Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report...

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Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near Threshold: A Test of Chiral QCD Dynamics Hall A Collaboration Meeting June 13,14 2013

Transcript of Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report...

Page 1: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Richard Lindgren - UVaCole Smith - UVa

Khem Chirapatimol - Chiang Mai University

E04- Status Report

Precision Measurements of π0 Electroproduction near Threshold: A

Test of Chiral QCD Dynamics

Hall A Collaboration MeetingJune 13,14

2013

Page 2: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

• Reaction H(e,e’p)π0 E=1192.38 MeV, 6 cm H target

• Measure pi0 absolute cross section from W= threshold up to 28 MeV in 1 MeV bins and Q2 from 0.05 to 0.15 (GeV/c)2 in bins of 0.015 (GeV/c)2

• Detect electron in HRSat 12.5,14.5,16.5, and 20.5 degree

Detect proton in BigBite at 43.5, 48, and 54 degrees. Cut on Missing mass Identifies pi0

• Extract four structure functions from pion CM theta and phi dependence. Use to test predictions of low energy Chiral based effective theories

Page 3: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Since Last Collaboration Meeting• Khem Chirapatimol at Chiang Mai University, Thailand.

Continuing data analysis on JLab computers• Weekly Skype Meetings • New and improved optimized optics data base for HRS

using our hydrogen sieve data.• Preliminary Results appearing in JLab 2012 Chiral

Dynamics Workshop Proceedings• Preliminary paper available without systematic errors• U. Meissner reaffirms intention to extend HBChPT

electroproduction calculation after seeing our data

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CD2012 Workshop Manuscript Preliminary Letter

Page 5: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

• Chiral Perturbation Theory (ChPT): Low energy effective theory based on spontaneous breaking of chiral symmetry in QCD.

• Long range degrees of freedom: Mesons and baryons

• Short distance physics encapsulated into Low Energy Constants (LECs) fitted to experiment.

• Precision measurement of (Q2,W) evolution of p(e,e’p)πo

reaction near threshold can test validity of low energy expansion once LECs are fixed.

• Total cross section, polarization observables, EM multipoles.

Chiral Dynamics Important Low Energy Theory

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Page 6: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Electroproduction Data: MAMI

Q2 = 0.10: Distler et al. PRL 80, 2294 (1998)Q2 = 0.05: Merkel et al. PRL 88, 1230 (2002)

2002

Q2 = 0.05 - 0.15: Merkel et al. arXiv:1109.5075

Theory: RChPT, Marius Hilt, Bosen 2011 HBChPT (1996) MAID

Conflicting measurements require more extensive data set

2009

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Page 7: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Analysis Goals• Extract total cross section for comparison with Mainz

data and models listed below.• Extract 4 structure functions for each W and Q2 point

using measured φ* distributions and compare with previous MAMI experiments and HBChPT, MAID07, DMT , Chiral-MAID, and SAID calculations.

• Extract model independent partial wave content of structure functions using Legendre polynomial fits (assume s,p-wave dominance.)

• Perform model dependent fits to estimate electromagnetic multipoles, needed for precise comparison to models.

• Extract beam asymmetry for comparison with Imaginary part of s wave

Lets focus on our total cross section results

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Page 8: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Q2 Dependence of σTOT from ΔW=0.5 to 7.5 MeV

Q2 < 0.10 (GeV/c)2 : Our σtot data agrees with HBChPT (BKM96) in the range 0.5 < ΔW < 4.0 MeVQ2 > 0.10 (GeV/c)2 : Our σtot falls off faster in Q2 than predicted by HBChPT, shows better agreement with new 4th order relativistic theory of M. Hilt (ChMAID).HBChPT may require non-higher order calculation. Meissner has agreed to extend HBChPT in electroproduction to 4th order

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Page 9: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

How does systematic errors on the electron arm affect our results

• We used a non-optimized HRS optics data set for our experiment. Since then, we have optimized the HRS optics and I’ll show the difference.

• We are also worried about mis-calibration of the energy/momentum and how it would affect total cross section near threshold. We did find unexplained changes in beam energy

• Effects on total cross section due to angle shifts in HRS vertical and horizontal seem to be negligible compared to other systematic errors. Only 1-3% on threshold cross section.

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Page 10: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

E05-102 Multi-foil C (Ge Jin)

E04-007 LH2 sieve run 6 cm target

beginnning of exp and also at end.

Non-optimized

Optimized

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Page 11: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Carbon Elastic Cross Sections

Cross section is sensitive to pointing errors, but not so much to energy calibration.

Fourier-Bessel fit to NIKHEF-K data taken from Offermann et al. and recalculated for E=1.192 GeV using DWBA phase-shift code from J. Heisenberg (R. Lindgren).

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Page 12: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Before beam correction After beam correction

Projected elastic W from for each sieve slit hole using Hydrogen target for Run 2147.Vertical line is expected position for hydrogen elastic.

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Page 13: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Tantalum RedCarbon BlackHydrogen Blue

Fitted centroids of elasticpeaks of all Ta, C and LH2 calibration runs. Note W errors seem to not depend on target mass.

Corresponding correctionto beam energy required to center elastic peaks.

Study of Systematics of Invariant Mass (W)

ΔW (GeV) vs Run No.

ΔEbeam (GeV) vs Run No.

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Page 14: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Effect on Total Cross Section Due to Shift in Momentum Calibration

- HBChPT

- DMT

- MAID07 JLAB 2012 220 keV shift in W JLAB 2012 Nominal W calibration

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Page 16: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

SummaryFirst• Replay data using new HRS data base optimized using our

hydrogen target data. Create DSTs for fast replay at UVA.• Finalize total cross section data for paper• Estimates of systematic errors on cross section and Q2 due to

W mis-calibration and possible incorrectly reconstructed angles at edges of acceptance are basically known.

• Complete and circulate PRL paper

Second• Must go back and look at BigBite arm systematic errors for

angular distribution measurements. Prepare long paper.• Large data set with unprecedented W, Q2 , C.M. coverage and

many available chiral theories to test. Prepare long paper.

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Page 17: Richard Lindgren - UVa Cole Smith - UVa Khem Chirapatimol - Chiang Mai University E04- Status Report Precision Measurements of π 0 Electroproduction near.

Comparison with MAMI 2011 MeasurementJLAB 2012

E=1.192 GeV ε=0.943

MAMI 2011E=0.880

GeVε=0.882

MAMI 2011 H. Merkel et al., arXiv:1109.5075v1 [nucl-ex]. 17

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