Three-prong τ decays with charged kaons

TLDR: In this article, the final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement, based on a sample of about 1.6 × 105 detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak.

Abstract: Final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement. The results are based on a sample of about 1.6 × 105 detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak. The following branching ratios have been measured: B(τ- → K−K+π−ντ) = (1.63 ± 0.21 ± 0.17) × 10−3, B(τ− → K−π+π−ντ) = (2.14 ± 0.37 ± 0.29) × 10−3, B(τ− → K−K+π−π0ντ) = (0.75 ± 0.29 ± 0.15) × 10−3, and B(τ− → K−π+π−π0ντ) = (0.61 ± 0.39 ± 0.18) × 10−3. The first two measurements are more precise than the current world averages, while the last two channels are investigated for the first time. The 95% C.L. upper limit on the branching ratio for the decay τ− → K−K+K−ντ is 0.19 × 10−3. A study of intermediate states occurring in the K−K+π−ντ and K−π+π−ντ decays is also presented.

Figures

Figure 3: Distribution of dE/dx for pions from ! !h , ! ! + 0. The solid curve is a sum of two Gaussians and the dashed curve represents the single standard Gaussian. See text for details.

Table 2: Results obtained from the ts to x distributions. The ts take into account both kaon and pion contributions. The kaon parameters x (K) and (K) are determined from Monte Carlo and xed in the ts to data. The errors of these parameters from Monte Carlo statistics are translated into systematic uncertainties on the branching ratios due to Monte Carlo statistics. The de nition for each quantity can be found in the text.

Figure 9: Fitted x distribution for same-sign tracks in a) ! K K+ and b) ! K K+ 0 , after tagging of the opposite-sign kaon. The plots with error bars correspond to data, the solid curves are the sum and the dashed curves show the tted K components while the dotted curves indicate the contributions.

Figure 13: The + invariant mass after background subtraction in the decay ! K + . The t function is the sum of a Breit-Wigner form and the expected K re ection.

Figure 12: The invariant mass spectra for the ! K + sample in data (dots with error bars) and Monte Carlo (histogram). The K + signal predicted by the model of Ref [4] is shown in the dashed histogram and the expected feedthrough background is given by the shaded histogram.

Table 4: Summary of systematic errors. All are relative in percent.

Full text

EUROPEAN LABORATORY FOR PARTICLE PHYSICS
CERN-PPE/97-69
June 17, 1997
Three-prong

decays with charged
kaons
The ALEPH Collab oration
1
Abstract
Final states with charged kaons in three-prong

decays are studied by exploit-
ing the particle identication from the dE/dx measurement. The results are based
on a sample of ab out 1
:
6

10
5
detected

pairs collected with the ALEPH de-
tector between 1991 and 1995 around the Z p eak. The following branching ratios
have been measured:
B
(


!
K

K
+




) = (1
:
63

0
:
21

0
:
17)

10

3
,
B
(


!
K


+




) = (2
:
14

0
:
37

0
:
29)

10

3
,
B
(


!
K

K
+



0


) =
(0
:
75

0
:
29

0
:
15)

10

3
, and
B
(


!
K


+



0


)=(0
:
61

0
:
39

0
:
18)

10

3
.
The rst two measurements are more precise than the currentworld averages, while
the last twochannels are investigated for the rst time. The 95% C.L. upper limit
on the branching ratio for the decay


!
K

K
+
K



is 0
:
19

10

3
. A study
of intermediate states o ccurring in the
K

K
+




and
K


+




decays is also
presented.
(To be submitted to Zeitschrift fur Physik C.)
1
See next pages for the list of authors.

