arX

iv:0

712.

0697

v2 [

hep-

ph]

6 Dec

2007

Investigating Possible Neutrino Decay in Long Baseline

Experiment Using ICAL as Far end Detector

Debasish Majumdar1 and Ambar Ghosal2

Saha Institute of Nuclear Physics

1/AF Bidhannagar, Kolkata 700 064, India

We investigate the effects of possible decay of neutrinos from a neutrino factory in a long

baseline experiment. We consider the neutrinos from a factory at CERN and the detector

to be the 50 kTon iron calorimeter (ICAL) detector proposed for India-based Neutrino

Observatory (INO). We found considerable depletion of muon yield at INO for certain

value of decay parameters.

High energy neutrino beams are now playing a very crucial role to determine the

yet unknown features of neutrino physics. Apart from determination of neutrino

mass hierarchy and determination of 13 based on neutrino oscillation theory, another

possibility could be to search neutrino decay over long baselines. The neutrino decay

scenario has been discussed earlier in Ref. [1, 2, 3, 4]. The neutrino decay scenario

has also been discussed in connection to atmospheric and solar neutrinos in Refs.

[5, 6, 7, 8, 9, 10, 11, 12]. Decay of Supernova neutrinos has also been adressed by

several authors [13, 14, 15, 16, 17]. The possible neutrino decay for cosmic ultra

high energy neutrinos are also studied [18] and also neutrino decay is addressed in

the context of recently proposed unparticle in [19, 20, 21]. Furthermore, MiniBooNE

collaboration [22] searching for e oscillation recently reported null result within

the energy range 475 < E < 1250 MeV and hence disfavours two neutrino oscillation

theory, however, excess of e events has been observed within the energy interval 300 1GeV dominant contribution will come from DIS. We have also included

resolution function of the detector obtained from exact simulation of the ICAL de-

tector which correlate the energy of the incident neutrino on the the detector to the

produced muons inside the detector [24].

In the present decay scenario, we consider that the neutrino states |2 and |3

are unstable and they decay into the stable state of |1. The exponential decay term

for the ithe neutrino state is given by exp(4piL/di) where L is the baseline length

in kilometers and

di = 2.5kmE

GeV

eV2

i(4)

where i = mi/ , mi being the mass of the neutrino mass eigenstate |i and being

the decay lifetime.

The purpose of this work is to investigate whether the effect of any possible decay

of neutrinos can be detected by an iron calorimeter detector suc as INO. For this

purpose we have chosen the long baseline neutrinos from a future neutrino factory at

CERN.

We have considered the oscillation of such neutrinos with decay. The neutrino

flavour and mass eigenstates are conencted by the MNS mixing matrix as |a =

Uai|i, where Uai are the 33 MNS mixing matrix of the flavour and mass eigenstates

of neutrinos. Here, a e, , (the flavour indices) and i = 1, 2, 3, the mass indices.

In order to incorporate the effect of any possible decay of the mass eigenstates |2

and |3, we fold the matrix elements Uai with exponential decay terms such that

Uai Uai exp(4piL/di) for i = 2, 3.

The matter effect induced due to the passage of neutrinos through earth matter

for traversing the CERN-INO baseline is also taken into account. We have taken an

average matter density of 4.14 gm/cc for the purpose. This average density for the

particular baseline considered is calculated using PREM [27] earth matter profile.

We have made a three flavour calculation and the oscillation parameters used in

the calculations are

m232= |m2

3m2

2| = 2.21 103eV2, m2

21= |m2

2m2

1| = 8.1 105eV2

3

for two mass square differences and

23 = 45o, 12 = 33.21

o, 13 = 9o.

for three mixing angles.

We calculate the variation of total muon yield at INO with the decay constant

for such a decay scenario. in two cases; a) variation with 2 for different fixed values

of 3 and b) variation with 3 values for different fixed values of 2. The results are

shown in Figs 3 and 4 respectively. From Fig. 3, one sees that decay effect due to

2 is most effective in the region 0.0001

m1 =m22 m

221 (8)

M = m1 +m2 +m3 (9)

Eqs. (5 - 9) is evaluated for normal hierarchy only. Using Eqs. (5 - 9) we compute

M and found that within the ranges of considered above M is always less than the

cosmological bound of 0.7 eV.

In summary, we have investigatd possible decay of light neutrinos in a long base-

line experiment for a neutrino beam from CERN neutrino factory to ICAL detector

proposed for INO covering a baseline length of 7152 Km. A unique facility of ICAL

detector, the charge identiofication, has opened up the possibility of such study. A

significant depletion of neutrino flux caused by the neutrino decay can be observed in

the form of depleted muon signal at INO for a reasonable choice of decay parameters

2, 3 and other neutrino oscillation parameter inputs from atmospheric and solar

neutrino experiments.

References

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[12] S. Choubey, S. Goswami, D. Majumdar, Phys. Lett. B 484, 73, (2000).

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6

Figure Captions

Fig 1. The flux from a neutrino factory vs different energies (E) for initial

muon energy E = 50 GeV. See text for details.

Fig. 2 The e flux from a neutrino factory vs different e energies (Ee) for initial

muon energy E = 50 GeV. See text for details.

Fig. 3 The variation of total muon yield at INO with decay parameter 2 for three

different fixed values of decay parameter 3.

Fig. 4 The variation of total muon yield at INO with decay parameter 3 for three

different fixed values of decay parameter 2.

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