Download - New Results on Rare Kaon Decays in NA48
1K. Holtz • NA48 Collaboration Moriond 17. - 24.03.2001
New Results on Rare Kaon Decays in NA48
Kirsten HoltzUniversität Mainz
on behalf of the
NA48 Collaboration(Cagliari,Cambridge, CERN, Dubna, Edinburgh, Ferrara,Firenze,
Mainz, Orsay, Perugia, Pisa, Saclay, Siegen, Torino, Vienna, Warsaw)
K. Holtz • NA48 Collaboration
2Moriond 17. - 24.03.2001
Overview
New Results on rare KS and KL decays:
•KS
•KS 0 e+e-
•KS,L +- e+e-
•KL 30 Dalitz plot slope
K. Holtz • NA48 Collaboration
3Moriond 17. - 24.03.2001
The NA48 Kaon Beams
1999: 2 days HIKs run: 2.3108 KS decays; no KL beam
1997-1999: 3.21010 KLdecays/year; 6.5107 KS
decays/year
K. Holtz • NA48 Collaboration
4Moriond 17. - 24.03.2001
Magnetic Spectrometer:
Liquid Krypton Calorimeter:
The NA48 Detector
% 99 efficiency plane
50cm 2mm
[GeV/c] p % 009 0 %50 p/p
y x,
z
. .
σ σ
%50 EMeV100
]GeV[E
%23E/E ..
Kevlar window
Drift chamber 1
Anti counter 6
Drift chamber 2
Magnet
Drift chamber 3
Helium tank
Anti counter 7Drift chamber 4
Hodoscope
Liquid krypton calorimeter
Hadron calorimeter
Muon veto sytem
K. Holtz • NA48 Collaboration
5Moriond 17. - 24.03.2001
• KS,L are sensitive to higher order loop effects of
Chiral Perturbation Theory, no short distance contributions
unambiguous prediction of branching ratio
• Br (KL already measured precisely
• Theoretical prediction (by PT):
Br (KS = (2.3 ± 0.2)×10-6
• NA31 measurement (1995):
Br (KS = (2.4 ± 0.9)×10-6
Ks
K. Holtz • NA48 Collaboration
6Moriond 17. - 24.03.2001
• Two clusters in LKR calorimeter required
• Kaon energy between 60 GeV and 170 GeV
• LKR center-of-gravity < 7 cm
• no hadronic energy, no DCH hits, no AKS/AKL hits
• decay region: -2 < zvertex< 5 m
KS 0 0 with two missing
’s shifts vertex down-stream by > 7m
K
ijji
m
dEE
LKrvertex -zz
KS Event Selection
0
100
200
300
400
500
-1500 -1000 -500 0 500 1000 1500Zvertex [cm]
2
signa
l
from AKS
from
K. Holtz • NA48 Collaboration
7Moriond 17. - 24.03.2001
KS Result
• 450 K candidates in signal region after all cuts• background subtraction:
11 ± 8 n(center-of-gravity side-band subtraction)
2 ± 2 KS
• maximum likelihood fit tosignal region + subtracting
KL contribution:
149 ± 21 K149 ± 21 KS S
• Normalization: 7.5 106 KS
0
100
200
300
400
500
-400 -200 0 200 400 600 800 1000 1200
Fitted KS KL
Data
background from 2(MC)
signal
Zvertex [cm]
Br (KS
statsyst10-6
K. Holtz • NA48 Collaboration
8Moriond 17. - 24.03.2001
• KL 0 e+e- : CP violating and CP conserving contributions
• KS 0 e+e- directly connected to the amplitude of the indirect
CP violations in KL 0 e+e-
• Theoretical expectation:
Br (KS 0 e+e-) = 5.2 × 10-9 as ~ O(1)
aS: strength of the indirect CP violating component in KL 0 e+e-
important for future measurements of KL 0 e+e-
• NA31 measurement (1993):
Br (KS 0 e+e- < 1.1 × 10-6 (90% CL)
KS 0 e+e-
2Sa
K. Holtz • NA48 Collaboration
9Moriond 17. - 24.03.2001
KS 0 e+e- Event Selection• two oppositely charged tracks • four clusters in LKR calorimeter:
two of them associated with tracks E/p > 0.9• center-of-gravity of the clusters in LKR < 10 cm
• |m - m| < 2.5 MeV/c2 (2.5 )
• |mee - mK0| < 2.5 MeV/c2 (3 )
• no hadronic energy, no AKS hits
background rejection:
• KS 0D 0
D (with 0D e+e-):
|me - m| > 30MeV/c2 (for all e combinations)
• KS 0 0
D (with 0D e+e-):
me+e- > 165 MeV/c2 (to take into account resolution
effects and multiple scattering)
forbidden region
forbidden region
Me[
GeV
/c
2]
Me[
GeV
/c
2]
Me[GeV/c2]
Me[GeV/c2]
KS 0 e+e- MC
KS 0D0
D MC
K. Holtz • NA48 Collaboration
10Moriond 17. - 24.03.2001
• 9 candidates remain after all cuts but me+e-
• all candidates are compatible with Ks 0 0D background
expectation of 12 events
no signal event found
• Normalization: 8 104 Ks 0 0
D
(integrated flux of 3 108 Ks )
• indirect CP violating amplitudeof KL 0 e+e-
KS 0 e+e- Result
0
1
2
3
4
5
6
7
0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2
DataEn
trie
s
CutKs 00D MC
mee[GeV/c2]
Br (KS 0 e+e- 10-7
at 90% CL
Br (KL 0 e+e- indirect CPV 10-10
K. Holtz • NA48 Collaboration
11Moriond 17. - 24.03.2001
• Main contributions to KL +- e+e- process:
• Interference of CP-even (IB) and CP-odd (M1) amplitudes causes large asymmetry in distribution of angle between +- and e+e- planes
• Ks +- e+e-: no significant asymmetry expected
KS,L +- e+e-
++ +
- -
-
KL KL
KL KSe+
e+
e+
e-
e-
e-
Direct Emission (E1,M1)
Inner Bremsstrahlung (IB) K Charge Radius
K. Holtz • NA48 Collaboration
12Moriond 17. - 24.03.2001
KS +- e+e- Event Selection
• two positive and two negative tracks• electron (E/p > 0.85) and pion (E/p < 0.85) identification
• Ks identified by using the tagging detector
• center-of-gravity of the clusters in LKR < 8 cm• no AKS hits, no hit in MUV detector
• 477.7 MeV/c2 < mee < 512.7 MeV/c2
background rejection:
• KS +- with in time conversion: 490.7 < m < 504.7 MeV
• KS + - 0
D (0D e+e-) with missing : p
2 < 0.02 GeV2/c2
0 0D (0
D e+e-) : |mp- m4 MeV/c2
p
K. Holtz • NA48 Collaboration
13Moriond 17. - 24.03.2001
PRELIMINARY
RESULTS
KS +- e+e- Result
• 1998 data:
56 KS +- e+e- events
first observation!
• Combined 1998+1999 (incl. Ks high intensity run 99)
MC Ks +- e+e-
MC Ks +- 0D
Data
Br (KS +-e+e- 4.50.7stat 0.4syst) 10-5
Br (KL +-e+e- ) IB =1.3 0.1) 10-7
Br (KS +-e+e- = 4.3 0.2stat 0.3syst) 10-5
No asymmetry is observed: Asee= (-0.2 3.4stat
1.4syst
K. Holtz • NA48 Collaboration
14Moriond 17. - 24.03.2001
• 1998 and 1999 data
• similar cuts applied like in KS +- e+e-
• additionally: 482.7 MeV/c2 < mee < 507.7 MeV/c2
• and: p2 < 510-4 GeV2/c2
KL +- e+e- Result
PRELIMINARY
RESULTS
ALee= (13.9 2.7stat
2.0syst
Br (KL +-e+e- ) = (3.1 0.1stat 0.2syst) 10-7
221
0.17
0.20M1
GeV 03.072.0/aa and
1.35g~ using
As measured by KTeV (Phys. Rev. Lett. 84(2000) 408) Data
MC
KL +-e+e-
=cos()sin()
1/
d/d
K. Holtz • NA48 Collaboration
15Moriond 17. - 24.03.2001
KL 30 Dalitz Plot Slope
• K 3Dalitz plot distributions:|M(u,v)|2 1 + gu + hv + ju2 + kv2 +…
• KL 30: simplification to
|M(R2,)|2 1 + h R2
with R2 = (u2+v2/3) and = arctan(u/ v)
only quadratic slope h left!