The ALEPH Collab oration
R. Barate, D. Buskulic, D. Decamp, P. Ghez, C. Goy, J.-P. Lees, A. Lucotte, M.-N. Minard, J.-Y. Nief,
B. Pietrzyk
Laboratoire de Physique des Particules (LAPP), IN
2
P
3
-CNRS, 74019 Annecy-le-Vieux Cedex, France
M.P. Casado, M. Chmeissani, P. Comas, J.M. Cresp o, M. Delno, E. Fernandez, M. Fernandez-Bosman,
Ll. Garrido,
15
A. Juste, M. Martinez, G. Merino, R. Miquel, Ll.M. Mir, C. Padilla, I.C. Park, A. Pascual,
J.A. Perlas, I. Riu, F. Sanchez, F. Teubert
Institut de F

isica d'Altes Energies, Universitat Autonoma de Barcelona, 08193 Bellaterra (Barcelona),
Spain
7
A. Colaleo, D. Creanza, M. de Palma, G. Gelao, G. Iaselli, G. Maggi, M. Maggi, N. Marinelli, S. Nuzzo,
A. Ranieri, G. Raso, F. Ruggieri, G. Selvaggi, L. Silvestris, P.Tempesta, A. Tricomi,
3
G. Zito
Dipartimento di Fisica, INFN Sezione di Bari, 70126 Bari, Italy
X. Huang, J. Lin, Q. Ouyang, T. Wang, Y. Xie, R. Xu, S. Xue, J. Zhang, L. Zhang, W. Zhao
Institute of High-Energy Physics, Academia Sinica, Beijing, The People's Republic of China
8
D. Abbaneo, R. Alemany, U. Becker, A.O. Bazarko,
20
P. Bright-Thomas, M. Cattaneo, F. Cerutti,
G. Dissertori, H. Drevermann, R.W. Forty,M.Frank, R. Hagelberg, J.B. Hansen, J. Harvey,P. Janot,
B. Jost, E. Kneringer, J. Knobloch, I. Lehraus, G. Lutters, P. Mato, A. Minten, L. Moneta, A. Pacheco, J.-
F. Pusztaszeri,
23
F. Ranjard, G. Rizzo, L. Rolandi, D. Rousseau, D. Schlatter, M. Schmitt, O. Schneider,
W. Tejessy, I.R. Tomalin, H. Wachsmuth, A. Wagner
24
European Laboratory for Particle Physics (CERN), 1211 Geneva 23, Switzerland
Z. Ajaltouni, A. Barres, C. Boyer, A. Falvard, C. Ferdi, P.Gay, C . Guicheney,P. Henrard, J. Jousset,
B. Michel, S. Monteil, J-C. Montret, D. Pallin, P. Perret, F. Podlyski, J. Proriol, P. Rosnet, J.-
M. Rossignol
Laboratoire de Physique Corpusculaire, Universite Blaise Pascal, IN
2
P
3
-CNRS, Clermont-Ferrand,
63177 Aubiere, France
T. Fearnley, J.D. Hansen, J.R. Hansen, P.H. Hansen, B.S. Nilsson, B. Rensch, A. Waananen
Niels Bohr Institute, 2100 Cop enhagen, Denmark
9
G. Daskalakis, A. Kyriakis, C. Markou, E. Simopoulou, I. Siotis, A. Vayaki
Nuclear Research Center Demokritos (NRCD), Athens, Greece
A. Blondel, G. Bonneaud, J.C. Brient, P. Bourdon, A. Rouge, M. Rumpf, A. Valassi,
6
M. Verderi,
H. Videau
Laboratoire de Physique Nucleaire et des Hautes Energies, Ecole Polytechnique, IN
2
P
3
-CNRS, 91128
Palaiseau Cedex, France
D.J. Candlin, M.I. Parsons
DepartmentofPhysics, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
10
E. Fo cardi, G. Parrini, K. Zachariadou
Dipartimento di Fisica, Universita di Firenze, INFN Sezione di Firenze, 50125 Firenze, Italy
M. Corden, C. Georgiop oulos, D.E. Jae
Supercomputer Computations Research Institute, Florida State University, Tallahassee, FL 32306-
4052, USA
13
;
14
A. Antonelli, G. Bencivenni, G. Bologna,
4
F. Bossi, P. Campana, G. Capon, D. Casper, V. Chiarella,
G. Felici, P. Laurelli, G. Mannocchi,
5
F. Murtas, G.P. Murtas, L. Passalacqua, M. Pepe-Altarelli

