Kaon physics at KLOE

1
Kaon physics at KLOE

• E. De Lucia INFN LNF
• for the KLOE Collaboration

2
Physics at the f resonance (I)

• Unique facility running at the f peak (DAFNE)
  sf 3.1 mb
• Extensively study all the possible decay
  channels with a
• multipurpose detector

Kaon physics

• KSKL and KK- pairs are produced in a pure
  quantum state (JPC1--)
• detection of a KS (KL) guarantees the presence
  of a KL(KS) with known momentum and direction
  (the same for KK?)

• unique feature is the production of pure and
• quasi monochromatic KS, KL, K and K- beams

• precision measurement of absolute BRs
• interference measurements in KS KL system

3
Physics at the f resonance (II)
Non-kaon physics

• Radiative f decays ( )
• f ? M g to probe the quark structure of the
  meson M
• h factory Nh ? 2x107/fb-1 (BR(f ?hg) 1.3)
• Hadronic cross-section measurement using the
  Initial State Radiation
• to vary the energy e e-? p p- g

ISR
For the theoretical estimate of the hadronic
contribution (amhadr) to the anomalous magnetic
moment of the muon (am) down to the threshold
energy for pp production
s
4
DAfNE

• ee- collider _at_ ?s 1019.4 MeV
• 2 IP (KLOE DEAR/Finuda)
• Separate e, e- rings to minimize
  beam-beam interactions
• Crossing angle 12.5 mrad
• Residual lab. momentum of f pf 13 MeV/c
• Injection during data-taking

Results presented in this talk from 2001/2 data
?L 450 pb-1 Grand total (2001/5) ?L
2.5 fb-1. L peak 1.31032 cm-2s-1
5
The KLOE detector
Electromagnetic Calorimeter
Drift Chamber

• Lead/scintillating fiber
• 98 coverage of solid angle
• 88 modules (barrel end-caps)
• 4880 PMTs (two side read-out)

• 4 m diameter 3.3 m length
• 90 helium, 10 isobutane
• 12582/52140 sense/tot wires
• All-stereo geometry

?S 0.6 cm ?L 340 cm ?? 95 cm
sE /E 5.4/ st 54 ps/


sr f 150 mm sz 2 mm sV 3 mm sp /p
0.4

• 50 ps(cal)

6
Unitarity test of CKM matrix Vus Vus / Vud

• Most precise test of unitarity possible at
  present comes from 1st row

Vud2 Vus2 Vub2 Vud2 Vus2 ? 1
D
Can test if D 0 at 10-3 level from
super-allowed nuclear b-decays 2VuddVud
0.0005 from semileptonic kaon decays
2VusdVus 0.0009

• Extract Vus from Kl3 decays. EM effects must
  be included

G(K ? pln(g)) ?
Vus fK0p-(0) 2 I(lt) SEW(1 dEM dSU(2) )
dVus
dG
dI(lt)
dfK0p-(0)
Relative uncertainty
0.5 ? 0.5 ?
G
Vus
I(lt)
fK0p-(0)

• Extract Vus/ Vud from ?(K????(?))/?(?????(?))
  ratio. Dominated by the theoretical uncertainity
  on the fK/f? evaluation from lattice QCD
• KLOE can measure all experimental inputs for
  neutral and charged kaons
• branching ratios, lifetimes, and form factors.

7
Neutral Kaons

• KS semileptonic decays
• KL dominant BRs
• KL lifetime
• KLe3 form factor slopes

8
Tagging of KS KLbeams
KS tagged by KL interaction in EmC
KL tagged by KS ? pp- vertex at IP

• KL crash
• 0.22 (TOF)

KS ? pp-
KL ? 2p0
KS ? p-en
e 30 (largely geometrical) KS angular
resolution 1 (0.3? in f) KS momentum
resolution 1 MeV
e 70 (mainly geometrical) KL angular
resolution 1 KL momentum resolution 1 MeV
9
Analysis of KS ?pen decays
Event selection (410 pb-1 )
Fit distributions of 5 variables in data with
various MC sources including peng
and ppg processes

