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Dark matter beams at LBNF
Accepted: March
matter beams at LBNF
Pilar Coloma 0 1 2
Bogdan A. Dobrescu 0 1 2
Claudia Frugiuele 0 1 2
Roni Harnik 0 1 2
0 P. O. Box 500, Batavia, IL 60510 , U.S.A
1 Theory Department, Fermi National Accelerator Laboratory
2 term in eq. (2.1) is replaced by i @
High-intensity neutrino beam facilities may produce a beam of light dark matter when protons strike the target. Searches for such a dark matter beam using its scattering in a nearby detector must overcome the large neutrino background. We characterize the spatial and energy distributions of the dark matter and neutrino beams, focusing on their di erences to enhance the sensitivity to dark matter. We produced by a Z0 boson in the GeV mass range is both broader and more energetic than the neutrino beam. The reach for dark matter is maximized for a detector sensitive to hard neutral-current scatterings, placed at a sizable angle o case of the Long-Baseline Neutrino Facility (LBNF), a detector placed at roughly 6 degrees o axis and at a distance of about 200 m from the target would be sensitive to Z0 couplings as low as 0.05. This search can proceed symbiotically with neutrino measurements. We also show that the MiniBooNE and MicroBooNE detectors, which are on Fermilab's Booster beamline, happen to be at an optimal angle from the NuMI beam and could perform searches with existing data. This illustrates potential synergies between LBNF and the short-baseline neutrino program if the detectors are positioned appropriately.
Beyond Standard Model; Neutrino Physics
-
Dark
1 Introduction
2
3
4
5
Production mechanisms for dark matter and neutrinos
Detection via neutral-current events
Optimal detector location and expected sensitivity
Conclusions
A Computation of the neutrino
ux from kaon decays
rience interactions with ordinary matter beyond gravity. Direct detection experiments [1]
have imposed impressive constraints on the interactions between nucleons and DM
particles of mass larger than about 5 GeV. These experiments lose sensitivity quickly at lower
masses because light dark matter particles moving at the viral velocities of our galactic
halo would yield very low recoil energies in collision with nuclei or atoms. Interactions of
DM with quarks or gluons are also explored at high-energy colliders, for example through
monojet searches [2{9]. If these interactions are due to a light mediator, however, the
collider searches are less sensitive.
Therefore, the question of how to conduct light dark matter searches is urgent and
compelling. A potentially promising direction is to use proton
xed-target experiments to
probe DM couplings to quarks [10{15] (other proposals for light DM searches have been
explored in [16{27]). An interesting type of mediator is a leptophobic Z0 boson. For a
Z0 mass in the
1{10 GeV range, the limits on its coupling to quarks are remarkably
loose [28]. A dark matter beam originating from the decay of a leptophobic Z0, produced
by protons accelerated in the Booster at Fermilab, may lead to a signal in the MiniBooNE
experiment [14]. This signal decreases fast for MZ0 above 1 GeV, because the Booster
proton energy is only 8 GeV. By contrast, protons accelerated at 120 GeV in the Main
Injector scattering o
nucleons may produce a leptophobic Z0 as heavy as
7 GeV, and
the DM particles originating in the Z0 decay may lead to neutral-current events in neutrino
detectors [15].
{ 1 {
Here we analyze the sensitivity of neutrino detectors to the DM beam produced in
leptophobic Z0 decays. We focus on a high-intensity proton beam of
100 GeV, as that
proposed at the Long-Baseline Neutrino Facility [29] (LBNF). We consider deep-inelastic
neutral-current scattering as the main signal. The challenge of using neutrino facilities to
look for a DM beam is that neutrino events represent an irreducible background. In [14] it
is proposed to conduct a special run of the beam in which the magnetic horns are turned
o , leading to a more dilute neutrino beam. Here we will take a di erent approach, namely
to exploit the di erence between the dark matter and a focused neutrino beam and consider
a detector that is located accordingly. This search for dark matter does not disrupt the
normal neutrino research program.
More speci cally, we will see that the signal and main background contributions have
very di erent energy and angular pro les, which can be exploited to enhance the signal
signi cance. We perform a simple optimization study using the signal signi cance in order
to determine the optimal position of a detector. We determine that an angle of
approximately 6 degrees with respect to the decay pipe direction would maximize the sensitivity.
Applying these results to the NuMI beamline, we
nd that the NOvA near detector, in
spite of being located slightly o -axis, does not provide a su cient suppression of the
neutrino background.
The paper is structured as follows. Section 2 reviews the main features of the model
considered. In section 3 we (...truncated)