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Rare Kaon Decays. Giuseppina Anzivino University of Perugia and INFN on behalf of the NA48/2 and KLOE Collaborations Heavy Quarks & Leptons 08 Melbourne, 5-9 June 2008. Overview. Mainly Precision tests of ChPT in rare Kaon decays In this talk: recent results from NA48/2 and KLOE - PowerPoint PPT Presentation
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Rare Kaon DecaysRare Kaon DecaysGiuseppina Anzivino
University of Perugia and INFN
on behalf of the
NA48/2 and KLOE Collaborations
Heavy Quarks & Leptons 08Heavy Quarks & Leptons 08
Melbourne, 5-9 June 2008Melbourne, 5-9 June 2008
6-6-2008
Giuseppina
Anzivino@HQ&L082
Overview
Mainly
Precision tests of ChPT in rare Kaon decays
In this talk:
recent results from NA48/2 and KLOE
not covered……… semileptonic decays (Vus related) (talk by P. Massarotti) leptonic decays and LFV (talk by T. Spadaro) future of very rare kaon decays (talk by M. Moulson) results from KTeV
6-6-2008
Giuseppina
Anzivino@HQ&L083
Outline
NA48/2 recent results in charged Kaon decays
K±→ ±eeBR and Form Factors (preliminary) K±→ ±BR and kinematics (preliminary) K±→ ±e+e-Branching Ratio (final)
KLOE recent results in neutral Kaon decays
KS→ Branching Ratio (final) KS→ e+e- Direct Search, Upper Limit (final) KS→ +-e+e- Branching Ratio (preliminary) KL→ eBranching Ratio (final)
6-6-2008
Giuseppina
Anzivino@HQ&L084
Experiments
LHCSPS
NA48/2NA48/2
KLOE
CERN
LNF
6-6-2008
Giuseppina
Anzivino@HQ&L085
NA48/2 @ CERN
Ke+e–
6-6-2008
Giuseppina
Anzivino@HQ&L086
Theoretical framework
(1) polynomial: W(z) = GFMK2∙f0∙(1+z)
(2) ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z)
(3) Dubna ChPT: W(z) = W(Ma, Mρ, z)
dee/dz ~ P(z)·|W(z)|2
Form-factor models:
z=(Mee/MK)2, P(z) phase space factor
(2) D’Ambrosio et al. JHEP 8 (1998) 4 (3) Dubnickova et al. hep-ph/0611175
(f0,) or (a+,b+) or (Ma,Mρ) determine a model-dependent BR
K * l+l-
suppressed FCNC processes one-photon exchange useful test for ChPT
Parameters of models and BR in full kinematical rangeModel-independent BR (z > 0.08) in visible kinematical range
6-6-2008
Giuseppina
Anzivino@HQ&L087
Kaon flux (2003+2004) K=1.701011
K±→DK±→e+
e-
7146 events (Mee>140 MeV) (BG 0.6%)12.23 x 106 events (BG 0.15%)
Data Samples
The BR is measured normalizing to K0D e+e–
→ particle ID efficiencies cancel at first order common selection criteria for signal and normalization channel
→ 3 track vertex, electron (pion) ID with E/p > 0.95 (< 0.85) K0
D BG suppressed using a kinematical cut Mee>140 MeV
6-6-2008
Giuseppina
Anzivino@HQ&L088
Fit results (preliminary)
= 2.350.18f0 = 0.5320.016
ρ(, f0) = –0.963
a+ = –0.5790.016
b+ = –0.7980.067
ρ(a+, b+) = –0.913
Ma = (0.9650.033) GeV
Mρ = (0.7110.013) GeV
ρ(Ma, Mρ) = 0.998
(1)
(2)
(3)
polynomial: W(z) = GFMK2∙f0∙(1+z)
ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z)
Dubna ChPT:W(z) = W(Ma, Mρ, z)
Model-Independent BR computed by integrating d/dz
BRMI (z>0.08) = (2.26±0.08)10–7
Analysis cut:z>0.08, or Mee>140MeV/c2Available data set
unable to distinguish among models
BR1 = (3.02 0.04stat) 10–7 BR2 = (3.11 0.04stat) 10–7
BR3 = (3.15 0.04stat) 10–7
6-6-2008
Giuseppina
Anzivino@HQ&L089
Results – BR in full kinematic range
BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7
preliminary!!
preliminary!!
