Recent results from KLOE

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Recent results from KLOE Cesare
Bini Universita La Sapienza and INFN Roma

1. The KLOE physics program
2. The KLOE detector
3. Status of the experiment
4. Results on neutral kaon decays
5. Results on f radiative decays
6. Conclusions and perspectives

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1. The KLOE physics program.

• ee? ? f W mf 1019.4
  MeV sf3 mb
• Decay channels
• ? KK? 49.2 Charged Kaon decays
  CP/CPT tests
• ? K0K0 33.8 Neutral Kaon decays
  CP/CPT tests ( e / e )
• ? pp?p0 15.5 3 pion decay
  ? rp (r shape parameters)
• ? hg 1.3 Radiative decays
  pseudoscalar h physics
• ? p0g 10-3
  
• ? hg 10-4
  ? pseudoscalar mixing angle
• ? ppg 10-4
  scalar ? f0
• ? hp0g 10-4
  ? a0
• ? h ee- 10-4 Conversion decays
  transition form factor Ffh
• ? p0ee? 10-5
  Ffp
  
• ee? ? pp-g Initial state radiation ?
  s(ee? ? pp-) 2mp lt W lt mf
• ee? ? f around f peak (energy scan) ? f
  resonance parameters

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2. The KLOE detector Drift chamber
Calorimeter (Pb-scint.fib.) Magnetic field
0.56 T
Drift chamber Large volume d4m l3.3m He
Isob 90-10 gas mixt. Momentum resolution
dp/p lt 0.4
Calorimeter Energy resolution s/E 5.4 /
?(E(GeV)) Time resolution st 55 ps /
?(E(GeV))?40 ps (cal.)?120 ps (coll.time)
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3. Status of the experiment
Data taken from april 1999 to december 2001 at f
peak 1 energy scan
Analysis status 2000 data
completed (25 pb-1 ? 7.5 x 107 f) 2001
data in progress (190 pb-1 ? 5.7 x
108 f) All results are still preliminary
Present day performance
peak average L(cm?2 s?1)
51031 3.51031 ?day L dt
(pb?1) 3 1.8
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4.Results on Neutral Kaon decays
Neutral kaons produced in a pure quantum JPC
1?? state pK 110 MeV lS 6 mm lL 3.5
m
Example of f ? KSKL
p0p0
pp-

• Tagging
• pure KS and KL beams
• ? analysis of kaon decays
• ? double ratio ? ( e / e )
• Interferometry studies

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• KS tagging by identification of KL interacting in
  the EmC (KL crash) 50 of KL
• ?Selection cuts
• Eclus gt 200 MeV
• cos(qclus) lt 0.7
• 0.1950 ? b ? 0.2475
• (b KL velocity in the f rest frame)
• ?Position of the KL ? KS momentum
• Tagging efficiency etag 30

b distribution of KL crash
Example of f ? KSKL ? pp- crash

KLOE has now about 6 107 tagged KS. All
channels are accessible. Results from 2000 data
(5.4 106 tagged KS) on (1) RG(KS
? pp- ) / G(KS ? p0p0 ) (2) BR(KS
? p? e? n )
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• RG(KS ? pp- ) / G(KS ? p0p0 )
• Motivations
• ? First part of double ratio
• ? Extractions of Isospin Amplitudes and Phases
  A0 A2 and d0-d2 ?? consistent treatment
• of soft g in KS ? pp- (g) (PDG data
  contain ambiguities)
• Cirigliano, Donoghue, Golowich 2000
  
• Selection procedure
• 1. KS tagging
• 2. KS ? pp-(g) two tracks from I.P
  acceptance cuts fully inclusive measurement
• (Eg up to Egmax170 MeV) eppg (Eg)
  from MC ? folded to theoretical g spectrum
• ? correction
• D (-3.4 0.1) x 10-3

