Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

A NEW LIMIT ON THE ORTHOMUON MASS

A.E. ASRATYAN and M.A. KUBANTSEV Institute for Theoretical and Experimental Physics, Moscow, USSR

Received 6 February 1978

Results of the CDHS group NC/CC measurements are used to obtain the 10.3 GeV lower limit on the orthomuon mass.

The purpose of this paper is to study the possible effect of M - (heavy muon, or or tholepton [1]) pro- duction on the NC/CC ratio as measured by the CDHS group in the SPS neutrino beam [2].

Orthomuon decay modes are supposed to be ,1

M - ~ v +hadrons, (1)

+ V-e (2) M- ~ e - + v

M- ~ u - +v + Y . (3) ,u /.t

In the CDHS experiment modes (1), (2) contribute to the NC sample, mode (3) to the CC sample. A most straightforward manifestation of M - product ion would be the growth of the NC/CC ratio with neutrino energy. No such increase is indicated by the CDHS data (NC/CC = 0.296 -+ 0.013 for E v < 100 GeV ((E v) = 60 GeV) and 0.293 -+ 0.017 f o r E v > 100 GeV ((E v) = 150 GeV), systematic error included [2]). This fact alone after some trivial manipulations with calculated M - product ion curves [5,6] can be used to derive re- strictions on the M - mass. In this way we obtain that the or thomuon must be heavier than 8.5 GeV (90% C.L., M - hadronic branching ratio B H is assumed to be equal to 0.7 [5]).

Much more sensitive to or thomuon production is

,1 Contributions of (possible) neutral currents (ff -M-)L,R are neglected as compared to charged ones since they would lead to trimuon states with definite invariant mass which are not observed. The possibility of "cascading" orthomuon [3] is also neglected as there is no evidence of a lepton cascade in the CDHS multilepton data [4].

the dependence of NC/CC on Ede p (energy deposit ion in calorimeter by all particles except the muon), which is equal to the net hadron energy in the case of M - production with the decay (1), (3) and to Ehadr + E e for events with decay (2). That is so because in events of M - production and hadronic decay (1) which form the bulk of the or thomuon contr ibution to the NC sample, the hadrons carry off a much larger proport ion o f E v than in 1/J events (see fig. 1). Therefore or thomuon production would effectively increase the observed NC/CC ratio towards larger Ede p. Calculated NC/CC (Edep) curves for m M = 8 GeV and various B H are pre-

o.3~ % '

: 8GeV

z

0.1

4 0 8 0 1 2 0 1 6 0 2 0 0

E DEp, GeV

Fig. 1. Distributions in Edep: curve 1: the reaction v# + N - tt- + hadrons, curves 2-4: orthomuon production with decays (1)-(3), respectively.

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Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

NC CC

0.6

0.4

0,2

ml¢: 8G eV

B~ =1.0

11.4

0 ; 0 t t 200 120 160 EDEp,GeV

Fig. 2. Effect of orthomuon production on the Ede p dependence of the NC/CC ratio.

sented in fig. 2 together with the CDHS data*2. In our

calculations we assume acc = 0.1, aNC = 0.2 +a (see ref. [2] above). One might argue that actually in a v

beam the "intrinsic" aNC could be larger, the resulting sharp fall-off of NC/CC(Edep) being compensated by orthomuon production. However, in a Y beam both ef-

fects (larger aNC and M- production) would flatten the observed NC y-distribution and we would have

obs - obs 0tNC(P ) > OtNC (p) ~ 0.2, in contradiction with the data. In our parametrization of the M- hadron decay structure function we follow ref. [7] (constant above q2 = 0.8 GeV 2 and zero below this value .4.

The results of a quantitative X 2 analysis with m M and B H as parameters are presented in fig. 3 where the 98% C.L. allowed region in the (m M, BH) plane is

shown. For a likely value of the hadronic branching

B H = 0.7 we obtain

m M > 10.3 GeV

t2 Errors quoted in fig. 2 are statistical only. t3 The parameters a describe the shape of the~-distributions:

1 + c~(1 _y)2 for neutrino and a + (1 - y ) for antineutrino. 4:4 Our results are insensitive to all reasonable variation of this

parametrization.

m l ,q"

GeV

10

8

6

i i ' ' 0 0 2 0 4 0,6 0.8 1.0 B.

Fig. 3.98% C.L. Lower limit on the orthomuon mass as fuJ~c- tion of the hadronic branching ratio B H.

which is well above the existing lower limit of 1.8 GeV [8].

Stimulating discussions with V.S. Kaftanov,

V.D. Khovansky and M.M. Savitsky are gratefully acknowledged.

References

[1] H. Fritzsch et al., Phys. Lett. 59B (1976) 256; J. Schechter et al., Phys. Rev. D8 (1973) 484. J. Schechter et al., Phys. Rev, D9 (1974) 1769; C.H. Albright et al., Nucl. Phys. B86 (1975) 535.

[2] M. Holder et al., Phys. Lett. 72B (1977) 254. [3] V. Barger et al., Phys. Rev. Lett. 38 (1977) 1190. [4] M. Holder et al., Phys. Lett. 70B (1977) 393. [5] A.E. Asratyan and M.A. Kubantsev, preprint ITEP-19S

(1973); C.H. Albright and C. Jarlskog, NucL Phys. B84 (1975) 467.

[6] M. Holder et al., Phys. Rev. Lett. 39 (1977) 433. [7] J.D. Bjorken and C.H. Llewellyn-Smith, Phys. Rev. D7

(1973) 887. [8] A.E. Asratyan et al., Phys. Lett. 49B (1975) 488.

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