DISCUSSION Is there a right-handed (‘sterile’) neutrino in the eV range? Alain Blondel.  My views and a few others

Where it started

The strongest claim for a eV sterile neutrino so far comes Phys.Rev.D64:112007,2001 DOI: 10.1103/PhysRevD.64.112007 Report number: LAUR-01-2390/UCR-HEP-E306 arXiv:hep-ex/0104049v3 NB there are earlier papers as well as (contradictory) PhD theses

At the basis of the experiment: background to golden channel is low, because there is no known neutrino interaction that produces a fast electromagnetic signal followed by a ‘slow neutron’ capture signal However we do not know all neutrino reactions at these low energies.

Can be fit by oscillation signal

Intrinsic issues with LSND (data taken 1992-1999) claim of  e oscillation The ‘signal’ (and thus the exccess) is not e specific, (e+ + e-   ) any electromagnetic shower in time coincidence with a neutron or even a event producing a +  e+ e decay with unseen + 2. There is no control on the background with e.g. a near detector. 3. the beam is made of    (/ ) followed by +  e+ e or much less −  e− e from a continuous delivery (it is not a pulsed beam where the pion decay (26 ns) and muon decay (2.2 s) would be separated. -- some pions decay at rest (DAR pi+ only ) and some in flight (DIF both pi+ and pi-) -- resulting muons stop and decay at rest e.g. −  e− e -- beam target is made of water + copper dump or «High Z» + copper dump. -- there are uncertainties on the relative rate of DIF and DAR related to the interaction length of pions in water and dump (and various spaces) DIF of negative pions creates backgrounds for e from muon decay.  it is hard to tell if effect observed ise appearance or some photon + neutron background

Physics photon backgrounds Here is what is said of the ‘various’ backgrounds there is no reference for the calculated backgrounds or further discussion or cross-checks The signal is not very large (down to 2. 10-3) and backgrounds are of order few 10-4 . It is notable that there are many sources of backgrounds and they are eliminated by an energy cut. How many neglected negligible backgrounds would be enough to make the signal? -- in particular it is not clear if the NC +n background is calculated for muon neutrinos and 12C only or if it is calculated for all three species and including for 13C and for the DIF which have a larger momentum? 13C has a very low binding energy (1.1% of natural carbon and 4 MeV Eb ) - - which is why they can populate the region above 20 MeV (up to 36 MeV) -- I asked these questions with no success. In absence of a near + far detector set-up it is impossible to conclude.

Genuine e backgrounds Some of the flux issues are discussed in three papers by HARP CDP group including measurements made in HARP in collaboration with LSND members (G. Mills et al) arXiv:1110.4265 , arXiv:1112.0907, arxiv:1112.3852 arXiv:1110.4265 analyses two backgrounds: I. resulting muons stop and decay at rest e.g. −  e− e 2.  event producing a +  e+ e decay with unseen + (there is a cut on the kinetic energy of muons) 3. arxiv:1112.0907 points out that there is (at least) one omitted source of background: 12Ngs nuclei from e + 12C  e- + 12Ngs followed by 12Ngs  12C e+ e claim (with solid arguments) that both backgrounds and their uncertainties seem to be underestimated.

-- note that the Karmen experiment with a pulsed beam at RAL never saw anything.

Next came another experiment with no near detector  BOONE proposal was supposed to check the LSND ‘anomaly’. It had 2 detectors. lack of money or interest  downgraded to miniBOONE with only one detector. If an experiment is worth doing it it worth doing well.

Alain Blondel NUFACT12 23-07- 2012

looks interesting….

final results. skip to slide 23

how about gammas?

note that most of excess is in region of gammas (0 misid, )  is assumed to originate from  resonance) NB replica target data were taken in HARP but not used or if used not clear how?

seems to confirm LSND

fundamental assumption needed: single gamma originates from  resonance and can be related to 0 production. What if both LSND and miniBOONE simply discovered a new source of gammas? in absence of a near-far detector ratio is is impossible to separate sterile neutrino and this ‘mundane’ explanation.

all based on  assumption

note that the significance is very sensitive to the low energy cut.

source detector active,  sterile active,  Sterile neutrino search: a global view: Detected by mixing between sterile and active neutrino ideal experiments: source detector active,  known process known process 1. disappearance, not necessarily oscillatory best is NC disappearance first order sterile 0. if sterile cannot be produced (too heavy) apparent deficit in decay rate active,  2.   appearance (at second order) Alain Blondel NUFACT12 23-07- 2012

if you want to see appearance you must see both disapearances!

NOTES 1. the disappearance experiments for e include the nuclear reactor deficit, which is however rather small O(3%) 2. the disappearance experiments for  include MINOS, MINOS+ (more recently NOvA) with near/far setup and ICECUBE (azimuthal angle = baseline variation). 3. in the case of MINOS + the disappearance test includes neutral currents

MINOS + DAYA Bay (+ Bugey) no disppearance at >= 5% level Is the interpretation of the 3.8  LSND effect as ‘sterile neutrino’ the correct one? arXiv:1607.01177 arXiv:1605.01990 both in 3+1 hypothesis MINOS + DAYA Bay (+ Bugey) no disppearance at >= 5% level IceCube in atmospheric neutrinos no sterile neutrino effect

With new result from MINOS + (run with high energy beam for NOvA) The light sterile neutrino seems very much dead.

An explanation of the LSND anomaly in terms of 3 active + 1 sterile neutrino is ruled out at 4.7 sigma – this is robust on more complicated models of sterile neutrino oscillation

See also the recent HEP-EPS presentation of C. Giunti https://indico.cern.ch/event/577856/ Status of Light Sterile Neutrinos

?

My personnal conclusion there are definitely interesting issues with such experiments as LSND, miniBOONE, and reactors which are not fully internally contrainted by a measurement as function as distance. it is very easy to explain each of the observed anomalies with a sterile neutrino oscillation calculation. However this does not provide evidence for sterile neutrino. The sterile neutrino (SN) hypothesis of a second order appearance is a very prescriptive model and leads to measurable and large consequences for first order disappearance this first order (>5%) disappearance is seen neither in electron nor muon neutrino oscillations experiments as a consequence the SN hypothesis is almost certainly not correct. other explanations should be investigated the SBN program at Fermilab in particular is part of this set of investigations.