We report on a new measurement of the \kl--\ks\ mass difference \dm\ using the CPLEAR full data sample of neutral-kaon decays to \semi. The result is $\dm = (0.5295 \pm 0.0020_{\stat} \pm 0.0003_{\syst}) \times 10^{10}$\ \hbs. It includes earlier data reported in Ref. \cite{deltam1}. A measurement of the \dsdq\ violating parameter \rex\ is also obtained

Angelopoulos, Angelos

Apostolakis, Alcibiades J

Aslanides, Elie

Backenstoss, Gerhard

Bargassa, P

Behnke, O

Benelli, A

Bertin, V

Blanc, F

Bloch, P

Carlson, P J

Carroll, M

Cawley, E

Chertok, M B

Danielsson, M

Dejardin, M

Derré, J

Ealet, A

Eleftheriadis, C

Faravel, L

Fetscher, W

Fidecaro, Maria

Filipcic, A

Francis, D

Fry, J

Gabathuler, Erwin

Gamet, R

Gerber, H J

Go, A

Haselden, A

Hayman, P J

Henry-Coüannier, F

Hollander, R W

Jon-And, K

Kettle, P R

Kokkas, P

Kreuger, R

Le Gac, R

Leimgruber, F

Mandic, I

Manthos, N

Marel, Gérard

Mikuz, M

Miller, J

Montanet, François

Müller, A

Nakada, Tatsuya

Pagels, B

Papadopoulos, I M

Pavlopoulos, P

Polivka, G

Rickenbach, R

Roberts, B L

Ruf, T

Schaller, L A

Schietinger, T

Schopper, A

Schäfer, M

Tauscher, Ludwig

Thibault, C

Touchard, F

Touramanis, C

van Eijk, C W E

Vlachos, S

Weber, P

Wigger, O

Wolter, M

Zavrtanik, D

Zimmerman, D

Physics Letters B

A. Angelopoulos

A. Apostolakis

E. Aslanides

G. Backenstoss

P. Bargassa

O. Behnke

A. Benelli

V. Bertin

F. Blanc

P. Bloch

P. Carlson

M. Carroll

E. Cawley

M.B. Chertok

M. Danielsson

M. Dejardin

J. Derre

A. Ealet

C. Eleftheriadis

L. Faravel

W. Fetscher

M. Fidecaro

A. Filipčič

D. Francis

J. Fry

E. Gabathuler

R. Gamet

H.-J. Gerber

A. Go

A. Haselden

P.J. Hayman

F. Henry-Couannier

R.W. Hollander

K. Jon-And

P.-R. Kettle

P. Kokkas

R. Kreuger

R. Le Gac

F. Leimgruber

I. Mandić

N. Manthos

G. Marel

M. Mikuž

J. Miller

F. Montanet

A. Muller

T. Nakada

B. Pagels

I. Papadopoulos

P. Pavlopoulos

G. Polivka

R. Rickenbach

B.L. Roberts

T. Ruf

M. Schäfer

L.A. Schaller

T. Schietinger

A. Schopper

L. Tauscher

C. Thibault

F. Touchard

C. Touramanis

C.W.E. Van Eijk

S. Vlachos

P. Weber

O. Wigger

M. Wolter

D. Zavrtanik

D. Zimmerman

Crossref

Measurement of the KL–KS mass difference using semileptonic decays of tagged neutral kaons

Angelopoulos, A.

Apostolakis, A.

Aslanides, E.

Backenstoss, G.

Bargassa, P.

Behnke, O.

Benelli, A.

Bertin, V.

Blanc, F.

Bloch, P.

Carlson, P.

Carroll, M.

Cawley, E.

Chertok, M B.

Danielsson, M.

Derre, J.

Ealet, A.

Eleftheriadis, C.

Faravel, L.

Fetscher, W.

Fidecaro, M.

Filipcic, A.

Francis, D.

Fry, J.

Gabathuler, E.

Gamet, R.

Gerber, H J.

Go, A.

Haselden, A.

Hayman, P J.

Henry-Couannier, F.

Hollander, R W.

Jon-And, K.

Kettle, P R.

Kokkas, P.

Kreuger, R.

Le Gac, R.

Leimgruber, F.

Mandic, I.

Manthos, N.

Marel, G.

Mikuz, M.

Miller, J.

Montanet, F.

Nakada, T.

Pagels, B.

Papadopoulos, I.

Pavlopoulos, P.

Polivka, G.

Rickenbach, R.

Roberts, B L.

Ruf, T.

Schdfer, M.

Schaller, L A.

