In this paper we discuss the recent finalized analyses by the KLOE experiment
at DA$\Phi$NE: the CPT and Lorentz invariance test with entangled $K^0
\bar{K}^0$ pairs, and the precision measurement of the branching fraction of
the decay ${ K^+} \rightarrow \pi^+\pi^-\pi^+(\gamma)$. We also present the
status of an ongoing analysis aiming to precisely measure the $K^{\pm} $ mass

Bloise, C.

Czerwinski, E.

De Lucia, E.

De Santis, A.

De Simone, P.

Di Domenico, A.

Gajos, A.

Kaminska, D.

Moskal, P.

Passeri, A.

Silarski, M.

Wislicki, W.

Acta Physica Polonica B

English

arXiv

C. Bloise

E. De Lucia

A. De Santis

P. De Simone

E. Czerwiński

A. Gajos

D. Kamińska

P. Moskal

M. Silarski

A. Di Domenico

A. Passeri

W. Wiślicki

Crossref

Kaon Physics with the KLOE Detector

In this paper, we discuss the recent finalized analyses by the KLOE experiment at DA$\Phi$NE: the CPT and Lorentz invariance test with entangled $K^{0}\bar{K}^{0}$ pairs, and the precision measurement of the branching fraction of the decay $K^{+} \rightarrow \pi^{+} \pi^{-} \pi^{+}  (\gamma)$. We also present the status of an ongoing analysis aiming to precisely measure the $K^{\pm}$ mass

Gajos, Aleksander

Kisielewska, Daria

Moskal, Paweł

Wiślicki, W.