Measurement BR107
Bloch et al., PL 56 (1975) B201 2.700.50
Alliegro et al., PRL 68 (1992) 278 2.750.26
Appel et al. [E865], PRL 83 (1999) 4482
2.940.15
NA48/2 preliminary (2008) 3.080.12
Including the uncertainty due to the model dependence
First measurement of CPV parameter (correlated K+/K– uncertainties excluded)
(Kee) = (BR+–BR–)/(BR++BR–)
= (–2.1 1.5stat 0.3syst)%
New
“naïv
e”
WA
NA48/2
‘75 ‘92 ‘99 ‘08
BR
(10
-7)
6-6-2008
Giuseppina
Anzivino@HQ&L0810
Results – FF slope
NA48/2 measurement of good precisioncompatible with earlier results
Contradiction of the data to VMD
further confirmed NA48/2 values of (f0, a+, b+)
in agreement with BNL E865 Measurement Process Result
Alliegro et al., PRL 68 (1992) 278 K++e+e– 1.310.48
Appel et al. [E865], PRL 83 (1999) 4482
K++e+e– 2.140.20
Ma et al. [E865], PRL 84 (2000) 2580 K+++– 2.45+1.30–0.95
NA48/2 preliminary (2008) Ke+e– 2.350.18
NA48/2
VMD models [PRD60 (1999) 053007]
‘92 ‘99 ‘00 ‘08
6-6-2008
Giuseppina
Anzivino@HQ&L0811
NA48/2 @CERN
K K e+e–
6-6-2008
Giuseppina
Anzivino@HQ&L0812
O(p4)
O(p6)
[G. D’Ambrosio and J. Portoles, Nucl., Phys. B386 (1996), 403]
[G. Ecker, A. Pich and E. de Rafael, Nucl., Phys. B303 (1988), 665]
A(z) loop diagrams contributionC(z) Wess-Zumino-Witten functional (10%)B=D=0
unitarity corrections effects can increase the BR by 30-40 %
relevant only at low m
Theoretical framework
6-6-2008
Giuseppina
Anzivino@HQ&L0813
BR dependence on ĉ
The spectrum dependence will be used to extract the ĉ value
Both decay spectrum and rate strongly depend on the single ĉ parameter The M spectrum has a pronounced cusp-like behaviour at 2 threshold.
[G. D’Ambrosio and J. Portoles, Nucl., Phys. B386 (1996), 403]
O(p4)
WDM
FM
6-6-2008
Giuseppina
Anzivino@HQ&L0814
K ±→± data sample and result
BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6
1164 events in 40% of the full data
~40 times larger wrt to world sample
3.3% BG mainly from (IB)
The only previous measurement (E787),
based on 31 events (5 BG events)BR=(1.100.32)·10–6 ; ĉ=1.8±0.6
MC O(p6) and ĉ=2 comparison data shape follows ChPT prediction Model independent measurement and extraction of ĉ is ongoing
preliminary!!
6-6-2008
Giuseppina
Anzivino@HQ&L0815
K ±→±e+e- - first observation120 candidate events (6.1%
BG)
BR(±e+e−)=(1.19±0.12stat±0.04sys)·10−8
Model-independent BR (Mee> 260 MeV/c2)
[final result published, PLB659 (2008) 493]
Shape analysis [using ChPT O(p6) model, F. Gabbiani, PRD59 (1999) 094022]:
ĉ=0.90±0.45
never observed before!!
