ISMD04
Detecting Earth-Skimming and
Mountain-Penetrating Tau
Neutrinos
G.-L.Lin
National Chiao-Tung University,
Taiwan
Outline
• Neutrino oscillations and Astrophysical Tau
Neutrino Fluxes
• The Rationale for Detecting EarthSkimming/Mountain-Penetrating 
• The Conversion Efficiency for 
• The Simultaneous Detections of EarthSkimming and Mountain-Penetrating 
• The Event Rate
• Conclusions
Neutrino oscillations and
astrophysical  fluxes
• Although  flux from the source is
generally suppressed compared to that of 
and e, the oscillation effects make the flux
of each flavor comparable at the Earth.
The idea of observing  in view of neutrino
oscillations, was suggested sometime ago.
Learned and Pakvasa 1995
For a source in a cosmological
distance, with
e :  : =1:2:0 , the oscillation
effects taking place as the neutrinos
reach the terrestrial detector make
e :  :  =1:1:1.
Athar, Jezabek, Yasuda 2000
Tau neutrino fluxes
Athar, Tseng and Lin, ICRC 2003
Detecting EarthSkimming/Mountain-Penetrating

The Rationale
The Earth-skimming detection strategy….
Domokos and Kovesi-Domokos, 1998
Fargion, 1997, 2002
Bertou et al., 2001
Auger, TA,…
Feng et al., 2001
Bottai and Giurgola, 2002
Tseng et al., 2003
Mountain-penetrating idea:
Hou and Huang, 2002
Ashra-NuTel
 N only scatters once.
 produced near the earth
surface.
effective interaction

region– 1 tau range!
Cherenkov
fluorescence
 Energy losses and decays

 N inelasticity
Earth-Skimming 
The “effective” tau lepton production probability
=Tau Range(R) / N interaction length()
R increases with energy, while  decreases
with energy. Hence it is favorable to detect
neutrinos of higher energies!
Flux?
The calculation of tau lepton range requires
the consideration of…
The tau lepton loses its energy in the
rock through 4 kinds of interactions:
(1). Ionization (): the tau lepton excites the
atomic electrons. H. A. Bethe 1934
(2). Bremsstrahlung ():


A. A. Petrukhin &V.V. Shestakov, 1968
A
(3). Pair Production ():


A
R. P. Kokoulin & A. A. Petrukhin,
1971
(4). Photo-nuclear interaction:



X
N
F2(x,Q2)
Basic component
The nucleus shadowing effect is considered:
F2A ( x, Q 2 )
a ( A, x, Q ) 
AF2N ( x, Q 2 )
2
Brodsky & Lu, 1990; Mueller & Qiu 1986;
E665 Collab. Adams et al., 1992;
Iyer Dutta, Reno, Sarcevic &Seckel, 2001.
Iyer Dutta, Reno, Sarcevic, & Seckel, 01
Tseng, Yeh, Athar, Huang, Lee, & Lin, 03
Log(E/GeV)
Tau lepton range approaches to 20 km in rock.
Mountain-penetrating is sufficient!
Mountain-penetrating and
Earth-skimming tau neutrinos/tau leptons
The N interaction length:
 1g / cm3  E 
4
 15
2 10 km

   10 eV 
Gandhi, Quigg, Reno, Sarcevic, 1998
0.363
,   2.65 g/cm 3 in rock
The “effective” tau lepton production probability
The Conversion Efficiency
for 
 and  propagations inside the Earth

NC

CC Energy loss

Decay NC
CC

Iong, master thesis, NCTU 04
20 km in rock
100 km in rock
20 km in rock
100 km in rock
minor absorptions
Simultaneous Detection of
Mountain-Penetrating and
Earth-Skimming 
---sensitive to new physics
TeV scale gravity, KK excitations…
E: initial  energy, E’: final  energy, r=Log(E/E’)
New physics-- a factor of 10 enhancement on N
Log(E’/eV)
Mountain-Penetrating
Rough estimate
E: initial  energy, E’: final  energy, r=Log(E/E’)
Log(E’/eV)
Earth-Skimming
Rough estimate
From 30 100 km, a drastic change on
the effect of enhanced (NX)!
Comparison of event rates in 2 medium
lengths probes the new physics.
For the mountain-penetrating case:
W=20 km
L=20 km
H=2 km
O
H
L
The solid angle is
20  2 km   0.1
20 km 
2
2
2
Not small
The Event Rate
AGN  flux from Kalashev, Kuzmin,
Semikoz, and Sigl, 03
F  dN / d log 10 E 
Log(E/GeV) Tseng et al., 03
GRB  flux from Waxman and
Bahcall 1997
Log(E/GeV)
Tseng et al., 03
GZK  flux from Engel, Seckel,
and Stanev, 01
Log(E/GeV)
Tseng et al., 03
Integrated tau lepton flux in units of
km-2yr-1sr-1
Energy & AGN
flux
1015-1016 2.2
eV
GRB
GZK
9.610-3
7.410-5
1016-1017
eV
1017-1018
eV
1018-1019
eV
4.9
7.110-3
1.110-2
0.2
5.410-4
8.210-2
1.110-5
3.310-2
Effective aperture (A)eff required for
1 event/yr, assuming a 10% duty cycle.
Energy &
Aperture
(km2 sr)
1015-1016
eV
1016-1017
eV
1017-1018
eV
1018-1019
eV
AGN
GRB
GZK
4.5
1000
2.0
1400
910
50
19000
120
290
Conclusions
• We have presented the essential features of
detecting Earth-skimming and mountainpenetrating  .
• The tau lepton flux already reaches its
maximum for a 20 km medium length. This
motivates the detections of mountainpenetrating  , in addition to the Earthskimming ones.
Simultaneous detections of mountain-penetrating
and Earth-skimming  probes the anomalous
NX cross section.
We give effective aperture required for detecting
1 event/yr assuming a 10% duty cycle.