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Tau Neutrino PhysicsIntroduction
Barry Barish
18 September 2000
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– the third neutrino
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The Number of Neutrinosbig-bang nucleosynthesis
D, 3He, 4He and 7Li primordial abundances
• abundances range over nine orders of magnitude • Y < 0.25 from number of neutrons when nucleosynthesis began (Y is the 4He fraction)
• Yobserved = 0.2380.0020.005
• presence of additional neutrinos would at the time of nucleosynthesis increases the energy density of the Universe and hence the expansion rate, leading to larger Y.
• YBBN= 0.012-0.014 N
1.7 N 4.3
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The Number of Neutrinoscollider experiments
• most precise measurements come from Z e + e
• invisible partial width, inv, determined by subtracting measured visible partial widths (Z decays to quarks and charged leptons) from the Z width • invisible width assumed to be due to N
•Standard Model value ( l)SM = 1.991 0.001 (using ratio reduces model dependence)
SM
l
l
invN
N = 2.984 0.008
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propertiesexistence
• Existence was indirectly established from decay data combined with reaction data (Feldman 81).
• DIRECT EVIDENCE WAS PRESENTED THIS SUMMER FROM FNAL DONUT EXPERIMENT
Observe the and its decays from charged current interactions
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propertiesexistence – DONUT concept
•calculated number of interactions = 1100 ( , e , )
• total protons on target = 3.6 1017
• data taken from April to September 1997
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propertiesexistence – DONUT detectors
Spectrometer
Emulsion-Vertex Detectors
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propertiesexistence – DONUT detectors
• 6.6 106 triggers yield 203 candidate events
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propertiesexistence – DONUT events/background
4 events observed4.1 1.4 expected0.41± 0.15 background
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properties
• expect for Majorana or chiral massless Dirac neutrinos
• extending SU(2)xU(1) for massive neutrinos,B Fm m eG 19 2
10 20 . 3 2 8/ 3
where m is in eV and B eh/2me Bohr magnetons.
• using upper bound meV < 0.6 10-11
• Experimental Bound < 5.4 10-7 from e e (BEBC)
magnetic moment
J = ½• J = 3/2 ruled out by establishing that the is not in a pure H -1 helicity state in
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properties
< 5.2 10-17 e cm from (Z ee) at LEP
charge
< 2 10-14 from Luminosity of Red Giants (Raffelt)
lifetime
electric dipole moment
> 2.8 1015 sec/eV Astrophysics (Bludman) for m < 50 eV
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properties direct mass measurements
• direct bounds come from reconstruction of multi-hadronic decays
LEP (Aleph)
from 2939 events 2 + + < 22.3 MeV/c2 and 52 events 3 + 2 + () + < 21.5 MeV/c2
combined limit < 18.2 MeV/c2
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propertiesdirect mass measurements
• method
two body decayph Ehphp
tau rest frame – hadronic energyh
mmh
2 +m2) / 2m
laboratory frameEh = (Eh
* + ph* cos)
interval bounded for different m
Ehmax,min = (Eh
* ph*)
two sample events 3 + 2 + () +
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propertiesdirect mass measurements
events & contours 0 MeV/c2 and 23 MeV/c2
Log-likelihood fit vs m
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propertiesdirect mass measurements + cosmological bounds
• bounds on m from cosmology
• combined with non observation of lepton number violating decay and direct mass limits
Unstable
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propertieslepton sector mixing
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propertiesoscillation probability
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propertiesoscillation phenomena
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oscillationsallowed regions
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oscillationsatmospheric neutrinos
Path length from ~20km to 12700 km
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atmospheric neutrinosratio of events to e events
ratio-of-ratios (reduces systematics): • R = (e)obs / (e)pred
hint #1 ratio lower than expected
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atmospheric neutrinosangular distributions
Superkamiokande
Hint #2 anisotropy up/down and distortion
of the angular distribution of the up-going events
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atmospheric neutrinosangular distributions with oscillations
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atmospheric neutrinosenergy dependence - oscillations
Hint #3
anomalies have been found in a consistent way for all
energies
Detectors can detect internal of external events produced in the rock below the detector – 100 MeV to 1 TeV
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propertiesmass difference – neutrino oscillations
SuperKamiokande
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atmospheric neutrinoshigh energy events – upward muons
MACRO Detector
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atmospheric neutrinosMACRO event types
Detector mass ~ 5.3 kton
Event Rate:(1) up throughgoing m
(ToF) ~160 /y(2) internal upgoing m
(ToF) ~ 50/y(3) internal downgoing m
(no ToF) ~ 35/y(4) upgoing stopping m
(no ToF) ~ 35/y
MACRO at Gran Sasso
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atmospheric neutrinosMACRO high energy events
MACRO results
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atmospheric neutrinosMACRO evidence for oscillations
Probabilities of oscillations (for maximal mixing)
• the peak probability from the angular distribution agrees with the peak probability from the total number of events
• probability for no-oscillation: ~ 0.4 %
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atmospheric neutrinosagreement between measurements and experiments
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atmospheric neutrinososcillation to sterile or tau neutrino??
