RECENT RESULTS FROM THE KLOE EXPERIMENT1 The Frascati ˚–factory complex DA NE1 is an e+e collider operating at a center of mass energy of ˘ 1020 MeV, the mass of the ˚-meson.At

RECENT RESULTS FROM THE KLOEEXPERIMENT

TheKLOE Collaboration∗

Presentedby StefanoMiscetti †

LaboratoriNazionalidi Frascati,INFN

00044,Frascati(RM) - ITALY

ABSTRACT

The Frascatie+e− collider, DAΦNE, operatesat a centerof massenergyaroundthemassof theφ-meson(

√s ∼ 1020 MeV) since1999.TheKLOE

experiment,designedto measureCPandCPTviolation parametersin theKSKL system,runsin oneof thetwo DAΦNE interactionregionsandhascollectedso far ∼ 500 pb−1. After a brief descriptionof the acceleratorcomplex andthedetector, we presentthephysicsmeasurementsobtainedusingthe year2000datasample(∼ 17 pb−1). Thesefirst measurementsarestatisticallylimited andarethereforefocussedonφ radiativedecaysandKS physics.We alsohighlight themeasurementsin progresson theentiredatasample.

∗TheKLOE collaboration:A. Aloisio, F.Ambrosino,A. Antonelli,M. Antonelli,C.Bacci,G.Bencivenni,

S. Bertolucci,C. Bini, C. Bloise,V. Bocci, F. Bossi,P. Branchini,S.A. Bulychjov, R. Caloi, P. Cam-

pana,G. Capon,G. Carboni,M. Casarsa,V. Casavola, G. Cataldi,F. Ceradini,F. Cervelli, F. Cevenini,

G.Chiefari,P. Ciambrone,S.Conetti,E.DeLucia,P. DeSimone,G.DeZorzi,S.Dell’Agnello,A. Denig,

A. Di Domenico,C. Di Donato,S.Di Falco,B. Di Micco,A. Doria,M. Dreucci,O. Erriquez,A. Farilla,

G.Felici,A. Ferrari,M. L. Ferrer, G.Finocchiaro,C.Forti,A. Franceschi,P. Franzini,C.Gatti,P. Gauzzi,

S.Giovannella,E. Gorini, E. Graziani,S.W. Han,M. Incagli,W. Kluge,V. Kulikov, F. Lacava,G. Lan-

franchi,J. Lee-Franzini,D. Leone,F. Lu, M. Martemianov, M. Matsyuk,W. Mei, L. Merola,R. Messi,

S. Miscetti, M. Moulson,S. Muller, F. Murtas,M. Napolitano,A. Nedosekin,F. Nguyen,M. Palutan,

E.Pasqualucci,L. Passalacqua,A. Passeri,V. Patera,E.Petrolo,L. Pontecorvo,M. Primavera,F. Ruggieri,

P. Santangelo,E. Santovetti, G. Saracino,R. D. Schamberger, B. Sciascia,A. Sciubba,F. Scuri, I. Sfil-

igoi, A. Sibidanov, T. Spadaro,E. Spiriti, G. L. Tong,L. Tortora,P. Valente,B. Valeriani,G.Venanzoni,

S.Veneziano,A. Ventura,S.Ventura,R.Versaci,G.W.Yu.† c© 2002by StefanoMiscetti,e-mail: [email protected]

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384

1 The Frascati φ–factory complex

DAΦNE1 is ane+e− collider operatingat a centerof massenergy of ∼ 1020 MeV, the

massof theφ-meson.At thedesignpeakluminosityof 5 × 1032 cm−2s−1, themachine

will produce∼ 1.5 kHz of φ’s. Theacceleratorcomplex consistsof aninjectionsystem

and a collider, composedby two main rings, in which electronand positronbeams

circulateseparately. Two interactionregions(IR) housethe experiments:KLOE2 on

oneside,DEAR(FINUDA)3,4 ontheoppositeone.Themainphysicsinterest,motivating

theconstructionof sucha complex, is themeasurementof theCP-violationparameter

ε′/ε using the KLOE detector. The two other experimentsare designedto operate

sequentiallyto performhigh-precisionmeasurementsin nuclearandatomicphysics.

Theinjectionsystemis basedona60m longLinac,whichcanaccelerateelectrons

(positrons)up to energy of 800 (550) MeV. An intermediate33 m long accumulator

ring is usedto dampthetransverseandlongitudinalemittancesof theLinacbeam,thus

relaxingtheinjectionrequirementsin thecollider. Thestrategy usedto achieve a high

luminosity consistsin accumulatinghigh-currentelectronandpositronbeams(5 A at

maximum)of 120buncheseach.Tworingsareneededin ordertominimizeperturbations

dueto beam-beamelectromagneticinteractions.The beamsintersectat the two IR’s

with a horizontalcrossingangleof ∼ 25 mrad. Theφ’s producedat resonanceenergy

havesmallmomentum(Pφ ∼ 13 MeV/c) in thelaboratoryframe.

At present,DAΦNE’speakluminosityis 7.8× 1031 cm−2s−1, still a factor7 smaller

thanthedesignvalue.This is obtainedwith ∼ 800 mA circulatingbeamcurrents.The

luminosity deliveredto KLOE is on average2.5 pb−1 per day (4 pb−1 at maximum).

This is achieved sinceKLOE is able to operatein the ”top-up” injection mode, i.e.

injectingelectronsandpositronswith colliding beamseveryfifteenminutes.Thismode

of operationis well suitedfor DAΦNE, becauseof its shortbeamlifetimes,which are

reflectedin asteepdrop-off of theluminositywith time.

KLOE hadthreedifferentdata-takingperiods: thefirst wasin 1999,mostlyspent

in machineanddetectorcommissioning.In year2000themachinedeliveredto KLOE

a total of 23 pb−1, which yielded the first relevant physics results. In year 2001 a

total integratedluminosity of 180 pb−1 hasbeencollected. In year2002datataking

hasresumedin May, with slighty higherluminosity, but with muchimprovedmachine

backgroundconditions,which is anotherkey issuefor many physicsmeasurements.

The2002runendedin September, addinganother300pb−1 on tape.

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φ decaychannel BR

K+K− 0.492 ± 0.007

KSKL 0.337 ± 0.006

π+π−π0+ ρπ 0.155 ± 0.006

ηγ 0.0013 ± 0.0003

Table1. Main decaychannelsof theφ mesonandtheir branchingratio (BR).5

2 The KLOE experiment

Themaindecaychannelsof theφ mesonarelistedin Tab. 1. Theacceleratorcomplex

DAΦNE is thereforenot only a factoryof KSKL but alsoa factoryof K+K−, ρ andη

mesons.In thecaseof thekaons,pure∗ monochromatic,low momentumKK beams

(PK ∼ 110, 126 MeV for theneutralandchargedpairsrespectively) areproduced.This

providesanefficient taggingin bothcases.Thelow speedof thekaonsis alsoa strong

motivationfor relyingon timeof flight in many stepsof theeventreconstruction.

