A. ALOISIO

A. ANTONELLI

A. DENIG

A. DI DOMENICO

A. DORIA

A. FARILLA

A. FERRARI

A. PASSERI

A. SCIUBBA

A. SIBIDANOV

B. DI MICCO

B. SCIASCIA

B. VALERIANI

C. BACCI

C. BINI

C. BLOISE

C. DI DONATO

C. FORTI

C. GATTI

D. LEONE

E. DE LUCIA

E. GRAZIANI

E. PASQUALUCCI

E. PETROLO

E. SANTOVETTI

E. SPIRITI

F. AMBROSINO

F. BOSSI

F. CERADINI

F. CERVELLI

F. CEVENINI

F. LACAVA

F. LU

F. MURTAS

F. NGUYEN

F. PERFETTO

F. SCURI

G. BENCIVENNI

G. CAPON

G. CARBONI

G. CHIEFARI

G. DE ZORZI

G. FELICI

G. FINOCCHIARO

G. LANFRANCHI

G. SARACINO

G. VENANZONI

G. XU

GORINI, Edoardo

I. SFILIGOI

I. VILLELLA

J. LEE FRANZINI

L. MEROLA

L. PASSALACQUA

L. PONTECORVO

L. TORTORA

M. ANTONELLI

M. DREUCCI

M. INCAGLI

M. L. FERRER

M. MARTEMIANOV

M. MATSYUK

M. MOULSON

M. NAPOLITANO

M. PALUTAN

M. PRIMAVERA

M. TABIDZE

M. TESTA

O. ERRIQUEZ

P. BRANCHINI

P. CAMPANA

P. CIAMBRONE

P. DE SIMONE

P. FRANZINI

P. GAUZZI

P. SANTANGELO

P. VALENTE

R. CALOI

R. D. SCHAMBERGER

R. MESSI

R. VERSACI

S. A. BULYCHJOV

S. BERTOLUCCI

S. CONETTI

S. DELL'AGNELLO

S. DI FALCO

S. GIOVANNELLA

S. MISCETTI

S. MULLER

S. VENEZIANO

S. VENTURA

T. CAPUSSELA

T. SPADARO

V. BOCCI

V. KULIKOV

V. PATERA

VENTURA, Andrea

W. KLUGE

W. MEI

English

Archivio Istituzionale della Ricerca- Università del Salento

arXiv:hep-ex/0402030 v1   20 Feb 2004KLOE Results on Rare K0 DecaysKLOE Collaboration∗Presented by S. Dell’Agnello† , INFN-LNF, Frascati (RM), 00044, ITALYAbstractThis paper describes the neutral Kaon dataset andphysics measurements of KLOE at DAΦNE. A brief dis-cussion on the prospects for detector upgrades and analysisof otherKS rare decays is also included.K0 DATASETThe KLOE detector is described in detail elsewhere [1].The experiment has integrated a luminosity of 25/170/280pb−1 in the years 2000/1/2, corresponding to 27/180/296·106 producedKLKS events. The highest instantaneousluminosity has been 8· 1031 cm−2 sec−1, while the highestdaily luminosity has been 4.5 pb−1.BENCHMARK K0 MEASUREMENTSKLOE has started itsK0 physics program with bench-mark measurements which have firmly established its ca-pability in this field. Most analysis share these features:• Request aKL or KS tag. The tagging efficiency ismeasured from data control samples (an ultimate 0.1%accuracy is expected for the full 0.5 fb−1 luminosity).• Trigger efficiency is measured mainly from the data.•√s, ande+e− interaction point (IP) are measured on-line run-by-run with Bhabha scattering events. Typi-cal accuracies for 0.1 pb−1 runs are:σ(√s) ∼ 40 keV,σ(PΦ) ∼ 30 keV,σ(XIP ) ∼ σ(YIP ) ∼ 30µm.∗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, T. Capussela, G. Carboni, F. Ceradini, F.Cervelli,F. Cevenini, G. Chiefari, P. Ciambrone, S. Conetti, E.De Lu-cia, P. De Simone, G. De Zorzi, 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. Fer-rari, M. L. Ferrer, G. Finocchiaro, C. Forti, P. Franzini, C.Gatti,P.Gauzzi, S. Giovannella, E. Gorini, E.Graziani, M. Incagli,W. Kluge, V. Kulikov, F. Lacava, G. Lanfranchi, J. Lee-Franzini, D. Leone, F.Lu, M. Martemianov, M. Matsyuk, W.Mei,L. Merola, R. Messi, S. Miscetti, M. Moulson, S. Müller,F.Murtas, M. Napolitano, F. Nguyen, M. Palutan, E.Pasqualucci,L. Passalacqua, A. Passeri, V. Patera, F. Perfetto, E. Petrolo,L. Pontecorvo, M. Primavera, P. Santangelo, E. Santovetti,G. Saracino, R. D. Schamberger, B. Sciascia, A. Sciubba, F. Scuri,I. Sfiligoi, A. Sibidanov, T. Spadaro, E. Spiriti, M. Tabidze,M. Testa, L. Tortora, P. Valente, B. Valeriani, G. Venanzoni,S. Veneziano, A. Ventura, S. Ventura, R. Versaci, I. Villella, G. Xu† E-mail: simone.dellagnello@lnf.infn.it• φ production time,Tφ, are reconstructed offline withaccuracyσ(Tφ) ∼ 50 psec.