Takasumi Maruyama (KEK) for J-PARC P56 working group

1. Neutrino-­nucleus (nucleon) Reaction Measurement by J-PARC MLF sterile neutrino search experiment (J-PARC P56) Takasumi Maruyama (KEK) for J-PARC P56 working group

2. Contents • Introduction of new J-PARC P56 experiment • Setup • Neutrino flux and Neutrino Interaction • Possible feed-backs to low energy neutrino interaction • Comparison to other experiments, LSND, KARMEN M. Harada et al, arXiv:1310.1437 [physics.ins-det] (A brand-new experiment proposed on 2-Sep-2013)

3. 3 GeV RCS Neutrino Beams(to Kamioka) Materials and Life Experimental Facility 30GeV MR CY2007 Beams Hadron hall JFY2008 Beams JFY2009 Beams J-PARC Facility (KEK/JAEA） 181MeV Linac South to North 400MeV (done) ５４０nsec 25Hz 300kW now & will be 1MW (beam is back from a few weeks ago; first beam after the accident.) Bird’s eye photo in January of 2008

4. Neutrino production and detector site (3F) Detector location is Still under discussion Neutron Hg target (& neutrino source) Detector@3rd floor (50 ton fiducial, 17m baseline) 3GeV proton

5. Using neutrinos from only m+ decay at rest Selecting muon decay (e~74%) • Neutrinos from only m+ decays are used. (m+ has long lifetime). (top) • Energy spectrum of m+ e+nmne decay is well known (bottom) • Useful to examine the excess of ne . • nm  ne oscillation is searched. • p-  m- decay chain is highly suppressed (10-3 compared to m+ ) • Proton energy of J-PARC is 3GeV, thus p+/p ratio is higher than LSND / KARMEN (0.8GeV) by 5-10 times

6. E.g.; energy spectra (SN vs DAR) arXiv:hep-ph/0307222 • J-PARC P56 provides similar neutrino energy range to those of Super-Nova

7. MLF mercury target and Intrinsic neBKG estimation Be H Mercury target 3GeV proton H For beam pipe Fe Be Target p- absorb m-capture suppression x p-/p+ LSND H2O 96% 88% 5x10-3 x 0.13 J-PARC Hg(+Fe+Be) 99% ~80% 1.7x10-3 x 1. ~ 1.7x10-3 Intrinsic background.

8. Detector considerations • Type, size, fiducial mass, constraints; • Double-Chooz type • Diameter 6m, height 4.4m; fiducial is 25 ton • Two identical detectors. (from MLF constraints) • Movable detectors. • 150 10” PMTs • good photo-coverage  <15%/sqrt(E). • 50cm noGd-LS buffer region  veto and self-shield

9. Detector; Liquid scintillator • Coincidence between positron and neutron signal (ne + p  e+ + n; Inverse Beta Decay; IBD). • Neutrons are captured by Gd, and emit gammas ( totalE = 8MeV, lifetime; a few 10 ms.) • Cross section of IBD is well known. (~2% uncertainty) (s = 9.3 x En2 x 10-44 cm2) • Energy spectrum of anti-neutrino is also well known.  event energy shape is also well known for signal and BKG • Positrons  “prompt” signal (En = Evis+0.8MeV) • Neutrons  “delayed” signal Prompt signal gamma gamma positrons Anti neutrinos electrons Delayed signal proton gamma neutron Gd

10. c 1998 600ms 120Hz target+beam stop configuration DIF, n bkg. p m + nm m e + ne + nm ne Linacbeam • Almost DC beam Cherenkov photon can be detected. -> angle meas. p-, m- absorbed before decay into n’s there should not be ne at the level of 7x10-4 Signal : ne p→e+n np→d g(2.2MeV)

11. KARMEN • KARMEN uses segmented Liquid scintillator • detector. (~50ton) (left plot) • Location is similar to P56, 17m from the ISIS • neutron target. (right plot) thick iron shield surrounds the detector. • ISIS gives pulsed proton beam, like J-PARC. But intensity of ISIS is weaker than J-PARC

12. Other neutrino interactions • This experiment aims to search for sterile neutrinos via neutrino oscillations. • Via IBD; ne + p  e+ + n • However, this experiment can also provide good opportunity to measure neutrino interactions precisely in the low energy region. • ne + C  e- + Ng.s. (Ng.s.  C + e+ + ne) (*) • ne + C  e- + N* • n + C  n + C* (11.51 MeV g emission) (*) • ne + e- ne + e- (*) (*) ; cross section is well known.