2.1 The physicsprogram

The KLOE scientificprogram2 is focussedon the studyof CP andCPT symmetries

with neutralkaons.Thedesignof theexperimentwasdrivenby themeasurementof the

directCPviolationvia the,by now classical,“doubleratiomethod”:

Rd =∣

∣

∣

∣

η±

η00

∣

∣

∣

∣

2

=N(KL → π+π−)

N(KS → π+π−)× N(KS → π0π0)

N(KL → π0π0)= 1 + 6 <(ε′/ε). (1)

Altough thefix targetexperiments(NA48, KTeV) havealreadyprovedtheexistenceof

directCPviolationin thekaonsystembyestablishingthat<(ε′/ε) isconsistentlydifferent

from zero,† anew measurementfrom KLOE couldallow usto reachasimilarsensitivity

with acompletelydifferentsystematics.But, to reachanaccuracy of theorderof 10−4,

anintegratedluminosityin therangeof severalfb−1’s is needed.However, if andwhen

thisstatisticswill becollected,sincetheKK pairsareproducedin apurequantumstate

(JPC = 1−−, thesameof theφ meson)otherinterestingCP, CPTparametersbecome

∗In thecaseof theneutralkaons,from unitarity andfrom σ(γγ → K0K0, JP = 0+), theratio of the

processes(e+e− → KSKS + KLKL)/(e+e− → KSKL) is few ×10−10.†The most recentmeasurementsreport: (20.7 ± 2.8) × 10−4 (KTeV), (14.7 ± 2.2) × 10−4 (NA48),

(16.7 ± 2.3) × 10−4 (world average).

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accessibleto KLOE by looking at thequantum-mechanicalinterferencepatternsin the

timeevolutionof theKSKL system.6

At present,althoughtheCP, CPTmeasurementsareoutof reach,many otherphysics

topicscanbestudiedwith thecollectedstatistics.Analysesontheyear2000datasethave

producednew resultson theφ radiativedecaysinto scalar(f0, a0) andpseudoscalar(η,

η′) mesons,on theKS semileptonicdecay, andon theratio of KS decaysinto charged

andneutralpion pairs. Using the whole dataset (500 pb−1), the goal is to improve

theaccuracy on theCabibboangle(Vus) throughprecisemeasurements(0.2%)of both

KL andchargedkaonsemileptonicdecays;a betterthan1% measurementof thee+e−

hadroniccrosssectionbelow 1 GeV, and several measurementsof rareKS andKL

decays.

2.2 The detector

At DAΦNE’s energiestheKS (KL) have a meandecaypathof 0.6 (340) cm respec-

tively, thusdriving theexperiment’s dimension.Indeed,theKLOE detector7 hasbeen

designedto maximizethe numberof reconstructedKL decays. It consistsof a large

trackingchamber, a hermeticelectromagneticcalorimeteranda superconductingmag-

netproviding a solenoidalfield of ∼0.52T. Thebeampipein theinteractionregion is

sphericalin shape,10cmin radiusin orderto containall KS decays,andis madeof an

Aluminum-Berylliumalloy.

The large, 2 m radiusand 3.7 m long, tracking volume is instrumentedwith a

drift chamber8 operatingwith a low-Z, 90%He-10%iC4H10 gasmixture,enclosedby

Carbon-fiber/Epoxywalls. Thelight A, Z materialshave beenchosento optimizethe

chamberresolution,andto reduceboththephotonconversions(0.01X0) andKL→KS

regeneration.The58concentriclayersof wires(52140wires,12582readoutchannels)

arestrungin anall-stereogeometry. Themomentumresolutionis σ(p⊥)/p⊥ ' 0.4%,

from asinglemeasurementof spatialresolutionof σrφ ∼ 150µm (σz ∼2 mm).

Theelectromagneticcalorimeter9 is a samplingcalorimetermadeof leadandscin-

tillating fiber layers,15X0 thick. Thesolid anglecoverage(98%)is ensuredby barrel

modulessurroundingthedrift chamberandby modulesof two endcaps,whicharebent

outwardsto eliminatedeadzonesin theoverlapregionbetweenbarrelandendcap.The

calorimetermodulesarereadoutatthetwoendsbyatotalof 4880photomultipliers.The

calorimeterhasbeendesignedto measuretimeandenergy for photonsof energy aslow

as20 MeV, with resolutionsof 54 ps/√

E(GeV) ⊕ 50 psin time and5.7% /√

E(GeV)

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Radiativedecay BR (PDG) decaytype

ηγ (1.30 ± 0.03) × 10−2 φ → P (0 − +)γ

π0γ (1.24 ± 0.10) × 10−3 φ → P (0 − +)γ

η′γ (6.7 ± 1.5 ) × 10−5 φ → P (0 − +)γ

f0γ (3.3+0.8−0.5) × 10−4 φ → S(0 + +)γ

a0γ (8.8 ± 1.7 ) × 10−5 φ → S(0 + +)γ

Table2. Radiativedecaysof theφ meson.

in energy.

3 KLOE first physicsresults

As alreadyexplained,theKLOE physicsprogramis really a functionof theintegrated

luminosity. In year2002,we have publishedfew papers10–14 on radiative decaysand

KS physicsthataresummarizedin thefollowing paragraphs.

3.1 Resultson φ radiati vedecays

The radiative decaysof theφ mesonoffer a probeto studythe natureof light scalar

andpseudoscalarmesons.Theseprocessesaresummarizedin Tab. 2. Thefirst papers

focusedthesearchon radiativedecayswith BR of ∼ 10−4.

3.1.1 The pseudoscalarsector

In thepseudoscalarsector, themagnitudeof theφ → η′γ decayis sensitiveto thess and

gluoniumcontentof theη′ whichis not fully excludedfrom theexistingmeasurements.

