Article: New precise measurement of the pion weak form factors in pi+-->e+ nugamma decay.
2009 Volume 103, Issue 5, Page(s) 51802
Abstract: We have measured the pi+-->e+ nugamma branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-chi2 fits to the measured (E(e+), E(gamma) energy distributions result in the weak form ...
| Abstract | We have measured the pi+-->e+ nugamma branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-chi2 fits to the measured (E(e+), E(gamma) energy distributions result in the weak form factor value of F(A)=0.0119(1) with a fixed value of F(V)=0.0259. An unconstrained fit yields F(V)=0.0258(17) and F(A)=0.0117(17). In addition, we have measured a=0.10(6) for the dependence of F(V) on q2, the e+ nu pair invariant mass squared, parametrized as F(V)(q2)=F(V)(0)(1+aq(2)). The branching ratio for the kinematic region E(gamma)>10 MeV and theta(e(+)gamma)>40 degrees is measured to be B(expt)=73.86(54)x10(-8). Earlier deviations we reported in the high-E(gamma)-low-E(e+) kinematic region are resolved without a tensor term. We also derive new values for the pion polarizability alpha(E)=2.78(10)x10(-4) fm3 and neutral pion lifetime tau(pi0)=(8.5+/-1.1)x10(-17) s. |
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| Language | English | |||||
| Publishing date | 2009-07-31 | |||||
| Publishing country | United States | |||||
| Document type | Journal Article | |||||
| ZDB-ID | 208853-8 | |||||
| ISSN | 1079-7114 ; 0031-9007 | |||||
| ISSN (online) | 1079-7114 | |||||
| ISSN | 0031-9007 | |||||
| DOI | 10.1103/PhysRevLett.103.051802 | |||||
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| Database | MEDical Literature Analysis and Retrieval System OnLINE |
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