Laboratori Nazionali dell'INFN (LNF-INFN), 00044 Frascati, Italy
L. Curtis, S.J. Dorris, A.W. Halley, I.G. Knowles, J.G. Lynch, V. O'Shea, C. Raine, J.M. Scarr, K. Smith,
P.Teixeira-Dias, A.S. Thompson, E. Thomson, F. Thomson, R.M. Turnbull
DepartmentofPhysics and Astronomy, University of Glasgow, Glasgow G12 8QQ,United Kingdom
10
O. Buchmuller, S. Dhamotharan, C. Geweniger, G. Graefe, P. Hanke, G. Hansp er, V. Hepp, E.E. Kluge,
A. Putzer, J. Sommer, K. Tittel, S. Werner, M. Wunsch
Institut fur Hochenergiephysik, Universitat Heidelb erg, 69120 Heidelberg, Fed. Rep. of Germany
16
R. Beuselinck, D.M. Binnie, W. Cameron, P.J. Dornan, M. Girone, S. Goo dsir, E.B. Martin, A. Moutoussi,
J. Nash, J.K. Sedgb eer, P. Spagnolo, A.M. Stacey, M.D. Williams
DepartmentofPhysics, Imperial College, London SW7 2BZ, United Kingdom
10
V.M. Ghete, P. Girtler, D. Kuhn, G. Rudolph
Institut fur Experimentalphysik, Universitat Innsbruck, 6020 Innsbruck, Austria
18
A.P. Betteridge, C.K. Bowdery,P. Colrain, G. Crawford, A.J. Finch, F. Foster, G. Hughes, R.W. Jones,
T. Sloan, M.I. Williams
DepartmentofPhysics, University of Lancaster, Lancaster LA1 4YB, United Kingdom
10
A. Galla, I. Giehl, A.M. Greene, C. Homann, K. Jakobs, K. Kleinknecht, G. Quast, B. Renk, E. Rohne,
H.-G. Sander, P.van Gemmeren, C. Zeitnitz
Institut fur Physik, Universitat Mainz, 55099 Mainz, Fed. Rep. of Germany
16
J.J. Aub ert, C. Benchouk, A. Bonissent, G. Bujosa, J. Carr, P. Coyle, C. Diaconu, F. Etienne,
N. Konstantinidis, O. Leroy, F. Motsch, P. Payre, M. Talby, A. Sadouki, M. Thulasidas, K. Trab elsi
Centre de Physique des Particules, Faculte des Sciences de Luminy, IN
2
P
3
-CNRS, 13288 Marseille,
France
M. Alepp o, M. Antonelli, F. Ragusa
2
Dipartimento di Fisica, Universita di Milano e INFN Sezione di Milano, 20133 Milano, Italy
R. Berlich, W. Blum, V. Buscher, H. Dietl, G. Ganis, C. Gotzhein, H. Kroha, G. Lutjens, G. Lutz,
W. Manner, H.-G. Moser, R. Richter, A. Rosado-Schlosser, S. Schael, R. Settles, H. Seywerd, R. St. Denis,
H. Stenzel, W. Wiedenmann, G. Wolf
Max-Planck-Institut fur Physik, Werner-Heisenberg-Institut, 80805 M unchen, Fed. Rep. of Germany
16
J. Boucrot, O. Callot,
2
S. Chen, Y. Choi,
21
A. Cordier, M. Davier, L. Duot, J.-F. Grivaz, Ph. Heusse,
A. Hocker, A. Jacholkowska, M. Jacquet, D.W. Kim,
12
F. Le Diberder, J. Lefrancois, A.-M. Lutz,
I. Nikolic, M.-H. Schune, S. Simion, E. Tourneer, J.-J. Veillet, I. Videau, D. Zerwas
Laboratoire de l'Accelerateur Lineaire, Universitede Paris-Sud, IN
2
P
3
-CNRS, 91405 Orsay Cedex,
France
P. Azzurri, G. Bagliesi, G. Batignani, S. Bettarini, C. Bozzi, G. Calderini, M. Carpinelli, M.A. Cio cci,
V. Ciulli, R. Dell'Orso, R. Fantechi, I. Ferrante, L. Foa,
1
F. Forti, A. Giassi, M.A. Giorgi, A. Gregorio,
F. Ligabue, A. Lusiani, P.S. Marro cchesi, A. Messineo, F. Palla, G. Sanguinetti, A. Sciaba, J. Steinberger,
R. Tenchini, G. Tonelli,
19
C. Vannini, A. Venturi, P.G. Verdini
Dipartimento di Fisica dell'Universita, INFN Sezione di Pisa, e Scuola Normale Sup eriore, 56010 Pisa,
Italy
G.A. Blair, L.M. Bryant, J.T. Chambers, Y. Gao, M.G. Green, T. Medcalf, P. Perrodo, J.A. Strong,
J.H. von Wimmersp erg-To eller
DepartmentofPhysics, Royal Holloway & Bedford New College, University of London, Surrey TW20
OEX, United Kingdom
10
D.R. Botterill, R.W. Clit, T.R. Edgeco ck, S. Haywood, P. Maley, P.R. Norton, J.C. Thompson,
A.E. Wright
Particle Physics Dept., Rutherford Appleton Lab oratory, Chilton, Didcot, Oxon OX11 OQX, United
Kingdom
10

