Presentation on theme: "Parity Violating Electron Scattering in Resonance region (Res-Parity) (P05-xxx) P. Bosted, Hall A meeting, June 2005 Physics Overview Motivation Experiment."— Presentation transcript:
Parity Violating Electron Scattering in Resonance region (Res-Parity) (P05-xxx) P. Bosted, Hall A meeting, June 2005 Physics Overview Motivation Experiment Count rates and Errors Expected Results Request Summary: Easy experiment, never done before, relevant to wider community
PARITY VIOLATING ASYMMETRY The cross section in terms of electromagnetic, weak and interference contribution Asymmetry due to interference between Z 0 and Electron can scatter off of proton by exchanging either a virtual photon or a Z 0 eeee P eeee P Z0Z0 +
Deep Inelastic asymmetry In the Standard Model and assuming quark degrees of freedom, at LO In the valence region, for a proton target: 1-0.75x
Resonance region asymmetry For a resonance A RL can be written in terms of response functions Isospin symmetry relates weak and EM vector current Enchanced d,s quark contributions Sensitive to axial hadronic current also Details have so far been worked out only for N (1232) sensitive to axial vector transition form factor
A Simple Model sin 2 W = 0.25 ->axial current suppressed Isospin symmetry Negligible strange and charm form factors PROTON DEUTERON Different dependencies in the resonant and DIS cases Resonant case the current is expressed through the square of the sum over parton charges DIS case the sum of the square gives the current Assume r(W) r(W) depends on (I=0)/(I=1)
QUARK-HADRON DUALITY In QCD can be understood from an OPE of moments of structure functions Duality is described in OPE as higher twist (HT) effects being small or cancelling For spin-averaged structure function, duality works remarkably well to low values of Q 2
DUALITY for the gamma-Z interference tensor ? Leading order criteria DATA NEEDED! Duality is satisfied if on average n / p = 2/3 PROTON Simple Model Average of the (1232) and the elastic peak tend to equal the DIS curve Higher resonances oscillate around the DIS curve DIS model Resonance model
PHYSICS MOTIVATION Provide the first measurements of the parity violating asymmetries over the full resonance region for proton, deuteron, and carbon. Explore both global and local quark-hadron duality with the previously un-studied combination of structure functions Sensitive to down and strange quark currents Sensitive to axial hadronic current
PHYSICS MOTIVATION The results are of practical importance : Modeling neutrino cross sections needed for neutrino oscillation experiments. Understanding backgrounds and radiative corrections for other PV experiments (E05-007 in near future) Understanding the role of higher twist effects If duality is verified small higher twist effects
NEUTRINO OSCILLATION Major world-wide program to study neutrino mass, mixing Interpretation needs neutrino cross sections in few GeV region on various nuclei (proton, oxygen, steel, …) Neutrino beams not monochromatic, flux hard to measure: direct cross section measurements problematic Rely on models. Res-Parity will constrain models (especially d,s quark currents, axial hadronic current, and nuclear dependence: is EMC effect same for u and d quarks?).
BACKGROUND IN E158 SLAC E158 measured PV in Moller scattering, with large systematic error from low Q 2 ep background Res-PV will constrain models used to estimate the background Result is improved confidence in the important E158 limits on physics beyond the Standard Model
Experimental Setup Electrons detected by the two HRS independently Fast counting DAQ handle up to 1MHz rate with 10 3 pion rej. C, 25-cm LD2, LH2 targets (highest cooling power) Pol e - beam, 4.8 GeV, 80 uA, 80%, D P b /P b = 1.2% Beam intensity asymmetry controlled by parity DAQ Target density fluctuation & other false asym monitored by the Luminosity Monitor
KINEMATICS AND RATES Rates similar to E05-007. Pion/electron ratio smaller Run low E settings in one HRS, high E in other x Y Q 2 E W 2 /e MHz A/A 0.175 0.50 0.6 2.8 3.9 0.6 0.8 4.5 0.245 0.39 0.7 3.2 3.1 0.2 0.9 4.0 0.359 0.29 0.8 3.6 2.3 0.0 1.0 3.8 0.575 0.19 0.9 4.0 1.5 0.0 1.2 3.2 for LD2 target
New Instruments and/or Upgrades Compton polarimeter: will use green laser (in progress); expect to achieve D P b /P b = 1.1% for electron analysis method; 25-cm long racetrack-shaped LH2/LD2 cell, 2.5 gm/cm 2 C target (as used in Hall C) FADC-based and scaler-based fast counting DAQs, both being developed by the E05-007 (PVDIS) collaboration.
