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

H(e,e’p)π°

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 = 0.012 mcb/sr Sigma Total = 12.56 x 0.012 = 0.150 mcb L=1.35 x 10 7 Hz/mcb Gamma = 0.0000220/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

Coverage of bigbite at 1.2 GeV

Time of Flight

π° Missing Mass Missing mass Missing mass with background subtraction

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

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

Preliminary result Beam Asymmetry ALT' vs phi* MAID DMT

ALT' vs W (all Q2 data)

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

ALT' vs cos(theta*) for different Q2

Mainz Data Harald Merkel 6th International Workshop on Chiral Dynamics July 6-10 2009 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

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

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)

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

Back up

Previous experiment

0-electro production on the proton totb Q2=0.10 (GeV/c)2 Distler PRL 80, 2294 (1998) LEC’s a3 = - 0.92 and a4 = - 0.99 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

-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

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, 12301 (2002) Distler et al. PRL 80, 2294 (1998) Fixes LEC’s a3 = - 0.92 and a4 = - 0.99 ChPT Bernard et al. NP A607, 379(1996) 22

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

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)

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

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.