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Bryan Moffit PAC32 Dry Run Precision Measurement of the Proton Elastic Cross Section at High Q 2 PAC32 12 GeV Proposal : PR12-07-108 Spokespersons:Bryan.

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Presentation on theme: "Bryan Moffit PAC32 Dry Run Precision Measurement of the Proton Elastic Cross Section at High Q 2 PAC32 12 GeV Proposal : PR12-07-108 Spokespersons:Bryan."— Presentation transcript:

1 Bryan Moffit PAC32 Dry Run Precision Measurement of the Proton Elastic Cross Section at High Q 2 PAC32 12 GeV Proposal : PR12-07-108 Spokespersons:Bryan Moffit (MIT) Shalev Gilad (MIT) Bogdan Wojtsekhowski (JLab) John Arrington (ANL)

2 Bryan Moffit PAC32 Dry Run Motivation Hadronic Current with internal structure Electric and Magnetic Form Factors Electron – Nucleon Scattering Fits well to Dipole form: Figure from Perdrisat et al. arXiv:hep- ph/0612014

3 Bryan Moffit PAC32 Dry Run Dipole Form Factor Vector Meson Dominance to Dispersion Relations Figures from Perdrisat et al. arXiv:hep-ph/0612014

4 Bryan Moffit PAC32 Dry Run More Models – Higher Q 2 Predictions from QCD? QCD Lagrangian: ● Nucleon Structure in terms of quark and gluon degrees of freedom GPDs: ● How does the active quark couple to the proton? Figure from 12 GeV Upgrade pCDR

5 Bryan Moffit PAC32 Dry Run More Models – Higher Q 2 Predictions from QCD? QCD Lagrangian: ● Nucleon Structure in terms of quark and gluon degrees of freedom GPDs: ● How does the active quark couple to the proton? Figure from 12 GeV Upgrade pCDR Figure from S. Ahmad et al. arXiv:hep-ph/0611046 Parametrization 1 Parametrization 2

6 Bryan Moffit PAC32 Dry Run Form Factor Scaling At high values of Q 2, asymptotic freedom [small α s (Q2)] allows for pQCD calculations. How high is that? Dimensional Scaling: Form Factors scale asymptotically as (Q 2 ) -(n- 1) n = participating valence quarks pQCD -> logarithmic departures from Q 2 dependence Figure from 12 GeV Upgrade pCDR

7 Bryan Moffit PAC32 Dry Run Form Factor Scaling At high values of Q 2, asymptotic freedom [small α s (Q2)] allows for pQCD calculations. How high is that? Dimensional Scaling: Form Factors scale asymptotically as (Q 2 ) -(n- 1) n = participating valence quarks pQCD -> logarithmic departures from Q 2 dependence Figure from 12 GeV Upgrade pCDR

8 Bryan Moffit PAC32 Dry Run Cross Section -> Form Factors Rosenbluth Separation ● Measure Cross Section at same Q 2 but different E and θ (varying є) ● At sufficiently high Q 2, G M P dominates. Figure from Qattan et al. PRL 94 (2005) 142301

9 Bryan Moffit PAC32 Dry Run Cross Section -> Form Factors Rosenbluth Separation ● Measure Cross Section at same Q 2 but different E and θ (varying є) ● At sufficiently high Q 2, G M P dominates.

10 Bryan Moffit PAC32 Dry Run This Proposal Measure Proton Elastic Cross Section at High Q 2 to high precision. Improved G M P allows for better extraction of G E P from future Polarization Transfer Experiments High Precision Cross Section important for extraction of G m n from QE measurements of the deuteron

11 Bryan Moffit PAC32 Dry Run Precision Test of FF Scaling Scaling Behavior at Q 2 ~ 7-8 GeV 2 ? What is the power of the Q2 dependence? How does GMP approach the pQCD limit?

