Transcript Neutrino tau - CEA-Irfu

-
Detection of UHE tau neutrinos with a
surface detector array
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OUTLINE

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
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Neutrino tau
Detection method → an alternative method
From theory we know…
Neutrino conversion efficiency
Results of tests of a prototype at high altitude
(3600m)
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Neutrino tau
•Standard acceleration processes in
astrophysics rarely produce τ .
•e : μ : τ =1:2:0
•In case of oscillation full mixing, the flux
ratios evolves towards
• e : μ : τ =1:1:1 for a very large range in
Δm2
~ 50%Eντ
ντ →CC → τ + h → shower(1) + shower (2)
ντ →NC → ντ + h
\→ τ → shower (1)
CC
1st shower:  decays into hadrons (0.64), this shower carries visible Eτ ~
0.5 Eν
2nd shower: neutrino-nucleon scattering, this shower carries 0.2 Eν
Eτ=(1-y)Eν 0.2<y<0.8 <y>=0.25 and Eτ=0.75 Eν
Motivation:
 μ ↔ τ oscillation of atmospheric neutrinos well established
No direct evidence for astrophysics τ appearance observed
yet
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Could the flavour ratios differ from 1:1:1?
•
High Energy neutrinos are belived to be produced
through the decays π+ →μ+ +νμ → e+ + νμ + νe + νμ
produced in pγ,pp,pn interactions. The ratio of the
fluxes of neutrinos is expected to be 1:2:0
•
if energy losses is considered (radiation) for µ from
high energy pion decay → suppression of contribution of
Neutrinos from
muon decay
π and μ decays
 Then we expect a ratio at source 0:1:0
 Reactor results give each mass eigenvalues contains
equal fraction of νμ –ντ then at Earth the ratio
is 1:2:2
Ref.J..F. Beacom N.F.Bell, D. Hooper,S.Pakvasa,
T.J.Weiler Phys. Rev. D 68 093005 2003
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νμ
νμ
νe
π+ 1
1
1
π- 1
1
νe
1
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Other scenarios if not 1:1:1
• Neutrino decay (Beacom, Bell, Hooper, Pakvasa& Weiler)
• CPT violation (Barenboim& Quigg)
• Oscillation to steriles with very tiny delta δm2
(Crocker et al; Berezinskyet
al.)
• Pseudo-Dirac mixing (Beacom, Bell, Hooper, Learned, Pakvasa&
Weiler)
• 3+1 or 2+2 models with sterile neutrinos (Dutta, Reno and
Sarcevic)
• Magnetic moment transitions (Enqvist, Keränen, Maalampi)
• Varying mass neutrinos (Fardon, Nelson & Weiner; Hung & Pas)
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Detection methods
UHEC neutrinos E>108 GeV are difficult to be detected:
 The atmosphere is transparent
→
low density
The Earth opaque to them, ν interaction length ≤ 2000 km
1.


•
•
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Detection by Large Volume detectors → Cerenkov:
rate
Φshower = NAv ρ∫(dΦν /dE) dEσν A
ντ channel is quite different from νμ
τ will decay and generate a cascade decay vertex and
showers are separated by several ten meters at PeV → double bang event.
This signature is constrained by effective volume
Similar to detection techniques used in low energy experiments (Super-K)
Technique with a proven capacity to detect neutrinos (atmospheric)
Cascade detection: e, τ
Muon tracking:
Effective volume >> instrumented Volume
Excellent pointing, Poor energy resolution
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Effective volume = instrumented volume
Poor pointing accuracy, Good energy
resolution
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ντ detection technique in a large Volume detectors
Cascade detection
Lτ =49 Eτ m/PeV
τ
ντ
ντ
km3
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Detection methods cont’d
2. Detection by Large Surface detector:
•
ρair =10-3 g/cm3 hence large acceptance → 104 km3 sr →
Auger
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Horizontal neutrino shower rate Φshower =NAv ρair ∫ (dΦν /dE) dEσν A
If we increase ρ of a factor ~2500 (i.e.rock) we can reduce the
acceptance
τ
→
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alternative method →
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An alternative method
→ Earth skimmed neutrinos
*
Earth skimming process implies:
 neutrino propagation in the Earth during which
interacts and regenerates (~10% →see Beacom et al.)
 tau propagation in the Earth during which looses
energy and decays in the atmosphere after exit from
Earth surface
.
