NEUT Review

1. NEUT Review Neutrino interaction simulation codes in Super-Kamiokande & K2K experiments Jun Kameda (ICRR) RCCN International workshop at Kashiwa (Dec.10,2004)

2. Introduction • NEUT is a neutrino interaction simulation • code developed & used in • Super-Kamiokande atmospheric neutrino analyses • and K2K experiment. • It has been developed from Kamiokande • experiment using available theories and data.

3. Total (NC+CC) CC Total CC quasi-elastic DIS CC single p NC single p0 1. Neutrino Interactions Charged current quasi-elastic scattering (CCQE) • + n l+ p Neutral current elastic scattering • + N n + N CC/NC Single p,(h,K ) production via resonances (h,K) n+ N l + N’ + p CC/NC Coherent pion productions n+16O l +16 O + p CC/NC Deep inelastic scattering nm+ N l + N’ + hadrons (l : lepton, N,N’ : nucleon, m : integer) Cross-sections NEUT covers Eν~a few 10MeV to ~1TeV. Above 1TeV region, only CC DIS is considered(Upward-going muon) . s/E (10-38cm2/GeV) Eν(GeV)

4. 2. Charged Current Quasi elastic scattering ν + N  l + N’ νμ + n  μ- + p • Dominant interaction • at Eν<1GeV region. • Important interaction • to measure neutrino energy in • long baseline experiments. Based on C.H.L. Smith, (Phys. Rep. 3,261(1972)) For bound nucleon effects, R.A.Smith et al., (Nucl.Phys.B43 605(1972) Axial vector mass (MA) =1.1GeV2 νμ + p  μ+ + n

5. m+ p m+ + n Free nucleon Bound nucleon • e+ p e+ + n • Fermi momentum of target nucleon • (fermi gas model with Pf = 225 MeV/c ) • Pauli blocking effects (Pf = 225 MeV/c) • Nuclear potential (V= -26MeV ,fixed potential) • are taken into account. • Cross sections • are suppressed • ~ 20% at 1GeV.

6. Angular correlation n l qnl Angular correlation between neutrino and outgoing lepton become better as En become higher. <qnl> ~ 40 degree at 1GeV

7. 3. Single meson production via resonances ν + N  l + N’ + π(K、η) Based on D.Rein, and L.M.Sehgal, Ann. of Phys. 133(1981) νμ + ｎ  μ- + p + π+ νμ + ｎ  μ- + Δ++ Resonant production amplitude is calculated by FKR model. (Phys.Rev.D3 2706(1971)) Up to W = 2GeV/c2 Resonances are taken Into account. (18 resonances) νμ + ｎ  μ- + p + π+ νμ + ｎ  μ- + p + π+ En (GeV) En (GeV)

8. Pionless decay of the resonances is taken into account. • Δ(N*)+ N  N’ + N’’ • 20% of delta resonances in oxygen are killed. • ( M.Hirata et al., Ann.Phys. 108(1977) ) • Pion,K,h interactions in nuclear are considred. • The pion’s cross section is calculated by a model by L.Salcedo et al. . • (Nucl. Phys. A484(1998) 79) • Scattering, absorption, charge exchange, pion productions are considered. Nuclear effects are important for p0 production rate, which is the background source for ne appearance search . ex.) p0 survives about 40% at p= 300 MeV/c

9. ν + 16O l + 16O + π± - + ( ) ( ) ( ) ν + 16O μ- + 16O + π^ ν + 16O ν + 16O + π0 Eν(GeV) 4. Coherent pion production ν + 16O ν + 16O + π0 Based on J.Marteau, et al. (Nucl. Inst. Meth. A451,76(2000)) En = 1GeV CC QE CC 1p CC coherent Scattered angle of the outgoing Lepton is small for coherent p production q between n and l (deg.)

10. 5. Deep Inelastic scattering ν + N  l + hadrons • Cross section is calculated by GRV94(DIS) PDF. • Correction for small q2 region is taken into account. • (for K2K experiment,(A.Bodek et al., Nucl Phys.Proc.. Suppl. 112.70-76.2002) ) νμ + N  μ- + X νμ + N  μ+ + X

11. Final kinematics for DIS is determined by • JETSET 7.4 package. (W> 2GeV/c2) • For low W region (1.3GeV/c2 < W < 2.0 GeV/c2), • our original codes is used. • pion multiplicity is determined from • experimental results and KNO scaling.

12. Other topics • Gammas from de-excitation of target nuclei is • simulated. • In K2K experiments, Carbon target & Fe target • interaction are also simulated. • Fermi momentum (225MeV250MeV for Fe, no change for C) • proton/neutron ratio is tuned. • Cross section for coherent p production depend Atomic number, and it is taken into account. • Nuclear effects are not modified for C and Fe. We checked the systematics from this approximation is small for K2K FD detectors.

13. Summary • I reviewed the NEUT codes. • K2K front detectors now have a huge amount of neutrino interaction data, and it will give a good information for neutrino interaction models.