A high precisionmeasurementof the branchingratio BR(φ → η′γ) is relevant for

clarifying this point. Accordingto thequarkmodel(assumingno gluoniccontentfor

η′) theπ0, η andη′ mesonsaredescribed,in thequark-flavourbasis,asfollows:

|π0〉 = 1/√

2 (|uu〉 + |dd〉) (2)

| η 〉 = cos(αp)/√

2(|uu〉 + |dd〉) + sin(αp)|ss〉 (3)

| η′〉 = − sin(αp)/√

2(|uu〉 + |dd〉) + cos(αp)|ss〉 (4)

(5)

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Fig. 1. Eventdensitydistributionsin theE1, E2 planefor dataafterpreliminaryevent

selection.

whereαp representsthepseudoscalarmixing anglein theflavourbasis.Fromtheabove

equations,andassumingtheφ mesonto bess , theratio of theBR’s for theprocesses

φ → η′γ (PSa)andφ → ηγ (PSb)is relatedto αp. A completederivationof this ratio

canbefoundin Ref.15andis parametrizedas:

Rφη′η =BR(PSa)

BR(PSb)= cotg(αp)

2

∣

∣

∣

∣

K(η′)

K(η)

∣

∣

∣

∣

3

F (αp, αv) (6)

whereK ’s aretheradiative photonmomentain theφ centerof massandF is a slowly

varyingfunctionwhichtakesintoaccountalsothecorrectquarkstructureof theφmeson.

theeventsPSa,PSbareselectedusingthedecaychains:

• φ → η′γ with η′ → ηπ+π− andη → γγ;

• φ → ηγ with η → π+π−π0 andπ0 → γγ;

The samefinal stateπ+π−γγγ is searchedfor both reactions,thusallowing the can-

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cellationof many systematiceffectsin themeasurementof Rφ−η′η. A goodseparation

betweentheη′γ andthedominantηγ events(S/B ∼ 1/100) is achievedby exploiting

thefactthattheradiativephotonhasmuchmoreenergy for thelatterevents(∼ 360 MeV

vs ∼ 60 MeV). Anothersourceof backgroundoriginatesfrom otherφ decayssuchas

φ → π+π−π0 andφ → KSKL. After a preliminaryevent selection,requiringa two

trackvertex closeto theIR andthreeneutralEMC clustersontime,akinematicfit to the

eventis performedapplyingmomentumconservationattheIR. Thisallowsusto greatly

improve themassdeterminationby adjustingthephotonenergies.A total efficiency of

22.8%,36.4%is foundfor thePSa,PSbdecaysafterapplyingalsoa looseχ2 cut and

a topologicalcut betweentheenergies(E1, E2) of thetwo mostenergeticphotons.In

Fig. 1 thescatterplot of E1, E2 is shown. Thetwo ellipsesaround360MeV aredueto

theradiativephotonof theηγ events,while thesignalfor η′ is concentratedin thecentral

ellipse.Selectingtheeventsin this region,andreconstructingtheinvariantmassof the

ππγγ system,aclearpeakat theη′ massvalueemergesovera low andflat background

(seeFig. 2). Thenumberof signaleventsis 124 ± 12stat ± 5syst.

Theratio of branchingratio is thenobtainedby normalizingto theηγ observedevents

andby takinginto accountsecondaryBR’s16 anddetectionefficiencies:12

BR(φ → η′γ)

BR(φ → ηγ)= (4.70 ± 0.47stat ± 0.31syst) × 10−3.

Thecorrespondingvaluefor thepseudoscalarmixingangleisαP = (41.8+1.9−1.6)

◦. Making

useof theφ → ηγ branchingratio16 weobtain:

BR(φ → η′γ) = (6.10 ± 0.61stat ± 0.43syst) × 10−5,

which is themostprecisedeterminationto date.Thisresultlimits thegluoniumcontent

in theη′ stateto belessthan15%.

3.1.2 The scalar sector

Although the existenceof the scalarmesonsf0(980) anda0(980) is well established,

their physical natureis still unclear. Both mesonshave a small width andsmall γγ

couplings,comparedto ordinarymesonsof thesamemass,while showing a largeKK

coupling.Themainhypothesesarethatthesestatesareqqqq, KK molecules.17,18 The

radiative decaysφ → a0γ, φ → f0γ offer a new methodto test the natureof these

mesons19 sincethevariousmodelscanbedisentangledby precisemeasurementsof the

branchingratiosandof thescalarmesonmassspectra.

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Fig. 2. φ → η′γ decay:distribution of theMππγγ invariantmass,after removal of the

ηγ identifiedevents;theestimatedresidualbackgroundis alsoshown.

Thedifferentisospinvaluesbetweenthesetwoscalarstranslatein differentaccessible

final states:thef0 (I=0) mainly decaysinto ππ while thea0 (I=1) decaysinto ηπ. We

havesearchedfor thefollowing decaychains:f0 → π0π0 (Sa)anda0 → ηπ0 (Sb)with

η → γγ, bothyielding a five photonfinal state. In thecaseof a0, anothersecondary

decayη → π+π−π0 (Sc)hasalsobeenexploited,givingafinal topologywith two tracks

andfivephotons.After apreliminaryselectionof 5 promptphotons(5 promptphotons

and2 tracksfrom the IR) a setof kinematicfits is performedto improve the energy

resolution.

In Fig. 3 we show thequality of thedatafor thesearch(Sa)by reportingtheχ2 of

the kinematicfit, the reconstructedπ0 massandvariousangulardistributions. Black

pointsaredatawhile thesolid curve is theMC expectationfor signal+background,the

backgroundis representedby theshadedarea.Thetotalefficiency is around41%andis

almostconstantasafunctionof theπ0π0 invariantmassMπ0π0 . Alsothetwootherdecays

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Fig. 3. Data-MCcomparisonfor φ → π0π0γ eventsafter preliminarselection: (a)

χ2/ndf ; (b) differencebetweenreconstructedandexpectedMπ0 value;(c),(d)angular

distributionswith all cutsapplied.cos θ is thepolarangleof theradiativephoton,cosψ

is theanglebetweentheradiativephotonandaπ0 in theπ0π0 rest-frame.

show a gooddata-MCcomparison.The decaySb still suffers of a 30% background

contaminationwhile Sc,althoughstatisticallylimited, is practicallybackgroundfree.

This is alsothefirst observationof suchadecay.

In the 16 pb−1 of the 2000datasample,we count2438± 61, 607±36, 197±15

signaleventsfor thechannelSa,Sb,Screspectively. Thesefirst studiesalreadycontain

much larger statisticsthan the previousVEPP-2Mexperiments. TheMπ0π0 (Fig. 4)

andMηπ0 (Fig. 5) spectraarethenreconstructedfor theselectedevents.Theobserved

distributionsareusedtoevaluatethebranchingratios,afterhavingnormalizedtheevents

to theφ productioncrosssection,asmeasuredin theφ → ηγ (η → γγ) threephoton

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m (MeV)

dBR

/dm

x 1

08 (M

eV-1

)φ→(f0+σ)γ

φ→f0γ

φ→σγ

Interference

-25

0

25

50

75

300 400 500 600 700 800 900 1000

Fig. 4. Differentialdecayrateasa functiononMπ0π0 . Thetotal fit andthe individual

contributionsarealsoshown.

process:

BR(φ → π0π0γ) = (10.9 ± 0.3stat ± 0.5syst ) × 10−5 (7)

BR(φ → ηπ0γ, η → γγ) = (8.51 ± 0.51stat ± 0.57syst) × 10−5 (8)

BR(φ → ηπ0γ, η → π+π−π0) = (7.96 ± 0.60stat ± 0.40syst) × 10−5 (9)

wheretheη decayBR’s in theηπ0γ final stateshave beenscaledaccordingto Ref.16.