12 Bryan Moffit PAC32 Dry Run Why at JLab? ● Availability of Beam Energy ● Similar range of ε as other JLab experiments ● Precision essential for Physics ● Readiness of Instrumentation Figure from P. Kroll arXiv:hep- ph/0612026 First three u-quark moments of Dirac form factor

13 Bryan Moffit PAC32 Dry Run Kinematics E beam Q 2 θ E' ε Hours Events ● 3 Beam Energies I = 80μA ● Both HRSs in symmetric configuration* ● 3 Redundant Q 2 ● Different ε ● 21.5 days for LH 2 ● 31 days requested * * * *

14 Bryan Moffit PAC32 Dry Run Technical Challenges ● Accurate measure and stability of beam current and energy ● Stability of target density/luminosity ● Reduced systematics w.r.t. Spectrometer acceptance – Improved analysis techniques – Some additional general use equipment

15 Bryan Moffit PAC32 Dry Run Target Configuration LH 2 : 20 cm Racetrack ● Vertical Flow Design ● Dedicated Studies of density stability ● Luminosity Monitor in datastream Solid Aluminum Foils (Dummy) ● Endcap subtraction Carbon Optics Targets ● 1-2 cm spacing along z lab for extended target optics/acceptance Solid Target / Racetrack Endcaps measured with X-ray attenuation Picture from 2005 HAPPEX- II

16 Bryan Moffit PAC32 Dry Run HRS Detector Package Main Trigger (electrons) - S2m AND Gas Cherenkov Secondary Triggers - S0 AND Gas Cherenkov - S0 AND S2m Gas Cherenkov with Lead Glass Counters - 10 4 pion rejection - 99.5% electron efficiency Additional VDC layer - Spare and on-site components - Updated/Improved VDC tracking code Figure from Hall A Webpage (modified)

17 Bryan Moffit PAC32 Dry Run Precision Angle Measurement (PAM) MSD from CMS (LHC) Electronics adaptation being evaluated by JLab DAQ group. All targets and detectors mounted to an aluminum frame - Accurate placement (~ few μm) Wire Scanners - Measure/Calibration of incoming beam angle Micro Strip Detector (MSD) - Accurate measure of scattering angle and improved HRS optics/acceptance studies Figure from Wojtsekhowski JLab TN 01-046

18 Bryan Moffit PAC32 Dry Run Systematic Uncertainties Normalizatio n Point to Point Statistics: 0.5 – 0.8% TOTAL (Scale + Rand. + Stat.) : 1.2 – 1.7 % Lower numbers indicate values estimated if PAM device functions as well as desired

19 Bryan Moffit PAC32 Dry Run Summary Precision Measurement of the Proton Elastic Cross Section at High Q 2 ● Provide additional experimental constraints for GPD and pQCD calculations ➢ Test 1/Q 4 scaling behavior and approach to pQCD limit ● Precision of σ ep and G M P will allow ➢ Better extraction of other nucleon Form Factors G E P, G M N We request 31 days to perform this measurement. THANKS!

20 Bryan Moffit PAC32 Dry Run Start of backup slides

21 Bryan Moffit PAC32 Dry Run Polarization Transfer Form Factor Extraction (Method 2): ● Polarization Transfer ● Measure components of the scattered proton polarization transferred from polarized electron Figure from Gayou et al. PRL 88 (2002) 092301 Figure from Perdrisat et al. arXiv:hep- ph/0612014

22 Bryan Moffit PAC32 Dry Run Measured G E /G M Ratio (e,e') Rosenbluth Separation (e,p) Super-Rosenbluth Polarization Transfer Figure from Qattan et al. PRL 94 (2005) 142301 Discrepancy explained by Two-Photon Exchange?

23 Bryan Moffit PAC32 Dry Run Two-Photon Exchange TPE Corrections ● Significant Є dependence ● Difficult to extrapolate from SLAC to JLab kinematics ● Does not impact σ e-p for other experiments at JLab kinematics ● Only important for G M P extraction Figure from Perdrisat et al. arXiv:hep- ph/0612014

24 Bryan Moffit PAC32 Dry Run Radiative Corrections Standard Corrections large, but well understood High Statistics -> Better Confirmation of Radiative Tail Calculations Two-Photon Corrections still quite uncertain. Large progress in calculations and experimental input to verify them. Not relevant for G E P or neutron FF extraction at JLab kinematics

25 Bryan Moffit PAC32 Dry Run Beam Energy Require use of eP and Upgrade ofArc energy methods for JLab 12 GeV Precision ~ 3-4 x 10 -4 Monitor stability and energy spread with ● OTR ● Tiefenback ● Synchotron Light Interferometer (SLI) Figure from Alcorn et al. NIM A522 (2004) Figure from Kevin Kramer Ph.D. Thesis (2003)

26 Bryan Moffit PAC32 Dry Run


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