We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q 2 = 0.108 (GeV/c) 2 and at a forward electron scattering angle of 30 • < θe < 40 • . The measured asymmetry is ALR( ep) = (-1.36 ± 0.29stat ± 0.13syst) × 10 −6 . The expectation from the Standard Model assuming no strangeness contribution to the vector current is A0 = (-2.06± 0.14) × 10 −6 . We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q 2 . We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G s E + 0.106 G s M = 0.071 ± 0.036 at Q 2 = 0.108 (GeV/c) 2 . As in our previous measurement at higher momentum transfer for G s E + 0.230 G s M , we again find the value for G s E + 0.106 G s M to be positive, this time at an improved significance level of 2 σ.

Article (Published Version) http://sro.sussex.ac.uk Alterev, I, Harris, Philip, Shiers, David and et al, (2009) Neutron to mirror-neutron oscillations in the presence of mirror magnetic fields. Physical Review D, 80 (3). 032003. ISSN 1550-7998 This version is available from Sussex Research Online: http://sro.sussex.ac.uk/16039/ This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the URL above for details on accessing the published version. Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way.Neutron to mirror-neutron oscillations in the presence of mirror magnetic fields We performed ultracold neutron storage measurements to search for additional losses due to neutron (n) to mirror-neutron (n 0 ) oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B 0 , ultracold neutron losses would be maximal for B % B 0 . We did not observe any indication for nn 0 oscillations and placed a lower limit on the oscillation time of nn 0 > 12:0sat 95% C.L. for any B 0 between 0 and 12:5 T.

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We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A ⊥ , at two Q 2 values of 0.106 (GeV/c) 2 and 0.230 (GeV/c) 2 and a scattering angle of 30−6 . The first errors denotes the statistical error and the second the systematic uncertainties. A ⊥ arises from the imaginary part of the two-photon exchange amplitude and is zero in the one-photon exchange approximation. From comparison with theoretical estimates of A ⊥ we conclude that πN-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. The contribution from the ground state proton to the imaginary part of the two-photon exchange can be neglected. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.