*
→ upward going air shower emerging from the ground
may be detected using the fluorescence light (low duty
cycle ~10%) or a directional detector.
J.F. Beacom, D. Fargion, J.L. Feng, E.W. Kolb and E. Zas
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Detection strategy: aim at the horizon
• strategy to detect
τ
is aim at the horizon
To do that we must have:
•
•
direction detection (i.e time of flight)
good geometric acceptance
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Different models evaluate the UHE neutrino flux
AGN: galaxies with extremely
Energetic processes in the nuclei.
They are the most
likely source of cosmic rays
above 1015 eV. AGNs are thought
to be fueled by matter accreting
onto black holes.
Z-burst:A very high energy (>1021
eV)
neutrino interacts with a relic
neutrino left over from the Big Bang.
This produces showers of particles,
some of which are neutrinos.
GZK:Any high energy hadron will
interact with the cosmic microwave
background (CMB). This will
eventually lead to the production of
neutrinos. The rate at which hadrons
interact with the CMB is controlled
by the injection spectrum of the
hadrons and the characteristics of
the universe.
The uncertainties in this rate can be
as high as 300%.
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topological defects (TDs) which
are relics of symmetry breaking
just after the Big Bang excluded
by Auger exp Pune Conf. 2005 11
AGN and GZK
Excluded by A-B10
Astr.Phys 22 339 05
AGN integrated flux ~104 km-2 yr-1sr-1
@ Eτ 108-1011 GeV
GZK is a factor 102 -103 less AGN
GZK mechanism:
⌐ p+ e- + νe
p+γcmb→Δ+ →n +π+
∟μ++ν
∟e++νe +νμ
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AGN
GZK
hep-ph/0011176
JCAP 0404 2004
Cosmological neutrino flux and sensitivity
for planned projects
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Search for ντ up-going
Tau events:
• τ shower: high multiplicity 10 particles/m2
• 64% hadronic decays n(π)ντ
• Curved shower wave front (detected by timing) unlike
the plane wavefront of atmospheric showers at
large angles
• Shower emerging from ground Θ>900
• Decay vertex above the ground
Backgrounds:
• Horizontal atmospheric shower, p interaction → low
multiplicity 0.01 particles /m2
• DIS with pions..muon bundles
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Time structure of tau shower
tau decay : shower with particles
spreaded in time → curvature radius
The shower Max occurs after 3-4 km the decay point
μ density in a time
window of 500 ns
Ordinary hadrons or nuclei
(p,Fe..) interact at the top of
the atmosphere.
Electromagnetic component
reduced, muons
→ plane wavefront
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A comment on acceptance for neutrino showers
Geometric Acceptance is function of Array Surface and shower radius mainly
hence →
 Effective area,A = (a sin(α-β)+2r)(b+2r)dΏ
where
 Surface of Array, S=axb
 r=shower radius of shower at first interaction point
 Emerging angle Β =Θzenith-90 ~ 50
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Horizontal array α~0, sinβ~10-2 hence → no emerging showers can be
detected, only horizontal → Auger surface detector
Inclined array sin(α-β)~0.6
 Detection and trigger efficiency good → no particular event topology
required
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Probability to get an emerging Tau
ν interaction length
in rock
neutrino cross section
Τau
Range
in air
The tau flux is determined by ratio tau range to
CC neutrino N interaction length
Ratio @ 1017-18 eV ~10-3 hence ν flux at energy>1017 eV
Rdecay = E/mτ cτ
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Charged particles as function of the depth of the shower
Gaisser_Hillas distribution
total
γ
μ
e
π
τ → πππντ

At large depth muons constant and electrons
drop; at 3 km electrons/muons ~100
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Laundau-Pomeranchuck-Migdal effect
retards the development of em component
M.T.Dova astro-ph/0505583
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The neutrino conversion efficiency, ε in the Earth crust
we computed the probability for τ of energy E to survive for a
slant depth x inside the crust of Earth and converting to τ within
[x, x+dx]
e(-x/λν) dx/λν (int.length,λν=1/NAσρ)
The probability for a tau lepton of energy E’ to survive for a slant
depth L-x inside the Earth crust and exit the crust with the
energy Eτ including the energy loss.
