Clark, A.R.

Elioff, T.

Field, R.C.

Frisch, H.J.

Johnson, R.P.

Kerth, L.T.

Wenzel, W.A.

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Lawrence Berkeley National LaboratoryRecent WorkTitleEXPERIMENTAL LIMIT ON THE BRANCHING RATIO FOR V^tf-#Permalinkhttps://escholarship.org/uc/item/1kh8j0k4AuthorsClark, A.R.Elioff, T.Field, R.C.et al.Publication Date1970-08-17eScholarship.org Powered by the California Digital LibraryUniversity of California' I 4 To be presented at XVth International Conference on High Energy  Physics, Kiev, USSR, August 26-Sept. 4, 1970 UCRL-20078 Prep ri nt EXPERIMENTAL LIMIT ON THE BRANCHING RATIO FOR K — 11 A. R. Clark, T. Elioff, R. C. Field, H. J. Frisch, R.P. Johnson, L. T. Kerth, andW. A. Wenzel August 17, 1970 	s• 	* - I • 	• 	 tt, ,,q • 6 1970 Ll çcoc' AEC Contract No. W-7405-eng-48 TWO-WEEK IOAN COPY This is a LIbrary Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. DIoIsIon, Ext. 5545 • 	 1 	flTT 	 co  4.4 _d•j \. 4.4 	1 	 - DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. r ..... . 	 . -if UNIVERSITY OF CALIFORNIA LAWRENCE RADIATION LABORATORY BERKELEY, CALIFORNIA 94720 TELEPHONE (415) 8432740 TELEX 335313 LAWRADLAB BERK TWX 910 , 366 , 7172 LAW RAD LAB CABLE IJCLRL BERKELEY August 26, 1970 ADDENDUM TO UCRLr20078, "Experimental Limit on the Branching Ratio for 	- £2" Analysis of approximately another 35 percent of our total data has : reduced- the limits on the branching ratio for each of the decay modes - - KL +- LI +- - e e KL 	++ - to 6.8 x 10 	(90% C.L.). There are no new dilepton candidates. To be presented at XVth International 	 UCRL-20078 Conference on High Enerr Physics, Kiev, USSR, August 26.-Sept. ii, 1970 EXPERDVIENTAL LBvIIT ON THE BRANCHING RATIO FOR KLO*  A. R. Clark, T. Elioff, R. C. Field, H. J. Frisch, R. P. Johnson, L. T. Kerth, and W. A. Wenzel Lawrence Radiation Laboratory University of California Berkeley, California August 17, 1970 The K - 	decay is generally considered to be a sensitive test of the existence of weak neutral currents. Higher—order weak interactions have also been considered as a possible source of this decay. 1 Theorists have used current algebra techniques with the experimental limit on -* 	to set an upper bound on the weak interaction cut—off. 2 With the additional hypothesis that this cut—off is due to the electromagnetic properties of the intermediate vector boson (lyE), loffe and Shabalin 2 have set an upper limit on the mass of the IVB. The K - 	£ decays can also be induced by electromagnetic inter- actions. 3 Using the measured 	-' yy rate and only the two photon intermediate state, branching ratios between 6 x 10 and 1 x 10 are generally predicted for the K - 	i decay. 5 However, other intermediate states may interfere, producing a unitarity limit different from that predicted from the two photon state. Martin et al. 6 have estimated that the effect is less than 20% for itTcy and 3t intermediate states. The K e e rate is suppressed by a factor of (m/m) relative to the KL 	jj rate in weak models which use V—A and also in electromagnetic models. - .2 - 	 - 	UCRL-2 0078  •. 	 ... The 	- ej rate is not predictable from any known inte±'action. Limits on this decay, which violates lepton number conservation, can be +-. compared with limits on ! ± - e± 	± y or 	- e±  e e . Table I shows the previously published experimental limits on the various dilepton decay modes of the K. Figure 1 shows the plan view of the detection apparatus. 7 The 6 m long decay volume began 7.6 in from the production target in the Bevatron External Proton Beam. Initially, data were taken with helium in both the decay volume and the volume between the spark chambers to reduce Coulomb scattering. The decay volume was later replaced with a vacuum box to reduce neutron—induced background. The momenta of the decay secondaries were measured in symmetric spectrometers, each with a 0.9 in x0.6 in aperture cture—frame magnet and five double gap magnetostrictive wire spark chambers. Two sets of x—y coordinates per trajectory were measured in each chamber. These chambers were designed with low mass to limit scattering. The aluminum wires were 75i in diameter, and the windows were 25i aluminized mylar (1000 R Al). The line integral of each magnetic field, which was uniform within 1% over 95% of the aperture, was set to correspond to the center of mass momentum of the K 0 L - +  i decay. Independent of kaon 0 momentum, therefore, secondaries from nearly transverse two—body decays emerged from the magnets essentially parallel to the incident kaon direction. J Downstream of the last spark chamber, two vertical counter hodoscopes selected trajectories with maximum horizontal divergences