3.KS ? p0p0 neutral prompt cluster
(Eggt20 MeV and (T-R/c) lt 5st )
at least 3 neutral prompt clusters
(p0? ee-g included)
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Result Nev (KS ? pp- ) 1.098 x 106 Nev (KS
? p0p0 ) 0.788 x 106 R 2.239 0.003stat
0.015syst ? stat. uncertainty at 0.14 level
? contributions to systematics tagging eff.
Ratio 0.55 photon counting
0.20 tracking
0.26 Trigger
0.23 -------------------------------------- Total
syst. uncertainty 0.68 PDG 2001 average is
2.197 0.026 ( without clear indication
of Egcut )
With 2001 data (180 pb-1) improvement on ?
absolute scale ? tagg.eff. Bias ? statistics
of control sub-samples ? Eg spectrum
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• (2) BR(KS ? p? e? n )
• Motivation
• ? If (CPT ok) .AND. (DSDQ at work)
• G(KS ? p? e? n ) G(KL ? p? e? n )
• BR(KS ? p? e? n ) BR(KL ? p? e? n ) x (GL/GS)
• ( 6.704 0.071
  ) x 10-4
• (using all PDG information).
• Only one measurement (CMD-2 1999)
• ( 7.2 1.4
  ) x 10-4
• Selection procedure
• ? Vertex with two tracks from I.P.
• ? kinematics (against huge pp- background)
• ? time of flight ( electron vs pion)
• ? final signal variable Emiss-pmiss
• BR evaluation
• ? normalization to KS ? p p- (s(BR)0.5)

ToF selection illustrated for MC 1. KS ?
p p- MC events
2. KS ? p? e? n MC events
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Result ? Nev(KS ? p? e? n) 627 30 after
the fit, residual background subtraction is
included BR(KS ? p? e? n ) (6.79 0.33stat
0.16syst) x 10-4 ? stat. uncertainty at 4.7
level ? contributions to systematics
tag eff, ratio 0.6
tracking vertex 2.0 time
of flight 0.8 trigger
t0 0.9
-----------------------------------
Total systematics 2.4
BR(KS ? p? e? n )
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5.Results on f radiative decays

1. f ? Pseudoscalar g ? hg ? p0g
   ? hg

According to quark model ? assuming no other
content (e.g. gluonic)) p0 (uu-dd)/?2 h
cosaP (uudd)/?2 sinaPss h -sinaP
(uudd)/?2 cosaPss ? assuming f ss state
(aV0)
? assuming no OZI-rule violations g(f ? hg)
FscosaVcosaP FqsinaVsinaP g(f ? hg)
FscosaVsinaP FqsinaVcosaP ( aV aP mixing
angles in the flavour base) ( Fs Fq form
factors)
G(f ? hg) Kh R
cotg2aP ( )3
G(f ? h g) Kh
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• Decay chain used (same topology 2T 3 photons /
  final states different kinematics)
• (a) f ? hg ? pp-p0g ? pp- 3g
• (b) f ? hg ? h pp-g ? pp- 3g
• Selection
• ? 2t (ET1ET2lt430 MeV) 3g kin. fit (no mass
  constraint)
• ? only (a) and (b) (negligible bkg.) BUT N(b)
  N(a) / 100

Results N(a) 50210 ? 220 N(b) 125 ?
13stat bck
Invariant mass spectrum of hg

• BR(f ? hg)
• R (5.0 ? 0.5stat ?
  0.3syst) x 10-3
• BR(f ? hg)
• aP ( 40.8 ? 1.7)o qP (-13.9 ? 1.7)o
• aP ( 39.3 ? 1.0)o J/y decays and
  others
• 
  Feldmann Kroll 2002
• BR(f ? hg ) (6.5 ? 0.6stat ? 0.4syst) x 10-5

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• 2. f ? Scalar (0 quantum numbers) g
  f0(980) I0, a0(980) I1
• ? p0p0g (f0g sg, f0 , s ? pp) ? 5g
  final state
  
• ? pp-g (
  ) ? 2t 1g final state huge background
  from
• 
  ISR (radiative return)
• 
  FSR interference (signal
  hidden)
• ? hp0g (a0g a0 ? hp)
  h ? gg ? 5g final state
  (40)
• 
  h ? p0p0p0 ? 9g final state
  (32)
• 
  h ? pp-p0 ? 2t 5g final
  state (23)

Motivations f0, a0, not easily interpreted as
qq states other interpretations suggested
? qqqq states (lower mass) Jaffe 1977 ?
KK molecule (m(f0,a0)2m(K)) Weinstein, Isgur
1990 ? f0(980) , a0(980) and s ? lowest
mass scalar qq nonet Tornqvist 1999 f ?
f0g , a0g ? sensitive to f0,a0 nature Achasov,
Ivanchenko 1989
phenomenological framework (kaon loop model)
? coupling constants
radiative g
g(fKK) from G(f?KK-)
g(f0KK) g(a0KK) f0, a0 model g(f0pp)
g(a0hp) M(p0p0) M(hp) spectra
f
f0,a0
Kaon loop final state
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f ? p0p0g