The above valuesincludepossiblecontributions from the resonantdecayφ → ρπ0,

followedby ρ → π0γ or ρ → ηγ. In orderto extractthef0 anda0 parametersfrom the

massspectra,afit hasbeenperformedontheMπ0π0 andMηπ0 distributionsrespectively.

Themodelspectrumis takenasthesumof f0γ (a0γ), ρπ andinterferenceterms.For the

scalarmesoncontributiontheformulationof Ref.19isused,whichisbasedonφcoupling

to a chargedkaonloop. Thevectormesontermis takenfrom VMD calculations.20 At

theend,thecontribution from theρπ final stateturnsout to benegligible in bothcases;

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Fig. 5. φ → ηπ0γ: Mηπ invariantmassdistributionsfor two differentsampleson data

after resolutionandefficiency unfolding: five photonssample(opencircles),andfive

photonsandtwo trackssample(blackcircles). Theresultsof thefit aresuperimposed

asasolid line. Dashedcurvesarethecontributionsof thesingleterms.

moreover, a goodfit to theMπ0π0 spectrumcanonly be obtainedincluding, together

with the f0, a contribution from anotherlight scalarmeson(σ) anda strongnegative

interferencetermbetweenthetwo. Branchingratiosarefinally obtainedfor thef0 final

state:10

BR(φ → f0γ, f0 → π0π0) = (14.9 ± 0.7) × 10−5,

andfor thea0 final state:11

BR(φ → a0γ, a0 → ηπ0) = (7.4 ± 0.7) × 10−5.

KLOE resultsonthescalarmesons,basedonthe2000datasample,arecompatiblewith

thefour quarksmodelin thecaseof thef0, but donotagreewith thesamemodelin the

caseof a0 decay.

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β* K L

Eve

nts/

10-3

K →

→S π0π0

KS π+π-

0

2k

4k

6k

8k

10k

12k

14k

16k

18k

20k

0.2 0.21 0.220.2 0.21 0.22 0.23 0.24

( )

K

K corr.

00.2 0.21 0.22 0.23 0.24

2k

4k

6k

8k

10k

12k

14k

→

→

S π0π0

S π+π-

Fig. 6. Distribution of β in the φ centerof masssystem,β∗, for KL interactingin

the calorimeterwith KS→π0π0andKS→π+π−selections.In the insertion,the same

distributionsareshown aftercorrectingfor thewrongbunchassignement.

3.2 KS physicsresults

As alreadystatedin the introduction,neutralkaonsat a φ–factoryareproducedin a

coherentJPC = 1−− quantumstate,which is a superpositionof KSKL stateswith

oppositemomenta:

|i〉 = 1/√

2(|KS , ~P 〉|KL ,−~P 〉 + |KL , ~P 〉|KS ,−~P 〉) (10)

Thisallowsthetaggingof pureandalmostmonochromatickaonbeams:thedetectionof

aKL (KS) tagsthepresenceof aKS (KL) in theoppositehemisphereof theapparatus.

In particular, averyrobustandalmost unbiasedKS tagisprovidedby theinteractionsof

KL in thecalorimeter:in about30%of thecasestheKL doesnotdecayin thedetector,

reachesthecalorimeterbarrelandinteractstherein.A time-of-flightmeasurementthen

allows a cleanselectionof theseinteractionssinceβKL∼ 0.218 (seeFig. 6). Results

from the2000datasetcomefrom 5.4 × 106 taggedKS.

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Fig. 7. Distributionsfor KS eventstaggedbyKL interactionin thecalorimeter:(top)

energy andcos θ spectrafor eventswith four neutralclusters,(bottom)distribution of

momentumfrom IR.

3.2.1 The ratio BR(KS → π+π−(γ))/BR(KS → π0π0)

Thefirst topicaddressedis themeasurementof theratio:

Rπ = BR(KS → π+π−(γ))/BR(KS → π0π0) (11)

which is a steptowardsthe determinationof <(ε′/ε) with the doubleratio method.

Althoughthedoubleratio is known with aprecisionof 0.1%thesingleratiosareknown

only with aprecisionof ∼ 2%. Ourgoalis to measureeachsingleratiowith aprecision

of 0.1%. The precisemeasurementof the singleratio for theKS, is alsorelevant for

the extractionof the isospinI = 0, I = 2 amplitudesandphasesfor theK → 2π

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Sourceof systematics RelativeError (%)

Eventcount 0.14

Tracking 0.26

Clustercounting 0.20

Triggering 0.10

Ratioof tagefficiencies 0.55

Cosmic-rayveto 0.21

Total error 0.70

Table3. Contributionsto thefractionalerroronRπ.

process.In our measurementof Rπ, effort wasspentto correctlytake into accountthe

soft radiationemittedin π+π−γ decay.

From the sampleof taggedKS decaysthe ratio of π+π−(γ) andπ0π0 branching

ratiosis extractedby selectingtwo categoriesof events:2 tracksfrom theIP for π+π−

decaymode,andat leastthreepromptphotonsfor theπ0π0. Thequality of thedatais

shown for bothsamplesin Figs.7a,b. While theselectionefficiency hasbeenevaluated

from theMonteCarlosimulation,all otherefficiencies,suchasthetrackreconstruction

efficiency andthephotondetectionefficiency havebeenevaluatedfrom data.

Moreover, specialeffort hasbeendevotedin theassessmentof theπ+π−(γ) selec-

tion efficiency asa functionof thecenterof massphotonenergy E∗γ , from zeroto the

maximumallowedenergy of ∼170MeV. In orderto performafully inclusivemeasure-

ment,theselectionefficiency hasbeenevaluatedfrom MonteCarloandfoldedinto the

theoreticalE∗γ spectrum.21 Thecorrectedratio is then:13

BR(KS → π+π−(γ) )

BR(KS → π0π0 )= 2.236 ± 0.003stat ± 0.015syst.

The contribution of the systematicserrorsare listed in Tab. 3. Our result is slightly

higherthanthecurrentworld averagevalue(Rπ = 2.197 ± 0.026) althoughthiscanbe

expected,sinceourmeasurementincludestheentireradiativespectrum.

