[Jlab-seminars] Physics Seminar Correction

[Luci Collins]

 > Hall C Physics Seminar
 > Wednesday March 27, 2013
 > F113 @ Noon-1 pm
 > Buddhini Waidyawansa
 > Title: “Beam Normal Spin Asymmetries from the Qweak Experiment”
 >
 > Abstract:  The beam normal spin asymmetry, Bn, in the scattering of a 
transversely polarized electron from an unpolarized target is 
proportionalto the imaginary part of the two photon exchange amplitude. 
Because it can be calculated from the sum of the amplitudes for all 
on-shell intermediate states, a measurement provides an integral test of 
our understandingof the fundamental e + p -->  X processes. However, Bn 
is highly suppressed hence is only accessible with apparatus designed to 
measure asymmetries to 1%. This parity-conserving observable is of 
special interest to experiments making precision parity-violating 
asymmetry measurements becausesmall amounts of residual transverse 
polarization in the beam can lead to percent-level corrections. The 
Qweak experiment is one such experiment which aims to make a 4% 
measurement  of the weak charge of the proton by extracting the 
parity-violating asymmetry in elastic e+p scattering  to an accuracy of 
2.5%. To better understand the small parity-conserving background coming 
from Bn at Qweak kinematics, we have performed elastic scattering 
measurements with fully transversely  polarized beam on the protonand 
Aluminum. Our Bn measurement from the proton is the most precise Bn 
measurement yet. This preliminary result of Bn from the proton will be 
presented.