B. Blo ch-Devaux, P. Colas, S. Emery, W. Kozanecki, E. Lancon, M.C. Lemaire, E. Lo cci, P. Perez,
J. Rander, J.-F. Renardy, A. Roussarie, J.-P.Schuller, J. Schwindling, A. Trabelsi, B. Vallage
CEA, DAPNIA/Service de Physique des Particules, CE-Saclay, 91191 Gif-sur-Yvette Cedex, France
17
S.N. Black, J.H. Dann, R.P. Johnson, H.Y. Kim, A.M. Litke, M.A. McNeil, G. Taylor
Institute for Particle Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
22
C.N. Booth, R. Boswell, C.A.J. Brew, S. Cartwright, F. Combley, M.S. Kelly,M.Lehto, W.M. Newton,
J. Reeve, L.F. Thompson
DepartmentofPhysics, University of Sheeld, Sheeld S3 7RH, United Kingdom
10
A. Bohrer, S. Brandt, G. Cowan, C. Grup en, P. Saraiva, L. Smolik, F. Stephan
FachbereichPhysik, Universitat Siegen, 57068 Siegen, Fed. Rep. of Germany
16
M. Ap ollonio, L. Bosisio, R. Della Marina, G. Giannini, B. Gobbo, G. Musolino
Dipartimento di Fisica, Universitadi Trieste e INFN Sezione di Trieste, 34127 Trieste, Italy
J. Rothberg, S. Wasserbaech
Experimental Elementary Particle Physics, UniversityofWashington, WA 98195 Seattle, U.S.A.
S.R. Armstrong, E. Charles, P. Elmer, D.P.S. Ferguson, S. Gonzalez, T.C. Greening, O.J. Hayes, H. Hu,
S. Jin, P.A. McNamara III, J.M. Nachtman, J. Nielsen, W. Orejudos, Y.B. Pan, Y. Saadi, I.J. Scott,
J. Walsh, Sau Lan Wu, X. Wu, J.M. Yamartino, G. Zob ernig
DepartmentofPhysics, University of Wisconsin, Madison, WI 53706, USA
11
1
Now at CERN, 1211 Geneva 23, Switzerland.
2
Also at CERN, 1211 Geneva 23, Switzerland.
3
Also at Dipartimento di Fisica, INFN, Sezione di Catania, Catania, Italy.
4
Also Istituto di Fisica Generale, Universitadi Torino, Torino, Italy.
5
Also Istituto di Cosmo-Geosica del C.N.R., Torino, Italy.
6
Supported by the Commission of the European Communities, contract ERBCHBICT941234.
7
Supported by CICYT, Spain.
8
Supported by the National Science Foundation of China.
9
Supported by the Danish Natural Science Research Council.
10
Supported by the UK Particle Physics and Astronomy Research Council.
11
Supported by the US Department of Energy, grant DE-FG0295-ER40896.
12
Permanent address: Kangnung National University, Kangnung, Korea.
13
Supported by the US Department of Energy, contract DE-FG05-92ER40742.
14
Supported by the US Department of Energy, contract DE-FC05-85ER250000.
15
Permanent address: Universitat de Barcelona, 08208 Barcelona, Spain.
16
Supported by the Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie, Fed.
Rep. of Germany.
17
Supported by the Direction des Sciences de la Matiere, C.E.A.
18
Supported byFonds zur Forderung der wissenschaftlichen Forschung, Austria.
19
Also at Istituto di Matematica e Fisica, Universita di Sassari, Sassari, Italy.
20
Now at Princeton University, Princeton, NJ 08544, U.S.A.
21
Permanent address: Sung Kyun Kwan University,Suwon, Korea.
22
Supported by the US Department of Energy, grant DE-FG03-92ER40689.
23
NowatSchool of Op erations Research and Industrial Engineering, Cornell University, Ithaca, NY
14853-3801, U.S.A.
24
NowatSchweizerischer Bankverein, Basel, Switzerland.

