Tau neutrino physics introduction
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Tau Neutrino Physics Introduction. Barry Barish 18 September 2000. n t – the third neutrino. The Number of Neutrinos big-bang nucleosynthesis. D, 3 He, 4 He and 7 Li primordial abundances. abundances range over nine orders of magnitude

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Tau Neutrino Physics Introduction

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Tau Neutrino PhysicsIntroduction

Barry Barish

18 September 2000


nt – the third neutrino


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 = 0.2380.0020.005

  • 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


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)

N = 2.984 0.008


 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 thet and its decays from nt charged current interactions


 propertiesexistence – DONUT concept

  • calculated number of interactions = 1100 ( nm, ne, nt)

  • total protons on target = 3.6 1017

  • data taken from April to September 1997


 propertiesexistence – DONUT detectors

Spectrometer

Emulsion-Vertex Detectors


 propertiesexistence – DONUT detectors

  • 6.6 106 triggers yield 203 candidate events


 propertiesexistence – DONUT events/background

4 events observed

4.1  1.4 expected

0.41± 0.15 background


 properties

J = ½

  • J = 3/2 ruled out by establishing that the is not in a pure H  -1 helicity state in 

magnetic moment

  • expect    for Majorana or chiral massless Dirac neutrinos

  • extending SU(2)xU(1) for massive neutrinos,

  • where m is in eV and B  eh/2me Bohr magnetons.

  • using upper bound mt < 18 MeV   < 0.6 10-11mB

  • Experimental Bound < 5.4 10-7mB from e  e (BEBC)


 properties

electric dipole moment

< 5.2 10-17 e cm from (Z  ee) at LEP

nt charge

< 2 10-14 from Luminosity of Red Giants (Raffelt)

lifetime

> 2.8 1015 sec/eV Astrophysics (Bludman) for mn < 50 eV


ntpropertiesdirect 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


nt propertiesdirect mass measurements

  • method

    • two body decay

    • t(Et,pt)  h (Eh,ph) + nt (En,pn)

    • tau rest frame – hadronic energy

    • Eh* = (mt2  mh2 +mn2) / 2mt

    • laboratory frame

    • Eh =  (Eh* +  ph* cos)

    • interval bounded for different mn

    • Ehmax,min = g (Eh*  b ph*)

two sample events

  3 + 2 + () + 


nt propertiesdirect mass measurements

events & contours

0 MeV/c2 and 23 MeV/c2

Log-likelihood fit vs mn


nt propertiesdirect mass measurements + cosmological bounds

Unstable nt

  • bounds on mnt from cosmology

  • combined with non observation of lepton number violating decay and direct mass limits


nt propertieslepton sector mixing


nt propertiesoscillation probability


nt propertiesoscillation phenomena


n oscillationsallowed regions


n oscillationsatmospheric neutrinos

Path length from ~20km to 12700 km


atmospheric neutrinosratio of nm events to ne events

  • ratio-of-ratios (reduces systematics):

  • R = (nm/ne)obs / (nm/ne)pred

hint #1

ratio lower than expected


atmospheric neutrinosangular distributions

Hint #2

anisotropy up/down and distortion of the angular distribution of the up-going events

Superkamiokande


atmospheric neutrinosangular distributions with n oscillations


atmospheric neutrinosenergy dependence - n 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


nt propertiesmass difference – neutrino oscillations

SuperKamiokande


atmospheric neutrinoshigh energy events – upward muons

MACRO Detector


atmospheric neutrinosMACRO event types

MACRO at Gran Sasso

  • Detector mass ~ 5.3 kton

  • Event Rate:

  • 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


atmospheric neutrinosMACRO high energy events

MACRO results


atmospheric neutrinosMACRO evidence for oscillations

Probabilities of nm nt 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 %


atmospheric neutrinosagreement between measurements and experiments


atmospheric neutrinososcillation to sterile or tau neutrino??

SuperKamiokande


atmospheric neutrinososcillation to sterile or tau neutrino??

MACRO

  • ratio (Lipari- Lusignoli, Phys Rev D57 1998) can be statistically more powerful than a c2 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.

  • nm nt oscillation favoured with large mixing angle:m2 ~ 2.5x10-3 eV2

  • sterile n disfavoured at ~ 2 slevel

test of oscillations

the ratio vertical / horizontal


atmospheric neutrinososcillation to sterile or tau neutrino??

SuperKamiokande

  • excluded regions using combined analysis of low energy and high energy data

  • Sobel n2000 stated ….


ntfuture speculations - supernovae

SN1987a

What can be learned about the nt from the next supernovae ….??


ntfuture speculations - supernovae

  • direct eV scale measurements of m(nm) and m(nt) from Supernovae neutrinos

  • early black hole formation in collapse will truncate neutrino production giving a sharp cutoff

  • allows sensitivity to m(ne) ~1.8 eV for SN at 10 kpc in Superkamiokande detector

  • (Beacom et al hep-ph/0006015)

Events in SK

Low: 0 < E < 11.3 MeV

mid: 11.3 < E < 30 MeV

High: 30 < E < 


ntfuture speculations - supernovae

  • rate in OMNIS, a proposed supernovae detector

  • tail: 6.1 eV  2.3 events

OMNIS

delayed counts vs mass nt


ntthe ultra high energy neutrino universe

OWL - Airwatch

GZK cutoff – neutrinos ??


ntthe ultra high energy neutrino universe

OSCILLATIONS

FLUXES OF nt AND nm

ARE EQUAL

  • neutrinos from interactions of ultrahigh energy cosmic rays with 3 K cosmic backgrond radiation

  • neutrinos from AGNs, GRBs, etc

  • Zbursts – relic neutrinos from big bang cosmology


ntthe ultra high energy neutrino universe


ntfuture speculations – cosmicnt’s

  • high energy n’s E > 106 GeV

  • neutrinos from proton acceleration in the cores of active galactic nuclei

  • vacuum flavor neutrino oscillationsenhance nt / nm ratio

  • detectable in under water / under ice detectors

  • (Athar et al hep-ph/0006123)


ntfuture speculations – cosmicnt’s

  • ntidentified by characteristic double shower events

  • charged currect interaction + tau decay into hadrons and nt

  • second shower has typically twice as much energy as first

  • “double bang”


ntfuture speculations – cosmicnt’s

  • shower size vs shower separation

  • identified events will clearly result from vacuum neutrino oscillations, since without enhancement expect nt / nm < 10-5

  • nt events can be identified in under water/ice detectors


Acceleratorslong baselinenm– nt oscillations

MINOS

K2K

CERN  GS


Acceleratorslong baselinenm– nt oscillations

nt appearance


Acceleratorsneutrino factory – neutrinos from muon collider

muon collider

Example

7400 km baseline

Fermilab  Gran Sasso

“world project”

neutrino beams

select nm’s or anti nm’s


Acceleratorsneutrino factory – neutrinos from muon collider

  • accurately determine n mixing matrix

  • perhaps even measure CP violation in n sector


Conclusions

  • direct observation of the tau neutrino by DONUT is an important milestone

  • properties of tau neutrino like other neutrinos ne, nm, nt

  • neutrino oscillations open up a variety of new future possibilities for nt in cosmology, astrophysics and future accelerators


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