate excitations exceeds the elastic intermediate state by orders of magnitude –In agreement with two- calculation by Afanasev et al. –Interference of one- exchange and two- exchange ("Compton") at the amplitude level
Normal Beam Asymmetry from 2γ-exchange Data from HAPPEX on the proton and 4 He targets Measures absorptive part of Compton scattering amplitude, integrated over photon virtualities and W Calculations by Afanasev&Merenkov
New Theoretical Predictions Metz et. al. pointed out that a non-zero A N can be due to two-photon exchange in a parton picture using a mechanism similar to g T =g 1 +g 2. Afanasev and Weiss calculate A N in a constituent quark picture. –Their predictions are shown to the right for proton and neutrons.
Relation to Ay experiment The A y experiment will run with the next group of 3 He experiments. A y will measure the target normal single spin asymmetry using inclusive quasi-elastic scattering. GPD parameterizations predict A y = 1.5%. Thus there is 2 order of magnitude fall off between quasi-elastic parton prediction and the recent DIS prediction. This suggests that A N is very sensitive to the transition from hardronic to partonic degrees of freedom.
Previous Measurement Only one previous measurement of the vertical target single spin asymmetry by S. Rock et al. at SLAC in Vertically polarized butanol target, 18 GeV electron beam. The average for all DIS points gives the proton asymmetry is A N p = ± %. No new measurement has been published in 35 years.
Goals of this Proposal Use the 336 hours polarized target normal beam already approved for E06-010/ Control systematic uncertainty to the 10 4 level. –Improved PID with d2n Gas Cherenkov –Luminosity monitoring with Hall A Lumis –Overall control of systematic bias –Advances in the 3 He target allow fast target spin flips. Provide tight limits on target single spin asymmetries: DIS Parity, A y, and Transversity. Test the predictions of the constituent quark model. Measure the target normal single-spin asymmetry on the neutron to 10 4 level.
Big Bite Spectrometer The Transversity experiments plan to use the standard BigBite electron detector package: Scintillator trigger plane Three wire chambers Lead glass calorimeter New d2n Gas Cherenkov
Big Bite Performance during GeN Big Bite was used successfully during the GeN experiment. The wire chambers showed good momentum and z position resolution.
New BigBite Gas Cherenkov for d2n Designed to have a 500 to 1 pion rejection. To be built and commissioned in July/August of 2007.
Trigger DAQ Single arm trigger Scintillator plane hit Number of photons in the Cherenkov Energy threshold in the calorimeter DAQ rate of less then 2kHz Deadtime less then 5%. Aggressive in setting the calorimeter threshold Independent from Transversity trigger!
Hall A Lumis The high rate HAPPEX parity experiments have built and installed luminosity monitors (Lumis) in the Hall A beam pipe. These detectors worked very well at 30 Hz for HAPPEX. With one Slug of HAPPEX data Using 14 minute time windows Systematic bias was Downstream of target In beam pipe
Transversity Kinematics Bite
Expected Results E= 6 GeV, target polarization = 42%. f is the neutron dilution factor. One Big Bite Setting gets all x bins at once. E Gev e Deg. Q 2 GeV 2 W GeV E GeV d (e,e ) nb/GeV/sr fRate Hz N DIS 10 6 A N n
Results Compared to SLAC proton. Two order of magnitude improvement!
Systematic Uncertainties This measurement will be dominated by systematic uncertainty. 1.Relative luminosity background 3.Quasi-elastic background ½ of the E data will be taken with beam in the scattering plane A N =0Clear measurement of our total systematic bias Random quad run structure of target polarization or Better control of Systematic drifts Blind the data analysis
Relative Luminosities After neutron dilution (A N ) sys = for all four x bins. The Hall A Lumis are accurate to in our time scale. Luminosity enters directly as an asymmetry systematic.
Backgrounds: Radaitive Corrections The modified Regge GPD model predicts for the lowest x bin a quasi-elastic signal spin asymmetry A y =10 2, with a 30% uncertainty. The A y experiment E 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 radaitive background of 10%.
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. Gas Cherenkov will have pion rejection of 500 to 1 for all x The pion asymmetry A will be measured very accurately.
Beam Time Request Density tests, position measurements, and linearity studies will be done in coordination with the Transversity experiments. Time (Hours) Production on Pol. 3 He 672 (Shared with E and E06-011) Reference Cell Runs Optics and Detector Checks 16 (Shared with E and E06-011) Target Overhead: Spin Rotation and Polarization 32 (Shared with E and E06-011) Total0 new Hours (Time shared with E and E06-011)
Summary Experimental goal: measure the target single-spin asymmetry A n N on the neutron during the Transversity experiments. A N is a clean probe to 2 response to DIS. Test the constituent quark model prediction of A n N. Look for the transition from hardronic to partonic degrees of freedom.
Theory Connection: Other Transverse Spin Experiments Great Interest in SSA in SIDIS with transversely polarized target –Collins and Sivers Effect –Recent results from HERMES, COMPASS, and JLAB For Sivers: the Brodsky-Hwang-Schmidt mechanism at quark-level, –Further theoretical development: Belitsky, Ji, and Yuan … –Similar mechanism may be at work in Inclusive scattering. Independent check of systematics of SSA from 2 -exchange for SIDIS. Complementary to the studies of dynamics of SSA in SIDIS.
Relation with other Experiments Jefferson Lab is unique High luminosity polarized 3 He target Large acceptance of the BigBite spectrometer + Unique Physics reach now = HERMES has data with the target spin normal to the scattering angle But few polarization flips a year leads to systematic challenges Systematic Check for these experiments: Transversity, A y, and 12 GeV target single-spin PV
3 He Polarized Target E will use the new potassium/ rubidium hybrid 3 He target. These cells will be used for the first time in GeN, and preliminary studies suggest that P T >50%. The target will be flipped every 10~20 minutes. Target densities will need to be monitored. Spin Duality saw differences. Improved because of rotating /4 plate
Overall Systematic Cancellation Half of the Transversity 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.
Pion Background Rejection The SAID model estimates a 3% pion asymmetry near our kinematics. Aggressive PID cuts can make the correction smaller then the statistical error. Analysis of L-HRS Pb-glass Calorimeter rejection of can be achieved with aggressive cuts. Monte Carlo Studies of AerogelCherenkov rejection of 15 for the lowest x bin can be achieved with aggressive cuts. Electron efficiency 94% 50% with aggressive cuts.
Expected Results with Cuts E= 6 GeV, target polarization = 42%. f is the neutron dilution factor. One Big Bite Setting gets all x bins at once. E Gev e Deg. Q 2 GeV 2 W GeV E GeV d (e,e ) nb/GeV/sr fRate Hz N DIS 10 6 A N n
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%.
Two-Photon Effects in Inclusive DIS m q 0 If A N n 0 Would require chiral symmetry breaking, due to strong interaction effects beyond the leading twist QCD picture of DIS.