Precision measurement of charge symmetry breaking innpelastic scattering at 347 MeV

Abstract

A nonzero difference of the analyzing powers due to charge symmetry breaking has been measured with high precision in np elastic scattering at a neutron beam energy of 347 MeV. The neutron beam and proton target were alternately polarized for the measurements of A n and A p . A mirror-symmetric detection system was used to cancel geometry-related systematic errors. From fits of the measured asymmetry angular distributions over the range of 53.4°р cm р86.9°, the difference in the zero-crossing angles of the analyzing powers was determined to be 0.438°Ϯ0.054°(stat.)Ϯ0.051°(syst.) in the center-of-mass system. Using the experimentally determined slope of the analyzing power dA/dϭ(Ϫ1.35Ϯ0.05)ϫ10 Ϫ2 deg Ϫ1 ͑c.m.͒, this is equivalent to ⌬AϵA n ϪA p ϭ͓59Ϯ7(stat.)Ϯ7(syst.)Ϯ2(syst.)͔ϫ10 Ϫ4 . The shape of ⌬A() in the vicinity of the zero-crossing angle has also been extracted. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with the results. ͓S0556-2813͑98͒06404-8͔PACS number͑s͒: 13.75. Cs, 11.30.Hv, 13.88.ϩe, 21.45.ϩv ͗P beam ϩ P target ͘•⌬A͑͒ϩ͑ P beam Ϫ P target ͒•͗A͑ ͒͘. ͑3͒However, at the zero-crossing angle, the second term and associated systematic errors disappear. Rather than measuring ⌬A directly at the zero-crossing angle, the difference of the individual zero-crossing angles, where the respective analyzing powers cross zero,

Measurement of the Antiquark Flavor Asymmetry in the Nucleon Sea

“…Extensive experimental searches for charge symmetry violation effects have shown that charge symmetry holds to the order of the protonneutron mass difference [5,6].…”

Measurement of the anti-quark flavor asymmetry in the nucleon sea

“…Extensive experimental searches for charge symmetry violation effects have shown that charge symmetry holds to the order of the protonneutron mass difference [5,6]. 5 Therefore, charge symmetry can not explain the discrepancy between the NMC measurement and the traditional Gottfried Sum result.…”

Constraints on a Parity-Conserving/Time-Reversal-Non-Conserving Interaction

“…Charge symmetry breaking (CSB) in neutron-proton elastic scattering manifests itself as a non-zero difference of the neutron (A n ) and proton (A p ) analyzing powers, ∆A = A n −A p = 2×[Re(b * f )+Im(c * h)]/σ 0 . The three precision experiments performed (at TRIUMF at 477 MeV [12] and at 369 MeV [13], and at IUCF at 183 MeV [14]) have unquestionably shown that charge symmetry is broken and that the results for ∆A at the zero-crossing angle of the average analyzing power, are very well reproduced by meson exchange model calculations (see Fig.1). As shown above a T-odd / P-even interaction corresponds to a term in the scattering amplitude which is simultaneously charge symmetry breaking.…”