Recent results from KLOE

Cesare Bini

Universita’ “La Sapienza” and INFN Roma

1. The KLOE physics program2. The KLOE detector3. Status of the experiment4. Results on neutral kaon decays5. Results on radiative decays6. Conclusions and perspectives

1. The KLOE physics program.

e+e W = m = 1019.4 MeV b

Decay channels K+K = 49.2% Charged Kaon decays + CP/CPT tests K0K0 = 33.8% Neutral Kaon decays + CP/CPT tests ( ’ / ) = 15.5% 3 pion decay (shape parameters) = 1.3% Radiative decays: pseudoscalar: physics = ~10-3 “ ’ = ~10-4 “ pseudoscalar mixing angle = ~10-4 scalar f0 = ~10-4 “ a0 e+e = ~10-4 Conversion decays: transition form factor F e+e = ~10-5 “ “ F e+e Initial state radiation (e+e ) 2m < W < m

e+e aroundpeak (energy scan) resonance parameters

2. The KLOE detector: Drift chamber Calorimeter (Pb-scint.fib.) Magnetic field = 0.56 T

Drift chamber: Large volume d=4m l=3.3m He – Isob 90-10 gas mixt. Momentum resolution p/p < 0.4%

Calorimeter: Energy resolution:/E = 5.4% / (E(GeV)) Time resolution

t = 55 ps / (E(GeV))40 ps (cal.)120 ps (coll.time)

Present day performance: peak averageL(cm2 s1) 5·1031 3.5·1031

day L dt (pb1) 3 1.8

3. Status of the experiment

Data taken from april 1999 todecember 2001~ at peak

+ 1 energy scan

Analysis status: 2000 data ~completed (25 pb-1 7.5 x 107 ) 2001 data in progress (190 pb-1 5.7 x 108 )

All results are still preliminary

4.Results on Neutral Kaon decays

Neutral kaons produced in a pure quantum JPC = 1state:

pK = 110 MeV S = 6 mm L = 3.5 m

pKpKpKpK

N

pKpKpKpKi

SLLS

2

2

1 0000

Tagging: pure KS and KL beams analysis of kaon decays double ratio ( ’ / )

Interferometry studies

Example of KSKL

KS tagging by identification of KL interacting

in the EmC (“KL crash”) [ ~50% of KL ]

Selection cuts:

Eclus > 200 MeV

|cos(clus)| < 0.7

0.1950 0.2475

( = KL velocity in the rest frame)

Position of the KL KS momentum

Tagging efficiency tag~ 30%

KS tagging by identification of KL interacting

in the EmC (“KL crash”) [ ~50% of KL ]

Selection cuts:

Eclus > 200 MeV

|cos(clus)| < 0.7

0.1950 0.2475

( = KL velocity in the rest frame)

Position of the KL KS momentum

Tagging efficiency tag~ 30%

* distribution of “KL crash”

Example of KSKL “crash”

KLOE has now about 6 107 tagged KS. All channels are accessible. Results from 2000 data (5.4 106 tagged KS) on: (1) R=(KS +- ) / (KS 00 ) (2) BR(KS e )

(1) R=(KS +- ) / (KS 00 ) Motivations: First part of double ratio Extractions of Isospin Amplitudes and Phases A0 A2 and 0-2 consistent treatment of soft in KS +- () (PDG data contain ambiguities)

[Cirigliano, Donoghue, Golowich 2000] Selection procedure: 1. KS tagging 2. KS +-() two tracks from I.P + acceptance cuts: fully inclusive measurement

(E up to E

max=170 MeV) (E*) from MC folded to theoretical spectrum

correction = (-3.4 ± 0.1) x 10-3

3.KS 00

neutral prompt cluster (E>20 MeV and (T-R/c) < 5t ) at least 3 neutral prompt clusters (0 e+e- included)

Result: Nev (KS +- ) = 1.098 x 106

Nev (KS 00 ) = 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 E

cut )

With 2001 data (180 pb-1) improvement on: absolute scale tagg.eff. Bias statistics of control sub-samples E

spectrum

(2) BR(KS e )

Motivation: If (CPT ok) .AND. (S=Q at work): (KS e ) = (KL e ) BR(KS e ) = BR(KL e ) x (L/S) = ( 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 “background”) time of flight ( electron vs pion) final signal variable = Emiss-|pmiss|

