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

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.

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 n+ N l + N’ + p (h,K) 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 Total (NC+CC) CC Total CC quasi-elastic DIS CC single p NC single p0 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)

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

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. Free nucleon Bound nucleon m+ p m+ + n e+ p e + + n Cross sections are suppressed ~ 20% at 1GeV.

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

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)

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

4. Coherent pion production + - ν + 16O l 　+ 16O + π± ( ) ( ) ν + 16O ν + 16O + π0 ( ) Based on J.Marteau, et al. (Nucl. Inst. Meth. A451,76(2000)) Eν　(GeV) ν + 16O ν + 16O + π0 ν + 16O μ- + 16O + π^ 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.)

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

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.

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.

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.