NA48/2 Rare Decay Page

Overview

This page intends to collect the status, the most current plots, and the recent presentations and publications of on-going rare decay analyses. All quoted numbers can be shown at conferences.

It can only be kept up-to-date with the active help of the people who do the analyses. Therefore, please send your plots/talks/papers and comments/suggestions to Rainer Wanke!

K± decays: Looking for K0L, K0S, or Hyperon decays from NA48 and NA48/1? Here you find them!

K± → π+ π e± ν (K±e4)

Measurement of ππ scattering lengths and relative form factors (2003+2004 data):

People involved in the analysis:

Brigitte Bloch-Devaux
Formerly: Spasimir Balev, Massimilano Fiorini, Gerard Marel, Lucia Masetti, Bernard Peyaud

Status of the analysis:   (6.11.2010)

In the whole 2003/2004 data set about 1.310 × 106 events with a background of about 0.95% were selected.

The form factors relative to fs were measured to
fs'/fs = 0.152 ± 0.007stat ± 0.005syst,
fs''/fs=− 0.073 ± 0.007stat ± 0.006syst,
fe/fs = 0.068 ± 0.006stat ± 0.007syst,
fp/fs =− 0.048 ± 0.003stat ± 0.004syst,
gp/fs = 0.868 ± 0.010stat ± 0.010syst,
gp'/fs = 0.089 ± 0.017stat ± 0.013syst,
hp/fs =− 0.398 ± 0.015stat ± 0.008syst.
All other form factors (including fe', fe'') were set to 0 in the fit.

The S-wave ππ scattering lengths a00 and a02 were measured from a fit to the phase difference δ0−δ1 as function of mππ. The result depends on the assumptions used in the fit: The paper has been published in EPJ C 70 (2010) 635.

Written documents and talks:

Blessed plots:   (by Brigitte Bloch-Devaux, 3.6.2009)

Analysis on the 2003 data only (now included in the 2003/2004 measurement!):

Status of the analysis:   (12.3.2008)

In the whole 2003 data about 677 500 events were found with a background of less than 0.5%.

The form factors were measured to
fs'/fs = 0.172 ± 0.009stat ± 0.006syst,
fs''/fs=− 0.090 ± 0.009stat ± 0.007syst,
fe/fs = 0.081 ± 0.008stat ± 0.009syst,
fp/fs =− 0.048 ± 0.004stat ± 0.004syst,
gp/fs = 0.873 ± 0.013stat ± 0.012syst,
gp'/fs = 0.081 ± 0.022stat ± 0.015syst,
hp/fs =− 0.411 ± 0.019stat ± 0.008syst.
All other form factors (including fe', fe'') were set to 0 in the fit.

The S-wave π π scattering lengths a00 and a02 are measured from a fit to the phase difference δ0 − δ1 as function of m(ππ). The result depends on the assumptions used in the fit: The paper has been published (EPJ C54 (2008) 411).

Written documents and talks:

Blessed plots:   (by Brigitte Bloch-Devaux, 26.6.2008)


K+ → π0 π0 e+ ν (K00e4)

People involved in the analysis:
Brigitte Bloch-Devaux
Formerly: Marco Gersabeck
Status of the analysis: (22.6.2006)
In super samples 1-3 of the 2003 data 9642 events are found with a background of about 2.9%, in the 2004 data 28025 events with a background of about 2.1%

Using the 2003 data only and K3π as normalization channel, the branching fraction was measured to

Br(K00e4) = (2.587 ± 0.026stat ± 0.019syst ± 0.029norm) × 10−5.

The form factors are measured from 2003+2004 data to

fs'/fs = 0.129 ± 0.036stat ± 0.020syst,
fs''/fs = −0.040 ± 0.034stat ± 0.020syst

with a correlation coefficient of ρ = −0.94. All other form factors (i.e. fe, fe', etc.) were set to 0 in the fit.

The results have been blessed on the Weekly Meeting, June 22, 2006, to be shown as preliminary on conferences.

Written documents and talks:

Blessed plots: (by Marco Gersabeck, 30.6.2006)


K+ → π+ π μ+ ν (K±μ4)

People involved in the analysis:

Andrey Belkin.
Formerly: Ludovic Houchu.

Status of the analysis:   (17.8.2009)

The analysis was finished (as diploma thesis), but not published.

Written documents and talks:

Blessed plots:

None.

K+ → π0 π0 μ+ ν (K00μ4)

People involved in the analysis:

Anna Korotkova

Status of the analysis:   (9.10.2014)

The analysis is on-going.

Written documents and talks:

Blessed plots:

None.

K+ → π+ e+ e

People involved in the analysis:

Evgueni Goudzovski, Eva Gersabeck
Formerly: Khai-Vinh Vi.

Status of the analysis:   (8.7.2009)

The analysis uses the whole NA48/2 data set and selects 7253 events with a background of 1.0%. From this, the model-independent branching fraction was determined to
Br(K+ → π+ e+ e−, z > 0.08) = (2.28 ± 0.03stat ± 0.04syst ± 0.06ext) × 10-7.
The total branching ratio was obtained as
Br(K+ → π+ e+ e−) = (3.11 ± 0.04stat ± 0.05syst ± 0.08ext ± 0.07model) × 10−7,
where the last uncertainty reflects the differences between the theoretical models in the invisible region z < 0.08.
The form factors were determined for a number of different models: Finally, the CP-violating asymmetry between K+ and K- was measured to
(BR+ − BR)/(BR+ + BR) = −0.021 ± 0.015stat ± 0.006syst.
This is the final result. It is published in PLB 677 (2009) 246.