• KS tagged by KL crash
• Two tracks from IP to EmC
• Kinematic cuts to reject background from KS ? pp
• Track-cluster association required
• e/p ID from TOF
• Identifies charge of final state

pe-
Obtain number of signal events from a constrained
likelihood fit of multiple data
distributions Normalize using KS ? pp-(g) events
in same data set
ep-
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KS? pen decay Results
Accepted by PLB
BR(KS ? p-en) (3.529 ? 0.057 ? 0.027) ?
10-4 BR(KS ? pe-n) (3.518 ? 0.051 ? 0.029) ?
10-4
BR(KS ? pen) (7.048 ? 0.076 ? 0.050)?10-4
BR(pen) KLOE 02, Phys.Lett.B535, 17
pb-1(6.91 ? 0.34stat ? 0.15syst) 10-4
Charge asymmetry

• ASAL if CPT and DSDQ
• AS ? AL signals CPT in
  mixing and/or decay with DS?DQ
• AS-AL4Re(d) if CPT holds in decays with
  DS?DQ

ASe (1.5 ? 9.6 ? 2.9)?10-3
With 2.5 fb-1 dAS ? 3 ? 10-3 ? 2 Re e
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KS ?pen results
Accepted by PLB
Test of DS DQ rule
BR(KLe3)
KLOE KS assuming DS DQ
t(KS) 89.58 ? 0.06 ps PDG t(KL) 51.01 ?
0.20 ns PDG KLOE 05 (avg.)
KTeV 04
0.40
KLOE 05
0.39
PDG 04
Test of CPT and DS ? DQ
?(x-) ( -0.2 ? 2.4 ? 0.7) 10-3
Factor 5 improvement w.r.t. current most precise
measurement (CPLEAR, s 1.3? 10-2 )
12
KS ? pmn first observation
Measurement never done before More difficult
than KSe3 1) Lower BR expect 4?10-4 2)
Background events from KS ? pp, p ? mn
same PIDs of the signal Event
counting from the fit to Emiss(pm) -Pmiss
distribution ? 3
stat error Efficiency estimate from KLm3 early
decays and from MC data control samples.
Coming soon
13
Dominant KL branching ratios

• Absolute BR measurements to 0.5-1
• from 328 pb-1 data sample
• KL tagged by KS ? pp-
• 13?106 for the measurement
• 4?106 used to evaluate efficiencies
• BRs to pen, pmn, and pp-p0
• KL vertex reconstructed in DC
• PID using decay kinematics
• Fit with MC spectra including radiative processes
  and optimized EmC response to m/p/KL
• BR to p0p0p0
• Photon vertex reconstructed by TOF using EmC (3
  clusters)
• erec 99, background lt 1

(7 of the sample)
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Dominant KL BRs and KL lifetime
Using the constraint ?BR(KL) 1 we get
PLB 632 (2006)
tL measurement from KL ? p0p0p0, 400 pb-1, f(t)
Lifetime measurement PLB 626 (2005)
tL 50.92 ? 0.17 ? 0.25 ns
KL lifetime, KLOE average tL 50.84 ? 0.23 ns
Vosburg, 72 tL 51.54 0.44 ns
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KLe3 form factor slopes

• 328 pb-1, 2 ? 106 Ke3 decays
• Kinematic cuts TOF PID to reduce background (
  0.7 final contamination )
• Separate measurement for each charge state
  (ep-, pe-) to check systematics
• t measured from p and KL momenta st/mp2 ?0.3

Accepted by PLB
Linear fit
l?103 c2/dof ep-
28.7 ? 0.7 156/181 pe- 28.5 ?
0.6 174/181 All 28.6 ? 0.5 330/363 l (28.6
? 0.5 ? 0.4) ? 10-3
Pole model MV 870(7) MeV
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KL? p p -

• Signal selection
• KL beam tagged by KS ? pp-
• KL vertex reconstructed in DC
• PID using decay kinematics
• Fit with MC spectra
• Normalization using KL ? pmn events in the same
  data set

• KLOE preliminary result
• BR(KL ? pp-) (1.963 ?0.012 ?0.017) ?10-3
• Agreement with KTeV PRD70(2004),092006
• BR(KL ? pp-) (1.975 ?0.012) ?10-3
• Confirms the discrepancy with PDG04 (2.080 ?
  0.025) ?10-3

• Using BR(KS? pp) and tL from KLOE and tS from
  PDG04
• e (2.216 ? 0.013) ?10-3 PDG04 e
  (2.280 ?0.013)?10-3