1 Intro duction
The study of

decays into strange particles is imp ortant in order to test low-energy
QCD phenomenology [1], SU(3)-symmetry breaking [2] and meson theories [3, 4, 5, 6].
Exp erimentally, such studies are well advanced for one-prong

decays while the situation
is still quite poor for the three-prong nal states. This is due in part to the relatively
small branching ratios and the diculty in identifying charged particles in a three-track
environment, esp ecially at the LEP energies where the pro duced

leptons are strongly
Lorentz-b oosted.
This pap er describ es an investigation of three-prong

decays involving charged kaons
with the measurement of the branching ratios for the decays


!
K


+


(

0
)


and


!
K

K
+


(

0
)


as the main goal (throughout this pap er charge-conjugate states
are implied). For convenience a same-sign (opp osite-sign) charged particle is dened to
have the same (opp osite) charge as the parent

. Since the
W

b oson only couples to

ud
or 
us
pairs in


decay, the weak current produces states with strangeness
S
=0
;

1
only, and consequently the
K
+




(

0
) and
K

K


+
(

0
) hadronic systems should not
b e pro duced. It is therefore p ossible to identify
K

K
+
K

and
K

K
+


(

0
) nal states
by tagging the opp osite-sign kaons, while the decay mo des with
K


+


(

0
) can be
selected with their characteristic same-sign kaons after subtracting the
K

K
+
K

and the
K

K
+


(

0
) contributions. This corresp ondence is exploited by tting dE/dx spectra
separately for same- and opp osite-sign tracks, thus obtaining the relevant branching
fractions without having to identify all three particles in the nal state. This pro cedure
is based on a precise recalibration of the track dE/dx in the environment of the closely
bunched three-prong jet of

decays.
A more complete particle identication is applied in order to study the dynamics of
these decays, particularly the resonance structure. Cuts are applied on the dE/dx of
all tracks, enhancing the purity of the
K

K
+


and the
K


+


samples at a cost
in eciency. Of sp ecial interest is the pro duction of p ossible intermediate states such
as
K


and
K
pro ceeding through the
K


+


decay, since their relative ratio can
distinguish the two axial strange resonances
K
1
(1270) and
K
1
(1400). This ratio can be
used to estimate the SU(3)-symmetry breaking for the
I
= 1
=
2 members of the two
o ctets [2]. Since the
K
1
(1270) is exp ected to also decayinto
K!
,itisinteresting to study
the
K