of ± 45 mrad from - 3 - 	 UCRL-20078 the beam line. A horizontal counter hodoscope was mounted in front of each upstream vertical hodoscope, and a large counter f or fast timing was mounted behind each downstream vertical hodoscope. The trigger logic, employing primarily MECL—II integrated circuitry, required a particle on each side which satisfied the angle requirement and counted in the horizontal hodoscope and the timing counter. Electrons which were bent inward at angles between 15 and 45 imrad were rejeôted. This eliminated a large fraction of the K 3 background without affecting the dilepton acceptance significantly. Electrons were identified in 2.3 meter long Freon Cherenkov counters, which were found to be more than 99.6% efficient during preliminary tests. Muons were identified by range measurements. The range detectors each contained a 1 in long carbon block followed by 17 cells of steel and scintillator. Each cell consisted of one or more 1.2 in x 1.2 in x 2.5 cm steel plates and a 1.2 in x 1.2 in x 1.9 cm plastic scintillator, arranged to give a muon range interval of approximately 7% f or momenta between 0.5 and 1.6 Gay/c. The signals from the Cherenkov and range counters were not used in the trigger (except as noted above) but were recorded for use later in the analysis. Data were accumulated, checked and stored on magnetic tape with a PDP cputer. The signals from each counter and the spark chamber information for each event were recorded on the tape; beam intensity and magnet currents were recorded each Bevatron pulse. - II. - 	 UCRLr-20078 The data we analyzed on a CDC 6600,computer. An event was considered a two—body candidate if the two reconstructed trajectories met within 2 cm in the decay volume, and the reconstructed parent particle originated at a point less than 5 cm from the production target. In addition, each secondary was required to have a momentum below2.l 0eV/c. These cuts retained essentially all of the two—body events from the 	- 	 mode. The two- pion invariant mass spectra from data taken with the vacuum decay volume are shown in Figures 2a and 2c for events appearing to originate within 7.6 cm and Ii- cm, respectively, of the target. All secondaries without an electron signature have been assumed to be pions. Figure 3a shows the same plot for the helium—box data, with a 5 cm target cut. The background is mostly from 	- iTiV decays, which were assumed to contribute a flat : background under the 	+ 	 peak. After subtraction there remained 254 1 000 K -, 	 events. The acceptance for 	- itit was measured to be (75 ± 4)% relative to that for the -~ decays, because of the lower c.m. momentum of the two pions. The equinent was designed to accept all charged two.—lepton modes equally well. A detailed estimate of the decay—in—flight loss of - 	 has not been made. We estimate this loss to be about 5%. 0 	+- To compare with the corrected sample of KL -4 it , there were no 0 	+.- 	 + KL - e e or KL e i events. Five possible KL - i i candidates survived the target cuts and had ranges within 3 cells of the predicted range for muons. These events appear in Figures 2d and 3b, which show - 5 - 	 IJCRL-20078 the invariant mass spectrum for two-muon candidates with the target and range cuts described above. For the analysis described above, an effective length parameterization of the magnetic field was used; this procedure retained good mass resolution but did not provide adeQuate rejection of events in which a secondary pion decayed in flight in the magnet. The 	- 	candidates were therefore examined in more detail, using a step-by—step integration of the trajectories through the magnets. These fits were compared with those from similar trajectories from 	-' 	 data. The secondaries in the dimuon candidate of mass 1199 MeV in Figure 2d have the wrong range to be muons by 6 and 9 standard deviations, respectively. We therefore exclude it as a candidate. In Figure 3b the dimuon candidates of mass 489 and 504 MeV c were rejected on the basis of the trajectory fits, which gave probabilities of less than l0 that the trajectory was that of a single particle. The candidate of mass 502 MeV/c showed poor trajectory, mass and range fits; we would expect less than 0.03% of the _ +L_events to fit so poorly. For the candidate of mass 96 MeV/c2 , the detaileçI analysis of one secondary trajectory showed that only 6% of the trajectories used for comparison had poorer fits; in addition the range of one secondary was shorter than that of 80% of muons of the same momentum. Each candidate is consistent with interpretation as a 0++ KL - 	v decay with the pion decaying in flight in the magnet. • 	 - 6 - 	 UCRL-20078 Interpreting these five candidates as background, we used the measured " o 	+ 	 18 KL - it Tc branchingratio to obtain the limit: P(K -+ 	 .P(K - 	 ( 111/j efficiency) x 	 x2.3 P(K 	all) 	r( 	all) 	N( 	observed) = 1.1 x 10 (90% Confidence tvel) 0 	+- 	0±± 	 0 	+ The limits on 	-, ee and 	e are the same as for These results arebased. on the analysis of approximately 50% of our data. Previous limits on these ratios are given in the table. 	