3.2.2 SemileptonicKS decay

The secondresult is the measurementof BR(KS → π±e∓ν(ν)) with 5% accuracy,

basedon thelargestsamplecollectedsofar. Theamplitudesof theK0K0 to undergoa

semileptonicdecaywith adeterminedleptoncharge(l±) aredescribedby thefollowing

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equationsdependinguponif the∆S = ∆Q rule is satisfiedor violated:

A(K0 → l+) = a+ b A(K0 → l−) = a∗ − b∗ (∆S = +∆Q) (12)

A(K0 → l−) = c+ d A(K0 → l+) = c∗ − d∗ (∆S = −∆Q) (13)

wherea,c (b,d) arecomplex amplitudesCPT conserving(violating). AssumingCPT

conservation, the ratio of the decayratesof theKS andKL integratedover the final

leptonchargeresultsto:

Γ(KS → l+) + Γ(KS → l−)

Γ(KL → l+) + Γ(KL → l−)= 1 + 4<(c/a) = 1 + 4<(x) (14)

To improve the presentlimits on <(x)16 it is necessaryto reach2% accuracy on the

measurementof theKS semileptonicbranchingratio. This will be accomplishedby

KLOE whentheongoinganalysisoverthewholedatasamplewill beconcluded.Using

thesamesample,wecanalsoperformthefirstmeasurementof theKS chargeasymmetry

Als:

Als =

Γ(KS → l+) − Γ(KS → l−)

Γ(KL → l+) − Γ(KL → l−)(15)

TheprecisionexpectedonAls is of theorderof 1%.

Theselectionof semileptonicKS → πeν candidateeventsalsostartsfromthesample

taggedby theKL interactionsin thecalorimeter:eventsareselectedby requiringtwo

tracksof oppositechargeformingavertex neartheIR. A cuton thetwo trackinvariant

massis appliedto reduceKS → π+π− background. Semileptoniceventsare then

identifiedon thebasisof π/e assignmentusingthe time-of-flight measurementfor the

two tracks.TheKL clustergivesanestimateof theKS momentum,thusallowing the

kinematicconstraintof theevent. Thedifferencebetweenthemissingenergy andthe

missingmomentumat thevertex is finally computed;sucha differenceshouldbezero

forKS → πeν decays.TheEmiss −pmiss spectrumis shown in Fig.8, togetherwith afit

to thesumof MonteCarlosimulationsof thesignalandKS → π+π− background.The

freeparametersof thefit arethesignal/backgroundnormalizationandthesignalyield,

giving 627±30events.

Correctingfor all the selectionanddetectionefficiencies,andnormalizingto the

numberof observedKS → π+π− events,themeasuredbranchingratio is:14

BR(KS → π±e∓ν(ν)) = (6.91 ± 0.34stat ± 0.15syst) × 10−4

in agreementwith the expectedvalue(6.70 ± 0.07) × 10−4 assumingthe validity of

∆S = ∆Q rule.16

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Fig. 8. KS semileptonicdecay: theexperimentalspectrumfor Emiss − pmiss shows a

clearpeakatzero,correspondingtoKS → πeν decays;amaximumlikelihoodfit with

theMonteCarlosignal+background(KS → π+π−) shapesis superimposed.

4 Physicsitemsunder study

Anothersetof interestingphysicsmeasurementsis alreadyin advancedstageover the

wholedatasample.Wereportthemin thefollowing chapters.

4.1 Measurementof the hadronic crosssection

The measurementof the hadroniccrosssection,σhad = σ(e+e− → hadrons), at low

energy is extremelyrelevant to improve the theoreticalerror on the anomalousmag-

neticmomentof themuon,aµ = (gµ − 2)/2. Thehadroniccontribution,aµhad, cannot

becalculatedat low energy with perturbative QCD while, following a phenomenolog-

ical approach,canbe evaluatedfrom the measurementof R(s) troughthe following

dispersionrelation:

aµhad = (

αmµ

3π)3

∫

4m2π

dsR(s)K(s)

s2, (16)

whereR(s) is σ(e+e− → hadrons) /4πα(s)2

3sandK(s) is the kernel. The 1/s2 factor

in eq.16 enhancesthecontribution of σhad at low energy to aµhad. Theerroron aµ

had

is thedominatingcontribution to thetotal theoreticalerroraµthe andit is relatedto the

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Q2(GeV 2)

0

5000

10000

15000

20000

25000

30000

35000

40000

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fig. 9. Raw spectrumof thee+e− → π+π−γ eventsselectedwith anacceptancecut:

θγ below 15◦ andabove165◦.

limited knowledgeof σ(e+e− → hadrons). The discrepancy betweentheoryandthe

mostrecentexperimentaldeterminationof aµ differsdependingif τ -leptondataareused

or not in evaluatingaµhad 22 (from 1.6to 3.0standarddeviations).Thissituationpushes

for a new precisemeasurementof σhad at low energy particularlyin theρ region. An

accuracy of 0.6%wasrecentlyachievedin this region.23

The novelty of the measurementcarriedout in KLOE is that, even operatingat a

fixedcenterof massenergy∼ Mφ, theσhad canbeevaluatedbetweenthe2π’sthreshold

andMφ usingthe radiative return, i.e. throughthe processe+e− → π+π−γ. In this

process,theemissionof photonsdueto initial stateradiation(ISR) lowerstheavailable

invariantmassof thehadronicsystem.

DefiningQ2 asthe invariantmassof theπ+π−systemandθγ to be the maximum

polarangleof theemittedphotonusedin theanalysis,themeasureddifferentialcross

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Fig. 10. The form factor|Fπ|2 asa functionof Q2. Thecurvesreportedare: theone

of thefit describedin thetext (black)andtheonefrom CMD-2 (grey). They areamost

indistinguishable.

sectionfor theprocesse+e− → π+π−γ is relatedto σhad asfollows:

Q2 · dσ(e+e− → π+π−γ)/dQ2 = σ(e+e− → hadrons) ·H(Q2, θγ) (17)

A solid theoreticalknowledgeof theradiatorfunction,H, is neededin orderto extract

σhad from the measuredcrosssection. Different theorygroupshave calculatedthese

correctionsuptonext to leadingorder(NLO) andimplementedit in anew MC generator

calledPHOKHARA.24 This generatoris alreadyusedin KLOE, theabsoluteaccuracy

claimedisof 0.5%.Comparedtothetraditionalmethodof theenergyscanthistechnique

offerstheadvantagethatthesystematics,onbothnormalizationanddefinitionof beam

energy, is commonto all measuredpoints. However, a precisedeterminationof FSR

andotherresonancecontribution (asfor instancee+e− → f0γ) is required.

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A moreextendedreporton theKLOE analysiscanbe foundelsewhere,25 herewe

recallonly thebasicanalysissteps.Theinitial sampleis selectedrequiringthepresence

of two chargedtrackscomingfrom IR andproducedwith polaranglesbetween40◦ ÷140◦. A powerful π-e discriminationis performedusinga likelihoodmethodbasedon

time-of-flightandshowershapein thecalorimeter. Cuttingonthetrackmassvariable‡ a

clearseparationbetweene+e−γ,µ+µ−γ andπ+π−γ isobtained.A residualbackground

contaminationof few %existsatlowQ2 values(< 0.4 GeV2) fromeventsφ → π+π−π0.