1.6 s agreement with prediction from Unitarity
Triangle
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CPT test the Bell-Steinberger relation
KS KL observables can be used for the CPT test
from unitarity
With BR(KS ? 3p0) lt 1.210-7 _at_ 90 C.L.
KLOE, PLB 619 (2005) the
main contribution to the uncertainty now comes
from h -
KLOE preliminary
Re ? (160.2 ? 1.3) ?10-5? Im ? (1.2 ? 1.9) ?
10-5
CPLEAR Re ? (164.9 ? 2.5) 10-5? Im ? (2.4
? 5.0) 10-5
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Charged Kaons

• K lifetime
• BR(Km2 )
• K semileptonic decays

19
Tagging K K-
Measurement of absolute BRs K beam tagged from
K- ? p-p0, m-n

• Two-body decays identified as peaks in the
  momentum spectrum of secondary tracks in the kaon
  rest frame 6x105 tags/pb-1
• Given the tag a dedicated reconstruction of K?
  tracks is performed, correcting for dE/dx losses
  of charged kaons in the DC

mn

pp0

K?mnm K?pp0
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Measurement of the K? lifetime

• Two different methods to measure t? allow cross
  checks on the systematic error.
• Common to both methods
• - Tag events with Km2 decay
• - Kaon decay vertex in the fiducial
  volume

16-30 ns
t (ns)
2nd method t? from the K decay time

• Use only Kp2 decays
• Use tag information to estimate the T0 i.e. the
  f?KK? time.
• Measure the kaon decay time t (tg Rg/c
  T0)gK, using the p0 clusters
• Lorentz factor gK slowly changing along the
  kaon path

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Measurement of BR(K???(?))
Signal selection

• Tag from K-??-?.
• 175 pb-1 1/3 used for signal selection,
• 2/3 used as efficiency sample
• Subtraction of p0 identified background.
• Count events in (225,400) MeV window
• of the momentum distribution in K rest
• frame (p hypothesis)

• Selection efficiency measured on data
• Radiated g acceptance computed by MC

BR(K ? mn(g)) PLB 632 (2006) 0.6366 ?
0.0009stat. ? 0.0015syst.

• ?(K???(?))/?(????(?)) ? Vus2/Vud2fK2/f?2
• From lattice calculations fK /f?
  1.198(3)(16?5)
• (MILC Coll. PoS (LAT 2005) 025,2005)

Vus / Vud 0.2294 ? 0.0026
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Measurement of BR(K?l3)

• 4 independent-tag samples Km2, Kp2, K-m2, and
  K-p2
• keep under control the
  systematic effects due to the tag selection
• Kinematical cuts to reject non-semileptonic
  decays,
• residual background is about
  1.5 of the selected K?l3 sample
• Constrained likelihood fit of m2 data
  distributions from ToF measurements
• count the number of signal
  events
• Selection efficiency from MC and correct for
  Data/MC differences.

Perform the BR measurement on each tag sample,
separately normalizing to tag counts in the same
data set, and average accounting for correlations
KLOE preliminary
BR(K?e3) (5.047 ? 0.019Stat ?
0.039Syst-Stat ? 0.004SysTag)10-2 BR(K?m3)
(3.310 ? 0.016Stat ? 0.045Syst-Stat ?
0.003SysTag)10-2

• Fractional accuracy of 0.9 for Ke3, 1.2 for
  Km3.
• The error is dominated by the error on Data/MC
  efficiency correction and the systematics
• due to the signal selection efficiency is under
  evaluation.

23
Vus from KLOE results (BRs and tL)
KL e3 KL m3 KS e3 K ? e3 K ? m3
BR 0.4007(15) 0.2698(15) 7.046(91)10-4 0.05047(46) 0.03310(40)
t 50.84(23) ns 50.84(23) ns 89.58(6) ps 12.384(24) ns 12.384(24) ns
c2/dof 1.9/4
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Vus and Unitarity

• tL 50.99(20) ns,
• average KLOE-PDG
• Including all new measurements
• for semileptonic kaon decays
• (KTeV, NA48, E865, and KLOE)

ltVusf(0)gtWORLD AV. 0.2164(4)
25
The Vus- Vud plane
unitarity
Fit results, P(c2) 0.66 Vus 0.2246 ?
0.0016 Vud 0.97377 ? 0.00027 Fit result
assuming unitarity, P(c2) 0.23 Vus 0.2264
? 0.0009
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Kaon Physics at KLOE Conclusions (I)

