43 research outputs found
Novi ishodi suradnje NA48 o rijetkim raspadima neutralnih kaona
Recent results obtained by the NA48 collaboration on neutral kaon rare decays are reported. A first observation of KS â Ï 0γγ and a detailed study of KL,S â Ï +Ï âe +e â have been performed.IzvjeĆĄÄujemo o nedavnim ishodima suradnje NA48 o rijetkim raspadima neutralnih kaona. NaÄinili smo prvo opaĆŸanje KS â Ï 0γγ i podrobno prouÄili raspad KL,S â Ï +Ï âe +e â
Phenomenological Constraints on Extended Quark Sectors
We study the flavor physics in two extensions of the quark sector of the
Standard Model (SM): a four generation model and a model with a single
vector--like down--type quark (VDQ). In our analysis we take into account the
experimental constraints from tree--level charged current processes, rare Kaon
decay processes, rare B decay processes, the decay, ,
and mass differences, and the CP violating parameters \frac
\epsilon^\prime}{\epsilon}, and . All the constraints
are taken at two sigma. We find bounds on parameters which can be used to
represent the New Physics contributions in these models (, and in the
four--generation model, and , and in the VDQ model)
due to all the above constraints. In both models the predicted ranges for
(the CP asymmetry in semi-leptonic decays), ,
, and can be significantly higher than the predictions of the
SM, while the allowed ranges for and for are
consistent with the SM prediction.Comment: 22 pages, 5 figures (v3: added a reference, updated a reference,
added missing units
On V_ud determination from kaon decays
The pion beta decay pi^+ -> pi^0 e^+ nu proceeds through pure weak vector
hadronic currents and, therefore, the theoretical prediction for it is more
reliable than for the processes with axial-vector current contribution. For
example, recently the pion beta decay has been used for V_ud determination. The
main aim of this letter is to point that kaon beta decay K^0 -> K^+(pi^+ pi^0)
e^- nu-bar analogously can be used for this purpose.Comment: 3 pages, no figures, one reference adde
Search for the dark photon in decays
A sample of fully reconstructed
decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is
analysed to search for the dark photon () production in the decay followed by the prompt decay. No signal is observed,
and an exclusion region in the plane of the dark photon mass and
mixing parameter is established. The obtained upper limits on
are more stringent than the previous limits in the mass range
9~
m MeV/c^2<70~
m MeV/c^2. The NA48/2 sensitivity to the dark
photon production in the decay is also evaluated
epsilon'/epsilon at the NLO: 10 Years Later
During the last four years several parameters relevant for the analysis of
the CP-violating ratio epsilon'/epsilon improved and/or changed significantly.
In particular, the experimental value of epsilon'/epsilon and the strange quark
mass decreased, the uncertainty in the CKM factor has been reduced, and for a
value of the hadronic matrix element of the dominant electroweak penguin
operator Q_8, some consensus has been reached among several theory groups. In
view of this situation, ten years after the first analyses of epsilon'/epsilon
at the next-to-leading order, we reconsider the analysis of epsilon'/epsilon
within the SM and investigate what can be said about the hadronic Q_6 matrix
element of the dominant QCD penguin operator on the basis of the present
experimental value of epsilon'/epsilon and todays values of all other
parameters.
Employing a conservative range for the reduced electroweak penguin matrix
element R_8=1.0+-0.2 from lattice QCD, and present values for all other input
parameters, on the basis of the current world average for epsilon'/epsilon, we
obtain the reduced hadronic matrix element of the dominant QCD penguin operator
R_6=1.23+-0.16 implying _0^NDR(m_c) ~ -0.8 _2^NDR(m_c). We compare
these results with those obtained in large-N_c approaches in which generally
R_6 ~ R_8 and _0^NDR(m_c) is chirally suppressed relatively to
_2^NDR(m_c). We present the correlation between R_6 and R_8 that is
implied by the data on epsilon'/epsilon provided new physics contributions to
epsilon'/epsilon can be neglected.Comment: 18 pages, 1 eps figure, version to appear in JHE
Order p^6 chiral couplings from the scalar K Pi form factor
Employing results from a recent determination of the scalar KPi form factor
F_0^KPi within a coupled channel dispersion relation analysis \cite{JOP01}, in
this work we calculate the slope and curvature of F_0^KPi(t) at zero momentum
transfer. Knowledge of the slope and curvature of the scalar KPi form factor,
together with a recently calculated expression for F_0^KPi(t) in chiral
perturbation theory at order p^6, enable to estimate the O(p^6) chiral
constants C_12^r=(0.3 +- 5.4)10^-7 and (C_12^r+C_34^r)=(3.2 +- 1.5)10^-6. Our
findings also allow to estimate the contribution coming from the C_i to the
vector form factor F_+^KPi(0) which is crucial for a precise determination of
|V_us| from K_l3 decays. Our result F_+^KPi(0)|_C_i^r=-0.018 +- 0.009, though
inflicted with large uncertainties, is in perfect agreement with a previous
estimate by Leutwyler and Roos already made twenty years ago.Comment: 19 pages, discussion of scale dependence of the chiral couplings
added; version to appear in JHE
Charged Kaon K \to 3 pi CP Violating Asymmetries at NLO in CHPT
We give the first full next-to-leading order analytical results in Chiral
Perturbation Theory for the charged Kaon K \to 3 pi slope g and decay rates
CP-violating asymmetries. We have included the dominant Final State
Interactions at NLO analytically and discussed the importance of the unknown
counterterms. We find that the uncertainty due to them is reasonable just for
\Delta g_C, i.e. the asymmetry in the K^+ \to pi^+ pi^+ pi^- slope g; we get
\Delta g_C = -(2.4 +- 1.2) 10^{-5}. The rest of the asymmetries are very
sensitive to the unknown counterterms. In particular, the decay rate
asymmetries can change even sign. One can use this large sentivity to get
valuable information on those counterterms and on Im(G_8) coupling --very
important for the CP-violating parameter epsilon'_K-- from the eventual
measurement of these asymmetries. We also provide the one-loop O(e^2 p^2)
electroweak octet contributions for the neutral and charged Kaon K \to 3 pi
decays.Comment: 43+2 pages, 2 figures. Version accepted in JHEP. Small changes in the
final numerics of CP asymmetries due to change in input valu