BR evaluation: normalization to KS + ((BR)~0.5%) both charge states are considered (well separated charge asymmetry)

ToF selection illustrated for MC: 1. KS + MC events

2. KS e MC events

Result:

Nev(KS e = 627 ± 30[after the fit, residual background subtraction is included]

BR(KS e ) = (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

e

)

5.Results on radiative decays

1. Pseudoscalar + ’

According to quark model: assuming: no other content (e.g. gluonic)) 0 = (uu-dd)/2 = cosP (uu+dd)/2 + sinPss ’ = -sinP (uu+dd)/2 + cosPss

assuming: = ss state (V=0)

assuming: no OZI-rule violations g( ’) = FscosVcosP – FqsinVsinP

g( ) = FscosVsinP + FqsinVcosP

( V P = mixing angles in the flavour base)

( Fs Fq = form factors)

( ’) K’

R = = cotg2P ( )3

( ) K

Decay chain used: (same topology 2T + 3 photons / final states different kinematics) (a) (b) ’

Selection: 2t (ET1+ET2<430 MeV) + 3: 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 spectrumof ’

BR( ’) R = = (5.0 0.5stat 0.3syst) x 10-3

BR( )

P = ( 40.8 1.7)o [ P = (-13.9 1.7)o ]

P = ( 39.3 1.0)o J/ decays and others [Feldmann Kroll 2002]

BR(’ ) = (6.5 0.6stat 0.4syst) x 10-5

. Scalar (0++ quantum numbers) + [f0(980) I=0, a0(980) I=1]

(f0 , f0 , ) 5 final state

(“ ) 2t + 1 final state: huge background from:

ISR (radiative return)

FSR + interference (signal “hidden”)

a0 a0 ) [ ]5 final state (40%)

[ ]9 final state (32%)

[ ] 2t + 5 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 lowest mass scalar qq nonet [Tornqvist 1999] f0 , a0 sensitive to f0,a0 nature [Achasov, Ivanchenko 1989]: phenomenological framework (kaon loop model) coupling constants

g(KK) from (K+K-) g(f0KK) g(a0KK) f0, a0 model g(f0) g(a0) M() M() spectra

f0,a0

Kaon loop final state

radiative

Main background sources (5 final states): e+e 0 Other background sources (not 5 final states): or

Selection procedure: 5 prompt E > 7 MeV kinematic fit (without mass const.) Result: Nev = 2438 61 BR()=(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 M spectrum (kaon loop): contributions from f0 + “strong” negative interference negligible contribution

Fit results: M(f0) = 973 1 MeV g2(f0KK)/4 = 2.79 0.12 GeV2

g(f0) /g(f0KK) = 0.50 0.01

g() = 0.060 0.008

BR( f0) = (1.49 0.07)x10-4

Measured in 2 final states: (Sample 1) (5) is the main background 5 selection (see ) + kinem. fit (Sample 2) (2t + 5) Negligible bckg with the same topology: e+e 0 2t + 4KSKL (KL prompt decay) 2t + 4/6 2t + 5 selection + kinem.fit

Results: (Sample1) Nev = 916 Nbck = 309 20 BR() = (8.5 0.5stat 0.6syst)x10-5

(Sample2) Nev = 197 Nbck = 4 4 BR() = (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 M spectra: dominated by a0 negligible

Fit results: M(a0) = 984.8 MeV (PDG) g2(a0KK)/4 = 0.40 0.04 GeV2

g(a0) /g(a0KK) = 1.35 0.09

BR( a0) = (7.4 0.7)x10-5

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)/4(GeV2)2.79 0.12 “super-allowed” “OZI-allowed” “OZI-forbidden” g(f0) /g(f0KK) 0.50 0.01 0.3-0.5 0.5 2

g2(a0KK)/4(GeV2)0.40 0.04 “super-allowed” “OZI-forbidden” “OZI-forbidden”

g(a0) /g(a0KK) 1.35 0.09 0.91 1.53 1.53

4q doesn’t describe a0 parameters; 4q compatible with f0 parameters;

f0/a0 ratio sensitive to isospin mixing [Close Kirke 2001]: BR( f0) g2(f0KK) = 6.0 0.6 ; = 6.9 1.0 BR( a0) g2(a0KK)

if Ff0(R) = Fa0(R) S= (47 2)o [no isospin mixing S = 45o]

f0 = ss f0 = (uu+dd)/ 2

a0 = (uu-dd)/2 a0 = (uu-dd)/ 2

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

radiative decays improve previous “PDG” knowledge Analysis of 2001 data (190 pb-1) in progress. Expected new results will be: rare KS decays [ , , limits on 3] KL decays [ , ….] K decays decays (6 x106 produced) [chiral perturbation theory checks] hadronic cross-section (e+e ) 2m < W < m

