Measurement Using Polarized e + /e Beams

Transcription

1 C 3q Measurement Using Polarized e + /e Beams Xiaochao Zheng Univ. of Virginia March 7, 009 Introduction Standard Model of Electroweak Interaction Neutral Weak Coupling Constants Test of the Standard Model Access to C 3q Using Electron vs. Positron Scattering Summary Xiaochao Zheng, International Workshop on Positrons at JLab 1/6

2 Electroweak Interaction A Historical View Let's start from electromagnetic interaction (QED, 190's): ek ' p p' ek p p Xiaochao Zheng, International Workshop on Positrons at JLab /6

3 Electroweak Interaction A Historical View Let's start from electromagnetic interaction (QED): M = e q j em p j em, e = eu p u p 1 M em j,e eu e eu e q eu e u e 1 q p u p em j, p p u p We can calculate many electromagnetic interactions using QED Xiaochao Zheng, International Workshop on Positrons at JLab 3/6

4 Electroweak Interaction A Historical View Charged pion and muon decay:... e. e = s = s Much longer than strong (10 3 s) or electromagnetic (10 16 s) decays Indicate a 4 th interaction: weak 193, based on QED, Fermi proposed: M EM = e u p u p 1 q eu e u e M weak = Gu n u p u e u e arbitrary strength assuming same current as in EM force charge lowering (raising) weak charged current Xiaochao Zheng, International Workshop on Positrons at JLab 4/6

5 Electroweak Interaction A Historical View 1956, when Parity violation was first proposed (and tested in 1957), the only modification needed is: M weak = Gu n u p u e u e M weak = G u n 1 5 u p u e 1 5 u e = 4G J J. (A mixture of and 5 automatically violate parity) select only left handed 's If further assume that weak interaction occurs by exchanging a (W) particle, similar to the photon in electromagnetic interactions, then M CC = g u u 1 M W q g u e u e G q M W g 8 M W Xiaochao Zheng, International Workshop on Positrons at JLab 5/6

6 Electroweak Interaction Neutral Current 1973, with developement of beams, found: e. e. N X N X cannot be explained by CC; magnitude of strength indicates a Neutral Current. M CC = 4G J CC J CC, M NC = 4 G J NC J NC, J NC = 1 u u J NC q = 1 u q c q c q V A 5 u q vector and axial vector coupling constants Xiaochao Zheng, International Workshop on Positrons at JLab 6/6

7 Electroweak Interaction The Standard Model 1961, construct a SU() L group using charged currents, with weak isospin T. Provide CC weak interactions carried by W +, W ; Linear combination of the two is a neutral current, but it couples only to Left handed fermions, while experimentally observed neutral currents exist for both R and L handed fermions; On the other hand, EM [U(1) ] also couple to both R and L H fermions. Suggest: Combine Neutral Current from SU() L and U EM (1) G g 8 M W q e q (weak interaction is much weaker than EM because M W is large, not because g<<e) Xiaochao Zheng, International Workshop on Positrons at JLab 7/6

8 Electroweak Interaction The Standard Model 1961, construct a SU() L group using charged currents, with weak isospin T. Combine Neutral Current from SU() L and QED [U EM (1) ] to construct: j em J NC J 3 j Y completes SU() L U(1) Y, Y: weak hyper charge observable theory Q = T 3 Y photon Z 0 A 3 Z W B Xiaochao Zheng, International Workshop on Positrons at JLab 8/6

9 Electroweak Interaction The Standard Model 1961, construct a SU() L group using charged currents, with weak isospin T. Combine Neutral Current from SU() L and QED [U EM (1) ] to construct: j em J NC J 3 j Y completes SU() L U(1) Y, Y: weak hyper charge observable theory Q = T 3 Y photon Z 0 A 3 Z W B Xiaochao Zheng, International Workshop on Positrons at JLab 9/6

10 Electroweak Interaction The Standard Model Mixing of the SU() L and U EM (1) is giving by:... the Weak Mixing angle W theory observable W 3 B Z A A = B cos W W 3 sin W m=0 Z = B sin W W 3 cos W m 0 Xiaochao Zheng, International Workshop on Positrons at JLab 10/6

11 Electroweak Interaction The Standard Model Mixing of the SU() L and U EM (1) is giving by:... the Weak Mixing angle W theory observable left handed fermions only W 3 B Z A A = B cos W W 3 sin W m=0 Z = B sin W W 3 cos W m 0 both left and right handed fermions In the Standard Model fermions e f f c A c V 1 1 J NC q = 1 u q c q c q V A 5 u q e, u, c sin W sin W d, s sin W Xiaochao Zheng, International Workshop on Positrons at JLab 11/6