2 • 	o 	+- In ternis of loffe and Shabalin's IVB calculation, this KL limit leads to a weak interaction cut—off of. 29 GeV (90% C.L.). In their model, this result suggests that the mass of the IVB is less than 2.6 GeV (90% C.L.). 	 - Li - 7 - 	 TJCRL-20078 REFERENCES A. Pais and S. B. Treiman, Phys. Rev. 176, 1974 (1968) B. L. loffe and E. P. Shabalin, Soviet Journal of Nuclear Physics 6, 603 (1968). R. N. Mohapatra, J. Subba Rao, and R. E. Mashak, Phys0 Rev0 Letter 20, 1081 (1968) and Phys. Rev. 171, 1502 (1968). 3 	C. Quigg and J. D. Jackson, UCRL-18487 (1968), unpublished.. This article contains an extensive list of references to previous works0 . M. Banner, .J0 W. Cronin,J. K0. Liu, and.J, E. Pilcher, Phys. Rev, Letters 21, 1103 (1968). C. Quigg and J. D. Jackson, OPo cit . , p 43. . B. R. Martin, E. de Rafael and J. Smith, 'Neutra1 Kaon Decays into Lepton Pairs Tt , unpublished0 	 . A complete description of the apparatus can be found in: Rolland P. Johnson, UCRL - 1979.April 1970 (Ph.D. Thesis, unpublished)0 80 A. Barbaro-G-altieri, S. E. Derenzo, L. R. Price, N. Barash-Schmidt, C. Brieman, M. Roos, P. Soding, C. G. Wohi, Rev0 Mod0 Phys. 42, 87 (1970) * This work was done under the auspices of the U. S. Atomic Enerr Commission. .0 TABLE I Branching Ratio Limits at 90% Confidence Level Rate 	 Previous Limit. • This experiment 0 	+- 2.1 x i0 	(a) 	< 1.1 x 10 P(K 	ail) 	 — fl(ee) < 1.5 x 10 	(a) 	< i.i x 10 P (ic - all) 	- P(K-'e < 3.7 x 10 	(b) 	< i.i x iO P (K 	all) P ( 	- e y) 	< 2.2 x 10 	(c) P( all) — P ( 	eee) 	< 6.8 x, lo 	(d) P(all) -. H. Foeth, M. Holder, E. Radeacher, A. Steude, P. Darriulat, J. Iutsch, K. Kleinknecht, C. Rubbia, K. Tittel, M. I. Ferraro, C. Grosso, Phys. Letters 30B, 282 (1969). V. L. Fitch, H. F. Roth, J. Russ, W. Vernon, Phys. Rev. 161, 1711 (1969); M. Bott—Bodenhausen X. deBouard, D. G. Cassél, D. Dekkers, H. Feist, B. I4ermod, I. Savin, P. Scharff, M. Vivargent, T. B. Willil±s, K. Winter, Phys. Letters 24B, 194, 1138 (1967). S. Parkr, H. L. Anderson, C. Rey, Phys. Rev. 133B, 768 (1961 ). • (d) S. Frankel, W. Frati, J. Halpern, L. Holloway, W. Wales, F. W. Betz, 0. Chamberlain, Phys. Rev. 130, 351 (1963); A. I. Babaev, M.Ya. Balats, V. S. Kaftanov,L. G. Landsberg, V. A. Lyubflnov, Yu. V. Obukhov, JETP 16, 1397 (1963). - 9 - 	 UCRL-20078 FIGURE CAPTIONS Figure 1 	Lay—out of apparatus. Figure 2 	Vacuum decay—volume data. The various cuts are described in the text. The histograms show invariant mass spectra of two--body candidates interpreted as: KLo -, +—, originating within 7.6 cm of the target; K - 	 originating within 7.6 cm of the target; KL o - 	7t 	originating within 4 cm of the target; o 	. KL -~ + p.—  , originating within 4 cm of the target. Figure 3 	Helium decay—volume data. The histograms show invariant mass spectra of two—body candidates interpreted as: K -originating within 5 cm of the target; KL - p. p. , originating within 5 cm of the target. EM a -10- - 	 E 	I) .0 CL EL e I H •:: 	' I H cn -N____ 8 	I 	 I(I)  € I I 17 C (0 0. "-"o 7m 0 U, 	S 0 I -1 1 - 60 50 40 30 > 20 ID 0 0 480 30 20  • Lu - 0 480 490 	 500 	 510 lu Invariant Mass (MeV) 490 	 500 	 510 ,r Invariant Moss (MeV) VACUUM DECAY VOLUME DATA 5 4 3 > 2 Lu 	I 0 Inoorioot Mos MeV) 4cm target Cut 20  1 	 no Orbit fits 67eoents 	(d. ) ' lo ll 0 480 	 490 	 500 	 510 LL Invariant Moss (MeV) XBL 705-1763 * ig2 12 510 IN > Ld to U, (a) L 490 	 500 irir Invariant Moss (MeV) -12- HELIUM DECAY VOLUME DATA > 0) U) C 0, > w 5cm tarqet cut no orbit fits 480 	 490 	 500 	 510 /L ' /.L Invariant Moss (MeV) XBL 708-1762 Fig. 3 (b) LL¼Jt'L. I NI %.j I I...,L This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the informa-tion contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not in-fringe privately owned rights; or Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any employee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such con tractor prepares, disseminates, or pro-vides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. 4 0 EM to txl 1-9 

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EXPERIMENTAL LIMIT ON THE BRANCHING RATIO FOR V^tf-#

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EXPERIMENTAL LIMIT ON THE BRANCHING RATIO FOR V^tf-#

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