An acceptancecut on θγ definethe samples:small-angle(θγ < 15◦) andlarge-angle

(θγ > 45◦).

At themoment,theanalysisis focusedon thesmall-angledatasample.Out of the

200pb−1 takenin 2001andalreadyreconstructed,we have analyzed∼ 73 pb−1. The

e+e− → π+π−γ event yield correspondsto ∼ 15000events/pb−1. In Fig. 9 the raw

spectrumis shown, the ρ − ω interferenceis clearly seen,evidenceof the excellent

momentumresolutionof thedrift chamber.

NeglectingFSRinterference,thepionform factorcanbeextracted,for eachi-th bin

in Q2, from theobservedraw spectrumof e+e− → π+π−γ,Nobsi , asfollows:

|Fπ(Q2i )|2 =

Nobsi

ε(Q2i ) · L · σpl(Q2

i ), (18)

whereε(Q2i ) is theglobalefficiency, L is the integratedluminosityandσpl(Q

2i ) is the

differentialcrosssectionfor e+e− → π+π−γ (seeeq.17)evaluatedto NLO andassum-

ing pointlike particles.Thesystematicerroron theefficiency is ∼ 2% while theerror

on theluminosityandonσpl is alreadybelow the1% level. Theform factorextracted

from eq.18 is shown in Fig.10andhasbeenfitted following theKS parametrization:

Fπ(Q2) =BWρ(1 + αBWρ)/(1 + α) + βBWρ′

1 + β, (19)

whereBW is a standardBreit-Wignershape.Themassandwidth of theρ andtheα,

β parameterswereleft to vary freelyon thefit while theotherparameterswerefixedto

thePDGvalues.Resultsarein goodagreementwith what foundby CMD-2 although

usinga slightly differentparametrization.As it canbeobservedin Fig. 10 thereis still

someresidualbackgroundto fight at low energiesandwe have not yet tried a serious

unfolding of the experimentalresolution. The goal is to publishthe form factorwith

errorsbelow 1%.

‡TheMtrk variableis obtainedapplying4-momentumconservation,underthehypothesisthat thefinal

stateconsistsof two particleswith samemassandonephoton.

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Fig. 11. Densitydistribution for theDalitz-plotof eventswith π+π−π0 final state.

4.2 Dynamicsof the decayφ → π+π−π0

About15%of theφ decaysproceedsto theπ+π−π0 final state,representingthelargest

non-kaonicφ decay. This processis dominatedby theρπ intermediatestatesand,by

simpleisospinarguments,we expectall thethreeρ chargedstatesto beproducedwith

similar rate. This decayis thereforewell suitedto performa studyof massor width

differencesamongρ+, ρ−, ρ0. In theliterature26 hasalsobeenshown thatadirectdecay

φ → π+π−π0 ispossiblealthoughwith amuchreducedrate.Thepublishedanalyses27,28

from CMD-2 (SND) rely on 12.000(500.000)events.KLOE reconstructsthis kind of

eventswith anoverallefficiency of 30%guaranteeingalargedatasamplewith verysmall

contamination.Even whenrestrictingthe analysisto 2000data,a sampleof 2 × 106

eventsis availableto derive themassesandwidthsof theρ andtheamountof thedirect

termandits interferencewith themainρπ term.

Thedynamicsof thedecayis describedby thedensityof theDalitz-plot. Thetwo

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Mρ0 (MeV) Γρ (MeV) ∆M0,± (MeV) ∆M+,− (MeV)

775.9± 0.6± 0.7 145.2± 1.2± 1.0 -0.5± 0.3± 0.7 +0.7± 0.4± 0.7

Table4. Resultsonmassesandwidthsof theρ.

σ (nb) ad φd

470± 11 0.093± 0.011± 0.015 2.45± 0.09± 0.10

Table5. Resultsoncrosssectionanddirecttermfor φ → π+π−π0.

standardvariables,X = T+ − T− andY = T 0, areused,with T beingthepionkinetic

energy. Theaccessiblephasespaceis boundedin thealmosttriangularregionasshown

in Fig. 11. Thedensitydistribution in theDalitz-plot shouldrevealthevectornatureof

theφ-meson.Sincetheπ’s,producedin thefinal state,arepseudoscalarstheonly way

to build avectoris by theproductof two of thepionmomenta(i.e. ~Pππ = ~Pπ+ × ~Pπ−).

Thedensityis thenproportionalto thesquareof theamplitude:

|Atot|2 = |~Pππ|2 · |∑

Ai|2, (20)

whereAtot = Adir+Aρπ+Aωπ. All theseamplitudesarecomplex functionsrepresenting

thedirectterm,themainintermediatestateρπ andthenegligible ωπ term.Theρπ term

is describedasthesumof threeBW shapes(k = 0,+,− dependinguponthecharge

stateof theρ) with a total width which dependson theinvariantmass,Q2k, of thefinal

stateπ+π−(π+π0, π−π0) asfollows:

Γk(Q2k) = Γk(Pπ(Q2)/Pπ(Mk))

3(mk/Qk), (21)

wheremk aretheρ massfor the threechargedstates,andPπ is themomentumof the

pionsin theircenterof masssystem.Thedatashown in Fig. 11hasbeenfit with eq.20

aftercorrectingfor selectionefficiency andintegratedluminosity. Theresultsarelisted

in Tabs.4,5 andarestill to beconsideredpreliminarysinceafew checksarein progress

on thesystematicerrorsconnectedto theevaluationof theselectionefficiency. At the

moment,wesummarizetheresultsasfollows:

• We do observe a dominantρπ termanddefinetelyestablishedtheexistenceof a

direct term with an amplitudeof ∼ 9% anda phaseof 2.4 radswith respectto

theρπ term. This is consistentwith theboundssetby CMD-2 whichperformeda

similar analysis.

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W (MeV)

cro

ss s

ectio

n (

µb )

0

0.2

0.4

0.6

0.8

1

1015 1020 1025 1030

Fig.12. Visiblecrosssectionfor theprocessφ → KSKL, withKS→π+π−, asafunction

of thecenterof massenergy,W . Thefit superimposedis correctedfor ISR effects.

• ThevalueofMρ is in agreementwith PDG,while thevalueof Γρ is slightly lower

thanPDGwhichquotes150MeV.

• No differenceis found,at a permil level, betweenρ± andρ0, in agreementwith

thePDGvalueof 0.4± 0.8MeV.

• No differenceis found,atapermil level, betweenρ+, ρ−. No entriesexistsof this

measurementin PDG.

