The G0 Experiment - UMD Physics

The G0 Experiment - UMD Physics

New Results from the G0 Experiment Elizabeth Beise, University of Maryland Parity-violating electron scattering from the nucleon Hydrogen and deuterium targets Strange quark contributions to electromagnetic form factors Axial-vector N- transition Weak interaction contribution to pion photoproduction Transverse beam spin asymmetries e p e p 2 CIPANP 2009 E. Beise, U Maryland 1 Spatial distribution of s-quarks in the nucleon Access via form factors: contribution to nucleon charge and magnetism courtesy of JLab G N Electromagnetic:

G , p 2 u, p 1 d , p G G G s, p 3 3 G u , p G d ,n and use G s , p G s ,n 2 4 sin G 1 4 sin G q EM charge charge symmetry G d , p G u ,n e q q N Weak charge 1 + 4 sin2W e

1 u +2/3 1 8/3 sin2W d s 1/3 1/3 1 + 4/3 sin2W 1 + 4/3 sin2W G uE ,,Mp 3 4 sin 2 W G E ,,Mp G EZ,,Mp d,p G E ,M G Es ,,Mp CIPANP 2009 2 W 2 , p E ,M , p

W E ,M ,n Z,p G E ,M G E ,M sin2W =.2312 G E ,,Mn G EZ,,Mp E. Beise, U Maryland 2 Parity Violating elastic e-N scattering polarized electrons, unpolarized target e 2 R L GF Q AE AM AA A R L 4 2 2 unpol forward, H back, H back, D AF a1F AB a1 B A a

d 1d e.g.: G0 at 687 MeV (Q2~ 0.6 GeV2) CIPANP 2009 a2 F a2 B a2 d p e p 2 a3 F GEs a0 F s a3 B GM a0 B a3 d G Ae a0 d a0 (ppm) a1 (ppm) a2 (ppm) a3 (ppm) AF -24 80 43

3 AB -39 22 63 12 Ad -50 19 13 14 E. Beise, U Maryland 3 Axial form factor seen by PV electron scattering G Ae (Q 2 ) G AZ (Q 2 ) (FA (Q 2 ) R e ) G As (Q 2 ) e' Z 0 e

+ + (FA + Re) at Q2=0 computed by Zhu etal, PRD 62 (2000) 033008 SAMPLE deuterium asymmetry data agree well but Q2 behavior is not well constrained CIPANP 2009 E. Beise, U Maryland 4 Summary of data at Q2 =0.1 GeV2 Solid ellipse: K. Pashke, private comm, [same as J. Liu, et al PRC 76, 025202 (2007)], uses theoretical constraints on the axial form factor Dashed ellipse: R. Young ,et al. PRL 97 (2006) 102002, does not constrain GA with theory note: Placement of SAMPLE band on the graph depends on choice for GA 2007 Long Range Plan s GE,M

1 % contrib p 100 GE,M 3 CIPANP 2009 (thanks to K. Pashke, R. Young) E. Beise, U Maryland 5 New Results from PVA4 S. Baunack et al., PRL 102 (2009) 151803 Q2 = 0.22 GeV2= 145 Ameas= 17.23 0.82 0.89 ppm Anvs = 15.87 1.22 ppm (uses theoretical constraint of Zhu et al., for the axial FF) GEs 0.050 0.038 0.019 GMs 0.14 0.11 0.11 % contribution to proton: electric: 3.0 2.5 % magnetic: 2.9 3.2 % Wang, et al. (arXiv:0807.09442), 1.8 1.1 % CIPANP 2009 E. Beise, U Maryland 6 Quasielastic PV (ee) in Deuterium Use Quasielastic scattering from deuterium as lever arm for Ad

GAe(Q2) p Ap n An d Parity conserving nuclear corrections to the asymmetry are generally small, 1-3% at backward angles. Calculation provided to us by R. Schiavilla includes final state interactions and 2-body effects. Diaconescu, Schiavilla + van Kolck, PRC 63 (2001) 044007 Schiavilla, Carlson + Paris, PRC 67 (2003) 032501 See also Hadjimichael, Poulis + Donnelly, PRC45 (1992) 2666 Schramm + Horowitz, PRC 49 (1994) 2777 Kuster + Arenhovel, NPA 626 (1997) 911 Liu, Prezeau, + Ramsey-Musolf, PRC 67 (2003) 035501 CIPANP 2009 E. Beise, U Maryland 7 2-body effects in the D asymmetry calculations from R. Schiavilla, see also R.S., J. Carlson, and M. Paris, PRC70, 044007 (2004). leading term of the asymmetry axial form factor coefficient has ~15% correction from 2-body effects CIPANP 2009