12 Test of The Standard Model Standard Model works well at present energy range (~50GeV?); But, conceptual reasons for theory of everything, hence new physics up to 10 (14 18) GeV. Test of the Standard Model: Direct searches (LHC) Indirect searches: New physics modify: sin W,c V e,c A e,c V q,c A q Search for forbidden processes ( decay, EDM......). at low energies; Xiaochao Zheng, International Workshop on Positrons at JLab 1/6

13 Testing the EW Standard Model Running of sin W and the NuTeV Anomaly (expected) Xiaochao Zheng, International Workshop on Positrons at JLab 13/6

14 Neutral Weak Couplings Asymmetries (ratios) in charged lepton N scattering can be used to measure products of c V, A e q,c V, A lepton L scatt. NC = [ c l q c A Vq l l 5 l q qc V c Aq l l q 5 qc A l c Aq l 5 l q 5 q ] A = + J NC e = u e 1 c V e c A e 5 u e J NC q = 1 u q c q c q V A 5 u q e, c q e, q V, A g V, A Xiaochao Zheng, International Workshop on Positrons at JLab 14/6

15 Neutral Weak Couplings e Charged lepton N scattering can be used to measure products of c V, A q,c V, A lepton L scatt. NC = [ c l q c A Vq l l 5 l q qc V c Aq l l q 5 qc A l c Aq l 5 l q 5 q ] C 1q C q C 3q parity violating e L, e R cross sections lepton charge conjugateviolating e L, e + cross sections R Xiaochao Zheng, International Workshop on Positrons at JLab 15/6

16 Current Knowledge on Weak Coupling Coeffecients C 3q =g e q C 1q =g e q A g V C q =g e q V g A A g A J. Erler, M.J. Ramsey Musolf, Prog. Part. Nucl. Phys. 54, 351 (005) Facility Process Q C iq Combination Result SM Value SLAC e D DIS 1.39 C 1u -C 1d 0.90± SLAC e D DIS 1.39 C u -C d 0.6± CERN D DIS (C u -C d )+C 3u -C 3d 1.80± CERN D DIS (C u -C d )+C 3u -C 3d 1.53± MAINZ e Be QE C 1u -0.64C 1d +.16C u -C d 0.94± Bates e C elastic 0.05 C 1u +C 1d 0.138± Bates e D QE 0.1 C u -C d 0.04± Bates e D QE 0.04 C u -C d 0.1± JLab e p elastic 0.03 C 1u +C 1d approved Cs APV 0-376C 1u -4C 1d 7.69± Tl APV 0-57C 1u -658C 1d 116.6± Fit e A low C 1u +C 1d ± All (R. Young, R. Carlini, A.W. C 1u -C new 1d ± Thomas, J. Roche, PRL 99, 1003 PVES C u +C d 0.063± (007) & priv. comm.) Data C u -C d 0.076± Xiaochao Zheng, International Workshop on Positrons at JLab 16/6

17 Current Knowledge on C 1,q all are 1 limit C 1u +C 1d MIT/ PDG best fit Cs APV Bates 0.8 SLAC/Prescott R. Young (combined) C 1u C 1d Tl APV R. Young (PVES) Qweak (expected) C u +C d R. Young SAMPLE (combined) 0.4 SLAC/ Prescott C u C d Expected: JLab 6 GeV PV DIS E (assuming small hadronic effects) Xiaochao Zheng, International Workshop on Positrons at JLab 17/6

18 Current Knowledge on Weak Coupling Coeffecients J. Erler, M.J. Ramsey Musolf, Prog. Part. Nucl. Phys. 54, 351 (005) Facility Process Q C iq Combination Result SM Value SLAC e D DIS 1.39 C 1u -C 1d 0.90± SLAC e D DIS 1.39 C u -C d 0.6± CERN D DIS (C u -C d )+C 3u -C 3d 1.80± CERN D DIS (C u -C d )+C 3u -C 3d 1.53± MAINZ e Be QE C 1u -0.64C 1d +.16C u -C d 0.94± Bates e C elastic 0.05 C 1u +C 1d 0.138± Bates e D QE 0.1 C u -C d 0.04± Bates e D QE 0.04 C u -C d 0.1± JLab e p elastic 0.03 C 1u +C 1d approved Cs APV 0-376C 1u -4C 1d 7.69± Tl APV 0-57C 1u -658C 1d 116.6± Fit e A low C 1u +C 1d ± All (R. Young, R. Carlini, A.W. C 1u -C new 1d ± PVES Thomas, J. Roche, PRL 99, 1003 C u +C d 0.063± Data (007) & priv. comm.) C u -C d 0.076± PDG00 (best): (C u C d )=±0.4 C 3u C 3d =±0.490 SM : 3 / Xiaochao Zheng, International Workshop on Positrons at JLab 18/6

