# Presentation: 215342

## Results from the       Forward Angle Experiment  a Measurement of Strange EM Form Factors of the Nucleons

**Results from the       Forward Angle Experiment ******** a Measurement of Strange EM Form Factors of the Nucleons**

**For the G****0**** Collaboration:**

**JLab E-00-006, D.H. Beck, spokesperon**

-  ***    ******Jianglai Liu***
***Univ. of Maryland***

**PANIC05, Santa Fe, NM Oct 24-28, 2005**

**Caltech, Carnegie-Mellon, William&Mary, Grinnell College, Hampton, IPN-Orsay, LPSN-Grenoble, JLab, Kentucky, LaTech, NMSU, TRIUMF,  UIUC, U Manitoba, U Maryland, UNBC, U Winnipeg, VPI, Yerevan **

## Flavor Decomposition of Nucleon Form Factors

**Assume charge symmetry**

**Strange quark E/M form factors**

- But how do we measure the GZ ????

**Proton and Neutron Electromagnetic Form Factors**

**Proton Weak Form Factors :**

## Parity Violation in the Elastic Electron Scattering

**kinematic factors**

**forward ep**

**backward ep**

**backward ed**

**Assuming EM and axial form factors are known (with errors), each measurement yield G****E****s****+********G****M****s**** where **

## G0 Forward Angle Experiment

- LH2 target, detect recoil protons
*Q**2* = 0.12-1.0 (GeV/c)2, E=3.03GeV
- Spectrometer sorts protons by Q2 in focal plane detectors (16 rings in total)
- Detector 14 acceptance: Q2 = 0.41,1.0
- Detector 15: Q2 = 0.44-0.88
- Detector 16: “super-elastic”, crucial for measuring the background
- Time-of-flight separates protons from pions
- Beam bunches separated by 32 ns
- Forward angle measurment completed May 04

## Analysis Overview

**Blinding Factor**

**Analysis Overview**

**Raw Asymmetries, ****A****meas**

_**Beam and instrumental corrections**_**:**
**Deadtime**
**Helicity-correlated beam properties**
**Leakage beam**
**Beam polarization**

**Background correction**

**Q****2**

**nucleon form factors**

**Unblinding**

**G****E****s****+********G****M****s**

## 499MHz Leakage Beam

**Use “cut0” region in actual data to measure leakage current and asymmetry throughout run. Worked out nicely.**

**~ 50 nA 499 MHz beam leaks into G****0**** beam (~ 40 uA)**
**Leakage current has large, ****varying asymmetry**** ****(*****A***** ****~ 600 ppm)****.**

******A****leak**** = -0.71********0.14 ppm (global uncertainty!)**

**BCM integrates charge, no sensitivity to the micro-structure!**

## Background Correction     Yield & Asymmetry “2-step” Fit

- Extract bin-by-bin dilution factor *f*b(t) by fitting time-of-flight spectra (gaussian signal + 4nd order polynomial background)
- Use results to perform asymmetry fit:** ****	****	****	****	****	****A****e**** = const, A****b**** = quadratic**

- 2/=31.1/40

- 2/=37.5/44

- detector 8

## Det. 15 Background Corrections

- Elastic peak broadened (~6 ns) because of increased Q2 acceptance.
- Smooth variation of the background yield and asymmetry over detector range 12-14, 16. So make linear interpretation over detector number to determine fb(t) and Ab(t).

-  GEANT MC: background asymmetry arises from hyperon (0,+,0) weak decay-particles rescatter into the detectors.

## Elastic Asymmetries

- “No vector strange” asymmetry, **A****NVS**, is **A(G****E****s****,G****M****s**** = 0)**
- Nucleon EM form factors: ***Kelly PRC 70 (2004) 068202***
- Inner error bars: stat; outer: stat & pt-pt sys

- Primary contributors to the global error band:
-  Leakage correction (low Q2)
-  background correction (high Q2)

## GEs+GMs, Q2 = 0.12-1.0 GeV2

- A ******2** test based on the random and correlated errors: the non-vector-strangeness hypothesis is disfavored at 89%!