E. Beise, U Maryland 9 Jefferson Laboratory G0 A C upgrade to 12 GeV now underway E ~ 6 GeV Continuous Polarized Electron Beam > 100 A up to 85% polarization concurrent to 3 Halls CIPANP 2009 E. Beise, U Maryland 10 The G0 experiment at JLAB Forward and backward angle PV e-p elastic and e-d (quasielastic) in JLab Hall C G s , G s and G e separated E superconducting toroidal magnet M A

over range Q 2 ~ 0.1 1.0 (GeV/c)2 scattered particles detected in segmented scintillator arrays in spectrometer focal plane custom electronics count and process scattered particles at > 1 MHz forward angle data published 2005 backward angle data: 2006-2007 CIPANP 2009 E. Beise, U Maryland 11 One octants scintillator array G0 Apparatus 20 cm LH2 Target CIPANP 2009 E. Beise, U Maryland 12 G0 Forward angle Results 2 2

4 2 GEp GMp s s Aphys ANVS G E GM 2 p (0) GF Q GE 1 RV EM form factors: J.J.Kelly, PRC 70, 068202 (2004) G0 Backward J. Liu, Univ Maryland 2006 JLab Thesis Prize HAPPEX-3 D.S. Armstrong et al., PRL 95 (2005) 092001 CIPANP 2009 E. Beise, U Maryland 13 G0 Backward Angle Electron detection: = 108, H and D targets Add Cryostat Exit Detectors (CED) to define electron trajectory Aerogel Cerenkov detector for /e separation (pe separation (p < 380 MeV/e separation (pc) 1 scaler per channel FPD/e separation (pCED pair (w/e separation (p and wo/e separation (p CER) Ee (MeV)

Q2 (GeV2) 362 0.23 687 0.62 Both H and D at each kinematic setting Common Q2 with HAPPEX-III and PVA4 CIPANP 2009 E. Beise, U Maryland 14 Summary of the G0 Backangle Run Run Coulombs Hours Gbytes data H 687 86 400 600

H 362 119 550 825 D 362 66 520 800 D 687 I 40 520 780 D 687 II 15 240 340 total 330 2300

3450 Run start to run end ~ 8940 hours! Beise Run Coordinator report March 2007 We measured an asymmetry in detected rate when the beam helicity flips: Y1 Y4 Y2 Y3 A ; 1,4 "" 2,3 " " Y1 Y2 Y3 Y4 (14 FPDs x 9 CEDs x 2 CER states x 8 octants) We measured 2,000 asymmetries 15 times per second In 2400 hours, we measured 250 billion asymmetries (or, each asymmetry is measured 13 million times) Beise Run Coordinator report, March 2007 Hydrogen raw electron data d 362 MeV octant # (azimuthal distribution) E. Beise, U Maryland 687 MeV 18 Hz/uA Hz/uA CIPANP 2009

Deuterium raw electron data d d 362 MeV octant # (azimuthal distribution) E. Beise, U Maryland 687 MeV 19 Hz/uA Hz/uA CIPANP 2009 Analysis Strategy Blinding Factors H, D Raw Asymmetries, Ameas ~10-50 ppm 0.75-1.25 4% on asymmetry Electromagnetic radiative corrections (from simulation) Q2 Determination (from simulation)

0.003 GeV2 CIPANP 2009 Corrections Scaler counting correction Rate corrections from electronics Helicity-correlated corrections Background corrections Beam polarization < 1% of Aphys < 0.1 ppm P= 0.8578 0.0007 (stat) .014 (sys) Unblind H, D Physics Asymmetries, Aphys s E s M G ,G ,G e A E. Beise, U Maryland Other measurements A(Ei , Q2) 20 Rate Corrections

