Supernova neutrino induced neutrons in liquid xenon dark matter detectors Pijushpani Bhattacharjee, 1, ∗ Abhijit Bandyopadhyay, 2, † Sovan Chakraborty, 3, ‡ Sayan Ghosh, 1, § Kamales Kar, 2, ¶ and Satyajit Saha 1, ∗∗ 1 Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India 2 Ramakrishna Mission Vivekananda Educational and Research Institute, Belur Math, Howrah 711202, India 3 Department of Physics, Indian Institute of Technology - Guwahati, Guwahati 781039, India Neutrinos from supernova (SN) bursts can give rise to detectable number of nuclear recoil (NR) events through the process of coherent elastic neutrino-nucleus scattering (CEν NS) in future large (multi-ton scale) liquid xenon detectors employed for dark matter search depending on the SN progenitor mass and distance to the SN event. Here we point out that in addition to the direct NR events due to CEν NS process, there is a secondary source of nuclear recoils due to elastic scattering of the neutrons produced through inelastic neutrino-nucleus scattering of the supernova neutrinos with the target xenon nuclei. We estimate the contribution of these supernova neutrino- induced neutrons (ν In) to the total xenon NR spectrum and find that the latter can be significantly modified at large recoil energies from that expected from the CEν NS process alone, with the ν In contribution dominating the total integral recoil energy spectrum for recoil energies > ∼ 20 keV. With the capability to measure the energies of individual recoil events, sufficiently large liquid xenon detectors may be able to detect these events due to ν In process triggered by neutrinos from reasonably close by SN burst events. We also note that the ν In contribution to the recoil spectrum receives dominant contribution from the charged current interaction of the SN νes with the target nuclei while the CEν NS contribution comes from neutral current interactions of all the six species of neutrinos with the target nuclei. This may offer the possibility of extracting useful information about the distribution of the total SN explosion energy going into different neutrino flavors. I. INTRODUCTION Core collapse supernova (CCSN) explosions [1] give out huge flux of neutrinos (and antineutrinos) of all flavors with energies up to a few tens of MeV over a time scale of ∼ 10 seconds [2]. These neutrinos carry almost all (∼ 99%) of the gravitational energy (∼ 10 53 erg) released due to collapse of the core of the massive progenitor star. A large number of experimental facilities around the world, employing a variety of neutrino detection tech- niques [3, 4], are waiting to detect the neutrinos from the next nearby (hopefully Galactic) CCSN, after the historic first detection of neutrinos from the supernova SN1987A located in the Large Magellanic Cloud (LMC) at a dis- tance of ∼ 50 kpc from Earth [5]. Detection of supernova neutrinos of different flavors from a single supernova by multiple detectors has the potential to yield extremely valuable information about not only the supernova pro- cess itself but also various aspects of fundamental physics of neutrinos themselves. Neutrinos are detected through their weak charged cur- rent (CC) and neutral current (NC) interactions with electrons and nuclei. A variety of interaction channels are possible; see, e.g., Ref. [3] for a review. In this pa- per we consider the possibility of SN neutrino detection ∗ Electronic address: pijush.bhattacharjee@saha.ac.in † Electronic address: abhijit@rkmvu.ac.in ‡ Electronic address: sovan@iitg.ac.in § Electronic address: sayan.ghosh@saha.ac.in ¶ Electronic address: kamales.kar@gm.rkmvu.ac.in ∗∗ Electronic address: satyajit.saha@saha.ac.in using elastic as well as inelastic neutrino-nucleus inter- action (see, e.g., Ref. [6] for reviews). In particular, we focus on the processes of coherent elastic neutrino nucleus scattering (CEν NS) [7, 8] and inelastic neutrino-nucleus scattering, the latter involving emission of neutrons in the final state. The CEν NS is a process that has recently received much attention [9–12] in the context of large (multi-ton scale) detectors [13] searching for the weakly interact- ing massive particle (WIMP) candidates of dark matter (DM) [14] through WIMP-induced nuclear recoils. In this process, neutrinos of sufficiently low (few to few tens of MeV) energy undergo coherent elastic scattering on the target nucleus with a cross section that is enhanced by the square of the number of neutrons in the target nucleus. The recoiling target nucleus of mass M gets a maximum kinetic energy of 2E ν 2 /M , where E ν is the neutrino energy. There is a trade-off between the cross section enhancement (requiring large mass nuclei) and the maximum recoil energy (∝ 1/M ), with the latter typically in the region of few keV for neutrino energy of ∼ 10 MeV and target nuclei with mass number in the region of ∼ 100 desired for reasonably large cross section (typically, O(10 −39 cm 2 )). Such low recoil energies, while very difficult to detect in conventional neutrino detectors, are, however, within reach of the large WIMP DM detec- tors. Thus, sufficiently large WIMP DM detectors with suitably chosen detector materials can also be sensitive to neutrinos from individual SN events. Importantly, the CEν NS, it being a NC process, is equally sensitive to all flavors of neutrinos (and antineutrinos), which offers a probe for estimating the total explosion energy going into neutrinos [9, 15], and also possibly for demarcating arXiv:2012.13986v2 [hep-ph] 17 Jan 2021