• Main background sources (5g final states)
• ee? ? wp0 w ? p0g
• f ? hp0g h ? gg
• Other background sources (not 5g final states)
• f ? hg h ? gg (3g) or h ? p0p0p0 (7g)
• Selection procedure
• ? 5 prompt g Eg gt 7 MeV
• ? kinematic fit (without mass const.)
• Result
• Nev 2438 ? 61
• ? BR(f ? p0p0g )(1.09 ? 0.03stat ?
  0.05syst)x10-4
• CMD-2 (0.92 ?0.08
  ?0.06)x10-4
• SND
  (1.14 ?0.10 ?0.12)x10-4
• Fit to the Mp0p0 spectrum (kaon loop)
• contributions from f ? f0g

Fit results
M(f0) 973 ? 1 MeV
g2(f0KK)/4p 2.79 ? 0.12 GeV2
g(f0pp) /g(f0KK) 0.50 ? 0.01
g(fsg) 0.060 ? 0.008
BR(f ? f0g ? p0p0g ) (1.49 ? 0.07)x10-4
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f ? hp0g
Measured in 2 final states (Sample 1) h ? gg
(5g)
? p0p0g is the main background ? 5g selection
(see p0p0g) kinem. fit (Sample 2) h ? pp-p0
(2t 5g) ?
Negligible bckg with the same topology
ee? ? wp0 w ? pp-p0
2t 4g f ? KSKL (KL prompt
decay) 2t 4/6g ? 2t 5g
selection kinem.fit
Results (Sample1) Nev 916 Nbck 309 ? 20
? BR(f ? hp0g) (8.5 ? 0.5stat ? 0.6syst)x10-5
(Sample2) Nev 197 Nbck 4 ? 4 ? BR(f ?
hp0g) (8.0 ? 0.6stat ? 0.5syst)x10-5
CMD-2 (9.0 ?2.4
?1.0) x 10-5 SND
(8.8 ?1.4 ?0.9) x 10-5 Combined fit to the
Mhp0 spectra dominated by f ? a0g
negligible f ? r0p0 ?hp0g
Fit results
M(a0) 984.8 MeV (PDG) g2(a0KK)/4p
0.40 ? 0.04 GeV2 g(a0hp) /g(a0KK) 1.35 ?
0.09 ?BR(f ? a0g ? hp0g) (7.4 ? 0.7)x10-5
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Interpretation of KLOE results on scalars (within
the context of kaon-loop framework) (preliminary)
parameter KLOE
result 4q model qq(1) model
qq(2) model g2(f0KK)/4p
(GeV2) 2.79 ? 0.12 super-allowed
OZI-allowed OZI-forbidden
g(f0pp) /g(f0KK) 0.50 ? 0.01
0.3-0.5 0.5
2 g2(a0KK)/4p (GeV2)
0.40 ? 0.04 super-allowed
OZI-forbidden OZI-forbidden
g(a0hp) /g(a0KK) 1.35 ? 0.09
0.91 1.53
1.53
f0 ss f0 (uudd)/ ? 2 a0
(uu-dd)/?2 a0 (uu-dd)/ ? 2
? 4q doesnt describe a0 parameters ? 4q
compatible with f0 parameters ? f0/a0 ratio
sensitive to isospin mixing Close Kirke 2001
BR(f ? f0g )
g2(f0KK)
6.0 ? 0.6
6.9 ? 1.0 BR(f ? a0g)
g2(a0KK) if Ff0(R)
Fa0(R) ? qS (47 ? 2)o no isospin mixing ? qS
45o
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• 6. Conclusions and perspectives
• ? DAFNE performance has improved considerably
• during the first two years of KLOE data
  taking
• ? KLOE detector well performing and under
  control
• ? From 2000 data (25 pb-1) results on
• KS decays
• f radiative decays
• improve previous PDG knowledge
• ? Analysis of 2001 data (190 pb-1) in progress.
  Expected new results will be
• rare KS decays
  ?pp-g , ? gg , limits on ? 3p
• KL decays
  ?gg , ? p0p0 .
• K? decays
• h decays (6 x106 h
  produced) chiral perturbation theory checks
• hadronic cross-section
  s(ee? ? pp-) 2mp lt W lt mf
• ? Data taking 2002 starting now ? 500 pb-1
  realistic by end of the year