19 Accessing C 3q from Electron, Positron Scatterings Not in the textbook S.M. Berman, J. R. Primack, Phys. Rev. D 9, 171 (1974) A l. L l. R = d l. N l. X d l. L R N l. X sensitive to C d l. N l. X 3q d l. N l. X Xiaochao Zheng, International Workshop on Positrons at JLab 19/6

20 Accessing C 3q from Electron, Positron Scatterings Not in the textbook S.M. Berman, J. R. Primack, Phys. Rev. D 9, 171 (1974) A l. L l. R = d l. N l. X d l. L R N l. X sensitive to C d l. N l. X 3q d l. N l. X A l. L l. R = d l. N l. X d l. L R N l. X d l. N l. X PV DIS asymmetry, SLAC E1 and JLab 6 & 1 GeV A d PV DIS = 3G F Q C [1R x] C [1R x]y C C R x 1u C 1d S u 5R S x4 R C x [sxs x] R S x= u xu xd xd x [cxcx] R C x= uxu xd xd x x x R V x= uxuxd xd x (small) (very small) (~1) Xiaochao Zheng, International Workshop on Positrons at JLab 0/6

21 Accessing C 3q from Electron, Positron Scatterings proton target: [ Al. l. L R Al L. l R. ]p = y y A p e L. e R. = 3 G F Q C u C 3u C 3d C 1u u C 1d dsy C u y y C u C 3u C 3d 4uds y= E Xiaochao Zheng, International Workshop on Positrons at JLab 1/6

22 Accessing C 3q from Electron, Positron Scatterings proton target: [ Al. l. L R Al L. l R. ]p = y y A p e L. e R. = 3 G F Q C u C 3u C 3d C 1u u C 1d dsy C u y y C u C 3u C 3d 4uds y= E not well known Xiaochao Zheng, International Workshop on Positrons at JLab /6

23 Accessing C 3q from Electron, Positron Scatterings proton target: [ Al. l. L R Al L. l R. ]p = y y A p e L. e R. = 3 G F Q C u C 3u C 3d C 1u u C 1d dsy C u y y C u C 3u C 3d 4uds y= E deuteron target: [ Al. l. L R = y y C C C C u d 3u 3d R. 1.5 V. 0.1 (dominant) Al. L l. R ]d C 1u C 1d Y C u R V A d e. L e. R = 3G F Q y y C u C 3u C 3d R V 5R s 4 R c Xiaochao Zheng, International Workshop on Positrons at JLab 3/6

24 Accessing C 3q from Electron, Positron Scatterings proton target: [ Al. l. L R Al L. l R. ]p = y y A p e L. e R. = 3 G F Q C u C 3u C 3d C 1u u C 1d dsy C u y y C u C 3u C 3d 4uds y= E deuteron target: [ Al. l. L R = y y C C C C u d 3u 3d R. 1.5 V. 0.1 (dominant) Al. L l. R ]d C 1u C 1d Y C u R V A d e. L e. R = 3G F Q y y C u C 3u C 3d R V 5R s 4 R c 108 ppm y y C 3u C 3d Q R V Xiaochao Zheng, International Workshop on Positrons at JLab 4/6

25 Accessing C 3q from Electron, Positron Scatterings Start from: e L,R (PV DIS) at JLab 1 GeV (two approaches) Hall A large acceptance solenoid device: PR09 01 Hall C baseline SHMS+HMS: PR (P.E. Reimer, X. Z, K. Paschke) E=11.0 GeV, E'=6.0 GeV, Q =3.3 GeV, W =7.3 GeV, x Bj =0.34 can achieve 1% (0.5% stat) on A d from 8 PAC days of 85uA 80% e beam on a 40cm liquid D target, extraction of C q, sin W Using PR kinematics, A 169ppm (~3/4 of A PVDIS d e. L e. R. d ) assuming e + luminosity is 5 times lower, can determine C 3u C 3d to +/ 0.05 (factor of 10 improvement) using 8 PAC days. Use proton target, can provide a different combination of C 3q. Problems: luminosity? systematics? two photon effects? other hadronic effects? Xiaochao Zheng, International Workshop on Positrons at JLab 5/6

26 Summary Neutral current couplings are fundamental quantities of the Standard Model. Comparison of polarized e+, e DIS cross sections can access C 3q. Xiaochao Zheng, International Workshop on Positrons at JLab 6/6