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` Proton Charge Radius • Protons and neutrons are the building blocks of the atomic nucleus • The root-mean-square proton charge radius is essential for understanding the structure of the proton • It is also an important input to high precision tests of the QED calculation on hydrogen Lamb shift Experimental Methods Proton Radius Puzzle PRad Experiment Experiment Layout Simulation Study Projection Proton Charge Radius Experiment (PRad) in Hall B On behalf of PRad Collaboration (Spokespersons: A. Gasparian, M. Khandaker, H. Gao, D. Dutta) Chao Peng Duke University Nucleon Bag of quarks and gluons A nucleus = 2 = 0 ∞ 2 4 2 1 2 • Electron-proton elastics scattering measurements • Hydrogen Lamb shift measurements proton charge radius can be determined by the combination of measured Lamb shift values and the QED calculations. 2 6 = − ( 2 ) ( 2 ) 2 =0 • The proton radius puzzle was raised by the Lamb shift measurements of muonic hydrogen at PSI The project is supported by U.S. Department of Energy under contract number DE-FG02-03ER41231 and NSF MRI award PHY-1229153 • PSI value is the most precise one (about 0.05%), but is 7 away from CODATA 2010 value • PRad experiment is a high precision measurement of proton charge radius based on electron-proton elastic scattering • It will extract the proton charge radius at unprecedentedly low four momentum transfer (Q 2 ) with a sub-percent uncertainty • It is a non-magnetic and calorimetric experiment, the Hybrid Calorimeter (HyCal) and Gas Electron Multiplier (GEM) will be used as the detectors • Background is suppressed by utilizing a window-less gas flow target, systematical uncertainties are controlled by measuring the MØller events simultaneously Hybrid Calorimeter (HyCal) Windowless gas-flow target The expected precision of PRad experiment is better than 1 % 0.8758(58) fm Q 2 (GeV/c) 2 G E Events from A. Gramolin’s generator Radius extraction from simulated data HyCal in the code Geometries in the code • Simulation code was developed based on GEANT4 • The major background source is the electron-nuclei scattering of beam halo from the target structure Size of the target cell is increased to reduce the background Empty target run to do subtraction • Two independent event generators with radiative corrections to ep and MØller process (one is developed by M. Meziane, I. Akushevich, and A. Afanasev; the other one is developed by A. Gramolin)

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Proton Charge Radius

• Protons and neutrons are the building blocks of the atomic nucleus

• The root-mean-square proton charge radius is essential for understanding the structure of the proton

• It is also an important input to high precision tests of the QED calculation on hydrogen Lamb shift

Experimental Methods

Proton Radius Puzzle

PRad Experiment

Experiment Layout

Simulation Study

Projection

Proton Charge Radius Experiment (PRad) in Hall B

On behalf of PRad Collaboration (Spokespersons: A. Gasparian, M. Khandaker, H. Gao, D. Dutta)

Chao Peng

Duke University

Nucleon

Bag of quarks and gluons

A nucleus

𝑟𝑝 = 𝑟𝐸2 =

∞

𝑟2 𝜌𝐸 𝑟 4𝜋𝑟2 𝑑𝑟

• Electron-proton elastics scattering measurements

• Hydrogen Lamb shift measurements

proton charge radius can be

determined by the combination of

measured Lamb shift values and the

QED calculations.

𝑟 2

6= −

𝑑𝐺𝐸𝑝(𝑄2)

𝑑(𝑄2)𝑄2=0

• The proton radius puzzle was raised by the Lamb shift measurements of muonic hydrogen at PSI

The project is supported by U.S. Department of Energy under contract number DE-FG02-03ER41231 and NSF MRI award PHY-1229153

• PSI value is the most precise one (about 0.05%), but is 7𝜎away from CODATA 2010 value

• PRad experiment is a high precision measurement of proton charge radius based on electron-proton elastic scattering

• It will extract the proton charge radius at unprecedentedly low four momentum transfer (Q2) with a sub-percent uncertainty

• It is a non-magnetic and calorimetric experiment, the Hybrid Calorimeter (HyCal) and Gas Electron Multiplier (GEM) will be used as the detectors

• Background is suppressed by utilizing a window-less gas flow target, systematical uncertainties are controlled by measuring the MØller events simultaneously

Hybrid Calorimeter (HyCal) Windowless gas-flow target

The expected precision of PRad experiment is better than 1 %

0.8758(58) fm

Q2(GeV/c)2

Events from A. Gramolin’s generator Radius extraction from simulated data

HyCal in the code Geometries in the code

• Simulation code was developed based on GEANT4

• The major background source is the electron-nuclei scattering of beam halo from the target structure

Size of the target cell is increased to reduce the background

Empty target run to do subtraction

• Two independent event generators with radiative corrections to ep and MØller process (one is developed by M. Meziane, I. Akushevich, and A. Afanasev; the other one is developed by A. Gramolin)

Update on the proton radius puzzle:

ATOMIC STRUCTURE Particle proton neutron electron Charge + ve charge -ve charge No charge 1 1 nil Mass

High Precision Measurement of the Proton Charge Radius A. Gasparian NC A&T State University, Greensboro, NC Outline Previous experiments and proton size

Neutron (no charge) Hydrogen 1 Proton 1 Electron Oxygen 8 Protons 8 Neutrons 8 Electrons a. b. proton (positive charge) electron (negative charge) Copyright

The Proton Radius Puzzle - Istituto Nazionale di Fisica ...menu2013.roma2.infn.it/talks/tuesday_fundamental_symmetries_2/2 … · The “Proton Radius Puzzle” is still with us after

High Precision Measurement of the Proton Charge Radiusmezianem/PRAD/PAC39_Gasparian.pdf · High Precision Measurement of the Proton Charge Radius ... tgt, typical for all ... NSF

The W Charge Asymmetry: Measurement of the Proton ......The W Charge Asymmetry: Measurement of the Proton Structure with the ATLAS Detector Kristin Lohwasser St. Catherine’s College,

Proton = + charge Neutron = neutral charge Electron = - charge

All about the size: puzzle of proton charge radius Chung-Wen Kao Chung-Yuan Christian University, Taiwan March 22 nd 2012, Colloquium Institute of physics,

The Lamb shift in hydrogen and muonic hydrogen and the proton charge radius

The ATOM The atom consists of three basic parts: The 3 parts: Proton: + charge( +1) Neutron: no charge (0) Electron: - charge (-1) The proton and neutron

Studying the Proton “Radius ... - physics.rutgers.edu