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ECT* Workshop on the Proton Radius Puzzle ECT* Workshop on the Proton Radius Puzzle Book of Abstracts October 29 - November 2, 2012 Trento, Italy October 8, 2012 A. Afanasev R.J. Hill J. Arrington M. Kohl J.C. Bernauer I.T. Lorenz A. Beyer J.A. McGovern E. Borie G.A. Miller M.C. Birse K. Pachucki P. Brax G. Paz J.D. Carroll R. Pohl C.E. Carlson M. Pospelov M.O. Distler B.A. Raue M.I. Eides S.S. Schlesser K.S.E. Eikema I. Sick A. Gasparian R. Gilman K.J. Slifer M. Gorchtein D. Solovyev K. Griffioen V. Sulkosky N.D. Guise A. Vacchi E.A. Hessels I. Yavin A. Afanasev Radiative corrections and two-photon effects for lepton-nucleon scat- tering J. Arrington Extracting the proton radius from low Q2 electron/muon scattering J.C. Bernauer The Mainz high-precision proton form factor measurement I. Overview and results A. Beyer Atomic Hydrogen 2S-nP Transitions and the Proton Size E. Borie Muon-proton Scattering M.C. Birse Issues with determining the proton radius from elastic electron scat- tering P. Brax Atomic Precision Tests and Light Scalar Couplings C.E. Carlson New Physics and the Proton Radius Problem J.D. Carroll Non-perturbative QED spectrum of Muonic Hydrogen M.O. Distler The Mainz high-precision proton form factor measurement II. Basic principles and spin-offs M.I. Eides Weak Interaction Contributions in Light Muonic Atoms K.S.E. Eikema XUV frequency comb spectroscopy of helium and helium+ ions A. Gasparian A Novel High Precision Measurement of the Proton Charge Radius via ep Scattering Method R. Gilman JLab Experiment E08-007: Proton Electromagnetic Form Factor Ra- tio at Low Q2 M. Gorchtein Hadronic contributions to Lamb shift in muonic deuterium K. Griffioen Howwellcananuclearchargeradiusbemeasuredwith low-Q2 electron scattering data? N.D. Guise Towards One-electron Ions in Rydberg States for a Rydberg Constant Determination Independent of the Proton Radius E.A. Hessels Progress towards a new separated-oscillatory-field microwave measure- ment of the atomic hydrogen n=2 Lamb shift R.J. Hill Model independent analysis of proton structure for hydrogenic bound states M.Kohl TheOLYMPUSexperimentatDESY I.T. Lorenz The size of the proton - closing in on the radius puzzle J.A. McGovern Proton polarisability contribution to the Lamb shift in muonic hydro- gen at fourth order in chiral perturbation theory G.A. Miller Proton Polarizability Contribution: Muonic Hydrogen Lamb Shift and Elastic Scattering K. Pachucki Directions toward the resolution of the proton charge radius puzzle G. Paz Model independent extraction of the proton charge radius from elec- tron scattering R. Pohl Lamb shift and hyperfine splitting in muonic hydrogen and deuterium M. Pospelov Extension of the Standard Model by muon-specic forces B.A. Raue Measurement of Two Photon Exchange effects in electron-proton elas- tic scattering S.S. Schlesser Nuclear polarizability contribution to the Lamb shift in muonic helium I.Sick Protonrms-radiusandtailofdensity p K.J.Slifer TheJeffersonLab g2 Experiment D. Solovyev Multiphoton processes in atomic physics and astrophysics V. Sulkosky Elastic µp Scattering at the Paul Scherrer Institute A. Vacchi Towards a measurement of the 1S hyperfine splitting in muonic hy- drogen I. Yavin Muonic hydrogen and MeVforces Extracting the proton radius from low Q2 electron/muon scattering John Arrington Physics Division, Argonne National Lab While electron scattering is the tool of choice for extracting nucleon form factors, there are several things which must be accounted for in extracting the form factors from scattering cross sections or asymmetry measurements. Further issues arise in obtaining charge and magnetic radii from the extracted form factors. I will discuss some these issues, focusing on experimental uncertainties, fitting proce- dures, and the impact of two-photon exchange and Coulomb distortion. These will be discussed in the context of the recent JLab extraction of the proton charge and magnetic radii, the differences between various electron scattering extractions, and projections for future measurements. In addition, I will present some new investigations into the impact of two-photon exchange and Coulomb corrections on the extraction of the charge radius. The Mainz high-precision proton form factor measurement I. Overview and results Jan C. Bernauer for the A1 Collaboration Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany. Present address: Laboratory for Nuclear Science, MIT, Cambridge, MA 02139, USA. Abstract. Form factors offer a direct approach to fundamental properties of the nucleons like the radius and charge distribution. In the talk, precise results from a measurement of the elastic electron-proton scattering cross section performed at the Mainz Microtron MAMI will be presented. About 1400 cross sections were measured with negative four-momentum transfers squared up to Q2 = 1(GeV=c)2 with statistical errors below 0.2%. The electric and magnetic form factors of