Correct the yields for random coincidences and electronic deadtime prior to asymmetry calculation Deadtimes (%) H 687 MeV randoms small except for D-687 (due to higher pion rate) Direct (out-of-time) randoms measured Validated with simulation of the complete electronics chain Data set Correction to Yield (%) Asymmetry systematic Correction error (ppm) (ppm) H 362 6 0.3 0.06 H 687 7 1.4 0.17 D 362 13 0.7

0.2 D 687 9 6 1.8 CIPANP 2009 E. Beise, U Maryland H 362 MeV 21 Backgrounds: Magnetic Field Scans D-687 CED 7, FPD 13 Use simulation shapes to help determine dilution factors Main contributions are Aluminum windows (~10%), pions (for D-687 data only). CIPANP 2009 Data set Asymmetry Correction (ppm) systematic error (ppm)

H 362 0.50 0.37 H 687 0.13 0.78 D 362 0.06 0.02 D 687 2.03 0.37 E. Beise, U Maryland 22 Experimental Physics Asymmetries all entries in ppm Data Set Asymmetry Stat Sys pt

H 362 -11.42 0.84 0.26 R O F D 362 -17.02 0.79 0.39 T O N H 687 -46.14 RY 2.36 0.80 A N I M I -55.87 L DE 687 3.22 1.91 R P N O

I T A T O QU0.37 Global 0.19 0.72 0.62 Largest correction is due to the 85% beam polarization H: systematic uncertainties dominated by beam poln D-687: rate corrections and beam poln contribute about equally to the systematic uncertainty CIPANP 2009 E. Beise, U Maryland 23 Asymmetries to Form Factors Aphys a0 aE GEs aM GMs a AGAe Electromagnetic form factors: Kelly (PRC 70 (2004)) also used in Schiavilla calculation for D does not include new low Q2 data from BLAST or JLab eventually use new fits (Arrington & Melnitchouk for p, Arrington & Sick for n) differences in fits become 0.5 1 % in the asymmetry Two-boson exchange corrections to Asymmetry: 0.5 -1.2% (see Tjon, Blunden & Melnitchouk, arXiv:0903.2759v1) includes D contributions, calculation for n in progress Ameas 1 ABorn CIPANP 2009

1 Z Z 1 E. Beise, U Maryland ABorn 24 Form Factor Results PR Using interpolation of G0 forward measurements EL IM IN AR Y NO TF OR Global Quncertainties UO TA TIO G0 forward/e separation (pbackward PVA4: PRL 102 (2009) Q2 = 0.1 GeV2 combined (G0,HAPPEX, SAMPLE & PVA4)

G0 forward/e separation (pbackward SAMPLE Zhu, et al. PRD 62 (2000) CIPANP 2009 Some calculations: Leinweber, et al. PRL 97 (2006) 022001 Leinweber, et al. PRL 94 (2005) 152001 Wang, et al arXiv:0807.0944 (Q2 = 0.23 GeV2) Doi, et al, arXiv:0903.3232 E. Beise, U Maryland N 25 Anapole form factor FA(Q2) Three scenarios 1. FA(Q2) is like GA(Q2) 2. FA(Q2) is flat (Riska, NPA 678 (2000) 79) 3. FA(Q ) ~ 1 + Q (Maekawa, Viega, van Kolck, PLB 488 (2000) 167) (shown here are the most 2 2 I M I

L E PR Y R A N R O F T NO N O I AT T O U Q extreme set of model parameters) CIPANP 2009 E. Beise, U Maryland 26 Summary Q2 behavior of strangeness contribution to protons charge and magnetism: continue to be small first results for the Q2 behavior of the anapole contributions to the axial form factor

other results to come soon from G0: transverse beam spin asymmetries (2- exchange) in H and D PV in the N- transition: axial transition f.f. PV asymmetry in inclusive production CIPANP 2009 E. Beise, U Maryland 27 The G0 Collaboration (backward angle run) Caltech, Carnegie Mellon, William and Mary, Hendricks College, Orsay, Grenoble, LA Tech, NMSU, Ohio, JLab, TRIUMF, Illinois, Kentucky, Manitoba, Maryland, Winnipeg, Zagreb, Virginia Tech, Yerevan Physics Institute PhD students: C. Capuano, A. Coppens, C. Ellis, J. Mammei, M. Muether, J. Schaub, M. Veerstegen, S. Bailey Analysis Coordinator: F. Benmokhtar CIPANP 2009 E. Beise, U Maryland 28

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