Written documents and talks:

Blessed plots:   (by Evgueni Goudzovski, 23.4.2009)


K+ → π+ μ+ μ-

People involved in the analysis:
Evgueni Goudzovski
Formerly: Teresa Fonseca Martin, Venelin Kozhuharov.
Status of the analysis: (23.01.2011)
The analysis uses the whole NA48/2 data set and selects 3120 events including a background of (3.3±0.7)%. From this, the branching fraction was determined to
Br(K+ → π+ μ+ μ−) = (9.62 ± 0.21stat ± 0.11syst ± 0.07ext) × 10−8.
Form factor measurement: Because of the statistics, the systematic and external uncertainties on the form factors are negligible. Finally, the CP-violating asymmetry between K+ and K− has been measured to
(BR+ − BR)/(BR+ + BR) = 0.011 ± 0.023
and the forward-backward asymmetry between kaon and opposite sign muon to
AFB = (Ncos θ(K,μ)>0 − Ncos θ(K,μ)<0)/(Ncos θ(K,μ)>0 + Ncos θ(K,μ)<0) = −0.024 ± 0.018
This is the final result. It is published in PLB 697 (2011) 107.
Written documents and talks:

Blessed plots: (by Evgueni Goudzovski, 1.11.2009)


K+ → π+ π0 γ

People involved in the analysis:
Silvia Goy Lopez, Mauro Raggi, Don Cundy.
Status of the analysis: (14.8.2010)
In the total 2003/04 data sample about 600k events have been selected, with very small backgrounds, From the fit to extract the fractions of Direct Emission (DE) and the interference (INT) between Direct Emission and Inner Bremsstrahlung (IB) we obtain for the range 0 < T < 80 MeV is

frac(DE) = (3.32 ± 0.15stat ± 0.14syst)%,
frac(INT) = (−2.35 ± 0.35stat ± 0.39syst)%.

The correlation coefficient between DE and INT is ρ = −0.92.
From this, the normalised electric and magnetic amplitudes are determined to

XE = (−24 ± 6) GeV−4,
XM = (254 ± 9) GeV−4.

In addition, the CP violating asymmetry between K+ and K- was determined to be less than 1.5 × 10−3
The paper has been published as EPJ C 68 (2010) 75.

Written documents and talks:

Blessed plots: (by Mauro Raggi and Silvia Goy Lopez, 14.8.2010)


K+ → π+ π0 e+ e

People involved in the analysis:
Milena Misheva, Mauro Raggi
Formerly: Yvonne Kohl
Status of the analysis: (09.10.2014)
In the total 2003 data sample about 1916 candidates have been observed including an estimated background of 56 events, which is the first observation of this decay channel. From these events the branching fraction is determined to
Br(K+ → π+ π0 e+ e) = (4.06 ± 0.10stat ± 0.06syst ± 0.13ext) × 10−6.
The result was blessed to be shown as preliminary on conferences on the analysis meeting of Oct 9, 2014.
Written documents and talks:

Blessed plots: (by Mauro Raggi, 12.12.2014)


K+ → π+ γ γ

People involved in the analysis:
Simone Bifani, Cristina Morales.
Status of the analysis: (19.2.2008)
In super samples 1-3 of the 2003 data 1164 events are found with a background of about 3.3% (mostly from K+ → π+ π0 γ). Using ChPT with ĉ = 2 and O(p6) corrections, the branching fraction was determined to

Br(K+ → π+ γ γ) = (1.07 ± 0.04stat ± 0.08syst) × 10−6.
This result has been blessed at the weekly meeting Feb 15, 2008, to be shown as preliminary on conferences.

Written documents and talks:

Blessed plots: (by Simone Bifani, 20.2.2008)


K+ → π+ γ e+ e

People involved in the analysis:
Carsten Handel, Rainer Wanke.
Status of the analysis: (7.1.2008)
In all 2003+2004 data we observe 120 signal candidate events with 7.3 ± 1.7 estimated background events. The measurement of the model-independent branching fraction gives

Br(K+ → π+ γ e+ e, m(eeγ) > 260 MeV) = (1.19 ± 0.12stat ± 0.04syst) × 10−8.

Using the calculation of F.Gabbiani (PRD 59 (1999) 094022), the value of the free O(p) parameter ĉ was determined to ĉ = 0.90 ± 0.45.
The paper has been published as PLB 659 (2008) 493 and as CERN preprint CERN-PH-EP/2007-033 and hep-ex/0711.4313.

Written documents and talks:

Blessed plots: (by Carsten Handel, 29.11.2007)


K+ → π+ π0 γ γ

People involved in the analysis:
Natalia Molokanova.
Status of the analysis: (1.7.2006)
The analysis is on-going.
Written documents and talks:

Blessed plots:


Last modified: Thu Oct 16 05:51:12 CEST 2014

Rainer Wanke