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Venice 080416

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Neutral fermions follow economic Majorana eq or the same Dirac eq as charged fermions ? ... Discussed a new possibility of using coherent atomic targets ... – PowerPoint PPT presentation

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Title: Venice 080416


1
Neutrino spectroscopy using atoms (SPAN)
  • Introduction
  • How to verify important ingredients of
    leptogenesis experimentally
  • Why atoms
  • Enhancement mechanism target coherence and
    resonance

hep-ph/0611362 and PRD, hep-ph/0703019, and to
appear
2
Leptogenesis requires
  • Majorana nature of neutrino masses, implying
    lepton number violation
  • Absolute magnitude of neutrino masses
  • lt 0.1 eV cf Giudice et al
  • CP violation in neutrino sector
  • We wish to resolve 1st 2 issues
    using atoms.

3
What 3 major methods of neutrino experiments have
achieved
  • Oscillation experiments
  • with large mixing
  • End point spectrum of beta decay
  • lt 2 eV
  • Neutrinoless double beta decay
  • lt 0.5 eV

4
Significance of discovering Majorana neutrino
  • Neutral fermions follow economic Majorana eq or
    the same Dirac eq as charged fermions ?
  • Leading to lepton number violation and
    lepto-genesis
  • particle anti-particle
  • missing partner for leptogenesis
  • Contributing to better understanding of seesaw
    mechanism and GUT

5
Attractive mechanism of small neutrino mass
generation
  • Seesaw mechanism
  • Heavy Majorana type of masses of neutrino
    partner , indicating physics beyond
    standard theory of particle physics, generates a
    tiny left-handed neutrino masses and mixing a la
  • Necessarily violates lepton number conservation
  • Agent of L-asymmetry generation provided by

6
M vs D in 2-component equations
7
Majorana vs Dirac equationschirally projected
solutions
8
Merits and demerits of atomic process
  • Infinitely many small energies are available
  • Systematics for mass spectroscopy 6 thresholds
    and M/D distinction
  • Small rate of neutrino pair emission
  • How to enhance the rate is crucial
  • resonance
  • target coherence

9
Neutrino interaction with atomic electron
4 Fermi interaction (after Fierz transformation)
MNS matrix elements
10
Unique signature of Majorana interference of
identical fermions
  • Effective only for pair emission
  • Appear only (ii) threshold proportional to m_i2
  • Can be positive or negative
  • Direct test of Majorana nature cf LV in

11
New enhancemet mechanism
  • Coherent target effect like superradiance
  • Neutrino pair emission more favorable in view of
    larger coherence region, determined by pair
    momenta, and not energy difference of levels
  • If anticipated large N3 (target number)
    dependence is realized, gas targets are feasible
  • Otherwise,
  • use of denser target in solid matrix or
    something similar (nano-space)

12
Superradiance case of photon emission for 2
level atom
13
Radiative neutrino pair emission
  • Emitted photon carries neutrino mass information
  • Background 2 gamma

14
Target examples
  • Ba case 2 types of transitions coexist
  • lambda ladder

15
Radiative neutrino pair emission from collective
excited atoms
  • Standard target shape pencil-like cylinder
    (length l) due to laser irradiation for
    preparation of excited states

16
Radiative pair emission has critical information
of neutrino mass threshold
  • Threshold distance from the background 2 photon
    peak

1 gamma spectrum of 2 gamma background is
discrete and sharply collimated with target
cylinder axis
17
Features of events
  • 2 photon background
  • back to back, energy of half level difference,
    well collimated to cylinder axis perhaps not
    difficult to separate
  • Radiative pair emission
  • broader structure of photon energy
    distribution
  • Ladder-type system has further resonace
    enchancement

18
Rough estimate of rates
  • Nu-pair
  • 2 gamma

19
Threshold behavior sensitive probe of mixing
20
Observability of relic neutrino w. T. Takahashi

hep-ph/0703019
  • Pauli blocking effect

21
Threshold reduction 1/2x1/2 1/4 Temperature
measurement possible ?Case of laser irradiated
pair emission
  • For m_1 lt 1meV, temperature measurement is not
    difficult

22
Experimental strategy
  • Verification of superradiance enhancement in 2
    gamma EM transition
  • Discovery of neutrino pair emission far away from
    threshold region, with large rates
  • Approach to threshold region for neutrino
    spectroscopy
  • Detection of relic neutrino at lightest threshold
  • SPAN collaboration

23
Summary
  • Discussed a new possibility of using coherent
    atomic targets
  • Excellent for neutrino mass spectroscopy, if the
    rate is large enough
  • If works ideally, a long path towards relic
    detection
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