• Combining slope h with slope parameters in K± decays
allows to probe the validity of the I = 1/2 rule
)p(ps ),ss(ss and
m/)s(sv , )/ms(su with
1,2,3K1,2,332131
0
221
203
π
ππ
3
K. Holtz • NA48 Collaboration
16Moriond 17. - 24.03.2001
KL 30 Dalitz Plot Slope
theoretical predictions unclear:
• J. Kambor et al. (PRL 68,1818 (1992))
h = (-12 ± 4) 10-3
• G. D’Ambrosio et al. (Phys. Rev. D50, 5767 (1994))
h +1.4 10-3
• L. Maiani, N. Paver (2. DANE Phys. Handbook (1995))
h = (-1.2 ± 3.6) 10-3
only one previous measurement:
• E731, 1992: h = (-3.3 ± 1.1stat ± 0.7syst) 10-3
based on 5 106 KL 30 decays
K. Holtz • NA48 Collaboration
17Moriond 17. - 24.03.2001
KL 30 Dalitz Plot Slope
• six clusters in LKR calorimeter• center-of-gravity of clusters in LKR < 10 cm
very clean events, no background left• ~ 14.5 106 30 events
11.8 106 MC events
fit of slope h:• divide data by normalized MC
(h=0) and fit slope in region 0 < R2 < 1.9 (to avoid resolution
effects at the edge)N
orm
aliz
ed
Even
tsD
ata
/ n
orm
aliz
ed
MC
R2
R2
Fit region
DataMonte Carlo
PRELIMINARY
RESULTh = (-6.1 0.9stat 0.5syst) 10-3
K. Holtz • NA48 Collaboration
18Moriond 17. - 24.03.2001
Summary
KS Br (KS ) = (2.6 0.4stat 0.2syst ) 10-6
(published in Phys. Lett. B493 (2000) 29-35)
KS 0 e+e-: Br (KS 0 e+e-1.4 10-7 at 90% CL
(final result to be published soon)
KS +- e+e-: Br (KS +-e+e- = 4.5 0.7stat 0.4syst)10-5
based on 1998 data (published in Phys. Lett.496 (2000) 137-144)
Br (KS +-e+e- = 4.3 0.2stat 0.3syst)10-5 preliminary result
Asee= (-0.2 3.4stat 1.4systpreliminary result
based on combined 1998 and 1999 data
KL +- e+e-: ALee= (13.9 2.7stat 2.0syst preliminary result
Br (KL +-e+e- ) =( 3.1 0.1stat 0.2syst ) 10-7 preliminary result
based on combined 1998 and 1999 data KL 30 Dalitz plot slope:
h = (-6.1 0.9stat 0.5syst) 10-3 preliminary result
K. Holtz • NA48 Collaboration
19Moriond 17. - 24.03.2001
Outlook
2000: No drift chambers running for neutral decays only Ks : ~ 30 1999 data
Ks 30 : expect statistical error on 000of ± 0.02
KL 30 Dalitz plot slope: more statistics, less systematics
2001: new drift chambers NA48 finishes Re(’/) measurement hoping for 50% - 100% more data for rare KL decays
2002: full year of high intensity Ks and hyperon data taking
the statistic of 1999 data
observation of Br (Ks 0e+e-)
neutral hyperon decays: expecting ~ 30000 0 beta decays
2003/2004: K± program
measurement of CP violation in K± ±±
form factor measurement of K± ±e±