PROJECTED STATISTICAL ERRORS Relative error of 5% to 10% per bin Local duality (3 resonance regions) tested at 4% level Global duality (whole region) tested at 2% level Ratio of proton/deuteron (d/u) and C/deuteron (EMC effect) tested to 3% level
SYSTEMATIC ERRORS Source A/A Beam Polarization Kinematic determination of Q 2 Detector and Electronic Linearity Electromagnetic radiative corrections Beam asymmetry Pion contamination Pair symmetric background Target purity and density fluctuations 0.012 0.010 0.005 0.002 Total0.020 The ratio of asymmetries on hydrogen or C to deuterium is almost free of experimental systematic errors, allowing a very precise comparison with theory
REQUEST E Target P HRS-L/R time 4.8 GeV LH2 4.0, 3.2 GeV 2 days 4.8 GeV LH2 3.6, 2.8 GeV 2 days 4.8 GeV LD2 4.0, 3.2 GeV 2 days 4.8 GeV LD2 3.6, 3.8 GeV 2 days 4.8 GeV C 4.0, 3.2 GeV 2 days 4.8 GeV C 3.6, 2.8 GeV 2 dyas Checkout 4 hours Pass Change from E05-007 8 hours Polarization measurements 8 hours e + asymmetry 4 hours Total 13 days
REQUEST (continued) Electronics same as E05-007 Compton polarimeter as for E05-007 High beam polarization, moderately good beam stability and charge asymmetry (less stringent than Happex or G0)
COLLABORATION Experience in PV (E158, Happex, G0) Augments E05-007 (DIS-PV: more people to develop needed equipment
SUMMARY FIRST weak current measurements in full resonance region. Surprises possible. Measure A p, A d, and A C for M = 0.8 GeV 2 Relatively easy (for PV) experiment using same equipment as E05-007 Emphasizes d-quark contributions, sensitive to strangeness and axial hadronic current New regime for study of duality, higher twist effects, and EMC effect Needed to constrain models, which in turn are used for neutrino oscillation studies, backgrounds to experiments like SLAC E158, radiative corrections for DIS-parity experiments.
DAQ: Comparison of two options FADC-based: Is what we eventually need (12 GeV program) Full event sampling for detailed off-line analysis; If there is a highly-rated experiment, 2 years is possible. Scaler-based: Similar to previous SLAC, and current Hall C scalers; Mostly work for the electronics group, easy to do; Still, need extra man-power and cost; Specialized; Only scaler info is recorded (on-line PID critical).
RELATION TO PR05-007 Complementary: lower W and Q 2 Study HT lower Q 2 near W=2 GeV, effects bigger Both proton and deuteron used Information needed for precision DIS- Parity to accurately calculate radiative corrections and constrain HT.
COLLABORATION W. Boeglin, P Markowitz Florida International University, Miami, FL C Keppel Hampton University, Hampton VA G. Niculescu, I Niculescu James Madison University, Harrionburg, VA P. E. Bosted (spokesperson), V. Dharmawardane (co-spokesperson), R. Ent, D. Gaskell, J. Gomez. M. Jones, D. Mack, R. Michaels, J. Roche, B. Wojtsekhowski Jefferson Lab, Newport News, VA T. Forest, N. Simicevic, S. Wells Louisiana Tech University, Ruston, LO K. Kumar, K. Paschke University of Massachusetts, Amherst, MA F. R. Wesselmann Norfolk state university, Norfolk, VA Yongguang Liang, A. Opper Ohio state university, Athens, OH P. Decowski Smith College, Northampton, MA R. Holmes, P. Souder University of Syracuse, Syracuse, NY S. Connell, M. Dalton University of Witwatersrand, Johannesburg, South Africa R. Asaturyan, H. Mkrtchyan (co-spokesperson), T. Navasardyan, V. Tadevosyan Yerevan Physics Institute, Yerven, Armenia
Pion Background /e ratio ranges 0.005 to 1.2 : average about 0.2 signal ~20x smaller than electron signal : net contamination average is 1% Pion asymmetry measured in 4 th layer lead glass (lead between 3 rd and 4 th layers to fill electron signal). Expect < 1ppm based on SLAC experiment
Kinematic Determination of Q 2 dA/A proportional to dQ 2 /Q 2 From standard HMS uncertainties of and 0.1% in E, central Q 2 determined to 0.8% Uncertainties in target, beam, collimater and quadrupole positions increase uncertainty in measured Q 2 to 1% Will be checked using normal counting mode at low beam current
RADIATIVE CORRECTIONS Un-radiated to radiated spin averaged cross section The ratio of radiated to un-radiated ed parity violating asymmetry (R p ) is close to unity Shape and magnitude of R p determined by the probablity for an electron to radiate a hard photon Radiative corrections for A p will be determined by an iterative fit to the data of this proposal systematic error in A p < 1% Determined by the x, Q 2 dependence of F 2
SFs for the interference tensor A RL in terms of structure functions for the interference tensor of EM and weak currents W1W1 W2W2 W3W3 Well measured Proportional to the weak interaction Can be use to study parity violating part of the weak neutral current Depending on the isospin of the final excited state the interference cross section is expected to show a resonance structure A RL can be used to test duality for a linear combination of W 1,2,3
OTHER PV EXPPERIMENTS Most electron PV experiments have focused on elastic channels SAMPLE at BATES, HAPPEX and G0 at Jlab, A4 at Mainz probe the strange quark form factors of the nucleon Qweak at Jlab searching for physics beyond the standard Model G0 plan to study N - transition No approved experiment to study the full resonance region! Essential in understanding the background in other PV experiments Largest systematic error of E158 Understand the role of HT effects