6-6-2008
Giuseppina
Anzivino@HQ&L0816
KLOE @ LNF
Mesurement of BR(KS )
6-6-2008
Giuseppina
Anzivino@HQ&L0817
Motivations
Important probe of ChPT Decay amplitude evaluated at leading order, O(p4) BR(KS ) = 2.1 x 10-6
No full O(p6) calculation exists Experimental value of the BR changed along the years, improving in precision Most recent measurement by NA48/1 BR(KS ) = (2.78±0.06±0.04) x 10-6
Differs from ChPT O(p4) by 30% possible large O(p6) contribution
In NA48, the KL background is a relevant component of the fit
In KLOE, the background from KL is reduced to zero (tagging)
D’Ambrosio and Espriu, Phys.Lett.B 175(1986) 237Kambor and Holstein, Phys.Rew.D 49(1994) 2346
6-6-2008
Giuseppina
Anzivino@HQ&L0818
Analysis strategy
Main background KS 20 with 2 photons lost in the beam-pipe and/or colliding into QCAL
veto these photons using a cut on arrival time
T = |TQCAL - RQCAL/c| < 5 ns Background reduction to 70 %
*
Full statistics (1.9 fb-1)700 x 106 KS events after KL-crash tag
count signal events by fitting M and cos *
in the KS
cms
Signal
Background
•• DATA
-- MC all
Nsig = 711 ± 35 (4.9% stat. error)
FCN/Ndof = 1.2
cos
6-6-2008
Giuseppina
Anzivino@HQ&L0819
Result
PT
O(p4) O(p6)
KLOE
There is a 3 discrepancy between KLOE and NA48 results
The NA48 measurement implies the existence of a sizeable O(p6) counterterm in ChPT
The KLOE result makes this contribution practically negligible
BR(KS → ) = (2.26 ± 0.12stat ± 0.06sys)·10−6
now published [JHEP05 (2008) 05]
NA48 Coll., Phys. Lett. B551 (2003) 7NA48 Coll., Phys. Lett. B493 (2000) 29NA31 Coll., Phys. Lett. B351 (1995) 579
6-6-2008
Giuseppina
Anzivino@HQ&L0820
Direct Search forKS e+e-
KLOE @ LNF
6-6-2008
Giuseppina
Anzivino@HQ&L0821
Search for FCNC in KS → e+e-
Exotic mediators could producetree level FCNC processes
Precise SM prediction, using ChPT, O(p4): BR(KSe+e-)=1.6 x 10-15 [Ecker and Pich, Nucl. Phys. B366, 189, 1991]
Most precise measurement by CPLEAR BR(KS e+e-) < 1.4 x 10-7 (90% C.L.)
In KLOE direct search of this decay using a pure KS beamAfter preselection: 1.1 Mevts in Data sample
Signal identification using a χ2 variable based on time of particles, E/p and cluster positionBackground rejection by kinematic cutsSignal box defined in the plane χ2 vs Minv (e
+e- hypotesis)
6-6-2008
Giuseppina
Anzivino@HQ&L0822
Result
BR(KS→e+e-) < 9.3 x 10-9 (90% C.L.)
NO events found in the signal boxUpper Limit evaluated normalizing to the number of KS→+- events
Previous result improved by more than one order of magnitude
6-6-2008
Giuseppina
Anzivino@HQ&L0823
Fit the distribution of (Emiss-Pmiss)ee
Normalize to the number of KS+-
2=117.6/92 Prob~4%
ee (E<10 MeV) bp dc+00+semil.
K+K-
Data sample (900 pb-1) N (ee) = 974 ± 53 = 0.02359 ±0.00031
Amplitude dominated by CP even IB component (needed to predict the CP violation in KL ee) CP test through measurement of angular asymmetry between and ee planes
CP test in KS → +-e+e-
BR=(4.48 ± 0.24stat ± 0.15syst)×10-5
6-6-2008
Giuseppina
Anzivino@HQ&L0824
R = (924 ± 23 ± 16) x 10-5
<X> = -2.3 ± 1.3 ± 1.4
R = (944 ± 14) x 10-5
<X> = -2.8 ± 1.8
Largely dominated by IB, negligible DEInterference IB-DE small (1%) → test of ChPT O(p6)
A 2-dimensional fit in (E*,
*) allow to measure both R and <X>
Fit results
KL → e
Adding ChPT constraintNA48 Coll., Phys.Lett. B605 (2005) 247
KTeV Coll., Phys. Rew. D71 (2005) 012001 arXiv:0710.3993
6-6-2008
Giuseppina
Anzivino@HQ&L0825
ConclusionsThe NA48/2 and KLOE experiments have produced
important experimental inputs to the Chiral Perturbation Theory,
the effective theory of strong interaction at low energy
Presented at this conference the most recent results fromNA48/2 charged kaon sector
Precise study of the Ke+e– decay (preliminary)Precise study of the K decay (preliminary)First observation of the Ke+e– decay (final)
KLOE neutral kaon sectorMeasurement of KS decay (final)Upper limit for KSe+e- (final)Measurement of KSe+e- decay (preliminary)Measurement of KLe decay (final)
Still a lot to come ……stay tuned!
