1. (Scuola Normale Superiore & INFN Pisa)
Recent NA48 results: |+–| from KL+–, DCPV in K3 decays, |Vus| from K0l.
Evgueni Goudzovski
(Scuola Normale Superiore & INFN Pisa)
on behalf of the NA48/2 Collaboration:
Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna
EPS HEP Conference 2007
Manchester / July 19-25, 2007

2. Overview
Presentation of several recent NA48 results:
Measurement of BR(KL+–) and the indirect CP violation parameter || with NA48 data (run 1999);
Study of the K3 decays: a search for direct CP violating charge asymmetries Ag with NA48/2 data (runs 2003/04);
Study of the semileptonic K0l decays, and measurement of the CKM matrix element |Vus| with NA48/2 data (run 2003).
NA48
NA48/1
NA48/2
NA62 (first phase)
Ke2/K2 run …
E. Goudzovski / Manchester, July 19th, 2007

3. NA48 CERN
A fixed target experiment  modern CERN kaon physics program
Jura mountains
France
NA48; NA62
SPS
LHC
Geneva airport
Switzerland N
E. Goudzovski / Manchester, July 19th, 2007

4. The NA48 detector Main detector components:
Magnetic spectrometer (4 DCHs):
4 views/DCH: redundancy efficiency;
used in trigger logic;
Δp/p = 1.0% %*p [GeV/c].
Hodoscope
fast trigger;
precise time measurement (150ps).
Liquid Krypton EM calorimeter (LKr)
High granularity, quasi-homogenious;
E/E = 3.2%/E1/2 + 9%/E % [GeV]; x=y=0.42/E1/ mm
Hadron calorimeter, muon veto counters, photon vetoes.
Beam pipe
Beams
E. Goudzovski / Manchester, July 19th, 2007

5. Indirect CP violation parameter || in KL+– decays
E. Goudzovski / Manchester, July 19th, 2007

6. CP violation parameter ||
Definition: (a fundamental observable of CP violation)
A(KL+–)
 =  + ’ =
A(KS+–)
Measurement method:
The quantity measured directly is BR(KL+–)/BR(KLe):  normalization to the largest decay mode;
Then || is computed as
BR(KL+–)
KS
|| =
KL
BR(KS+–)
External input: best single measurements
KS lifetime: KS = (  )10–10 s (NA48 ’02);
KL lifetime: KL = (5.0840.023)10–8 s (KLOE ’06);
BR(KLe) =  (NA48 ’04 + improved KL30: KTeV, KLOE);
BR(KS+–) =  (KLOE ’06).
E. Goudzovski / Manchester, July 19th, 2007

7. E/p for pions and electrons
||: event selection
Dedicated 2-days run in 1999: ~80 million 2-track events recorded
KL+–
KLe
CP-violating process: suppression of the main channels by 4-5 orders of magnitude required;
Small background well understood in terms of simulation achieved: 0.5%;
Events selected: 47,142.
Selection based on electron identification by LKr energy deposit: electrons have E/p  1;
Equally small background achieved: 0.5%;
Events selected: 4,999,126.
E/p for pions and electrons
Events
E. Goudzovski / Manchester, July 19th, 2007

8. ||: results || = = (2.223 0.012) 10–3
Phys. Lett. B645 (2007) 26
The directly measured value:
R = BR(KL+–) / BR(KLe) = (4.835  0.022stat.  0.016syst.)  10–3
Corrections and uncertainties on R
Uncertainty source
Correction
Uncertainty
Particle ID
+1.34%
0.05%
K2 background
–0.49%
0.03%
Muon ID
+0.48%
0.18%
Trigger
–1.29%
0.11%
Energy spectrum
0.20%
Radiative corrections
0.10%
MC statistics
Totally
+0.04%
0.33%
Branching fraction:
BR(KL+–) = (1.941  0.019)  10–3
Includes the +– (IB) component;
Direct emission (CP conserving) component was subtracted.
The CP violation parameter:
BR(KL+–)
KS
|| =
= (2.223 0.012) 10–3
KL
BR(KS+–)
E. Goudzovski / Manchester, July 19th, 2007

9. ||: comparison of results
BR(KL+–) / BR(KLe), 10–3
|+–|, 10–3
Good agreement with KTeV and KLOE results;
These new measurements contradict the PDG’04 value
E. Goudzovski / Manchester, July 19th, 2007

10. 2. Direct CP violation parameter Ag in K3 decays
E. Goudzovski / Manchester, July 19th, 2007

11. CP violation parameter Ag
Two decay modes: BR(K±±+)=5.57%; BR(K±±00)=1.73%.
Matrix element:
|M(u,v)|2 ~ 1 + gu + hu2 + kv2
Kinematics:
si = (PKPi)2, i=1,2,3 (3=odd );
s0 = (s1+s2+s3)/3;
u = (s3-s0)/m2;
v = (s2-s1)/m2. V
“Charged” mode
g = (21.134±0.017)%
|h|, |k| ~ 10-2
Kaon rest frame:
u = 2mK∙(mK/3Eodd)/m2;
v = 2mK∙(E1E2)/m2. U
Direct CP-violating quantity:
the slope asymmetry
Ag = (g+g)/(g++g)  0
E. Goudzovski / Manchester, July 19th, 2007