•
The neutrino conversion efficiency : ε=∫ e(-x/λν) e(L-x/λτ) dx/λν is
convoluted with decay length and longitudinal shower development
and neutrino flux 1/E2 gives :
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The
τ
sample versus θ and ε for Eν = 108 -1011 GeV
Toy MonteCarlo
L
ντ
L= 250
500 km
92.50 95.00
L in rock (km)
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events with at
least 10 part/m2
on the array and
Tau decay length
from ground
L= 200-300 km
Detector at 8 km
ε ~ 1.0 – 1.5%
To detect τ
shower requiring at
least 10 part/m2
it must decay at
4-5 km from the
ground level
Colors: nu interactions where
tau reaches the ground with
shower max
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ε as function of detector distance and L
for Eν = 108 -1011 GeV
92.50
950
±200
conversion efficiency ε
Detector aperture
versus L at different
2 sr
A=∫
S
cos(θ-α)dΩ=
S
0.15
km
Ω
eff
eff
detector distances
L bin=100 km
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Rate calculation
Assuming a neutrino energy
spectrum following a power law
Φ(E) ~ 10-6/E2 (Gev-1cm-2s-1sr-1)
∫Φ(E)dE ~ 3x103 (km-2yr-1sr-1)
integrated between 108 – 1011 GeV
N τ shower = ∫Φ(E)Pdet τau(E)dEdtdAdΏBr=
50 x 0.15 x 0.64 ~ 4.8 (km-2yr-1)
or a upper flux limit for a spectrum Φ(E) ~ 10-7/E2
*(single tower → 1.6)
**No tau regeneration taken into account
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Predictions for Auger and future experiments:
Ice-Cube and Nemo
Auger fluorescence
Bugaev et al.
astro-ph/0311086
Guzzo et al hep-ph/0312119
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Results from Corsika 6.204
tau shower 5x1018 eV
particle μ,e γ tau shower density and momentum at the detector level
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Determination of Mountain slope
β=Θ-90
The slope of the mountain slope, θ angle and L
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Performances studies of the array
The unit of the array
 How many tower?
 Angular resolution: 0.50 (core
inside the array)
 Duty cycle 100%
 We can improve the acceptance if
we put 2 modules close
 separate em component by lead
layer under study
60 cm
lead
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Number hits versus number towers
>500 tower no large improvements in density
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From Décor-Nevod at large zenith angle
10-9
10-4
Albedo muon intensity
Muon intensity
O. Saavedra talk at Cosmic Ray Physics
Workshop Moscow 17 Oct 2005
10-5
Bundles ~ 10-5 m-2 s-1 sr-1
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Trigger 1
To define a trigger we have to remind
 Electrons do not escape at that energies
 Muons from νµ do not produce visible signal
 Neutrino related showers can be easily distinguished from
those induced by hadrons in high atmosphere by multiplicity
 Muon bundles high multiplicity small area ~10-5 m-2 s-1 sr-1
1st Level record data bank (TDC
charge flag etc..)