• Completely inclusive measurements of kaon
  semileptonic BRs with fractional
• accuracies from ?0.4 to ?1.3
• First direct measurement of BR(KS ? pmn) coming
  soon with a statistical
• accuracy of ?3.
• Two independent measurements of tL 0.5
  fractional accuracy.
• KLe3 form factors pole model.
• Significant contribution to
  determination of Vus f(0) to 0.2
• 0.3 fractional accuracy on BR(Km2(g))
  measurement
• Independent determination of Vus at 1 level
• Preliminary result on K? lifetime.
• Preliminary result on KL ? p p -

27
Kaon Physics at KLOE Conclusions (II)
Perspectives with 2.5 fb-1 of collected data

• Fractional accuracy of lt 1 on the BR for KS ?
  pen and for K?l3
• More and better measurements of form-factor
  slopes (Ke3 and Km3).
• Measurement of BR(KS ? pmn), accuracy lt 2
• Improve by a factor 10 the limit BR(KS ? 3p0) lt
  1.210-7 _at_ 90 C.L.
• obtained from a direct search on 450 pb-1
  PLB 619 (2005)
• First measurement of BR(KS ?pp-p0) from a
  direct search, with 60 accuracy
• Measure the ratio BR(K en)/BR( K mn) to
  probe e-m universality
• 
  (about 6x104 Ke2 events produced)

28
SPARES
29
KS? pen decay Strategy

• Kcrash tag
• 2 tracks from IP with associated EmC clusters
• and with Mpp lt 490 MeV (reject KS ?pp(g))
• p/e identification using TOF
• two possible mass hypothesis
• m- me m- mp
• m mp m me
• two differences between expected flight times
• comparing Ddt (e,p) with Ddt (p,e) we can
• identify p, e and determine the sign of the
  charge ? AS accessible
• reject the background from pp and pm

(e,p)
(p,e)
Ddt (e,p) t-CLU tCLU L1 /c ?(e) L2
/c ?(p) Ddt (p,e) t-CLU tCLU L1 /c
?(p) L2 /c ?(e)
30
Semileptonic decay amplitudes definitions
CP T CPT DSDQ
a ?0 ?0
b ?0 ?0 0
c ?0 ?0 0
d ?0 ?0 0 0
CPT violation
CPT violation DSDQ violation
DSDQ violation
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KS? pen test of DSDQ rule
BR(KLe3)
Test of DS DQ rule
KLOE KS assuming DS DQ
t(KS) 89.58 ? 0.06 ps PDG fit t(KL) 51.01
? 0.20 ns PDG KLOE 05 (avg.)
KTeV 04
0.40
KLOE 05
0.39
PDG 04
ratio of DS DQ violating and conserving
amplitudes (CPT cons.) SM pred.O(10-7)
?x ( -0.5 ? 3.1 ? 1.8) ? 10-3
Factor 2 improvement w.r.t. current most precise
measurement (CPLEAR, s 6.1? 10-3 )
t(KS) PDG t(KL)
KLOE 05 (avg.) BR(KL ? pen) KLOE
32
KS? pen test of CPT

• ?x- CPT viol., DS DQ viol.

AL KTeV s0.75?10-4 ?d CPLEAR
s 3.4? 10-4
AS -AL 4 ( ?x- ?d )
Factor 5 improvement w.r.t. current most precise
measurement (CPLEAR, s 1.3? 10-2 )
?x- ( -0.8 ? 2.4 ? 0.7) ? 10-3

• ?y CPT viol., DS DQ cons.