13. Cross sections, #events • J-PARC P56 has larger stat. 10 times than those of previous experiments. -> stat error 1/3 • The detector and beam of P56 also has better quality, therefore systematic uncertainties will be improved. • Ratio between charged current vs neutral current gives extra information. M. Shaevitz, 2011 Workshop on Baryon & Lepton Number Violation

14. Energy and angle distributions of e- arXiv:hep-ex/0105068 Forward scattering ~isotropic (a); ne + e- ne + e- scattering (left Ee, right; angle between neutrino and e-) (b); ne + C  e- + Ng.s. (Ng.s.  C + e+ + ne) (c); ne + C  e- + N* (excited states)

15. ne + C  e- + Ng.s.(Ng.s.  C + e+ + ne) • Top-right; hep-ex/0105068(LSND) Cross section ds/dE • Prompt signal has following features; • Q-value is 17.3MeV　　　 （En = 17.3MeV + Ee-) • Reconstructed neutrino energy measured by LSND experiment is shown by bottom-right plot. • This is also possible background Ee<16.83MeV

16. ne + C  e- + Ng.s. (Ng.s.  C + e+ + ne) • Delayed signal from Ng.s. b decay can be detected • End point of positron energy is 16.83MeV. • Lifetime is 15.9 ms • Positron energy of the b decay is described by following eq. δ；　Za/be, Emax=16.83, Ee : positron total energy • Branching ratio of this b decay is about 94.6%. • KARMEN / LSND, previous experiments observed this. b decay energy spectrum

17. KARMEN Prompt e- energy Prompt e- time from beam arXiv:hep-ex/0203021 e+ energy time between e- and e+

18. Test for other detectors / materials ? • Energy spectra of neutrinos are very clear • Ideal test facility / experiment to measure low energy neutrino cross sections (O(10MeV)) . • We can test not only liquid scintillator but also other detectors / materials (E.g.; Water, Liquid Argon, etc..). • Previous experiments, LSND, KARMEN already measured the cross sections. J-PARC P56 can improve precision of the measurements. • Number of events are increased by factor of 5-10. (because of higher proton energy (3GeV) than others (800MeV)) • Ultra-pure neutrinos from m+ can be available. (LSND experiment suffers from neutrinos from p / K due to almost DC beam) • Detector will be improved • Monochromatic ~30MeV neutrinos from p and ~250MeV neutrinos from K+ is also available. (on bunch -> vs BKG rate)

19. On-bunch beam • Decay-at-Rest neutrino source provides monochromatic ~30MeV neutrinos from p and ~250MeV neutrinos from K+ on-bunch. (top plot, no time selection case) • This is also a good chance to measure the neutrino interactions. • One difficulty is to manage backgrounds from neutrons or neutrinos.  challenging, but not impossible.

20. Monochromatic nm (~30MeV) from p is used KARMEN measurement (~15 % precision) Theoretical prediction (a few % precision)

21. BKG measurement at MLF 1F 1ton scintillator • Top-left; scintillator location • at MLF 1st floor • Top-middle; • 50×50×450cm3 scintillator • Top-right; • horizontal -> timing • vertical ;-> activity energy • Bottom-middle; comparison • between data and MC. • (for neutron background) • -> agreed well Neutron which produces BKG. MC (PHITS) BL13; 1ton data (normalized by area) PHITS (MC) Neutron BKG @3F is Smaller than 1F by 104 • Bottom-left; simulation prediction of neutron flux. Neutron flux at 3F is smaller than that of 1F by order of 104. -> will be confirmed soon.

22. Summary • J-PARC MLF provides a good opportunity to measure the neutrinos cross section in meson Decay-At-Rest energy region (O(10MeV)) in detail. • Statistical error and systematic uncertainty of measurements from previous experiments, LSND, KARMEN will be improved by J-PARC P56. • Cross sections for other materials (detector) can be measured using the good quality beam. • If you are interested in the measurements, or implementing MC, let us know.