4.3 A precisedetermination of the neutral kaon mass

Theneutralkaonmasscanbemeasuredusingtheprocessφ → KS, L with KS→π+π−

if theφ-massis usedto accuratelycalibratethescaleof thecenterof massenergy, W .

Dueto thesmallmassdifference,∆M = (Mφ − 2Mk) ∼ 26 MeV, it is convenientto

expressW asa functionof kaonquantities:

W = EKS+ EKL

∼ 2Ek (22)

and

M2k = W 2/4 − P 2

k (23)

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405

497.4

497.5

497.6

497.7

497.8

497.9

498

CMD NA48 KLOE

neutral kaon mass (MeV/c2)

Fig. 13. Comparisonof thethreemostprecisemeasurementsof theneutralkaonmass.

in thiswayweget: ∆Mk ∼ δW/2. Similarly, thefractionaluncertaintiesonMk dueto

afractionalerroronPk is reducedby afactorβ2k ∼ 0.05, allowing ahighprecisionmass

measurement.For thisanalysis,wehaveusedthe11pointsof theφ-scanperformedin

2001(seeFig.12). Eachcollectedpointconsistsof ∼ 50 nb−1 of integratedluminosity.

TheaverageW value,of eachrun,isobtainedfitting thee+e− invariantmassdistribution

in Bhabhaevents; relative precisionfor eachpoint is ∼ 3 keV. The ISR affects the

availablecenterof massenergy of an amountwhich is processdependent;we called

fk(W ) the correctionfor φ → KSKL events. In this way for eachrun, we obtain

Wk = W − fk(W ). By measuringthemomentaof thekaonsandusingtheaverageφ

momentumobtainedwith Bhabhaeventswe getthemassthrougheq.23. Singleevent

precisiononMk is around430keV.

To calibratethescaleof thecenter-of-massenergy, we have measuredtheφ-mass

fitting the line shapeof the processe+e− → φ → KS, L with KS→π+π−; the fitting

functiontakesinto accounttheISR andtheinterferenceeffectsof theρ andω mesons

with theφ. Theonly freeparametersarethemassandwidth of theφ andthepeakcross

section.Theresultof thefit is superimposedondatain Fig. 12. Weget:

Mφ = (1019.329 ± 0.011stat) MeV.

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Fig. 14. DistributionofMγγ for theeventswith aKL tagandtwo photonsconnectedto

theneutralvertex.

Thevaluefound,with asimilarfitting procedure,by theCMD-2experiment29 is instead:

Mφ = (1019.504 ± 0.011stat ± 0.033syst) MeV.

In this casethe energy scaleis measuredusingthe resonancedepolarizationmethod.

Comparingthe two valueswe getaW -scalecorrectionfactorof 1.00017(i.e. a mass

shift of around170keV). Theaveragevalueof thekaonmassobtainedis:

MK = (497.584 ± 0.005stat) MeV.

Small contributionsto the systematicerror onMK aregiven by the momentumscale

(6 keV) andby the fk(W ) correction(7 keV); the dominantcontribution is still due

to thedeterminationof theenergy scalewhich correspondsto ∼ 18 keV. In Fig. 13, a

comparisonbetweenour resultandothermeasurementsof thekaonmassis shown.

4.4 BR measurementof the KL → γγ decay

Altough still statisticallylimited, thereare interestingphysics topicsalso in rareKL

decays.At present,we arecarryingout a precisemeasurementof theBR(KL → γγ)

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Fig. 15. Distribution of τK for theKL eventswith morethanthreephotonsconnected

to theneutralvertex.

sinceits valueis a goodtestfor Chiral PerturbationTheorypredictions.This decayis

verypreciselymeasuredby NA4830 throughtheratioR2γ,3π0 :

R2γ,3π0 =BR(KL → γγ)

BR(KL → π0π0π0)= (2.81 ± 0.01stat ± 0.02syst) × 10−3. (24)

In our search,we first selecta KL tagged-samplerequiringa KS→π+π− decay.

Wethenreconstructtheneutralvertex connectedto theKL, NV, usingthepositionand

timing of theneutralclusters,NC,associatedto thisvertex andtheknowledgeof theKL

flight directionprovidedby theKL tag.At theendof thisprocedure,aspatialresolution

of ∼ 1 ÷ 2 cmonNV is obtained.Weretainfor furtheranalysistheeventshaving only

two photonsconnectedto NV. After few topologicalcutsareapplied,andplotting the

invariantmassof thetwo photons,acleanpeakattheKL mass(seeFig.14)is observed.

The backgroundis small andis concentratedat low massvalues(Mγγ < 400 MeV).

Thesignal/backgroundratio obtainedintegratingover thewholespectrumis 12. In a

sampleof 150 pb−1 we count8537± 117 events. Normalizationis performedwith

theKL→3 π0 eventscountedin the samesample. They areobtainedwith the same

techniquecountingall theeventswith NC ≥ 3. TheresultingratioR2γ,3π0 is:

R2γ,3π0 = (2.84 ± 0.04 ± 0.03) × 10−3 (25)

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At present,weareanalyzingall availablestatisticsandworkingonreducingthesystem-

atic errors. Using the normalizationsampleof KL→3 π0 we have alsomeasuredthe

lifetime of theKL asreportedin Fig. 15.

4.5 Physicsreachwith chargedkaons

Similarly to theKSKL pair, theφ-mesondecays49% of thetime into aK+K− which

correspondsto a K± productionrate of 1.5 × 106/pb−1. At the moment,we have

collected∼ 0.8×109K+K−. Alsofor thisprocess,auniquefeatureof KLOE is tagging

i.e. observingaK+(K−) in onesideof thedetectorallowsto establishthedirectionand

thepresenceof theK−(K+) in theoppositehemisphere.Giventheavailablerates,we

canmeasurewith highaccuracy theproductioncrosssectionandall thedecaybranching

ratiosof thechargedkaons.

Oneinterestingmeasurementwhichis beingcarriedoutis thedeterminationof |Vus|fromKl3 decays:K± → π0l±ν calledK+

l3 andK0 → π±µ∓ν calledK0l3 wherel stands

eitherfor electronor muon. The mostaccuratetestof the unitarity condition,on the

CKM-matrix, isprovidedby themeasurementsof |Vus|, |Vud| and|Vub| matrixelements;

presentexperimentalvalueindicatesa (1.0 ÷ 2.7)σ effectof deviation from unitarity.5

Thepartialwidth of agenericKl3 decay31 is givenby:

Γ(Kl3) =G2

FM5K

192π3·SEW ·C2

K |Vus ·f+(0)|2 ·IK(m2K ,m

2π,m

2l , f+,0(q

2))×(1+δk), (26)

whereGF is theFermiconstant,IK is thephase-spaceintegralandf+(q2), f0(q2) arethe

form factorsof hadronicvectorcurrentwith changeof strangeness.Theseform factors

incorporatealsotheisospinbreakingcorrection(betweenK±,K0) andthesecondorder

SU(3)breakingeffectarisingfroms−d, u quarkmassdifference.Radiativecorrections

arefactorizedin thetwotermsSEW (electroweakshort-distancecorrection)andδk (QED

long distancecorrection).Thewidth, Γ(Kl3), is usuallymeasuredasBR(Kl3) × ΓK .