• Monte Carlo simulation (MC) are used mainly foracceptance and geometry corrections. The MC pho-ton and track reconstruction efficiencies are properlyscaled to data control samples.An important measurement performed by KLOE is theratio of the branching ratios (BR) ofKS → ππ decays.KS → ππ DecaysKS decays are tagged via the reconstruction ofKL in-teractions in the EM calorimeter. The measurement ofΓ(KS → π+π−(γ))/Γ(KS → π0π0) is a benchmark forthe measurement ofǫ’/ ǫ via the double ratio method andit can shed light on the∆I = 1/2 suppression rule. Italso gives information on the values of the strong phaseshifts (δ0 − δ2) and the electromagnetic isospin break-ing (γ0 − γ2). The KLOE result is fully inclusive ofπ+π−γ final states, it has an unprecedented statistical ac-curacy of∼0.1% and is limited at present by the sys-tematic uncertainty which is estimated primarily from thedata. Γ(KS → π+π−(γ))/Γ(KS → π0π0) = 2.236±0.003(stat)± 0.015(syst) [2] (see Figure 1). The present0.7% systematic error is expected to scale down to be-low 0.2% for 0.5 fb−1. From this measurement we extractχ0 − χ2 = (48± 3)◦ (χI = δI + γI ), which is to be com-pared to the estimate from the PDG widths ofχ0 − χ2 =(56± 8)◦ [3]. Other estimates are:δ0 − δ2 = (45± 6)◦ [4]from chiral perturbation theory (χPT) andδ0 − δ2 = (47.7± 1.5)◦ [5] from ππ scattering.Figure 1: KLOE measurement performed with 17 pb−1(1.1·106/0.8·106 taggedKS → π+π−/KS → π0π0) com-pared to previous results and to the PDG average.Invariant Mass and LifetimesKLOE has also performed preliminary measurements oftheKS invariant mass (KS → π+π− channel) and of theKL lifetime, reaching accuracies which are better or com-parable to previous measurements (see figures 2 and 3).Figure 2: TheKS mass as measured by CMD-2 (left datapoint), NA48 (center) and KLOE (right, see [6]).025005000750010000125001500017500200000 5 10 15 20 25 30 35Entries         1272709  48.73    /    56P1   .1785E+05   45.02P2   51.59   .4236τKL  (ns)Figure 3: The KLOEKL → 3π0 lifetime (statistical erroronly): (51.6± 0.4) nsec. PDG: (51.7± 0.4) nsec [7].The KS → π+π− lifetime has also been studied andfound to be consistent with the PDG average (see fig. 4).The vertex resolution is∼1/3 of the decay length (∼6 mm).Figure 4: TheKS → π+π− decay length distribution [8].BR(KL → γγ)This BR has a large long-distance contribution via thepseudoscalar mesons (π0, η, η′). It can be calculated inχPT and is sensitive to the pseudoscalar meson mixing an-gle, θP . Its value enters and dominates the long-distancecontribution inKL → µ+µ−. The measurement reportedhere is based on 362 pb−1 and1.6×108 KL decays taggedby observingKS → π+π− [9]. The largeKL → 3π0background is suppressed by exploiting the 2-body kine-matics, yielding 27375 estimated signal events (see figure5). We measure the ratioΓ(KL → γγ)/Γ(KL → 3π0)= (2.79± 0.02± 0.02)×10−3. The NA48 measurementis (2.81± 0.01± 0.02)×10−3 [10]. Using the PDG valueof BR(KL → 3π0), KLOE gets BR(KL → γγ) = (5.89± 0.07stat⊕syst ± 0.08BR(KL→3π0))×10−4. This valueof the BR is in agreement withχPT, if θP is close to theKLOE measurementθP = (-12.9+1.9−1.6)◦ [11].02004006008001000300 350 400 450 500 550 600 650 700Mγγ (MeV/c2)Figure 5: γγ invariant mass spectra: data (points) andMonte Carlo (histogram) used to measure BR(KL → γγ);signal is at the right peak.BR(KS → πeν)KS decays are tagged via reconstruction ofKL inter-actions in the EM calorimeter. TheKS → π+π− back-ground, which is 103 times larger, is suppressed by exploit-ing the 3-body kinematics and thee/π discrimination basedon time-of-flight measurement with the calorimeter. Theremaining background (∼5%) is given byKS → π+π−with π → µν inside the drift chamber. The data is fit tothe sum of signal and background MC shapes and normal-ized to the KLOE-measured BR(KS → π+π−) to get thesignal branching