Schietinger, T.

Schopper, A.

Thibault, C.

Touchard, F.

Touramanis, C.

Measurement of the K L−K S mass difference usingsemileptonic decays of tagged neutral kaonsA. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, P. Bargassa,O. Behnke, A. Benelli, V. Bertin, F. Blanc, P. Bloch, et al.To cite this version:A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, P. Bargassa, et al.. Measure-ment of the K L − K S mass difference using semileptonic decays of tagged neutral kaons.Physics Letters B, Elsevier, 1998, 444, pp.38-42. <in2p3-00000315>HAL Id: in2p3-00000315http://hal.in2p3.fr/in2p3-00000315Submitted on 15 Jan 1999HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHCERN–EP/98–152October 7, 1998Measurement of the KL–KSmass difference using semileptonic decays of tagged neutral kaonsCPLEAR CollaborationA. Angelopoulos1) , A. Apostolakis1) , E. Aslanides11) , G. Backenstoss2) , P. Bargassa13) , O. Behnke17) ,A. Benelli2), V. Bertin11) , F. Blanc7), P. Bloch4), P. Carlson15) , M. Carroll9) , E. Cawley9),M.B. Chertok3) , M. Danielsson15) , M. Dejardin14) , J. Derre14), A. Ealet11), C. Eleftheriadis16) ,L. Faravel7), W. Fetscher17) , M. Fidecaro4) , A. Filipcˇicˇ10) , D. Francis3) , J. Fry9), E. Gabathuler9) ,R. Gamet9), H.-J. Gerber17) , A. Go4), A. Haselden9) , P.J. Hayman9), F. Henry-Couannier11) ,R.W. Hollander6) , K. Jon-And15) , P.-R. Kettle13), P. Kokkas4) , R. Kreuger6) , R. Le Gac11),F. Leimgruber2) , I. Mandic´10) , N. Manthos8) , G. Marel14), M. Mikuzˇ10) , J. Miller3), F. Montanet11) ,A. Muller14) , T. Nakada13), B. Pagels17), I. Papadopoulos16) , P. Pavlopoulos2) , G. Polivka2) ,R. Rickenbach2) , B.L. Roberts3) , T. Ruf4), M. Scha¨fer17), L.A. Schaller7) , T. Schietinger2) ,A. Schopper4) , L. Tauscher2) , C. Thibault12) , F. Touchard11) , C. Touramanis9) , C.W.E. Van Eijk6),S. Vlachos2) , P. Weber17), O. Wigger13) , M. Wolter17), D. Zavrtanik10) and D. Zimmerman3)AbstractWe report on a new measurement of the KL–KSmass difference m using the CPLEAR full datasample of neutral-kaon decays to e. The result is m = (0:5295 0:0020stat 0:0003syst) 1010h=s. It includes earlier data reported in Ref. [1]. A measurement of the S = Q violatingparameter Re(x) is also obtained.(Submitted to Physics Letters B)1) University of Athens, Greece2) University of Basle, Switzerland3) Boston University, USA4) CERN, Geneva, Switzerland5) LIP and University of Coimbra, Portugal6) Delft University of Technology, Netherlands7) University of Fribourg, Switzerland8) University of Ioannina, Greece9) University of Liverpool, UK10) J. Stefan Inst. and Phys. Dep., University of Ljubljana, Slovenia11) CPPM, IN2P3-CNRS et Universite´ d’Aix-Marseille II, France12) CSNSM, IN2P3-CNRS, Orsay, France13) Paul Scherrer Institut (PSI), Switzerland14) CEA, DSM/DAPNIA, CE-Saclay, France15) Royal Institute of Technology, Stockholm, Sweden16) University of Thessaloniki, Greece17) ETH-IPP Zu¨rich, Switzerland1 IntroductionWe present the final measurement of the mass difference m = m(KL) m(KS) in the CPLEARexperiment, using neutral kaons of initially defined strangeness decaying to e. With respect to theprevious measurement [1] we have improved the statistics by about a factor of two and reduced thesystematic errors by 60% (mainly owing to a better background rejection).From the CPLEAR sample of neutral kaons decaying to e we extract four decay rates R as afunction of the decay eigentime  of the kaon, depending on the strangeness of the neutral kaon (K0 orK0) at the production time and on the charge of the decay lepton (e+or e ):R+()  R(K0t=0! e+ t=) ; R ()  R(K0t=0! e +t=) ;R ()  R(K0t=0! e +t=) ; R+()  R(K0t=0! e+ t=) : (1)The mass difference m is obtained from the asymmetryAm() =[R+() +R ()]  [R+() +R ()][R+() +R ()] + [R+() +R ()]=2 cos(m)e  L+ S2(1 + 2Re(x))e  S+ (1  2Re(x))e  L, (2)where a possible violation of the S = Q rule is taken into account by the parameter Re(x) [2], andwhere  Sand  Ldenote the decay widths of KSand KLrespectively. This formalism is only valid ifthere is no CPT violation in the S =  Q transitions. This determination of m does not depend onthe phase of the CP-violation parameter + .2 The detectorThe CPLEAR experiment used initially pure K0 and K0 states produced in the pp annihilationchannels K+ K0 and K +K0, each with a branching ratio of 0:2%. The initial strangeness of theneutral kaon was tagged by the charge of the accompanying charged kaon. Antiprotons provided by theLow Energy Antiproton Ring (LEAR) at CERN annihilated at rest in a 16 bar hydrogen gas target (asphere of 7 cm radius) with a rate of  106 s 1. In the CPLEAR detector [3], the tracking was per-formed with two layers of proportional chambers, six layers of drift chambers and two layers of streamertubes. The charged particle identification (K, , e) was achieved with a sandwich of scintillator–Cherenkov–scintillator counters (S1–CE–S2). The whole apparatus, including a lead/gas sampling elec-tromagnetic calorimeter, was located inside a solenoidal magnet (B = 0.44 T). The online event selectionwas performed by hardwired processors, which provided a complete topological and kinematic eventreconstruction.For the second-half of the data-taking the apparatus was upgraded, by introducing a new propor-tional chamber around a smaller, cylindrical target (1.1 cm radius, 27 bar hydrogen pressure) in orderto get, at the first trigger level, a fast counting of charged tracks arising from annihilation. This upgradeallowed some of the trigger conditions to be relaxed by accepting only neutral kaons decaying after thechamber, thus removing annihilation pionic background.3 Analysis methodA detailed description of the event selection can be found in [1]. The main tools used to selectthe events are kinematic constrained fits and particle identification techniques based on measurementsof energy loss in scintillator counters, number of photons in Cherenkov counters, and time of flight [4].The total sample contains 1:2 106 semileptonic decays in the decay time interval between 1 and 20 S.Before entering the data in the asymmetry (2), experimental acceptances (normalization) and backgroundneed to be considered.Most of the experimental acceptance factors are common to the four rates and cancel in (2). Wecorrected for any residual difference between the rate acceptances by introducing three normalizationfactors, defined as  = (K+ )=(K +), where the efficiencies involved, (K; ), are those of the charged parti-cles at the production vertex (primary vertex normalization);1Figure 1: a) Proportion of different background channels relative to the semileptonic signal. b) Decay-time distribution for real data (squares) and simulated data (open diamonds). The expected backgroundcontribution is shown by the solid line.a) b)  = (e +)=(e+ ), which takes into account the different detection efficiencies, (e) for theparticles in the two final states (secondary vertex normalization); ! = (Ke)=(Ke), which is the ratio of the efficiencies for detecting an event with equal andopposite curvature sign for the primary charged kaon and the decay lepton (curvature correlation).Owing to the form of the asymmetry (2), only the last normalization factor, !, is important in thismeasurement of m. The other two factors,  and , enter in the asymmetry as (1   ) and (1   ),and only to second order, since both sides of the asymmetry contain K0 and K0, and e+ and e . Theywere handled in the same way as in the time-reversal analysis [5], leading to a neglible contribution tosystematic errors.Special care was taken to minimize any detection efficiency correlation between tracks, and trackisolation criteria were applied to avoid such correlations both at the online selection and in the offlineanalysis. We have ensured with a high statistics Monte Carlo simulation that the normalization factor !was equal to unity (with an error of 4 10 4) for the data sample taken with the less restrictive triggerin the upgraded apparatus. For earlier data samples, taken with a more restrictive trigger, a small bias(! = 0:99570:0009) was observed and corrected. This bias was calibrated by simulating the restrictivetrigger decision on the unbiased sample. The overall correction is small compared to the statistical errorof the measurement ((m) = (+0:0006  0:0001)  1010 h=s).An important point in this analysis is the accuracy with which we can determine the backgroundcontamination in the final data sample. With respect to Ref. [1], by refining the selection criteria we havereduced the amount of background by a factor of three at small decay times, with only a small loss insignal, and the corresponding systematic error by a factor of two.Using a Monte Carlo simulation, we have determined the relative background contributions fromvarious neutral-kaon decays, namely e and  (when the electron, or muon, and pion assignementare exchanged), + , + 0 and 00 (with one Dalitz decay or one converted photon), as shown inFig. 