ASAL 4 (?e-?y)
?e from PDG not assuming CPT
Comparable with best result (CPLEAR from
unitarity, s 3.1? 10-3 )
?y ( 0.4 ? 2.4 ? 0.7) ? 10-3
33
KL? pp- CP violation
Number di KL ? pmn from fit of
Number of KL ? pp- from fit of
34
CPT test the Bell-Steinberger relation
Measurements of KS KL observables can be used
for the CPT test from unitarity
a- h- B(KS?pp-)
a00 h00 B(KS?p0p0)
a- g h- B(KS?pp-g)
a-0 tS/tL h- 0 B(KL?pp-p0)
a000 tS/tL h 000 B(KL?p0p0p0)
akl3 2tS/tL B(KLl3) Re ? - Re y??i( Im d Im
x) 2tS/tL B(KLl3) (ASAL)/4??i( Im d
Im x)
35
CPT test inputs to the Bell-Steinberger relation
B(KS?pp-)/B(KS?p0p0)2.2549?0.0059 B(KS?pp-g)lt9
?10-5 B(KL?pp-g)(29?1) ?10-6 B(KL?pln)0.6705?0.
0022 B(KS?pp-p0)(3.2?1.2) ?10-7 B(KL?pp-p0)0.1
263?0.0012 B(KS?p0p0p0)lt1.2 ?10-7 fSW
(0.7590.001) f000 f-0 f-g0,2p
tS 0.08958 0.00006 ns tL 50.84
0.23ns AL(3.32?0.06) ?10-3 AS(1.5?10.0)
?10-3 B(KL?pp-)(1.963 ? 0.021 )
?10-3 B(KL?p0p0)(8.65 ?0.10) ?10-4 f- 0.757
0.012 f00 0.763 0.014 Im x (0.8 0.7)
?10-2
KLOE measurements
Im x from a combined fit of KLOE CPLEAR data
36
CPT test accuracy on ai
We get the following results on each term of the
sum
10-4
2tS/tL B(KLl3) (ASAL)/4??i Im
x
a- h- B(KS?pp-)
Im
a-0 tS/tL h- 0B(KL?pp-p0)
a00 h00 B(KS?p0p0)
Re
a000 tS/tL h 000B(KL?p0p0p0)
a- g h- B(KS?pp-g)
37
KS? p0p0p0 search for a CP violating decay
Observation of KS ? 3p0 signals CP violation in
mixing and/or in decay SM prediction GS GL ?
?0002, gt BR(KS ? 3p0) 210-9 Present
published results BR(KS ? 3p0) lt 1.410-5
(direct search, SND, 99) BR(KS ? 3p0) lt
7.410-7 (interferometry, NA48, 04)
BR(KS ? 3p0) lt 1.210-7 (direct search, KLOE,
05) 90 C.L.

• Data sample 450 pb-1
• 4 x 107 KL-crash tag KS?neutrals
• Require 6 prompt photons
• large background 40K events
• Analysis based on g counting and kinematic fit in
  the 2p0 and 3p0 hypothesis
• After all analysis cuts (?3? 24.4)
• 2 candidate events found
• 3.13?0.82stat?0.37syst expected bckg

38
KS? p0p0p0 test of CPT
A limit on BR(KS ? 3p0) translates into a limit
on h000
The CPT test from unitarity was limited by the
knowledge of h000 at the 10-5 level now it is
limited by uncertainties on other factors, e.g.
h -
with full statistics of 2.5 fb-1 improved
background rejection gt BR limit improved by a
factor 10
39
KLe3 form factor slopes Pole Model Results
40
Search for KS? p0pp -

• Decay mainly CP-conserving (DI 3/2)
• BR useful to constrain K ? 3p amplitudes
• from cpt
• PDG 04 BR (3.21.2-1.0) ? 10-7
• Based on interference measurements
• CPLEAR, E621 New NA48 preliminary
• Never observed directly
• Preselection criteria (e 7)
• KL crash vertex 2 g clusters
• Kinematic fit rejects gt 99 of bkg
• 6 constraints m(p0) m(KS)
• Remaining backgrounds
• f ? KK- Cut on momentum of secondaries at ends
  of p tracks
• KS ? p0Dp0(D) Associate tracks to clusters, get
  e/p ID from TOF
• Both types Veto on extraneous prompt clusters

41
Search for KS? p0pp -

• Preliminary results with 740 pb-1 01 02 04
  data
• Signal efficiency 1.5 (including KL-crash
  eff)
• Candidates 6 events
• Background (sidebands) 3.5 events
• Number of events observed consistent with
  expectation
• Statistical error 100
• Evaluation of systematic error in progress
• Scaling these values to 2 fb-1 we expect
• Measurement of BR(KS ?pp-p0) with 60 error
• About the same precision as interference-based
  measurements
• First measurement of BR from a direct search