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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 PhysicsIntroduction Barry Barish 18 September 2000
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
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
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 • Zbursts – relic neutrinos from big bang cosmology
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