Precision Measurement of ParityViolating Asymmetry in Introduction 2

Precision Measurement of Parity-Violating Asymmetry in Introduction 2 Deep Inelastic e- H Scattering (PVDIS) Using a 6 Ge. V Beam at JLab What is parity violation? — Low energy tests of the Standard Model of particle physics in the electroweak and hadronic sectors The parity symmetry states that the physical laws behind all natural Xiaochao Zheng (UVa), Robert Michaels (JLab), Paul Reimer (ANL), Ramesh Subedi (UVa) phenomena must be the same as those behind their mirror images. Jefferson Lab Experimental Hall A It has been long confirmed that parity is conserved in strong JLab Experiment 08 -011 and electromagnetic interactions. However, the postulate that parity is violated in weak interactions was proposed by Lee and Yang in 1956, and was soon confirmed experimentally by Wu. The ultimate, long term goal of the JLab PVDIS program is to study both the Standard Model of EW interactions and hadronic phenomena. Our first step is to use a 6 Ge. V beam -- JLab E 08 -011 (planned for 2009): PVDIS at JLab 12 Ge. V Provide precision test of the Electroweak Standard Model, complementary to other experiments: Use 85 m. A, 6 Ge. V, 80% polarized beam on a 25 -cm LD 2 target; A polarized electron Two Hall A High Resolution Spectrometers detect scattered electrons; High-energy direct searches (such as LHC) may discover new particles. and its mirror image Measure Ad at Q 2=1. 10 and 1. 90 Ge. V 2 to about 3% (stat. ), with similar systematic However to study their coupling properties we must use low- and medium energy experiments; uncertainties. for C 1 q's, we can extract 2 C 2 u-C 2 d; Will also provide crucial guidance to the Qweak (JLab Hall C, future): only C 1 q's; PR 12 -07 -102, assuming small 12 Ge. V program. Only PVDIS is sensitive to C 2 q's (new physics in the quark axial coupling). and the Z 0 -exchanges. In deep inelastic scattering, the internal structure of the target nuclei or nucleon is revealed at the quark and gluon level. results. asymmetry comes from the interference term between the photon- C 2 q's from E 08 -011 handed electrons, causing a cross-section asymmetry. This experiment. This will be used to extract There is a difference in scattering probability between left- and right- after completion of the future Qweak Expected best knowledge on C 1 u and C 1 d right-handed; assuming hadronic effects are small For polarized electrons, the mirror image of a left-handed electron is Expected results on sin 2 q. W from Expected results on 2 C 2 u-C 2 d from E 05 -007, What is PV Deep Inelastic electron Scattering (PVDIS)? Assuming hadronic effects are small and using the expected known values Moller (SLAC E 158, completed): pure-leptonic; PVDIS asymmetry from a deuterium target: hadronic effects Expected constraint on CSV from PR 12 -07 -102 Expected results on 2 C 2 u-C 2 d from PR 12 -07 - Experimental upgrade needed: 102, assuming small hadronic effects upgrade from IR to green laser to provide 1% precision Provide possible direct observation of: Non-perturbative QCD effects in the EW sector; Charge symmetry violation at the quark level. (All these are not yet calculable in QCD ! Direct observations will be very exciting. ) From Ad one can extract C 1, 2 q and sin 2 q. W. providing a test of the electroweak (EW) standard model (SM); RC(x), RS(x), RV(x) are related to parton distribution functions, thus Ad is The new electronics will be installed in parallel to the regular DAQ References 1 R. Michaels, P. E. Reimer, X. Zheng, et al, JLab Proposal PR 08 -011. sensitive to internal structure of the nucleon, which is described by QCD 2 K. Paschke, P. E. Reimer, X. Zheng et al. , JLab 12 Ge. V Proposal PR 12 -07 -102. – the SM of strong interactions. 3 JLab 12 Ge. V electroweak physics meeting, Initiative on the large acceptance solenoid device, August 12 -13, 2008. In 1972, PVDIS result from SLAC E 122 was consistent with sin 2 q. W=1/4, confirmed the Standard Model prediction; However, PVDIS measurement has not been performed again.