K. K. Li

Absorption cross section of π±, K±, p and p on nuclei between 60 and 280 GeV/c

Abstract Absorption cross sections of π±, K±, p and p have been measured on targets of Li, C, Al, Cu, Sn and Pb at 60, 200, and 280 GeV/c.

Further evidence for the decay K+ ---> pi+ neutrino anti-neutrino

Additional evidence for the rare kaon decay K+ to pi+ neutrino-antineutrino has been found in a new data set with comparable sensitivity to the previously reported result. One new event was observed in the pion momentum region examined, 211<P<229 MeV/c, bringing the total for the combined data set to two. Including all data taken, the backgrounds were estimated to contribute 0.15 pm 0.05 events. The branching ratio is B=1.57^{+1.75}_{-0.82} 10^{-10}.

Evidence for the decay K+ ---> pi+ neutrino anti-neutrino

An event consistent with the signature expected for the rare kaon decay K+ --> pi+ nu anti-nu has been observed. In the pion momentum region examined, 211 pi+ nu anti-nu, the branching ratio is (4.2 +9.7/-3.5) x E-10.

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.

Further search for the decay K+-->pi(+)nunu;

A search for additional evidence for the rare kaon decay K^+ -->pi^+ nu nubar has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event.A search for additional evidence for the rare kaon decay K{sup +}{yields}{pi}{sup +}{nu}{nu} (bar sign) has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event. No new events were found in the pion momentum region examined, 211<P<229 MeV/c . Including a reanalysis of the original data set, the backgrounds were estimated to contribute 0.08{+-}0.02 events. Based on one observed event, the new branching ratio is B(K{sup +}{yields}{pi}{sup +}{nu} {nu}(bar sign))=1.5{sup +3.4}{sub -1.2}x10{sup -10} . (c) 2000 The American Physical Society.

OBSERVATION OF THE DECAY K+ PI + GAMMA GAMMA

The first observation of the decay K + ! � + is reported. A total of 31 events was observed with an estimated background of 5.1±3.3 events in the � + momentum range from 100 MeV/c to 180 MeV/c. The corresponding partial branching ratio, B(K + ! � + , 100 MeV/c < P�+ < 180 MeV/c), is (6.0±1.5{stat}±0.7{sys})×10 7 . No K + ! � + decay was observed in the � + momentum region greater than 215 MeV/c. The observed � + momentum spectrum is compared with the predictions of chiral perturbation theory.

Further search for the decay K+ ---> pi+ nu anti-nu in the momentum region P < 195-MeV/c

We report the results of a search for the decay

Observation of the decay K+ ---> pi+ mu+ mu-

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