Czerwiński, Eryk

Silarski, Michał

Jagiellonian Univeristy Repository

Vol. 46 (2015) ACTA PHYSICA POLONICA B No 1KAON PHYSICS WITH THE KLOE DETECTOR∗C. Bloise, E. De Lucia, A. De Santis, P. De SimoneLaboratori Nazionali di Frascati dell’INFN, Frascati, ItalyE. Czerwiński, A. Gajos, D. Kamińska, P. Moskal, M. SilarskiThe Marian Smoluchowski Institute of Physics, Jagiellonian UniversityKraków, PolandA. Di DomenicoDipartimento di Fisica, Sapienza Università di Roma, Roma, ItalyandINFN sezione di Roma, Roma, ItalyA. PasseriINFN sezione di Roma Tre, Roma, ItalyW. WiślickiNational Centre for Nuclear Research, Warszawa, Polandon behalf of the KLOE-2 Collaboration(Received December 3, 2014)In this paper, we discuss the recent finalized analyses by the KLOE ex-periment at DAΦNE: the CPT and Lorentz invariance test with entangledK0K̄0 pairs, and the precision measurement of the branching fraction ofthe decay K+ → π+π−π+(γ). We also present the status of an ongoinganalysis aiming to precisely measure the K± mass.DOI:10.5506/APhysPolB.46.5PACS numbers: 13.25.Es, 14.40.Df1. IntroductionThe KLOE experiment at DAΦNE, the Frascati φ-factory, measuredall the most relevant branching ratios of KL, KS, and K± mesons, their∗ Funded by SCOAP3 under Creative Commons License, CC-BY 3.0.(5)6 C. Bloise et al.lifetimes, the K → π form factors, and several parameters and observablesallowing to perform CP, CPT symmetries tests, and a verification of thevalidity of Cabibbo unitarity and lepton universality (a review can be foundin Ref. [1]).In this paper, we focus the discussion on the two most recent resultson kaon physics: a CPT and Lorentz invariance test with entangled K0K̄0pairs, and the precision measurement of the branching fraction of the decayK+ → π+π−π+(γ). Among the ongoing analyses, there are:(a) the measurement of the charged kaon mass,(b) the study of semileptonic KS decays and CPT symmetry tests,(c) the study of rare KS decays with an improved KS tagging technique,(d) the direct T-symmetry test with entangled neutral kaons.The status of analysis (a) is also presented in this paper, while (b), (c) and(d) are the subjects of separate contributions in this issue [2–4].2. CPT and Lorentz-invariance testIn year 2014, KLOE obtained the best sensitivity ever reached in thequark sector on testing CPT and Lorentz invariance, based on 1.7 fb−1 ofintegrated luminosity [5]. The test was performed on the entangled neu-tral kaon pairs, in the φ → KSKL → π+π−π+π− final state, studying theinterference pattern as a function of sidereal time and particle direction incelestial coordinates.Data reduction is based on two decay vertices with only two tracks each.For each vertex several requirements, invariant mass |mrec −mK | < 5 MeV,missing mass√E2miss + |~pmiss|2 < 10 MeV, −50 MeV2 < m2miss < 10 MeV2,and kaon momenta compatible with the 2-body decay hypothesis, have beenapplied for the selection of a pure, well reconstructed data sample. The miss-ing momentum is obtained from the analysis of Bhabha scattering events inthe same run. A global likelihood function is built in order to kinematicallyconstrain the event and to improve on the event reconstruction quality and,in particular, on the vertex resolution.Main background source is the kaon regeneration on the spherical beampipe, suppressed by selecting events with both KS and KL decaying insidethe beam pipe, giving at the end of the analysis chain a contamination at2–3% level. Background contributions and analysis selection efficiencies arederived from MC simulation to which corrections from real data are applied.Full analysis chain was repeated several times varying all the cuts for theevaluation of the systematic uncertainties. The sum in quadrature of all theeffects ranges between 30% and 40% of the statistical error.Kaon Physics with the KLOE Detector 7The CPT test is based on the distribution of the difference ∆τ in thedecay proper time between neutral kaons. Due to the fully-destructive quan-tum interference at ∆τ = 0, the distribution is very sensitive to CPT-vio-lating effects, especially for the selected decays inside the beam pipe. Ef-fects of CPT and Lorentz-invariance breaking in the low energy regime re-lating with modifications of the space-time structure at the Planck scale,are described by the Standard Model Extension, SME [6], providing theparametrizationδk ∼ i sinφSWeiφSWγK(∆a0 − ~βK ·∆~a)/∆m, (1)where γK and ~βK are the kaon γ-factor and velocity in the laboratoryframe, φSW = arctan(2∆m/∆Γ ) is the superweak phase, ∆m = mL −mS,∆Γ = ΓS−ΓL are the mass and width differences for the neutral kaon masseigenstates, and ∆aµ are the four CPT-violating coefficients. In this context,the intensity of kaon decays as a function of ∆τ is expressed byI(∆τ) = C12e−Γ |∆τ |[|η1|2e∆Γ2∆τ + |η2|2e−∆Γ2∆τ − 2Re(η1η∗2e−i∆m∆τ)](2)with Γ = (ΓS + ΓL)/2,η1,2 ' εk − δk (~p1,2, t1,2) ,C12 '12(ΓS + ΓL)|〈f1|T |KS〉〈f2|T |KS〉|2 .It is used to fit the experimental distributions shown in Fig. 1.020406080020406080-10 0 10 -10 0 10 -10 0 10FitData ts∈[00,06] hrp1pφ<0I(∆τ) (dN/τS)FitData ts∈[06,12] hrp1pφ<0FitData ts∈[12,18] hrp1pφ<0FitData ts∈[18,24] hrp1pφ<0FitData ts∈[00,06] hrp1pφ>0∆τ (τS)I(∆τ) (dN/τS)FitData ts∈[06,12] hrp1pφ>0∆τ (τS)FitData