Measuringalsotheq2 dependenceof theform factor:

f+,0(q2) = f+,0(0) ·

(

1 +λ+,0

m2π

q2)

, (27)

theintegralIK canbeevaluatedleavingasthebasicobservabletheproduct|Vus ·f+(0)|.The form factor at q2 = 0 is determinedby theory and it is the dominant(0.86%)

contributiontotheerroron|Vus|. ThedeterminationofVus fromKl3 decays5 corresponds

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to: Vus = 0.2196 ± 0.0026 (1.18%relative error). Theerrorson themeasurementcan

beparametrizedas:

∆|Vus||Vus|

=[

0.5 ×(

∆BR

BR⊕ ∆τk

τk

)]

⊕(

0.05 × ∆λ+

λ+

)

⊕(

∆f+(0)

f+(0)

)

, (28)

whereτk is theK mesonlifetime. Asidefromthetheoreticalerroronf+(0), thereisalso

a0.6%errorontheBR measurements(still drivenbyKe3 decays).As explainedabove,

themeasurementin bothK+e3 andK0

e3 eventsallowsoneto testthecurrentunderstanding

on SU(2),SU(3)breakingeffectsanda new measurementof BR for bothK+e3 andK0

e3

is necessary. This is alsoa strongmotivation to determinethesevaluesin the same

experiment.

Thestrategy for themeasurementof BR(K+e3) is to usethevery cleansignatureof

the decaysK± → π±π0 andK± → µν to tag the otherchargedkaon in the event.

The taggingefficiency is estimateddirectly on datausingfor instance,the redundant

calorimetricinformation.Fromthestatisticalpointof view, weexpectto reacharelative

erroron theBR below 0.1%usingthewholeavailablestatistics.

5 Futur eprospects

Many otherphysicstopicsarebeingcarriedout by thecollaborationand,altoughin a

verypreliminarystateto discusspublicly, it is interestingto list thework in progressto

show thephysicsreachof theexperiment.As far asthehadronicphysicsis concerned,

thefactor30 increasein statisticswill allow usto:

• performan exhaustive studyof the f0(980), a0(980), η′ mesonswith a factor5

reductionon the relative statisticalerror. In the meanwhileworking on the sys-

tematicssideweexpectto reach:

1. ∼ 1-2%precisionon theBR for theprocessesφ → f0γ, φ → a0γ;

2. ∼ 3% precisionon theBR for theprocessφ → η′γ anda stringentlimit on

gluoniumcontent;

• look for theinterferenceschemebetweenthef0(980)andthefinal stateradiation

in e+e− → π+π−γ at largephotonpolarangles;

• startthestudyof rarephysicsin theη sector. Wehaveatthemoment∼ 5×106 η’s.

We expectto setupperlimits on rareC-violatingdecayssuchasη → γγγ. The

high statisticssamplewill also permit to measurethe Dalitz-plot slopesof the

decayη → π0π0π0 andη → π+π−π0.

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In thekaonsectorwe intendto to thefollowing:

• usingthesemileptonicdecayof theKS we canperforma testof the∆S = ∆Q

ruleandmeasurewith 1%precisionthechargeasymmetry;

• improve theprecisionin thedeterminationof Rπ to 0.1%while showing alsofor

thefirst time thedifferentialdecayratefor KS → π+π−(γ) asa functionof Eγ;

• measurethe BR of the CP violating decayof theKL (e.g to π0π0, π+π−) with

around1%precision;

• measureall singleKL decayto betterthan1%;

• startthesearchon rareKS decays(e.g.KS→π0π0π0,KS→π+π−π0);

• measuretheincoherentregenerationcrosssectionofKL onBe/C;theboostof the

φ mesonoriginatesalsoa ∼ 10 MeV spreadin thekaonmomentapermittingto

performthismeasurementalsoasa functionof PK ;

• Altough with limited statistics,the quantuminterferometryschemeis beingob-

servedin φ → KSKL → π+π−π+π− channel.Theintentionis to show this and

all theotherinterferometryeffects.

On theφ sectorwe expectto measureto betterthan1% all maindecaychannelsof the

φ mesonwhile performingalsothemeasurementof Γee andΓµµ.

6 Conclusions

DAΦNE performancehasimprovedconsiderablyafterthefirst two yearsof datataking

delivering now a luminosity of > 3.5 pb−1 per day in the KLOE interactionregion.

A long winter shutdown is scheduledto roll-in the FINUDA detectorin the opposite

interactionregion while installing a new interactionregion in KLOE. The goal is to

reacha peakluminosity of 5 × 1032cm−2s−1 in order to startCP-CPTstudiesin the

2003-2004data-takingperiods.

TheKLOE detectoris fully operationalandreconstructiondetailsarewell under-

stood. From the small sampleof the 2000datataking, we have resultsonKS andφ

radiative decayswhich improve thepreviousPDGvalues.At themoment,the recon-

structionof datasummarytapesfor all datacollectedup to now is completedandthe

analysisis startedon the whole statistics: new resultsareexpectedon rareKS, KL

decaysandonmany itemsof chargedkaons,η, η′, ρ, a0 andf0 mesons.Wealsoexpect

to publishaveryprecisemeasurementof thehadroniccrosssectionat low energies.

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7 Acknowledgments

We thankthe DAΦNE teamfor their efforts in maintaininglow backgroundrunning

conditionsandtheir collaborationduringall data-taking.

We alsothankGiuseppeFabioFortugnofor his efforts in ensuringgoodoperations

of theKLOE computingfacilities.

Thiswork wassupportedin partby DOEgrantDE-FG-02-97ER41027;by EURO-

DAPHNE,contractFMRX-CT98-0169;by theGermanFederalMinistry of Education

andResearch(BMBF) contract06-KA-957;

by Graduiertenkolleg ’H.E. Phys.andPart. Astrophys.’ of DeutscheForschungsge-

meinschaft,ContractNo. GK 742;by INTAS, contracts96-624,99-37;andby TARI,

contractHPRI-CT-1999-00088.

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RECENT RESULTS FROM THE KLOE EXPERIMENT1 The Frascati ˚–factory complex DA NE1 is an e+e collider operating at a center of mass energy of ˘ 1020 MeV, the mass of the ˚-meson.At