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

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

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

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. Target   absorb    capture suppression x     LSNDH2O 96%88% 5x10 -3 x 0.13 J-PARCHg(+Fe+Be) 99%~80% 1.7x10 -3 x 1. ~ 1.7x10 -3 Intrinsic background. MLF mercury target and Intrinsic e  BKG estimation 3GeV proton Fe Mercury target Be H H For beam pipe

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

10. c 1998      absorbed before decay into ’s there should not be e at the level of 7x10 -4 Signal : e p→e + n np→d  MeV) 600  s 120Hz target+beam stop configuration DIF, n bkg. Linac beam  Almost DC beam Cherenkov photon can be detected. -> angle meas.      e + e +  e

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; e + p  e + + n However, this experiment can also provide good opportunity to measure neutrino interactions precisely in the low energy region. – e + C  e - + N g.s. (N g.s.  C + e + + e ) (*) – e + C  e - + N* – + C  + C* (11.51 MeV  emission) (*) – e + e -  e + e - (*) (*) ; cross section is well known.

13. Cross sections, #events Averaged xs J-PARC P56 (/4year/50t) LSNDKARMEN Cross section I.B.D.7.2x10 -41 800--- ~10 arXiv:hep-ex/0203021 Well known e + C  e - + N g.s. 8.9x10 -42 23000 ~3000 arXiv:hep-ex/0105068 ~1500 arXiv:hep-ex/9806024 Well known e + C  e - + N* 4.3x10 -42 11000 ~1500 arXiv:hep-ex/0105068 --- + C  + C* 2.8x10 -42 O(10000)--- ~500 Phys.Lett. B267 (1991) 321-324 Well known e + e -  e + e - ~3.0x10 -43 O(1000) ~1000 arXiv:hep-ex/0101039 ---Well known 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 (a); e + e -  e + e - scattering (left Ee, right; angle between neutrino and e-) (b); e + C  e - + N g.s. (N g.s.  C + e + + e ) (c); e + C  e - + N* (excited states) Forward scattering ~isotropic

15. e + C  e - + N g.s. (N g.s.  C + e + + e ) Top-right; hep- ex/0105068(LSND) Cross section d  /dE Prompt signal has following features; – Q-value is 17.3MeV （ E = 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. e + C  e - + N g.s. (N g.s.  C + e + + e ) Delayed signal from N g.s.  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 ； Z  /  e, Emax=16.83, Ee : positron total energy Branching ratio of this  decay is about 94.6%. KARMEN / LSND, previous experiments observed this.  decay energy spectrum

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

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  + can be available. (LSND experiment suffers from neutrinos from  / K due to almost DC beam) – Detector will be improved – Monochromatic ~30MeV neutrinos from  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  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. Theoretical prediction (a few % precision) KARMEN measurement (~15 % precision) Monochromatic  MeV  from  is used

21. 1ton scintillator PHITS (MC) MC (PHITS) BL13; 1ton data (normalized by area) Neutron which produces BKG. Neutron BKG @3F is Smaller than 1F by 10 4 Top-left; scintillator location at MLF 1 st floor Top-middle; 50×50×450cm 3 scintillator Top-right; horizontal -> timing vertical ;-> activity energy Bottom-middle; comparison between data and MC. (for neutron background) -> agreed well Bottom-left; simulation prediction of neutron flux. Neutron flux at 3F is smaller than that of 1F by order of 10 4. -> will be confirmed soon. BKG measurement at MLF 1F

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.