ts∈[12,18] hrp1pφ>0∆τ (τS)FitData ts∈[18,24] hrp1pφ>0∆τ (τS)-10 0 10Fig. 1. Fit to the distribution of the difference in proper time of neutral kaons as afunction of sidereal time and particle direction in celestial coordinates [5].8 C. Bloise et al.The results [5] are the most sensitive measurements in the quark sector ofSME:∆ao = (−6.0± 7.7stat ± 3.1syst)× 10−18GeV ,∆ax = (0.9± 1.5stat ± 0.6syst)× 10−18GeV ,∆ay = (−2.0± 1.5stat ± 0.5syst)× 10−18GeV ,∆az = (3.1± 1.7stat ± 0.5syst)× 10−18GeV .For comparison, the accuracy reached by similar measurements in B and Dsystems is of O(10−13) GeV [6].3. The K+ → π+π−π+(γ) branching fractionThe measurement of the branching fraction (BR) ofK+ → π+π−π+(γ) isbased on a sample of ∼ 17 million tagged K+ mesons. The K+ are taggedby the reconstruction of 2-body K− decays that provide the normaliza-tion sample for the measurement of the absolute BR. The analysis pro-cedure consists of (i) the selection of K+ candidates (tagging procedure)by the identification of K− → π−π0 and K− → µ−ν samples, indepen-dently treated; (ii) the reconstruction of the K+ path from the kinematicalconstraints given by the K− momentum and φ momentum (from Bhabha-scattering events); (iii) the backward extrapolation of any charged tracknot belonging to the K− decay chain; (iv) the reconstruction of the K+decay vertex radial position (ρxy) and the closest-approach distance (CAdi)between the track and the K+ flight path; (v) the selection of events withat least two tracks with CAdi ≤ 3 cm and ρxy ≤ 26 cm, outside the driftchamber (DC) sensitive volume (for a better control of systematics fromtagging procedure); (vi) the measurement of the missing-mass distribution,M2miss = (∆EK+−ππ)2 − |∆PK+−ππ|2. The analysis is fully inclusive ofradiative decays.The dependence of the K+ → π+π+π− signal sample on the tag se-lection (tag-bias) has been derived from Monte Carlo simulations and usedas a correction factor in the BR evaluation. The relating systematic erroris estimated by changing the selection criteria of the 2-body kaon decayreconstruction.The other sources of systematic errors are the analysis cuts and theuncertainty of the kaon lifetime [7]. Results of their evaluation are shownin Table I. In a sample of 12,065,087 (5,171,239) K− → µ−ν̄ (K− → π−π0)tagging events, we found NK→3π = 48, 032 ± 286 (20, 063 ± 186) signalevents, corresponding to the fully consistent measurements of the absolutebranching fractionsBR(K+ → π+π−π+(γ))|TagKµ2 = 0.05552± 0.00034stat ± 0.00034syst , (3)BR(K+ → π+π−π+(γ))|TagKπ2 = 0.05587± 0.00053stat ± 0.00033syst . (4)Kaon Physics with the KLOE Detector 9The average, BR(K+ → π+π−π+(γ)) = 0.05565±0.00031stat±0.00025syst[8]has a 0.72% accuracy, that is a factor ' 5 better with respect to the previousmeasurement [9].TABLE ISummary table of the fractional systematic uncertainties [8].Source of systematic uncertainties K−µ2 tags [%] K−π2 tags [%]DCA, DCA12, cos(θ12) cuts 0.52 0.41p∗mπ cut 0.08 0.11m2miss cut 0.05 0.14fiducial volume 0.11 0.10selection efficiency estimate 0.16 0.16tag bias 0.16 0.32K± lifetime 0.12 0.12Total fractional systematic uncertainty 0.60 0.594. The charged kaon massThe world average of the charged kaon mass, MK± , has a precision of13 keV [10] obtained mostly from two precision measurements on kaonicatoms [11, 12] that differ by 60 keV or 4.6σ. A new precision measurement,at 10 keV level, is desirable to reduce the bias that could arise from theaverage of the previous results. The ongoing analysis on the KLOE sampleof K± → π±π−π+ aims to reach a precision of 5–7 keV using ' 2.5 fb−1 ofintegrated luminosity. TheK± → π±π−π+ channel is the best suited amongkaon dominant decays for a precision measurement of the mass due to thelowest Q-value (Q = 75 MeV) that corresponds to the best invariant massresolution and minimal sensitivity to several bias sources. The candidatesare selected through the same procedure applied for the BR measurement(Sec. 3), changing only the requirements on the number of secondaries atthe decay vertex, from 2 to 3, to obtain the 3-pion invariant mass, and onthe vertex position, ρxy ≥ 26 cm, to select decays inside the DC to avoidbiases from track extrapolation through the DC walls. On a Monte Carlosample including all of the φ decays, to which we apply the same procedureas on real data, we are studying some quality cuts, mostly to reduce theinvariant mass distribution tails: (i) on the χ2 of the tracks selected as pioncandidates (currently χ2 ≤ 6); and (ii) on the difference between the pionmomentum at the first hit in the DC and its extrapolation at the decayvertex (currently |pfirst hitπ | ≤ |pVπ | ≤ 30 MeV). On the same MC sample, wehave studied several functions and fit procedures. We found good fit results10 C. Bloise et al.using a function that is the convolution of a Breit–Wigner with a GaussiandistributiondNMπππ=γ2π√2πσ∫e−(t−Mπππ)22σ2(t−MK±)2 + γ24dt .Consistent results are obtained from the binned χ2 minimization and un-binned maximum-likehood fit procedures.Besides the Monte Carlo sample of (' 23 000) K± → π±π−π+ decaysanalyzed so far, a fast simulation program (toy-MC) has been developed forthe evaluation of effects such as (i) the presence of radiative decays; (ii) biasand asymmetric distribution of the reconstructed pion momentum, pπ, due,for instance, to the treatment of energy loss and multiple scattering in theDC; (iii) an arbitrary scale affecting pπ. From these studies, we can alreadyrule out any bias on the charged kaon mass from radiative decays. For theevaluation of the momentum scale factor αp, the analysis of the charged kaon2-body decays is in progress. The scale factor gives a bias to the kaon massthat depends on the Q-value of the decay channel, bigger for Kµν than forKππ and Kπππ decays. After correcting for other possible effects (point (ii)),we can obtain αp from the comparison of the 2-body decays.0100200300400500600700488 490 492 494 496 498 500Blinded dataEvents / 0.028 MeVMeVFig. 