ratio. Using 170 pb−1 of 2001 data wereport the preliminary measurement (which supersede ourfirst published result obtained with 17 pb−1 [12]):• BR(KS → π∓e±ν(ν̄)) = (6.81± 0.12± 0.10)· 10−4• BR(KS → π−e+ν) = (3.46± 0.09± 0.06)· 10−4• BR(KS → π+e−ν̄) = (3.33± 0.08± 0.05)· 10−4.These results agree with the Standard Model expectationsand improves significantly the previous CMD-2 measure-ment: (7.2± 1.4) · 10−4 [13]. Work is in progress to takeinto account the contribution of radiativeKS semileptonicdecays, to employ an improved version of the MC. Figures6 and 7 show preliminary estimates of the number of signalevents in 0.5 fb−1.Figure 6:KS → π+e−ν̄ signal (peak at 0) and background(mostlyπ decays in flight) in∼ 0.5 fb−1.Figure 7:KS → π−e+ν signal (peak at 0) and background(mostlyπ decays in flight) in∼ 0.5 fb−1.KS Charge Asymmetry and Test of CPTThe charge asymmetry of theKS semileptonic decay,AS , has been measured for the first time by KLOE. Thepreliminary result for 170 pb−1 is:AS = (19 ± 17 ± 6) · 10−3. (1)A non-zero difference betweenAS and theKL semilep-tonic asymmetry,AL, would imply the violation of the CPTconservation law:AS − AL = 4 Re(δK − D), (2)where: δK is the CPT violation in theK0 mixing andDis a term containing theK0 semileptonic decay amplitudesof the weak Hamiltonian, which violates both CPT and the∆S = ∆Q rule. The world-average value ofAL is (3.322±0.055)·10−3. For comparison: the CPLEAR measurementof CPT violation is [14]Re(δK) = (2.9± 2.7)·10−4 if ∆S= ∆Q is assumed andRe(δK) = (3.0± 3.4)·10−4 if ∆S =∆Q is not assumed.Test of ∆S = ∆Q RuleIn the Standard Model the are no∆S 6= ∆Q transitionsat the lowest order. Such transitions are described by thephenomenological parametersx (∆S 6= ∆Q in theK̄0 de-cay toe+) andx̄ (∆S 6= ∆Q in theK0 decay toe−), whichcontain theK0 semileptonic amplitudes. The combinationx+ = (x + x̄)/2 describes the amount of∆S 6= ∆Q whenCPT is conserved.x+ can be expressed as:BR(KS → πeν)/τSBR(KL → πeν)/τL=ΓsemilSΓsemilL= 1 + 4 Re(x+). (3)The value measured by KLOE with 170 pb−1 of 2001 datais: Re(x+) = (3.3 ± 5.2 ± 3.5) · 10−3, which is to becom-pared withRe(x+) = (−1.8±4.1±4.5)·10−3 (andIm(x+)= (1.2 ± 1.9 ± 0.9) · 10−3) by CPLEAR [14]. An updateof this meaasurement with 0.5 fb−1 will follow soon.MEASUREMENT OF VUSKLOE is giving a significant contribution to the mea-surement of theVus CKM matrix element, which con-strains the internal consistency of the Standard Model. Theexperimental inputs to extractVus from the Kaon semilep-tonic decays are BRs and lifetimes. The theoretical inputsare the linear slopes of theKℓ3 form factors,λ±, and thevalues of these form factors at zero 4-momentum transferto the leptons,f±(0). The uncertainty onVus for Ke3 (forwhichf− is negligible) depends on these inputs as:δVusVus=12δBRBR⊕ 12δττ⊕ 120δλ+λ+⊕ δf+(0)f+(0). (4)In addition to the above mentionedKS semileptonic BR,KLOE has also preliminary measurements of theKL BRsin both the electron and muon channel, based on a statistics0.2050.210.2150.220.225K+e3 K0e3 K+µ3 K0µ3E865KLOE KSKLOE KLKLOE KLFigure 8: Vus · f+(0) vs semileptonic Kaon decay modefrom old (black points) and the recent E865 measurement.The KLOE preliminary results are also indicated.of 78 pb−1. Our measurements ofVus ·f+(0) are consistentwith oldK0e3 andK0µ3 measurements and are lower than therecent E865 result [15], as shown in figure 8.KLOE will have BR(K+e3) soon and plans on measur-ing BRs with≪1% accuracy. KLOE can also improve themeasurements ofλ+, λ0, τL andτS .CONCLUSIONS AND PROSPECTSCurrentK0 physics program is driven significantly bystatistics (0.5 fb−1) and, to a lesser extent, by the DAΦNEbackground level (which, however, has been constantlydecreasing through the years). The MC has been vastlyimproved: (i) background