12. Theory & experiment |Ag| Experimental precisions before NA48/2:
E. Gámiz et al., JHEP 10 (2003) 42
[Ag~10-3, dominated by systematics]
SM estimate (NLO ChPT): Agc = (–1.41.2)10–5;
Agn = (1.10.7)10–5.
Smith et al. (1975) “neutral”
10-2
Ford et al. (1970)
|Ag|
HyperCP prelim. (2000)
TNF (2005) “neutral”
10-3
NA48/2
proposal
G. D’Ambrosio et al., PLB480 (2000) 164
Models beyond the SM predict substantial enhancement partially within the reach of NA48/2.
“neutral”
10-4
“charged”
SUSY &
10-5 SM
New
physics
Asymmetry of integrated decay widths is strongly suppressed.
10-6
E. Goudzovski / Manchester, July 19th, 2007

13. K3 asymmetry: method
M=1.7 MeV/c2
Time stability of Ag
Events
Control
3.11x109 events selected
Control
M(3), GeV/c2
Measurement method:
Observable: the ratio of u-projections of reconstructed K+ and K– kinematic distributions;
Achieve cancellation of major systematic effects by combining data collected with opposite beam line/spectrometer polarities;
Monitor residual fake instrumental asymmetries with control quantities.
E. Goudzovski / Manchester, July 19th, 2007

14. K3 asymmetry: result
arXiv: , submitted to EPJC
g = (0.6 ± 0.7stat ± 0.4trig ± 0.5syst)  10-4
g = (0.6 ± 0.9)  10-4
Ag = (1.5 ± 1.5stat ± 0.9trig ± 1.1syst)  10-4
Ag = (1.5 ± 2.1)  10-4
FINAL RESULT
based on the full statistics accumulated in 2003 and 2004 runs
Measurements of Ag
A factor ~20 better precision than the previous measurements;
Uncertainties dominated by those of statistical nature;
Result compatible with the Standard Model predictions, no evidences for New Physics;
NA48/2 design goal reached!
Ag  104
preliminary 2003
final
final 2003
HyperCP (2000)
Ford et al. (1970)
NA48/2
(results superseding each other)
E. Goudzovski / Manchester, July 19th, 2007

15. K00 asymmetry: result
arXiv: , submitted to EPJC
M=1.1 MeV/c2
Events
Control
Control
M(3), GeV/c2
|V|
Statistical precision in Ag0 similar to “charged” mode:
Ratio of “neutral” to “charged” statistics: N0/N±~1/30;
Ratio of slopes: |g0/g±|3/1;
A favourable Dalitz-plot distribution (gain factor f~1.5).
Final result with sample
(based on 91106 events)
Ag0 = (1.8±1.8)10-4 U
E. Goudzovski / Manchester, July 19th, 2007

16. 3. CKM matrix element |Vus| with the K0l decays
E. Goudzovski / Manchester, July 19th, 2007

17. Extraction of |Vus| from Kl3
GF2
(Kl3) = BR(Kl3)/K =
mK5 SEW |Vus|2 |f+(0)|2 IK (1+K)
3843
Short-distance radiative correction
The measured quantity
Phase space integral containing form-factor parameterization
Long-distance correction (isospin symmetry breaking)
Analysis method: measurement of BR(Ke3)/BR(K0), BR(K3)/BR(K0)
 normalization to a large and well-know mode with a similar signature.
Data sample: ~3 days of dedicated running (very soft trigger) in 2003
Event samples collected
Decay channel K+ K–
Background level
K0e
56,195
30,898
~10–4
K0
49,364
27,525
~0.2%
K0
461,837
256,619
E. Goudzovski / Manchester, July 19th, 2007

18. Kl3 and |Vus|: results |Vus|f+(0) = 0.21930.0012 [Ke3]
Eur. Phys. J. C50 (2007) erratum
BR(Ke3) measurements
BR(Ke3)/BR(K0) = 0.0009stat.0.0004syst. %
ISTRA+ 2007
BR(K3)/BR(K0) = 0.0006stat.0.0003syst.
BNL E
NA48/2
2007
BR(Ke3) = (5.1680.019stat.0.008syst.0.030norm.)%
BR(K3) = (3.4250.013stat.0.006syst.0.020norm.)%
Both measurements above the PDG’06 average, but agree with other experiments normalizing to 0;
Comparison to KLOE: a hint that the PDG’ value of BR(0) is biased (waiting for KLOE 0!)
KLOE (2007 absolute measurement)
PDG’06 %
BR(K3) measurements
|Vus|f+(0) =  [Ke3]
NA48/2 2007
=  [K3]
Errors dominated by those of long-distance corr.
PDG’06
|Vus| = 0.0013other0.0019th. =
KLOE (2007 absolute measurement)
= 0.0023
Combined Ke3 and K3 result: compatible to CKM unitarity
Error dominated by the theoretical uncertainty of f+(0)
E. Goudzovski / Manchester, July 19th, 2007

19. Conclusions
A selection of new NA48 kaon physics results obtained in 2007:
Precise |+–| measurement:  in agreement with KTeV and KLOE results
Precise search for direct CP violating charge asymmetry in the 3-pion decays of the K:  order of magnitude improvement in precision  in agreement with the SM predictions
Precise measurement of |Vus| with semileptonic K decays:  agreement with other experiments normalizing to 0  disagreement with absolute measurements  slight disagreement with the PDG
E. Goudzovski / Manchester, July 19th, 2007