2. The 3-pion invariant mass for all selected data (Mπππ + X; blinded data).Dashed area: fit to the convolution of a Breit–Wigner with a Gaussian function.Kaon Physics with the KLOE Detector 11A blind analysis of the invariant mass distribution is in progress on real data(Fig. 2). We have obtained ' 45 000 events after all the analysis chain, witha negligible level of contamination that has been evaluated by the MonteCarlo simulation, B/S ' 10−4.5. ConclusionsWe presented two recent KLOE results: the CPT and Lorentz symme-try test, which constitutes the best limit in the quark sector of SME, andthe precision measurement of the branching fraction of the decay K+ →π+π−π+(γ). Among the ongoing analyses, we discussed the status of themeasurement for the precise determination of the charged kaon mass.As a future perspective, the KLOE-2 experiment aims to continue and ex-tend the physics program of its predecessor by collecting O(10 fb−1) of dataat the upgraded DAΦNE with an improved KLOE detector. The KLOE-2physics program has been described in detail in Ref. [13] and among themain issues includes KS physics, neutral kaon interferometry, tests of dis-crete symmetries and quantum mechanics, test of the CKM unitarity, andother topics of kaon physics.Improvements are expected thanks to the increased luminosity and thebetter quality of reconstructed data. The upgrade of the KLOE detectorconsists of the addition of (i) an inner tracker [14, 15] based on cylindricalGEM technology for the improvement of tracking and decay vertex resolutionclose to the interaction point (IP), (ii) a e± tagging system [16–18] for theγγ physics, and (iii) two calorimeters [19–21] in the final focusing regionto improve acceptance and efficiency for photons coming from the IP andneutral kaon decays inside the detector volume.We warmly thank our former KLOE colleagues for the access to the datacollected during the KLOE data taking campaign. We thank the DAΦNEteam for their efforts in maintaining low background running conditionsand their collaboration during all data taking. We want to thank our tech-nical staff: G.F. Fortugno and F. Sborzacchi for their dedication in en-suring efficient operation of the KLOE computing facilities; M. Anelli forhis continuous attention to the gas system and detector safety; A. Balla,M. Gatta, G. Corradi and G. Papalino for electronics maintenance; M. San-toni, G. Paoluzzi and R. Rosellini for general detector support; C. Piscitellifor his help during major maintenance periods. This work was supported inpart by the EU Integrated Infrastructure Initiative Hadron Physics Projectunder contract number RII3-CT-2004-506078; by the European Commissionunder the 7th Framework Programme through the ‘Research Infrastructures’action of the ‘Capacities’ Programme, Call: FP7-INFRASTRUCTURES-12 C. Bloise et al.2008-1, Grant Agreement No. 227431; by the Polish National Science Cen-tre through the Grants No. 2011/03/N/ST2/02641, 2011/01/D/ST2/00748,2011/03/N/ST2/02652, 2013/08/M/ST2/00323, and by the Foundation forPolish Science through the MPD programme and the project HOMINGPLUS BIS/2011-4/3.REFERENCES[1] F. Bossi et al. [KLOE Collaboration], Riv. Nuovo Cim. 31, 531 (2008).[2] D. Kamińska, Acta Phys. Pol. B 46, 19 (2015), this issue.[3] M. Silarski, Acta Phys. Pol. B 46, 25 (2015), this issue.[4] A. Gajos, Acta Phys. Pol. B 46, 13 (2015), this issue.[5] D. Babusci et al. [KLOE-2 Collaboration], Phys. Lett. B730, 89 (2014).[6] V.A. Kostelecky, N. Russell, Rev. Mod. Phys. 83, 11 (2011).[7] F. Ambrosino et al. [KLOE Collaboration], J. High Energy Phys. 01, 073(2008).[8] D. Babusci et al. [KLOE-2 Collaboration], Phys. Lett. B738, 128 (2014).[9] I. Chiang et al., Phys. Rev. D6, 1254 (1972).[10] K.A. Olive et al. [Particle Data Group], Chin. Phys. C38, 090001 (2014).[11] A. Denisov et al., JETP Lett. 54, 558 (1991).[12] K. Gall et al., Phys. Rev. Lett. 60, 186 (1988).[13] G. Amelino-Camelia et al. [KLOE-2 Collaboration], Eur. Phys. J. C68, 619(2010).[14] A. Balla et al., JINST 9, C01014 (2014).[15] A. Di Cicco, G. Morello, Acta Phys. Pol. B 46, 73 (2015), this issue.[16] D. Babusci et al., Nucl. Instrum. Methods A617, 81 (2010).[17] F. Archilli et al., Nucl. Instrum. Methods A617, 266 (2010).[18] D. Babusci et al., Acta Phys. Pol. B 46, 81 (2015), this issue.[19] F. 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Kaon physics with the KLOE detector

Kaon physics with the KLOE detector

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