the proton were extracted with fits of a large variety of form factor models directly to the cross sections. The charge and magnetic radii are determined to be 1 2 2 rE = 0:879(5)stat:(4)syst:(2)model(4)group fm; 1 2 2 rM = 0:777(13)stat:(9)syst:(5)model(2)group fm; strengthening the discrepancy between determinations using electronic and muonic systems. We extended the data set with the world data from unpolarized and polarized scattering ex- periments, which were updated to the same level of radiative corrections. A phenomenological model for two-photon-exchange contributions is used to account for the discrepancy between the results from unpolarized and polarized scattering experiments. A continuous, simultaneous fit up to Q2 = 10(GeV=c)2 is achieved. Atomic Hydrogen 2S-nP Transitions and the Proton Size Axel Beyera;∗, Arthur Matveeva, Christian G. Partheya, Janis Alnisa, Randolf Pohla, Nikolai Kolachevskya, Thomas Udema and Theodor W. H¨anscha;b a Max Planck Institute of Quantum Optics, 85748 Garching b Ludwig Maximilian University, 80799 Munich ∗ [email protected] The 'proton size puzzle', i.e. the discrepancy between the values for the proton charge radius extracted from precision spectroscopy of atomic hydrogen and electron-proton- scattering on the one hand [1] and the 2S Lamb shift measurement in muonic hydrogen on the other [2], attracted great interest both of experimentalists and theoreticians for the last two years. Still, no convincing argument to explain or resolve this discrepancy could be found so far. Transition frequency measurements in atomic hydrogen with improved accuracy can help to solve this puzzle or at least to rule out hydrogen experiments as a possible source for the discrepancy. Furthermore, as soon as the puzzle will be resolved and a more accurate value for rp will be available, these measurements can provide stringent tests to bound state QED calculations utilizing the new rp value. In this talk we report on the setup which has been developed for the measurement of the one-photon 2S-4P transition frequency in atomic hydrogen: In contrast to previous measurements of 2S-nl transitions in other groups, our experiment is based on a cold thermal beam of hydrogen atoms optically excited to the metastable 2S state. The setup for the 2S excitation is the same as has successfully been used for the measurement of the 1S-2S transition frequency in our group and provides a reliable and well controlled source of 2S atoms [3]. In addition, the experiment benefits from technical advances, such as subhertz line width diode lasers both for 1S-2S and 2S-4P spectroscopy [4] or direct measurement of the absolute transition frequency via a frequency comb, which have not been available for older measurements. During 13 measurements days a total number of 11,652 individual line profiles for the 2S1=2-4P1=2 transition have been recorded, including 6 different velocity distributions of 2S atoms. The resulting statistical uncertainty of 0.8 kHz is more than one order of magnitude smaller than the one of the previous best measurement of this transition [5]. The study of systematic effects is underway and will be discussed in this talk. |||||||| [1] Mohr et al., arXiv:1203.5425 [2] Pohl et al., Nature 466 (7303), 2010 [3] Parthey et al., Phys. Rev. Lett. 107.203001, 2011 [4] Kolachevsky et al., Opt. Lett. 36.004299, 2011 [5] Berkeland et al., Phys. Rev. Lett. 75.2470, 1995 Issues with determining the proton radius from elastic electron scattering Michael C. Birse Theoretical Physics Division, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK The charge radius of the proton has proved remarkably hard to pin down accu- rately. There is a long history of determinations from elastic ep scattering but recent values still range between 0.84 and 0.9 fm, and even fits by different groups to the same data can be in disagreement. This range spans the values extracted from the Lamb shifts in muonic and electronic hydrogen and so the \proton radius puzzle" remains. Underlying this is the need to extrapolate the available data to Q2 = 0 in order to determine the slope of the form factor there. This extrapolation can be sensitive to corrections applied to the data and to assumptions about low-momentum physics that are built in to the parametrisation used to fit the data. I explore some of these issues and the sensitivity of the extracted charge radius to them. Muon-proton Scattering E. Borie Karlsruhe Institute of Technology, Institut f¨ur Hochleistungsimpuls and Mikrowellentechnik (IHM), Hermann-von-Helmholtzplatz 1, D-76344 Eggenstein-Leopoldshafen, Germany A proposal for muon-proton scattering at PSI [1] has been made in an attempt to help resolve the proton radius puzzle. The proposal will directly test whether or not µ − p and e − p scattering are the same and will perform measurements with µ± and e± at low Q2 in order to study the two-photon exchange contributions in greater detail.
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