Search for Violation ofCPInvariance inτ±Decay

Abstract

In an experiment at the Brookhaven alternatinggradient synchrotron, we have analyzed ~3.2 million r decays (i^-77*77*77*), ~1.6 million for each charge of the kaon. The purpose of the experiment was twofold: (1) To search for a violation of CP invariance in T decay by comparing the r + and T~ Dalitz plots. Any difference would indicate a CP violation outside the neutral kaon system, and hence one which could not occur via the "superweak" interaction. 1 (2) To determine the structure of |M| 2 , the square of the r-decay matrix element. All existing data on r decay 2 (1964). ., Phys. Rev. Lett. 225, 374 (1969).^Instead of using the coincident 7r + 7r"~ rates, we used the single-arm pion rates, since, for the average of the polarization at the four points of highest polarization, they gave (± 1.0 %) the same value for P as did the coincident rates. This allows us to study the angular dependence of Fig. 2 with better statistics. The fact that the production plane of single pions photoproduced from complex nuclei can serve as an analyzer is entirely reasonable. That is because the dominant source of such pions is photoproduced p° mesons. These are concentrated in a forward cone which is small compared with the p° decay cone. As a result, detecting a single pion from the decay fixes the decayplane azimuth with fair accuracy. This assumption yields an upper limit for the analyzing power. 12 G. E. Bacon, Nature (London) 166,, 794 (1950). 13 D. Cromer and J. Waber, Acta Crystallogr. lis, 104 (1965). 14 Do Luckey and R. Schwitters, Nucl. Instrum. Methods 81, 164 (1970).(-58 000 r~, -37000 r + events) are consistent with the linear approximation \M\ 2 dXdYaz(l+aY)dXdY, where a is a constant, and X= V3" \T 1 -T 2 \/Q and Y-(3T 3 -Q)/Q are the Dalitz-Fabri coordinates. 3 Here T 1? T 2 , and T 3 are the cm. kinetic energies of the two "even" pions (same charge as the kaon's) and the "odd" pion, respectively; Q = 7\ + T 2 + T 3 . In addition to reducing the uncertainty in the slope parameter a, this high-statistics experiment should give new information as to the presence of higher terms in the expansion of \M\ 2 . In this Letter we report the final resultsWe report a comparison of the Dalitz-plot distributions of 1.6 million T + decays (K + -*"7r + 7r + 7r"") and an equal number of r""decays. No significant asymmetry has been found in any region of the plot. In terms of the difference in the slope parameters a + and a~ for the odd-pion cm.-energy spectra, the asymmetry is A= fa + -a~)/fc + +a~) = -0,0070 ±0.0053. We also present a preliminary result for the slope parameter itself: a = 0.283 ±0.005. New measurements of the r* decay rates and their difference confirm previous results.1370

Electromagnetic properties of pions at low energies

“…48 получить можно на уровне достоверности ^ 30% . Кроме того, экспериментальные результаты 4в не включают систематических ошибок, вероятность которых особенно велика в области вблизи краев плоскости Далитца, наиболее существенной для анализа ππ-рассеяния.…”

“…б) Численное значение константы / (48). в) Противоречие с гипотезой РСАС (48). г) Распад π° -*• 2γ в σ-модели (48).…”

“…в) Противоречие с гипотезой РСАС (48). г) Распад π° -*• 2γ в σ-модели (48). д) Связь с аннигиляцией е + е~ -*• адроны (52).…”

Search for Direct Cp Violation in Charged Kaon Decays From Na48/2 Experiment

“…is at the level of 10 −3 [1], while SM predictions for A g are below 10 −4 [2]. However, some theoretical calculations involving processes beyond the SM [3] predict substantial enhancements of the asymmetry, which could be observed in the present experiment.…”

Search for direct CP violating charge asymmetries in K±→π±π+π- and K±→π±π0π0 decays

“…Theoretical calculations involving processes beyond the SM [14] allow a wider range of A g , including substantial enhancements up to a few 10 −4 . In the past years, several experiments have searched for the CP violating slope asymmetry in both π ± π + π − and π ± π 0 π 0 decay modes by collecting samples of K + and K − decays [15,16]. These measurements set upper limits on A g at the level of a few 10 −3 , limited by systematic uncertainties.…”