DUNE sensitivities to the mixing between sterile and tau neutrinos
Received: July
DUNE sensitivities to the mixing between sterile and
Pilar Coloma 0 1 2 4
David V. Forero 0 1 2 3
Stephen J. Parke 0 1 2 4
0 Blacksburg , VA 24061 , U.S.A
1 13083-859 , Campinas, SP , Brazil
2 P. O. Box 500, Batavia, IL 60510 , U.S.A
3 Center for Neutrino Physics , Virginia Tech , USA
4 Theoretical Physics Department, Fermi National Accelerator Laboratory
Light sterile neutrinos can be probed in a number of ways, including electroweak decays, cosmology and neutrino oscillation experiments. At long-baseline experiments, the neutral-current data is directly sensitive to the presence of light sterile neutrinos: once the active neutrinos have oscillated into a sterile state, a depletion in the neutral-current data sample is expected since they do not interact with the Z boson. This channel o ers a direct avenue to probe the mixing between a sterile neutrino and the tau neutrino, which is currently only weakly constrained by current data from SuperK, IceCube and NOvA, however, these constrains will continue to improve as more data is collected by these experiments. In this work, we study the potential of the DUNE experiment to constrain the mixing angle which parametrizes this mixing, 34, through the observation of neutral-current events at the far detector. We nd that DUNE will be able to improve signi cantly over current constraints thanks to its large statistics and excellent discrimination between neutral- and charged-current events.
Beyond Standard Model; Neutrino Physics; CP violation
Oscillation probabilities in the 3 + 1 framework
Rejection power for the three-family hypothesis, for 24; 34 6= 0
Expected allowed regions in the 24
Summary and conclusions
A Complete expressions for the relevant mixing matrix elements in our
1 Introduction 2 3 4
Simulation
Results
4.1
4.2
4.3
parametrization
B
2-function
1
Introduction
In the past decade, a tremendous experimental e ort has been carried out in order to
constrain scenarios with additional neutrinos with masses below the electroweak scale.
LEP data places severe constraints on the invisible decay of the Z. Hence, if there are
additional neutrinos below the electroweak scale, they cannot couple to the Standard Model
weak bosons (i.e., they should be sterile). Light sterile neutrinos can lead to observable
phenomena in a number of electroweak processes through their impact on the unitarity
of the leptonic mixing matrix, including meson decays, muon decay, neutrinoless double
beta decay and charged lepton
avor violating transitions (see e.g., refs. [1, 2] for recent
global ts using these observables). Nevertheless, if their masses are light enough so that
they are kinematically accessible in these processes, unitarity is e ectively restored at low
energies and the bounds from electroweak processes fade away. In this case the best limits
are derived from oscillation data [3{8], see e.g., refs. [
9, 10
] for a detailed discussion of these
constraints.
In recent years, the eV-scale has recently been put on the spot due to a set of
experimental anomalies independently reported in LSND [11], MiniBooNE [12, 13], reactor [14, 15]
and Gallium experiments [16]. The current and next generation of oscillation experiments
will attempt to refute or con rm these hints. The Icecube experiment has recently put
impressive limits on the mixing between sterile neutrinos and muon neutrinos U 4 [17, 18],
{ 1 {
to constrain the cross-product jUe4j2jU 4j2 [23]. Conversely, placing equally competitive
limits on the mixing with tau neutrinos is a much more di cult task, due to the technical
challenges associated to the production and detection of a
beam.
Indirect constraints on the mixing with
can be derived from the observation of
matter e ects in atmospheric neutrino oscillations. For example, the IceCube experiment
90% CL) for an active-sterile mass splitting above 0:1 eV2 [4].1 A non-zero
have set the limit jU 4j2 < 0:15 (at 90% CL) for an active-sterile mass splitting equal to
1 eV2 [18] while the Super-Kamiokande experiment have set the bound jU 4j2 < 0:18 (at
24 and 34
active-sterile mixing produces striking signatures in the zenith and energy distribution of
cascade events in IceCube DeepCore, and after some years of data taking it is possible
to probe the 34 parameter space [25]. On the other hand, a more direct test for the
mixing between sterile neutrinos and tau neutrinos can be performed using long-baseline
experiments. At long-baseline experiments most of the initial
ux has oscillated into
tau neutrinos by the time it reaches the far detector, thanks to
by the atmospheric mass-squared splitting. The OPERA experiment has constrained the
impact of sterile neutrinos on this oscillation channel, using charged-current
events at the
far detector, setting the bound 4jU 4j2jU 4j2 < 0:116 (at 90% CL) for an active-sterile
masssquared splitting above 0:1 eV2 [26]. However, their results are severely limited by statistics,
since the
charged-curren (...truncated)