+



0
channel, which provides another handle on axial resonance pro duction.
The results presented here are based on the data collected by ALEPH from 1991 to
1995, corresp onding to 201,753 pro duced

pairs.
2 The ALEPH detector
A detailed description of the ALEPH detector can b e found elsewhere [7]. Only the most
imp ortant features relevant for this analysis are briey mentioned in the following.
Charged particle momenta are measured by a magnetic sp ectrometer consisting of a
precision vertex detector, a cylindrical drift chamb er (the inner tracking chamb er or ITC),
and a large time pro jection chamber (TPC). A 1.5 T axial magnetic eld is provided
by a sup erconducting solenoidal coil. The transverse momentum resolution for high-
1

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Three-prong decays with charged kaons" ?

Final states with charged kaons in three-prong decays are studied by exploiting the particle identi cation from the dE/dx measurement. The following branching ratios have been measured: B ( ! K K ) = ( 1:63 0:21 0:17 ) 10, B ( ! K + ) = ( 2:14 0:37 0:29 ) 10, B ( ! K K 0 ) = ( 0:75 0:29 0:15 ) 10, andB ( ! K + 0 ) = ( 0:61 0:39 0:18 ) 10. A study of intermediate states occurring in the K K and K + decays is also presented. See next pages for the list of authors. The ALEPH Collaboration R. Barate, D. Buskulic, D. Decamp, P. Ghez, C. Goy, J. -P. Lees, A. Lucotte, M. -N. Minard, J. -Y. Nief, B. Pietrzyk Laboratoire de Physique des Particules ( LAPP ), INP-CNRS, 74019 Annecy-le-Vieux Cedex, France M. P. Casado, M. Chmeissani, P. Comas, J. M. Crespo, M. Del no, E. Fernandez, M. Fernandez-Bosman, Ll. Garrido, A. Juste, M. Martinez, G. Merino, R. Miquel, Ll. M. Mir, C. Padilla, I. C. Park, A. Pascual, J. A. Perlas, I. Riu, F. Sanchez, F. Teubert Institut de F isica d'Altes Energies, Universitat Aut onoma de Barcelona, 08193 Bellaterra ( Barcelona ), Spain A. Colaleo, D. Creanza, M. de Palma, G. Gelao, G. Iaselli, G. Maggi, M. Maggi, N. Marinelli, S. Nuzzo, A. Ranieri, G. Raso, F. Ruggieri, G. Selvaggi, L. Silvestris, P. Tempesta, A. Tricomi, G. Zito Dipartimento di Fisica, INFN Sezione di Bari, 70126 Bari, Italy X. Huang, J. Lin, Q. Ouyang, T. Wang, Y. Xie, R. Xu, S. Xue, J. Zhang, L. Zhang, W. Zhao Institute of High-Energy Physics, Academia Sinica, Beijing, The People 's Republic of China D. Abbaneo, R. Alemany, U. Becker, A. O. Bazarko, P. Bright-Thomas, M. Cattaneo, F. Cerutti, G. Dissertori, H. Drevermann, R. W. Forty, M. Frank, R. Hagelberg, J. B. Hansen, J. Harvey, P. Janot, B. Jost, E. Kneringer, J. Knobloch, I. Lehraus, G. Lutters, P. Mato, A. Minten, L. Moneta, A. Pacheco, J. F. Pusztaszeri, F. Ranjard, G. Rizzo, L. Rolandi, D. Rousseau, D. Schlatter, M. Schmitt, O. Schneider, W. Tejessy, I. R. Tomalin, H. Wachsmuth, A. Wagner European Laboratory for Particle Physics ( CERN ), 1211 Geneva 23, Switzerland Z. Ajaltouni, A. Barr es, C. Boyer, A. Falvard, C. Ferdi, P. Gay, C. Supported by the UK Particle Physics and Astronomy Research Council.