**“****Model” uncertainty is the EW rad. corr. unc. Dominated by the uncertainty of G****A****e****.**
-  **3 nucleon form factor fits; spread indicate uncertainties.**
***   ***
***|Kelly-FW| *****heavily driven by the difference in G****E****n****.**

## World Data with G0

- Q2=0.1 GeV2

- Q2=0.48 GeV2

- 95.5% CL

**Strange quark contributes to ********p**** at -10% level.**

## Speculations of the Q2 dependence of GEs & GMs

- Emerging picture:
-  **At low Q****2**** end, despite the small ********, the data are positive, consistent with a large and positive G****M****s****.**
** ****Data go toward zero around Q****2****~0.2, which suggests ****G****E****s**** might have a negative bump there. **
**  ****Data curve back up again for Q****2****>0.3 (note the growing ********), indicating that G****M****s**** stays positive.**

**Speculations of the Q****2**** dependence of G****E****s**** & G****M****s**

**For G****0****, ******** increases with Q****2**

## Summary

- The successful G0 forward angle experiment yield the first measurement of parity-violating asymmetries over broad Q2 range. *PRL ****95****, 092001(2005)*
- World data: GMs and GEs are both likely nonzero
**G****M****s**** large and positive at low Q****2**
**G****M****s**** might decrease with Q****2****, but stay positive up to Q****2****=1.0 (GeV/c)****2**
**G****E****s**** might have a negative bump at Q****2****~0.2 (GeV/c)****2**
- G0 H2/D2 backward angle runs in 2006 will enable a separation of **G****E****s**, **G****M****s**, and **G****A****e** ... Stay tuned.

**We gratefully acknowledge the support from our funding agencies and the strong technical support from TJNAF and many other groups ....**

***Doug Beck’s plenary talk (10 am, Oct 26): Overview of strangeness of the nucleon.***

## Backup Slides

## The G0 Collaboration

-  **D.S.Armstrong****1****, J.Arvieux****2****, R.Asaturyan****3****, T.Averett****1****, S.L.Bailey****1****, ****G.Batigne****4****, ****D.H.Beck****5****, E.J.Beise****6****, J.Benesch****7****, L.Bimbot****2****, J.Birchall****8****, ****A.Biselli****9****, P.Bosted****7****, E.Boukobza****2,7****, H.Breuer****6****, R.Carlini****7****, R.Carr****10****, N.Chant****6****, Y.-C.Chao****7****, S.Chattopadhyay****7****, ****R.Clark****9****, ****S.Covrig****10****, A.Cowley****6****, D.Dale****11****, C.Davis****12****, W.Falk****8****, J.M.Finn****1****, T.Forest****13****, G.Franklin****9****, C.Furget****4****,D.Gaskell****7****, J.Grames****7****, K.A.Griffioen****1****, ****K.Grimm****1,4****,****B.Guillon****4****, ****H.Guler****2****, ****L.Hannelius****10****, R.Hasty****5****, ****A. Hawthorne Allen****14****, T.Horn****6****, K.Johnston****13****, M.Jones****7****, P.Kammel****5****, R.Kazimi****7****, ****P.M.King****6,5****, A.Kolarkar****11****, E.Korkmaz****15****, W.Korsch****11****, S.Kox****4****, ****J.Kuhn****9****, J.Lachniet****9****, L.Lee****8****, ****J.Lenoble****2****, E.Liatard****4****, ****J.Liu****6****, B.Loupias****2,7****, ****A.Lung****7****, ****G.A.MacLachlan****16****, D.Marchand****2****, ****J.W.Martin****10,17****, K.W.McFarlane****18****, ****D.W.McKee****16****, R.D.McKeown****10****, F.Merchez****4****, H.Mkrtchyan****3****, B.Moffit****1****, M.Morlet****2****, ****I.Nakagawa****11****, ****K.Nakahara****5****, M.Nakos****16****, ****R.Neveling****5****, ****S.Niccolai****2****, S.Ong****2****, S.Page****8****, V.Papavassiliou****16****, S.F.Pate****16****, ****S.K.Phillips****1****, M.L.Pitt****14****, M.Poelker****7****, T.A.Porcelli****15,8****, G.Quéméner****4****, B.Quinn****9****, W.D.Ramsay****8****, ****A.W.Rauf****8****, J.-S.Real****4****, ****J.Roche****7,1****, ****P.Roos****6****, ****G.A.Rutledge****8****, ****J.Secrest****1****, N.Simicevic****13****, G.R.Smith****7****, ****D.T.Spayde****5,19****, S.Stepanyan****3****, M.Stutzman****7****, V.Sulkosky****1****, V.Tadevosyan****3****, ****R.Tieulent****4****, J.van de Wiele****2****, W.van Oers****8****, E.Voutier****4****, W.Vulcan****7****, G.Warren****7****, S.P.Wells****13****, S.E.Williamson****5****, S.A.Wood****7****, C.Yan****7****, ****J.Yun****14**
**1****College of William and Mary, ****2****Institut de Physique Nucléaire d'Orsay,**
**3****Yerevan Physics Institute, ****4****Laboratoire de Physique Subatomique et de Cosmologie-Grenoble, ****5****University of Illinois, ****6****University of Maryland, ****7****Thomas Jefferson National Accelerator Facility, ****8****University of Manitoba, ****9****Carnegie Mellon University, ****10****California Institute of Technology, ****11****University of Kentucky, ****12****TRIUMF, ****13****Louisiana Tech University, ****14****Virginia Tech, ****15****University of Northern British Columbia, ****16****New Mexico State University, ****17****University of Winnipeg, ****18****Hampton University, ****19****Grinnell College**

