1. E04-007 STATUS REPORT Khem Chirapatpimol University of Virginia
Co-spokespersons: J. Annand, D. Higinbotham, B. Moffit,
R. Lindgren, V. Nelyubin, and B. Norum
Ph. D. students K. Chirapatpimol, M. Shabestari
and
Hall A collaboration
December 9, 2010

2. H(e,e’p)π°

4. E04-007: Threshold H(e,e’p)π° Layout
LHRS: 12.5, 14.5, 16.5, 20.5 deg
(Q2=0.045 to 0.15 GeV2)
Beam
Dump
HRS
Electron e
Snout p
BigBite: 43.5, 48, 54 deg
Flange
with special
0.003” Ti Exit
Window
MWDC (6 Planes)
Mainz
sig_T+eSig_L = mcb/sr
Sigma Total = x = mcb
L=1.35 x 10 7 Hz/mcb
Gamma = /MeV
Omega electron = 0.006
Sig_exp = Gamma x Sig_tot X Omega electron e
3 mm and 30 mm
scintillator Arrays
Luminosity
1 x 1037 Hz/cm2
Custom Helium
Bags

5. Coverage of bigbite at 1.2 GeV

6. Time of Flight

7. π° Missing Mass
Missing mass
Missing mass with background subtraction

8. π° Missing Mass For different W ∆W=0-10 MeV ∆W=10-20 MeV ∆W=20-30 MeV

9. π°Phi cm distribution for different bb angle
BB=54 deg
BB=48 deg
BB=43.5 deg

10. Preliminary result
Beam Asymmetry ALT' vs phi*
MAID
DMT

11. ALT' vs W (all Q2 data)

12. ALT' vs W for different Q2 MAID DMT ChPT Q2=0.076 Q2=0.056 Q2=0.097

13. ALT' vs cos(theta*) for different Q2

14. Mainz Data Harald Merkel 6th International Workshop on Chiral Dynamics
July
Bern, Switzerland
Q2=0.1 (GeV/c)2
Distler PRL 80, 2294 (1998)
Q2=0.05 (GeV/c)2
Merkel et al.
PRL 88, 1230 (2002)
Range of Q2 data we have
Gonna be 5-8 data point
Depend on statistic
HBChPT was fitted to old data set up to Q2=0.1

15. In Progress H- Elastics Simulation tg_th tg_ph momentum data
Different of reconstructed value of BB and expected value calculated form LHRS variables
tg_th
tg_ph
momentum
data
simulation

16. Data BB_tg_th – exp_tg_th vs BB.tr.x (vertical in lab frame)
exp_tg_th= expected tg_th calculated
from lhrs vriables
Missing mass from data(blue)
And simulation (black)

17. Still To Do Thank you Refine acceptance cuts
Improve simulation of BigBite magnet and detector resolution
BigBite wire chamber tracking efficiency
Target background subtraction
Thank you

18. Back up

19. Previous experiment

20. 0-electro production on the proton
totb
Q2=0.10 (GeV/c)2
Distler PRL 80, 2294 (1998)
LEC’s
a3 = and a4 =
Q2=0.05 (GeV/c)2
Merkel et al. PRL 88, 1230 (2002)
ChPT
Bernard, et al. NP A607,
379(1996)
MAID -----
Finally here is a comparison of the total cross section as a function of Q2 and W with ChPT predictions.
We see in all four panels even near threshold the Q2 dependence is several sigma away from the data.
The data appears to have higher power of Q2 dependence than predicted by ChPT.
Our measurements would measure this in a fine grid of 0.01(GeV/c)2 in order to determine the Q2 dependence.
A bin of 0.02/.05 is a bin that is 40% the size of the independent variable.
Large deviations between ChPT and data
Need data in a finer grid in Q2 20

21. -photoproduction on the proton Q2=0
(Unitary Cusp)
𝑔+𝑝→ 𝑝 0 +𝑝 𝑔+𝑝→ 𝑝 + +𝑛→ 𝑝 0 +𝑝 0
+n  + p p n
The figure shows the combined results of three experiments at MAMI and Saskatoon(SAL).
The importance of pion loops is shown in this almost classic example of photo production of neutral pions.
The classic LET result is -2.3 x 10-3/m. The measured value is -1.3 p/m 0.05 x 10-3/m.
The fact that this could be explained by one loop corrections was a real triumph of ChPT.
Classic LET result is -2.3 x 10-3/m. (Born terms)
Measured value is -1.3 x 10-3/m 21

22. Q2=0.10 (GeV/c)2 Q2=0.05 (GeV/c)2 0-electro production on the proton
ChPT
MAID
Fit s+p
Q2=0.10 (GeV/c)2
ChPT
Q2=0.05 (GeV/c)2
Electroproduction data on the proton has been taken at NIKHEF in 92 first by Blaine Norum and his student Pat Welch and by Brink in 97 and Mainz in 98, 02, and 03.
I will only show the data from Mainz taken with CW machines which has much smaller error bars.
This compares the T+L cross section with fits to the data from Bernard et al. These fits determine the LECs.
It also shows the quality of the fits.
Merkel et al. PRL 88, (2002)
Distler et al. PRL 80, 2294 (1998)
Fixes LEC’s
a3 = and a4 =
ChPT Bernard et al.
NP A607, 379(1996) 22

23. 0-electro production on the proton
Mianz data are from Distler PRL80 (1998) 2294 and Merkel PRL. 88 (2002)12301
AmPS NIKHEF data are from Welch PRL 69 (1992) 2761

24. 0-electro production on the proton Q2=0.05 Weis Eur. Phys. J. A 38,
From MAMI recent experiment
0-electro production
on the proton
Q2=0.05
Weis Eur. Phys. J. A 38,
27-33(2008)

25. 25

26. E04-007: Installed In Hall A BigBite Spectrometer Steel Shield Walls
1 Tesla Dipole
Hadron Detector Package

27. Side note on ChPT fitting
The detail of interaction are absorbed into parameters called Low Energy Constants(LEC’s), which obtained by measurement. Once LEC’s are determined, one can predict the evolution of cross section with Q2 and W.
The low energy effective theory known as chiral perturbation theory(ChPT), start with a Lagrangian embodying the underlying symmetries of QCD expressed in terms of the relevant degrees of freedom: the pion and nucleon.
Scattering or production processes can be described in terms of small quantities Q/M, and mπ /M.