Do there exist sterile neutrino?

Since Pauli have postulated in 1933 the existence of neutrino it remains one of the most interesting particles in nuclear physics

J.Allen, 1957

W. Pauli proposed the existence of a neutral particle of low mass as “a desperate way out”. (1930 ) E. Fermi renamed Pauli's particle as the "neutrino" and had incorporated the particle into a theory of β-decay. (1934) Pauli: “I have invented something that cannot be detected” (It is obviously that he has underestimated ingenuities of the experimenters.) F. Reines and C. Cowen detect ν from Savannah River reactor p(ν ,e+)n (1956)

W. Pauli proposed the existence of a neutral particle of low mass as “a desperate way out”. (1930 ) E. Fermi renamed Pauli's particle as the "neutrino" and had incorporated the particle into a theory of β-decay. (1934) Pauli: “I have invented something that cannot be detected” (It is obviously that he has underestimated ingenuities of the experimenters.) F. Reines and C. Cowen detect ν from Savannah River reactor p(ν ,e+)n. (1956)

Pontecorvo pioneers the thinking about oscillations, inspired by the neutral Kaon system: neutrino antineutrino (1957).

Idea was not generally accepted.

Required large mixing of neutrinos and this went against accepted wisdom.

Mikheyev and Smirnov develop theory or resonant oscillations. (1987)

Solar neutrino experiments proved neutrino oscillations. (2001)

From history

(1967) Pontecorvo coins the wording “sterile neutrino”

(1990 - ) Research of the neutrino oscillation is started. For the interpretation of sets of obtained results were demanded sterile neutrinos.

The theory intensively tries to build now a new physics beyond the standard model for accommodation sterile neutrinos.

Now

• If accept sterile neutrino hints, then should be checked and

quantified neutrino oscillations in all channels:

– νe and νe appearance

– νμ and νμ disappearance

– νe and νe disappearance

New experiments are very needed

But in experiments the inconsistent results are received

Hints for High Δm2~1 eV2 Oscillation ⇒ Sterile Neutrinos? or Something Else?

• Positive indications:

– LSND/MiniBooNE νμ→ νe appearance signal

– MiniBooNE low-energy excess (νμ→ νe ?)

– Reactor disappearance anomaly (νe→ νe )

– Gallex-Sage reduced calibration source rate (νe disappearance?)• Negative indications:

– CDHS and MiniBooNE restrictions on νμ disappearance

– MiniBooNE restrictions on νμ disappearance

– Karmen restrictions on νμ→ νe – Other negative results

The cross sections for neutrino capture to the two lowest excited states in 71Ge have been overestimated (W. Haxton) Maximum contribution of these excited states – 5%. If the contribution of these states to the predicted rate were to be zero then R = 0.92 ± 0.06 and the fit to the expected value of 1.0 becomes quite reasonable (χ2 /dof = 4.58/3, GOF =21%).

The measurements of (3He, t) reaction on Ga cross section were carried out in RCNP (Research Center for Nuclear Physics), Japan (H. Ejiri) last year.

“ At RCNP we recently re-measured the GT transition strengths to various states in 71Ge with the main objective to extract the GT strength values to the g.s., the 175 keV and the 500 keV states with highest resolution and highest possible accuracy using the (3He,t) reaction at 420 MeV and the Grand Raiden spectrometer. …. one arrives at a value of 6.9 ± 1.8% for the contribution from the excited states in 71Ge to the neutrino capture cross section. This is a slightly larger value than the one, which was roughly estimated by Bahcall and therefore slightly amplifies the discrepancy observed in the calibration measurements.”

“… it may be worthwhile to review past measurements of the 71Ge EC Q-value and lifetime, which together define the final ft-value.”

[TRIUMF Research Proposal]

We propose to measure the electron capture Q-value of We propose to measure the electron capture Q-value of 7171Ge Ge

leading to the ground state of leading to the ground state of 7171Ga using the TITANGa using the TITAN ((TRIUMF's Ion TRIUMF's Ion

Trap forTrap for Atomic and Nuclear science Atomic and Nuclear science)) ion trap ion trap mass measurement mass measurement facility.facility. The exact mass difference is The exact mass difference is an important quantity, which an important quantity, which enters into the neutrino cross section on enters into the neutrino cross section on 7171Ga, and which needs to be Ga, and which needs to be known with high precision. known with high precision. 7171Ga was the material, which was used in Ga was the material, which was used in the solar neutrino experiments SAGE and GALLEX and subsequently the solar neutrino experiments SAGE and GALLEX and subsequently for the detector calibration with neutrinos from a for the detector calibration with neutrinos from a 5151Cr calibration Cr calibration source. source. A renewed mass measurement using the ion trap technique A renewed mass measurement using the ion trap technique will help to clarify the origin of a rather long-standing and still will help to clarify the origin of a rather long-standing and still unresolved discrepancy of the calibration measurements performedunresolved discrepancy of the calibration measurements performedby both neutrino by both neutrino experiments, SAGE and GALLEX. experiments, SAGE and GALLEX.

TRIUMF Research Proposal TRIUMF Research Proposal

Q-value measurement for the Q-value measurement for the 7171Ge electron capture Ge electron capture Spokespersons : D. Frekers, J. Dilling, H. Ejiri Spokespersons : D. Frekers, J. Dilling, H. Ejiri

The TITAN Beamline

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