Data taking 2002 starting now 500 pb-1 realistic by end of the year

Detector calibrated on-line (run by run ~ ½ hour): - Drift Chamber s-t relations “ momentum scale (MK) - Calorimeter energy scale (e+e- ) “ time scale + offset “ - s and p evaluated (Bhabha KS, KL)

Start reconstruction and event classification (~ 1 hour delay)

Efficiencies are evaluated and monitoredusing 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 trigger efficiency in case of KSKL configuration if KS triggers measure KL

trigger efficiency if KL triggers measure KS

trigger efficiency

Decay chain used: (same topology 2T + 3 photons / final states different kinematics) (a) (b) ’

MC

Selection: 2 tracks (ET1+ET2<430 MeV) + 3 photons: kin. fit (no mass constraint) only (a) and (b) selected (negligible bkg.)

[MeV

]

MC

E1 vs E2 (after kin. fit) [MeV]

(a) vs. (b) [N(b) ~ N(a) / 100] Photon energy spectrafrom MC cut on E

(E1, E2 two largest energy photons)

spectrum (MeV) for

spectrum (MeV) for ’E1 vs. E2 for MC ’

Data

E1 vs E2 (after kin. fit) [MeV]

Results on data (17 pb-1)

N(a) = 50210 220 N(b) = 125 13stat +bck

Invariant mass spectrumof ’ is ok.

N(’) () BR( ) BR() R = x x = (5.3 0.5stat 0.4syst) x 10-3

N() (’) BR(’ ) BR() P = (40.0 1.6)o [ P = (-14.7 1.6)o in the octet-singlet base] ( P = (39.3 1.0)o world average [Feldmann Kroll 2002])

BR(’ ) = (6.8 0.6stat 0.5syst) x 10-5

(improve respect to previous measurements)

5.Results on radiative decays

1. Pseudoscalar + ’

Mesons below 1 GeV accessible: is ~ ss state (M) probe quark s content of meson M

Meson finalstate

Kaon loop K+K-

Meson coupling to KK loop: probeof s content

Meson coupling to final state

According to quark model: assuming: no other content (e.g. gluonic)) 0 = (uu-dd)/2 = cosP (uu+dd)/2 + sinPss ’ = -sinP (uu+dd)/2 + cosPss

assuming: no OZI-rule violations g( ) = FscosVsinP + FqsinVcosP

g( ’) = FscosVcosP – FqsinVsinP

( V P = mixing angles in the flavour base)( Fs Fq = form factors)

assuming: f = ss state (V=0)

( ’) K’

R = = cotg2P ( )3

( ) K

(1) R=(KS +- ) / (KS 00 ) Motivations: First part of double ratio Extractions of Isospin Amplitudes and Phases A0 A2 and 0-2 consistent treatment of soft in KS +- () (PDG data contain ambiguities) [Cirigliano, Donoghue, Golowich 2000] Selection procedure: 1. KS tagging 2. KS +-() two tracks from I.P + acceptance cuts. fully inclusive measurement (E

up to E

max=170 MeV)

3.KS 00

neutral prompt cluster (E>20 MeV and (T-R/c) < 5t ) at least 3 neutral prompt clusters (0 e+e- included)

Soft photon emission: (E*) not uniform correction Theoretical spectrum folded with experimental efficiency = (-3.4 ± 0.1) x 10-3

. Scalar (0++ quantum numbers) + [f0 I=0, a0 I=1, I=0]

(f0 , f0 , ) 5 final state

(“ ) 2t + 1 final state: huge background from:

ISR (radiative return)

FSR + interference (signal “hidden”)

a0 a0 ) [ ]5 final state (40%)

[ ]9 final state (32%)

[ ] 2t + 5 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];

f0 , a0 sensitive to f0,a0 nature [Achasov, Ivanchenko 1989]:

f0,a0

Kaon loop

Finalstate