## G0 in Hall C

- G0 in Hall C

**beam**
**monitoring **
**girder**

**superconducting  magnet**
**              ****(SMS)**

**scintillation detectors**

**cryogenic supply**

**cryogenic target service module**

**electron beamline**

**Lumi monitors**

## Beam Performance

**Beam Performance**

**All parameters converge to zero!**

| AQ (ppm) | -0.14 |
| --- | --- |
| x (nm) | 3 ± 4 |
| y (nm) | 4 ± 4 |

## Electronics Deadtime Corrections

- To the first order

***This shows up as ***
***a decrease of normalized yield with I******beam****** (almost like a target density reduction)***
***a correlation between A******m****** and A******Q***** .**

-  The DT effect is largely corrected based on the model of the electronics
-  The residual **A****Q** correlation is removed by the linear regression
-  The final residual Aphys dependence is corrected based on Aphys and fresidual (~0.050.05 ppm).

## Helicity Correlated Beam Properties 		and Their Corrections

- So require

-   Small ΔPi
-  _Small sensitivity to P__i_

- Azimuthal symmetry  large reduction of detector sensitivity to beam positions
- Response of spectrometer to beam changes well understood
- False asymmetries (and the uncertainty) due to helicity-correlated beam parameters very small (~-0.02 ppm)

## Results of the Hyperon Simulation

**Results of the Hyperon Simulation**

- Source explained; used measured data in the correction.

- Use KaonMAID as generator for 0,+, 0

**Hyperon polarizations:**

## Detector 15 Asymmetry

- Compare interpolated background asymmetry and data

- Assume elastic asymmetry in each bin is a constant. Take interpolated **f****b**** and A****b**, fit three **A****e**.

## Summary of Systematic Effects

| Source | Uncertainty |
| --- | --- |
| Electronics deadtime | 0.05 ppm |
| Helicity-correlated differences in beam properties | 0.01 ppm |
| 499 MHz (2 ns) leakage beam | 0.14 ppm |
| Beam polarization (Hall C Møller) | 1 % |
| Transverse beam polarization | 0.01 ppm |
| Inelastic background subtraction | 0.2-9 ppm |
| Radiative corrections | 0.3 % |
| Detector Q2 | 1 % |

## Global Fits to World Data

**à**** la Kelly**

**Toy model, minimal physics input**

**dipole form**

** ****Kelly form ensures ****G****E****s****(0)=0, G****E****s********1/Q****4**** when Q****2**** large **
** ****Fixed ****b****3**** = 1****, all other variables float**
** ****Fit all 24 data points: 18 G****0****, 3 HAPPEX, 2 A4, 1 SAMPLE**

## Results of the fit

**Results of the fit**

***Excellent fit***
*********2****** = 14.9***
***19 d.o.f.***

_***Correlation Coeff.***_

## GEs and GMs Separately

-  **Compare G****E****s**** with G****E****n****, and G****M****s**** with G****M****p**
** ****Remember the factor of ****-1/3****   **

**G****E****s**** and G****M****s**** Separately**

***-1/3************s******/************p****** = -18%***

***-1/3G******E******s******(0.2)/G******E******n******(0.2)~40%***