6-6-2008
Giuseppina
Anzivino@HQ&L0826
SPARES
6-6-2008
Giuseppina
Anzivino@HQ&L0827
Preliminary results
BRMI
=2.26 0.03stat 0.03syst 0.06ext = (2.26 0.08) 10-7
z>0.08
= 2.35 0.15stat 0.09syst = 2.35 0.18
f0 = 0.532 0.012stat 0.008syst 0.007ext = 0.532 0.016
BR1= 3.02 0.04stat 0.04syst 0.08ext = (3.02 0.10) 10-7
a+ = –0.579 0.012stat 0.008syst 0.007ext = –0.579
0.016
b+ = –0.798 0.053stat 0.037syst 0.017ext = –0.798
0.067
BR2= 3.11 0.04stat 0.04syst 0.08ext = (3.11 0.10) 10-7
Ma = 0.965 0.028stat 0.018syst 0.002ext = 0.965 0.033 [GeV/c]
Mρ = 0.711 0.010stat 0.007syst 0.002ext = 0.711 0.013 [GeV/c]
BR3= 3.15 0.04stat 0.04syst 0.08ext = (3.15 0.10) 10-7 BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7
Including uncertainty due to the model dependence, (full z range)
(K±ee) = (BR+–BR–) / (BR++BR–) = (–2.1±1.5stat±0.3syst)%
CPV parameter (first measurement! correlated K+/K– uncertainties excluded):
(1)
(2)
(3)
6-6-2008
Giuseppina
Anzivino@HQ&L0828
Corrections/uncertaintiesParamete
rElectron
ID Beam
simulation
Radiativecorrection
s
Backgroundto Ke+e–
Triggerinefficiency
Fittingprocedur
e
External(PDG)
BRmi107 0.02 0.01 0.01 –0.010.01 –0.010.01 0 0.06
Model (1): linear form-factor
0.01 0.04 0.05 –0.040.04 –0.030.03 0.03 0
f0 0.001 0.006 0.004 +0.0020.002
+0.0010.001
0.003 0.007
BR1107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08
Model (2): ChPT form-factor [D’Ambrosio, Ecker, Isidori, Portoles, hep-ph/9808289]
a+ 0.001 0.005 0.004 –0.0010.001
–0.0020.002
0.004 0.007
b+ 0.009 0.015 0.022 +0.0170.017
+0.0150.015
0.010 0.017
BR2107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08
Model (3): Dubna ChPT [Dubnickova et al., hep-ph/0611175]
Ma/GeV 0.004 0.009 0.009 +0.0080.008
+0.0060.006
0.006 0.002
Mρ/GeV 0.002 0.003 0.004 +0.0030.003
+0.0030.003
0.002 0.002
BR3107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08
6-6-2008
Giuseppina
Anzivino@HQ&L0829
KS tagging
1.6 fb-1 of collisions data analyzed for KS
1.3 fb-1 of collisions data analyzed for KSe+e-
Both analyses use a clean KS beam from
KL-crash tagging based on KL interactions on EMC
KL-crash ( ~ 30%)
This algorithm searches KL interacting directly on EMC.KL-crash calorimetric clusters are selected using cuts on energy and *.
KS angular resolution: ~ 1° KS momentum resolution: ~ 2 MeV
KL-CRASH0.22
Two searches of rare KS decays :