SuperKamiokande
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atmospheric neutrinososcillation to sterile or tau neutrino??
test of oscillations the ratio vertical / horizontal
• ratio (Lipari- Lusignoli, Phys Rev D57 1998) can be statistically more powerful than a 2 test: 1) the ratio is sensitive to the sign of the deviation 2) there is gain in statistical significance
• disadvantage: the structure in the angular distribution of data can be lost.
oscillation favoured with large mixing angle:m2 ~ 2.5x10-3 eV2
sterile disfavoured at ~ 2 level
MACRO
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atmospheric neutrinososcillation to sterile or tau neutrino??
• excluded regions using combined analysis of low energy and high energy data
•Sobel 2000 stated ….
SuperKamiokande
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future speculations - supernovae
SN1987a
What can be learned about the from the next supernovae ….??
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future speculations - supernovae
• direct eV scale measurements of m() and m() from Supernovae neutrinos
• early black hole formation in collapse will truncate neutrino production giving a sharp cutoff
• allows sensitivity to m(e) ~1.8 eV for SN at 10 kpc in Superkamiokande detector
(Beacom et al hep-ph/0006015)
Events in SKLow: 0 < E < 11.3 MeVmid: 11.3 < E < 30 MeVHigh: 30 < E <
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future speculations - supernovae
rate in OMNIS, a proposed supernovae detector
tail: 6.1 eV 2.3 events
OMNIS delayed counts vs mass
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the ultra high energy neutrino universe
OWL - Airwatch
GZK cutoff – neutrinos ??
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the ultra high energy neutrino universe
• neutrinos from interactions of ultrahigh energy cosmic rays with 3 K cosmic backgrond radiation
• neutrinos from AGNs, GRBs, etc• Zbursts – relic neutrinos from big bang cosmology
OSCILLATIONS
FLUXES OF AND ARE EQUAL
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the ultra high energy neutrino universe
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future speculations – cosmic ’s
• high energy ’s E > 106 GeV
• neutrinos from proton acceleration in the cores of active galactic nuclei
• vacuum flavor neutrino oscillations enhance / ratio
• detectable in under water / under ice detectors
•(Athar et al hep-ph/0006123)
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future speculations – cosmic ’s
identified by characteristic double shower events
charged currect interaction + tau decay into hadrons and
second shower has typically twice as much energy as first
“double bang”
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future speculations – cosmic ’s
• shower size vs shower separation
• identified events will clearly result from vacuum neutrino oscillations, since without enhancement expect / < 10-5
• events can be identified in under water/ice detectors
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Acceleratorslong baseline – oscillations
K2K
MINOS
CERN GS
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Acceleratorslong baseline – oscillations
appearance
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Acceleratorsneutrino factory – neutrinos from muon collider
muon collider
neutrino beamsselect’s or anti ’s
Example7400 km baseline
Fermilab Gran Sasso“world project”
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Acceleratorsneutrino factory – neutrinos from muon collider
• accurately determine mixing matrix• perhaps even measure CP violation in sector
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Conclusions
• direct observation of the tau neutrino by DONUT is an important milestone
• properties of tau neutrino like other neutrinos e
• neutrino oscillations open up a variety of new future possibilities for in cosmology, astrophysics and future accelerators