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Detector calibrated on-line (run by run ½
hour) - Drift Chamber s-t relations
momentum scale (MK) - Calorimeter
energy scale (ee-? gg)
time scale offset - ?s and pf evaluated
(Bhabha KS, KL)
? ? Start reconstruction and event
classification ( 1 hour delay)
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Efficiencies are evaluated and monitored using
data control samples ? photon detection
efficiency 99 on most of the energy
range decrease below 100 MeV ?
tracking efficiency 97.5 decrease at
small pT and q ? trigger efficiency in
case of KSKL configuration if KS triggers ?
measure KL trigger efficiency
if KL triggers ? measure KS
trigger efficiency
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• Decay chain used (same topology 2T 3 photons /
  final states different kinematics)
• (a) f ? hg ? pp-p0g ? pp- 3g
• (b) f ? hg ? h pp-g ? pp- 3g

Selection ? 2 tracks (ET1ET2lt430 MeV) 3
photons kin. fit (no mass constraint) ? only
(a) and (b) selected (negligible bkg.)

• (a) vs. (b)
• N(b) N(a) / 100
• Photon energy spectra
• from MC ? cut on Eg
• (E1, E2 two largest energy
• photons)

g spectrum (MeV) for hg
g spectrum (MeV) for hg
E1 vs. E2 for MC hg
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Results on data (17 pb-1) N(a) 50210 ? 220
N(b) 125 ? 13stat bck Invariant mass
spectrum of hg is ok.

• N(hg) e(hg) BR(h ? pp-p0) BR(p0
  ? gg)
• R x x
  (5.3 ?
  0.5stat ? 0.4syst) x 10-3
• N(hg) e(hg) BR(h ? pp-h)
  BR(h ? gg)
• ? aP (40.0 ? 1.6)o qP (-14.7 ? 1.6)o in
  the octet-singlet base
• ( aP (39.3 ? 1.0)o world average
• Feldmann Kroll 2002)
• BR(f ? hg ) (6.8 ? 0.6stat ? 0.5syst) x 10-5
• (improve respect to previous measurements)

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5.Results on f radiative decays
Mesons below 1 GeV accessible f is ss state ?
G(f?Mg) probe quark s content of meson M

• f ? Pseudoscalar g
• ? hg
• ? p0g
• ? hg

Meson coupling to final state
g
Meson
f
final state
According to quark model ? assuming no other
content (e.g. gluonic)) p0 (uu-dd)/?2 h
cosaP (uudd)/?2 sinaPss h -sinaP
(uudd)/?2 cosaPss ? assuming no OZI-rule
violations g(f ? hg) FscosaVsinaP
FqsinaVcosaP g(f ? hg) FscosaVcosaP
FqsinaVsinaP ( aV aP mixing angles in the
flavour base) ( Fs Fq form factors) ?
assuming f ss state (aV0)
Kaon loop KK-
Meson coupling to KK loop probe of s content
G(f ? hg) Kh R
cotg2aP ( )3
G(f ? h g) Kh
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• RG(KS ? pp- ) / G(KS ? p0p0 )
• Motivations
• ? First part of double ratio
• ? Extractions of Isospin Amplitudes and
• Phases A0 A2 and d0-d2 ?? consistent
• treatment of soft g in KS ? pp- (g)
• (PDG data contain ambiguities)
• Cirigliano, Donoghue, Golowich 2000
  
• Selection procedure
• 1. KS tagging
• 2. KS ? pp-(g)
• two tracks from I.P acceptance cuts.
• fully inclusive measurement
• (Eg up to Egmax170 MeV)
• 3.KS ? p0p0
• neutral prompt cluster

Soft photon emission eppg (Eg) not uniform ?
correction Theoretical g spectrum folded with
experimental efficiency ? D (-3.4
0.1) x 10-3
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• 2. f ? Scalar (0 quantum numbers) g f0
  I0, a0 I1, s I0
• ? p0p0g (f0g sg, f0 , s ? pp) ? 5g
  final state
  
• ? pp-g (
  ) ? 2t 1g final state huge background
  from
• 
  ISR (radiative return)
• 
  FSR interference (signal
  hidden)
• ? hp0g (a0g a0 ? hp)
  h ? gg ? 5g final state
  (40)
• 
  h ? p0p0p0 ? 9g final state
  (32)
• 
  h ? pp-p0 ? 2t 5g final
  state (23)

Motivations f0, a0, not easily accomodated in
a qq nonet ? qqqq states (lower mass)
Jaffe 1977 ? KK molecule
(m(f0,a0)2m(K)) Weinstein, Isgur
1990 f ? f0g , a0g ? sensitive to f0,a0
nature Achasov, Ivanchenko 1989
g
f0,a0
f
Final state
Kaon loop