Search for light pseudoscalar sgoldstino in K- decays

A search for the light pseudoscalar sgoldstino production in the three body K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the 25 GeV negative secondary beam of the U70 proton synchrotron. No signal is seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence level, is found to be around 9*10**-6 in the effective mass m(P) range from 0 till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in Phys.Lett.

High statistic measurement of the K- -> pi0 e- nu decay form-factors

The decay K- -> pi0 e- nu is studied using in-flight decays detected with the ISTRA+ spectrometer. About 920K events are collected for the analysis. The lambda+ slope parameter of the decay form-factor f+(t) in the linear approximation (average slope) is measured: lambda+(lin)= 0.02774 +- 0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+ = 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +- 0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst).Comment: 11 pages, 8 figures. Accepted by Phys.Lett.

Measurement of the Dalitz plot slope parameters for K- -> pi0 pi0 pi- decay using ISTRA+ detector

The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay have been measured using in-flight decays detected with the ISTRA+ setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K events with four-momenta measured for the pi- and four involved photons were used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst), h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are consistent with the world averages dominated by K+ data, but have significantly smaller errors.Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-1

Extraction of Kaon Formfactors from K^- -> mu^- nu_mu gamma Decay at ISTRA+ Setup

The radiative decay K->mu nu gamma has been studied at ISTRA+ setup in a new kinematical region. About 22K events of K^- -> mu^- nu_mu gamma have been observed. The sign and value of Fv-Fa have been measured for the first time. The result is Fv-Fa=0.21(4)(4).Comment: 11 pages, 21 figures, submitted to Phys. Lett.

Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+ Setup

Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h < 10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case.Comment: Published in Phys. Lett.

High statistic study of the K- -> pi0 mu- nu decay

The decay K- -> pi0 mu- nu has been studied using in-flight decays detected with the "ISTRA+" spectrometer. About 540K events were collected for the analysis. The lambda+ and lambda0 slope parameters of the decay form-factors f+(t), f0(t) have been measured : lambda+ = 0.0277+-0.0013 (stat)+-0.0009 (syst), lambda0 = 0.0183+-0.0011(stat)+-0.0006(syst), and d(lambda0)/d(lambda+)=-0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=-0.0007 +- 0.0071, fS/f+(0)=0.0017 +- 0.0014. No visible non-linearity in the form-factors have been observed.Comment: 11 pages, 8 EPS figures, accepted by Physics Letters

Flavor Changing Neutral Currents involving Heavy Quarks with Four Generations

We study various FCNC involving heavy quarks in the Standard Model (SM) with a sequential fourth generation. After imposing $B\to X_s\gamma$, $B\to X_sl^+l^-$ and $Z\to b\bar{b}$ constraints, we find ${\cal B}(Z\to s\bar{b}+\bar{s}b)$ can be enhanced by an order of magnitude to $10^{-7}$, while $t\to cZ, cH$ decays can reach $10^{-6}$, which are orders of magnitude higher than in SM. However,these rates are still not observable for the near future.With the era of LHC approaching, we focus on FCNC decays involving fourth generation $b^\prime$ and $t^\prime$ quarks. We calculate the rates for loop induced FCNC decays $b^\prime\to bZ, bH, bg, b\gamma$, as well as t^\prime\to tZ,\tH, tg, t\gamma. If $|V_{cb'}|$ is of order $|V_{cb}| \simeq 0.04$, tree level $b^\prime\to cW$ decay would dominate, posing a challenge since $b$-tagging is less effective. For $|V_{cb'}| \ll |V_{cb}|$, $b'\to tW$ would tend to dominate, while $b'\to t^\prime W^*$ could also open for heavier $b'$, leading to thepossibility of quadruple-$W$ signals via $b'\bar b'\to b\bar b W^+W^-W^+W^-$. The FCNC $b'\to bZ, bH$ decays could still dominate if $m_{b'}$ is just above 200 GeV. For the case of $t'$, ingeneral $t^\prime\to bW$ would be dominant, hence it behaves like a heavy top. For both $b'$ and $t'$, except for the intriguing light $b'$ case, FCNC decays are in the $10^{-4} -10^{-2}$ range, and are quite detectable at the LHC.For a possible future ILC, we find the associated production of FCNC $e^+e^-\to b\bar s$, $t\bar c$ are below sensitivity, while $e^+e^-\to b^\prime\bar b$ and$t^\prime\bar t$ can be better probed.Tevatron Run-II can still probe the lighter $b'$ or $t'$ scenario. LHC would either discover the fourth generation and measure the FCNC rates, or rule out the fourth generation conclusively.Comment: 31 pages, 15 eps figures, version to appear in JHE

High statistics study of the K- -> pi0 e- nu decay

The decay K- -> pi0 e- nu has been studied using in-flight decays detected with the "ISTRA+" spectrometer working at the 25 GeV negative secondary beam of the U-70 PS. About 550K events were used for the analysis. The lambda+ parameter of the vector form-factor has been measured: lambda+ = 0.0286 +- 0.0008 (stat) +- 0.0006(syst). The limits on the possible tensor and scalar couplings have been obtained: f(T)/f+(0)=0.021 +0.064 -0.075 (stat) +- 0.026(syst) ; f(S)/f+(0)=0.002 +0.020 -0.022 (stat) +- 0.003(syst)Comment: LaTeX-2e, epsfig.sty, 10 pages, 7 figures in EPS forma

Flavor changing single top quark production channels at e^+e^- colliders in the effective Lagrangian description

We perform a global analysis of the sensitivity of LEP2 and e^+e^- colliders with a c.m. energy in the range 500 - 2000 GeV to new flavor-changing single top quark production in the effective Lagrangian approach. The processes considered are sensitive to new flavor-changing effective vertices such as Ztc, htc, four-Fermi tcee contact terms as well as a right-handed Wtb coupling. We show that e^+ e^- colliders are most sensitive to the physics responsible for the contact tcee vertices. For example, it is found that the recent data from the 189 GeV LEP2 run can be used to rule out any new flavor physics that can generate these four-Fermi operators up to energy scales of \Lambda > 0.7 - 1.4 TeV, depending on the type of the four-Fermi interaction. We also show that a corresponding limit of \Lambda > 1.3 - 2.5 and \Lambda > 17 - 27 TeV can be reached at the future 200 GeV LEP2 run and a 1000 GeV e^+e^- collider, respectively. We note that these limits are much stronger than the typical limits which can be placed on flavor diagonal four-Fermi couplings. Similar results hold for \mu^+\mu^- colliders and for tu(bar) associated production. Finally we briefly comment on the necessity of measuring all flavor-changing effective vertices as they can be produced by different types of heavy physics.Comment: 34 pages, plain latex, 7 figures embadded in the text using epsfig. Added new references and discussions regarding their relevance to the paper. Added more comments on the comparison between flavor-changing and flavor-diagonal contact terms and on the importance of measuring the Ztc verte

T-odd correlation in the K+ ->pi l nu gamma decays beyond Standard Model

The dependence of the T-odd correlation on the effective Lagrangian parameters in the $K^+ \to \pi l \nu \gamma, l=e, \mu$ decays is analyzed. It is shown that the introduced observable is perspective in a search for new physics in the vector and pseudovector sector of the Lagrangian. As for scalar and pseudoscalar sectors, the T-odd correlation studies will not allow one to improve current restrictions on parameters of models beyond SM.Comment: 18 pages, 1 figur