2nd Level select up-ward tracks
3rd Level multiplicity logic with a
coincidence gate (~10µs)
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Trigger 2
detector
Event trigger logic:
Sub-array → µ bundles flag
Event by multiple sub-array
o Rate Level 1: 10-2 Hz each tower
zenith angle 930
o Rate Level 2: 10-3 Hz each tower
Cut on charge to select up-ward and down ward
tracks -> 10-6 Hz only up-ward tracks
o Rate Level 3: NCMRateL2x(RateL2xgate)M = 10-24 Hz
Sub-array
Sinlge tower at 930 measures a flux of ~10-7 cm-2 s-1 sr-1
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Electronics board
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Test performed with a prototype at Jungfraujoch Station (3600 m)
Switzerland
Field of view
Up-going tracks
Time of flight
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Preliminary results (April 05) from 2 towers
Tower1
Tower2
950
3 cm Lead in front tile2 of
Tower2 (yellow plot)
ADC tile1 vs tile2
Tower1
Tower2
1000
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Time resolution
central region,
-3ns to +3ns
Signal region, ±3ns
tile C1
tile C2
time resolution
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The tiles
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Preliminary test results at Jungfraujoch Station
Flux measured
at Jungfraujoch
Station 3600 m
P>30 MeV/c
•
•
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Decor experiment
P>7 GeV/c
at sea level
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西部高山后面的宇
活动星系核、暴、
CRTNT proposal
宙
GZK, TD, Z-burst等
Z. Cao. M.A. Huang, P. Sokolsky
Y. Hu
超高能
超高能中微子天
Astro-ph/0411677
电子中微子
μ中微子文学
中
微
子
振
荡
τ中微子
效应
荧光/契伦科夫光
空气簇射
x16
AGN event rate:
8~10 event/yr
using
16 telescopes
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τ中微子大气荧光/C光
成像望远镜
3m
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2.5m
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Conclusions
Conventional horizontal arrays are not
optimally adapted to Earth skimming
events
→ a new strategy to be considered is:
 to aim at the horizon and detect the
direction of the shower by time of
flight
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R&D
1- development of the electronic board with high resolution TDC (ACAM) and
MATACQ chip to sample the signal al High Frequency ( 1GHz sampling)
(see http://www.caen.it/nuclear/product.php?mod=V1729)
2- buy 20-30 PM's and 10-15 solar Power supplies
3- design the mechanics to move within 15 deg in zenith each tower and the pointing
system
4- define material to be used to built the detector (alluminium, PVC
and possible stress due to gradient of the temperature)
5- study an other PM reading (fibers?) to improve the separation of up-ward
down-ward tracks
6- study possible part id (by lead + 5 mm scintillator plate read by fibers+PM 4ch)
and the signal shape to separate PID
8- Study Trigger by MC, how store the data and its managment
7- built 10-15 towers and move them at the final destination to test the system
wireless device (GPS-GSM Motorola12+) and Daq. test the longitudinal as well as
transversal time resolution
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setup
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Cost estimate
Scintillating tiles
----
1000 PMT Hamamatsu low voltage
$275k
mechanics
$70k
Frame detector,cables
$60k
Electronics board
$300k
Power supply
$100k
GPS-GSM Motorola 12+
$25k
DAQ
$100k
installation
$100k
total
$1030k
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Neutrino cross section
R2
R1
Making measurements
n at different
θ angle we can estimate
σν
e
u
t
r
Neutrino cross section
i
n
o
• R= Φτ (E)/Φν (E)=∫0L dz∫NρdEν (dσcc /dEτ ) e-zNρσ
• R1/R2 ≈ (1- e-L1 Nρσ )/ (1- e-L2 Nρσ )
•
<σ>=ln(R1-R2 )/Nρ(L2 – L1 )
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1017 ≤Eν ≤1020 eV
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• MC Trigger studies and array
• Improve e/mu ID (i.e. preshower) and define final version
• Front-end configuration/trigger
• Mechanics
• Test PMT as function of temperature
• Test Solar power system Hip-55172 Sanyo 55Watts
17V/3.3A
• Test on wireless lan devices (ADlink)
• Test prototype on site
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