events from data are injectedinto simulated events on a run-by-run basis; (ii) the de-tector/trigger response, materials and geometry have beenrefined, (iii) generators for radiativeK0 decays have beenadded. The new MC allows us to tackle the nextKS raredecays. For example, with 0.5 fb−1 we set the preliminarylimit BR(KS → 3π0) < 2.2 · 10−7, 90% CL (5 events ona background of 3.1± 1.9), the best limit to date.The results on BR(KS → πeν), BR(KL → γγ) andBR(KS → 3π0) show that KLOE can measure rare decays.A factor 10 luminosity increase is needed to measure thenext more rareKS decays andǫ′/ǫ.In the prospect of a long term running of KLOE (andmore than 5 fb−1 statistics) some detector upgrades arestrongly advisable and beficial to the analysis.• New and smaller KLOE-DAΦNE interaction re-gion (IR). As a consequence, new and smaller EMcalorimeters around the IR quadrupoles (QCAL) arenecessary in order not to introduce large dead regionsinto the detector volume).• With the new IR+QCAL there will be room for a newcompact inner vertex detector inside the drift chamber(10< radius< 25 cm), capable of measuringalso thelongitudinal coordinate. This detectod will have thefollowing features:- help the track pattern recognition at small radiiwhere beam background is more severe;- improve vertexing at IP and interferometry forall-charged events, likeKSKL → π+π−π+π−,KSKL → π+π−πeν andKSKL → πeνπeν;- help the identification of Kaon interactions in thedrift chamber inner wall (esp. Q-exchange);- the beam pipe at IP will be made of pure Beryl-lium, to ease complexity in offline event re-construction; the current spherical geometry canbe abandoned in favor of an easier machinableshape.• The readout granularity of existing calorimeter will beincreased by removing light guides and phototubes,to be replaced by smaller light-collections elements.This would improve the energy clustering algorithmand enhance particle ID (PID)The specific choices for the new inner vertex detectorand calorimeter readout devices are to be studied. It shouldbe noted that in 2002 KLOE has completed its first suc-cessful detector upgrade: the drift chamber has been instru-mented with ADCs to help PID by means of dE/dx, whichis effective especially for charged Kaon physics.KLOE expects to collect∼ 2 fb−1 in the physics runstarting in spring 2004, which should benefit from the up-grades performed by DAΦNE in 2003, which included anew IR with simplified optics.REFERENCES[1] KLOE Collaboration: The KLOE Detector Technical Pro-posal, LNF-93/002, 1993; Nucl. Instr. and Meth. A488(2002) 1; Nucl. Instr. and Meth. A482 (2002) 363; Nucl.Instr. and Meth. A483 (2002) 649; Nucl. Instr. and Meth. A492 (2002) 134.[2] KLOE Collaboration, Phys. Lett. B538, 21 (2002).[3] Cirigliano, V., Donoghue, J., and Golowich, E., Eur. Phys. J.,C18, 83 (2000).[4] Gasser, J., and Meissner, U.-G., in Proceed. of the JointLepton-Photon Symposium and EPS Conference, Geneva,1991, edited by S. Hegarty et al., World Scientific, 1992, p.202.[5] Colangelo, G., Gasser, J., and Leutwyler, H., Nucl. Phys.,B603, 125 (2001).[6] http://www.lnf.infn.it/kloe/pub/knote/kn181.ps, KLOE pub-lic Note 181.[7] KLOE Collaboration, Phys. Lett. B556 (2003).[8] KLOE Collaboration, Nucl. Instr. and Meth. A488 (2002) 1.[9] KLOE Collaboration, Phys. Lett. B556 (2003).[10] NA48 Collaboration Phys. Lett. B551 (2003).[11] KLOE Collaboration, Phys. Lett. B541 (2002).[12] KLOE Collaboration, Phys. Lett. B535 (2002).[13] R. Akhmetshin et al. Phys. Lett. B456 (1999).[14] CPLEAR Collaboration, Phys. Lett. B444 (1998).[15] E865 Collaboration, hep-ex/0305042.

KLOE results on rare K0 decays

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KLOE results on rare K0 decays

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