J. Hu

Improved measurement of the K+ ---> pi+ nu anti-nu branching ratio

An additional event near the upper kinematic limit for K+ to pi+ nu nubar has been observed by Experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+ to pi+ nu nubar)= 1.47 (+1.30, - 0.89) x 10-10 based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9.

New measurement of the K+-->pi+ nunu branching ratio.

A.V. Artamonov, B. Bassalleck, B. Bhuyan, ∗ E.W. Blackmore, D.A. Bryman, S. Chen, 4 I-H. Chiang, I.-A. Christidi, † P.S. Cooper, M.V. Diwan, J.S. Frank, T. Fujiwara, J. Hu, J. Ives, D.E. Jaffe, S. Kabe, S.H. Kettell, M.M. Khabibullin, A.N. Khotjantsev, P. Kitching, M. Kobayashi, T.K. Komatsubara, A. Konaka, A.P. Kozhevnikov, Yu.G. Kudenko, A. Kushnirenko, ‡ L.G. Landsberg, § B. Lewis, K.K. Li, L.S. Littenberg, J.A. Macdonald, § J. Mildenberger, O.V. Mineev, M. Miyajima, K. Mizouchi, V.A. Mukhin, N. Muramatsu, T. Nakano, M. Nomachi, T. Nomura, T. Numao, V.F. Obraztsov, K. Omata, D.I. Patalakha, S.V. Petrenko, R. Poutissou, E.J. Ramberg, G. Redlinger, T. Sato, T. Sekiguchi, T. Shinkawa, R.C. Strand, S. Sugimoto, Y. Tamagawa, R. Tschirhart, T. Tsunemi, ¶ D.V. Vavilov, B. Viren, Zhe Wang, 3 N.V. Yershov, Y. Yoshimura, and T. Yoshioka

Study of the decay K+→π+νν̄ in the momentum region 140<Pπ<199MeV/c

Experiment E949 at Brookhaven National Laboratory has observed three new events consistent with the decay K+ => pi+,nu,nubar in the pion momentum region 140 pi+,nu,nubar events to seven. Combining this observation with previous results, assuming the pion spectrum predicted by the standard model, results in a branching ratio of (1.73+1.15-1.05)e-10. An interpretation of the results for alternative models of the decay K^ => pi+,nothing is also presented.

Measurement of the muon decay parameter {delta}

The muon decay parameter {delta} has been measured by the TWIST collaboration. We find {delta}=0.74964{+-}0.00066(stat.){+-}0.00112(syst.), consistent with the standard model value of 3/4. This result implies that the product P{sub {mu}}{xi} of the muon polarization in pion decay, P{sub {mu}}, and the muon decay parameter {xi} falls within the 90% confidence interval 0.9960<P{sub {mu}}{xi}{<=}{xi}<1.0040. It also has implications for left-right-symmetric and other extensions of the standard model.

New measurement of the

A.V. Artamonov, B. Bassalleck, B. Bhuyan, ∗ E.W. Blackmore, D.A. Bryman, S. Chen, 4 I-H. Chiang, I.-A. Christidi, † P.S. Cooper, M.V. Diwan, J.S. Frank, T. Fujiwara, J. Hu, J. Ives, D.E. Jaffe, S. Kabe, S.H. Kettell, M.M. Khabibullin, A.N. Khotjantsev, P. Kitching, M. Kobayashi, T.K. Komatsubara, A. Konaka, A.P. Kozhevnikov, Yu.G. Kudenko, A. Kushnirenko, ‡ L.G. Landsberg, § B. Lewis, K.K. Li, L.S. Littenberg, J.A. Macdonald, § J. Mildenberger, O.V. Mineev, M. Miyajima, K. Mizouchi, V.A. Mukhin, N. Muramatsu, T. Nakano, M. Nomachi, T. Nomura, T. Numao, V.F. Obraztsov, K. Omata, D.I. Patalakha, S.V. Petrenko, R. Poutissou, E.J. Ramberg, G. Redlinger, T. Sato, T. Sekiguchi, T. Shinkawa, R.C. Strand, S. Sugimoto, Y. Tamagawa, R. Tschirhart, T. Tsunemi, ¶ D.V. Vavilov, B. Viren, Zhe Wang, 3 N.V. Yershov, Y. Yoshimura, and T. Yoshioka

K^{+} \to \pi^{+} \nu \bar{\nu}

A.V. Artamonov, B. Bassalleck, B. Bhuyan, ∗ E.W. Blackmore, D.A. Bryman, S. Chen, 4 I-H. Chiang, I.-A. Christidi, † P.S. Cooper, M.V. Diwan, J.S. Frank, T. Fujiwara, J. Hu, J. Ives, D.E. Jaffe, S. Kabe, S.H. Kettell, M.M. Khabibullin, A.N. Khotjantsev, P. Kitching, M. Kobayashi, T.K. Komatsubara, A. Konaka, A.P. Kozhevnikov, Yu.G. Kudenko, A. Kushnirenko, ‡ L.G. Landsberg, § B. Lewis, K.K. Li, L.S. Littenberg, J.A. Macdonald, § J. Mildenberger, O.V. Mineev, M. Miyajima, K. Mizouchi, V.A. Mukhin, N. Muramatsu, T. Nakano, M. Nomachi, T. Nomura, T. Numao, V.F. Obraztsov, K. Omata, D.I. Patalakha, S.V. Petrenko, R. Poutissou, E.J. Ramberg, G. Redlinger, T. Sato, T. Sekiguchi, T. Shinkawa, R.C. Strand, S. Sugimoto, Y. Tamagawa, R. Tschirhart, T. Tsunemi, ¶ D.V. Vavilov, B. Viren, Zhe Wang, 3 N.V. Yershov, Y. Yoshimura, and T. Yoshioka

branching ratio

The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and

New measurement of the K+→π+νν̄ branching ratio

P_{\mu}^{\pi}

Measurement of P(mu)xi in polarized muon decay

is the degree of muon polarization in pion decay, has been measured. The value P_{mu}^{pi}xi = 1.0003 +- 0.0006 stat. +- 0.0038 syst. was obtained. This result agrees with previous measurements but is over a factor of two more precise. It also agrees with the Standard Model prediction for P_{mu}^{pi}xi and thus leads to restrictions on left-right symmetric models.

Precise measurement of parity violation in polarized muon decay

We present a new high precision measurement of parity violation in the weak interaction, using polarized muon decay. The TWIST collaboration has measured