1a. The agreement between the observed decay-time distribution and the simulated one is very good(Fig. 1b). By changing the analysis cuts, on both real and simulated data, we estimated that we controlthe contributions of all background channels to better than 10%.4 Fit and systematic errorsA fit of Eq. (2) to the data was performed letting m and Re(x) free. The dilution in the asym-metry caused by the background (see Section 3) was taken into account as in Ref. [1]. The starting pointof the fit was fixed at 1 Sto avoid any possible residual annihilation background.The systematic errors were evaluated by letting the variable describing the error source to varyduring the fit procedure within its uncertainty. The systematic errors related to normalization and back-2ground were already mentioned in Section 3. We discuss now the regeneration effects and the precisionof the decay-time measurement.Since in the construction of Amall terms linear in the regeneration amplitudes cancel, correctionsfor regeneration effects are not essential for this measurement of m.Extensive studies have shown that after the kinematic constrained fits, the absolute time-scale isknown with a precision of 2  10 4 [3, 6]. The decay-time resolution was computed using simulateddata, and found to vary from 0.05 Sto 0.20 Sas a function of the neutral-kaon decay time. Foldingthe resolution distributions to the Amasymmetry results in a shift of +0:0013 1010 h=s for the valueof m and  2:9  10 3 for the value of Re(x). The uncertainty of this correction was estimated to be10%. Finally, the uncertainty on  S[2] was also considered.The systematic errors of m and Re(x) are summarized in Table 1.Source (m) (Re(x))[1010 h=s] [10 3]background level 0:0002 4:4normalization 0:0001 0:1decay-time resolution 0:0001 0:3absolute time-scale 0:0001 0:3 S0:0001 0:7Total 0:0003 4:5Table 1: Systematic errors5 ResultsFigure 2: The asymmetry Amversus the neutral-kaon decay time (in unit of S). The solid line repre-sents the result of the fit.The measured asymmetry, together with the fitted function, is plotted in Fig. 2. Fit residuals areshown in the inset. Our final results are the following:m = (0:5295  0:0020stat 0:0003syst) 1010h=s ; (3)Re(x) = ( 1:8 4:1stat 4:5syst) 10 3; (4)2= d.o.f. = 0:94 : (5)3The correlation coefficient between m and Re(x) is equal to 0:40.Our m measurement is the single most accurate value and has the same error as the presentworld average. The Re(x) measurement improves the present limit on possible S = Q rule violationby a factor of three.6 Acknowledgements:We would like to thank the CERN LEAR staff for their support and cooperation as well as the tech-nical and engineering staff of our institutes. This work was supported by the following institutions: theFrench CNRS/Institut National de Physique Nucle´aire et de Physique des Particules, the French Commis-sariat a` l’Energie Atomique, the Greek General Secretariat of Research and Technology, the NetherlandsFoundation for Fundamental Research on Matter (FOM), the Portuguese JNICT and INIC, the Ministryof Science and Technology of the Republic of Slovenia, the Swedish Natural Science Research Coun-cil, the Swiss National Science Foundation, the UK Particle Physics and Astronomy Research Council(PPARC), and the US National Science Foundation.References[1] R. Adler et al., CPLEAR Collaboration, Phys. Lett. B 363 (1995) 237.[2] C. Caso et al., Particle Data Group, Eur. Phys. J. C 3 (1998) 1.[3] R. Adler et al., CPLEAR Collaboration, Nucl. Instrum. and Methods A 379 (1996) 76.[4] Electron-muon-pion separation in the CPLEAR experiment using the particle Identification Detec-tor, Internal Note, CPLEAR/DET/95-02, Jan. 1995.[5] A. Angelopoulos et al., CPLEAR Collaboration, First direct observation of time-reversal non-invariance in the neutral-kaon system, submitted to Phys. Lett. B.[6] Determination of the position accuracy in CPLEAR, Internal Note, CPLEAR/DET/96-03, Oct.1996.4

Measurement of the $K_{L}-K_{S}$ mass difference using semileptonic decays of tagged neutral kaons

Measurement of the $K_{L}-K_{S}$ mass difference using semileptonic decays of tagged neutral kaons

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Measurement of the KL−KSK_{L}-K_{S}KL​−KS​ mass difference using semileptonic decays of tagged neutral kaons

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Measurement of the $K_{L}-K_{S}$ mass difference using semileptonic decays of tagged neutral kaons