K2K near detector:

1. Oscillation maximum Probability dip No oscillation # of interactions Oscillated (ideal energy reconstruction) K2K near detector: Measurement of the nmflux in absence of oscillations and of the beam direction 3 different detectors: 1 Kton Water Čerenkov:Small replica of Super-K; Fiducial mass 25ton. Muon range detector: MRD: Iron target 330 ton fiducial mass Neutrino beam monitor: Momentum and direction of muons Scintillating fiber detector in water (SciFi): fine grained water target CCQE identification Fiducial mass 6 ton. SciBar Since October 2003 the Lead Glass has been replaced with a scintillating bars 2.5x1.3x300 cm detector, 11 ton Fid. Study of low energy neutrino interactions (osc. Max. @ 0.6 GeV)

2. Events: • WC: only muon id. • SCIFI (water) 1 or 2 tracks, muon id. • SCIBAR (plastic scint.) 1 or 2 tracks, muon id. • For the events with 2 tracks make a classification in QE and • nQE just looking at the angle of the track wich is not the muon

3. m– Incomingnmdirection known q Proton undetectable belowČerenkov threshold Energy measurement of thenm in SuperKamiokandeusing the 1Rm sample under the hypothesis of the quasi-elastic scattering (dominant process at low energy): nm + n m– + p dE~60MeV <10% measurement Under the assumption that the initial neutron was at restthe kinematics of QE-CC can be used to find the energy of the incomingnm: QE inelastic En (reconstructed) – En (true)

4. For the events with 2 tracks make a classification in QE and nQE just looking at the angle of the track wich is not the muon, should be within 25° from the expected proton direction Scibar For the 3 classes of events fit the muon variables data vs MC in bins of energy Analysis based on the muon apart from the division in classes, no proton id, no measurement of prton energy

5. WC SCIFI SCIBAR

6. No significative differences SCIFI-SCIBAR, large difference in WC

8. Formation Zone Intranuclear Cascade: D.Autiero NUINT04 The formation length was introduced in analogy to the Landau Pomeranchuk effect to explain the suppression of the intranuclear cascade at high energies The tracking of hadrons trhough the nucleus with known cross sections is performed only for hadrons formed inside the nucleus. Formation time in the rest frame of the hadron sampled from an exponential with average: t0 is of the order of a few fm/c. In the lab frame t=tSgs only low energy hadrons participate Z. Phys C 43 (1989) 439 Z. Phys C 52 (1991) 643 The FZIC code performs a complete sampling of the nucleus in the impulse approximation assigning momenta and positions to the nucleons and then propagates the hadrons trough the nuclear medium developing the cascade First application to neutrino interactions by Battistoni, Lipari, Ranft, Scapparone hep-ph 9801426

9. The NOMAD detector Spectrometer: Dp/p = ±3.5% for p < 10 GeV/c ECAL resolution: WANF neutrino beam: <E>=24 GeV for nm 48 GeV for nm CC

10. Nomad typical events: nm + N m– + X m– track ne + N  e– + X Energy depositions in the ECAL ne + N  e+ + X

11. 1 fm/c 2 fm/c 5 fm/c No INC Proton and neutron yields increase with the INC (DIS, Nomad beam and target, pure MC level): Low momenta Large angles p Momentum (GeV/c) Angle wrt incoming neutrino (rad) n Look for the protons in order to tune the model Momentum (GeV/c) Angle wrt incoming neutrino (rad)

12. Formation time tuning, after fragmentation tuning: INC improves the agreement data-MC, (minimum found at 2 fm/c) No INC 2 fm/c Charged hadrons multiplicity Charged hadrons multiplicity 2 fm/c No INC Total event charge Total event charge

13. Hadrons spectra and angular distributions No INC 2 fm/c - - + + Hadrons momenta (GeV/c) Hadrons momenta (GeV/c) No INC 2 fm/c - + - + Hadrons angular dist. (rad) Hadrons angular dist. (rad)

14. Looking for the presence of the protons from INC …. Hadron with the largest angle (wrt incoming neutrino) in the event No INC 2 fm/c Negatives Negatives Hadron with largest angle (rad) Hadron with largest angle (rad) No INC 2 fm/c Strong improvement of the agreement data-MC for the positives due to the INC protons Positives Positives Hadron with largest angle (rad) Hadron with largest angle (rad)

15. Looking for the presence of the protons from INC …. Spectra for hadrons with 0.5<q<1.57 No INC 2 fm/c Negatives Negatives Momentum (GeV/c) Momentum (GeV/c) No INC 2 fm/c Positives Positives p p p p Momentum (GeV/c) Momentum (GeV/c)

16. Backward protons (kinematically forbidden for neutrino interactions on stationary nucleons) are a very sensitive observable for the tuning of INC Nomad has published a paper on the production of backward particles: P.Astier et al. Nuc. Phys. B 609 (2001), see also M. Veltri Nuint01 proc. Protons can be identified by range looking in the sample of backward stopping particles Invariant cross section: # of BP per DIS nm CC

17. NEG-N: invariant spectrum in NOMAD for various formation times The slope is not affected by the formation time, the rate is quite sensitive to the formation time The formation time tuned on the hadronic distributions predicts the correct rate of BP. On the contrary one can constrain the formation time from the measurement of BP which gives: 2 +0.9–0.5 fm/c

18. Ar Pi0 momentum spectrum O/C GeV/c

19. 50000 events /run Resonances Rein & Seghal model Particles in the final state: Ar vs O +3% Pi0 with a softer spectrum (-9%) Ar vs O +17% protons

21. Upper limit, neglecting completely nuclear effects (19%)

22. Upper limit II, fitting the invariant mass of the NEUT events with NUX (no nuclear effects)  18% discrepancy

29. When adding protons and detector mass isn’t enough… D. Harris, proton driver review For any of these experiments, detectors see different mixes of events between near and far. Cross section uncertainties don’t all cancel! Looking for differences between n and anti-n probabilities of at most 15-20%…need to measure probabilities to 5% or better for a 3s determination! Problem: no cross sections at these energies are known any better than about 20%... Minerna will provide precise n measurements, but we still need anti-n cross sections… NOvA pre-PD rates

30. Some remarks: 1) The LAr detector will be the ideal detector to study the nuclear effects and accurately model the MC on Ar (MC validator): Capability to measure exclusive states Particle id (ionization) Energy measurement Homogeneus and hermetic detector, reconstruction systematics reduced 2) The ice target will allow to measure also the interactions on oxigen (on a subsample of the phase space) and cross-check the model 3) The WC detector will allow to correlate accurately the (beam*interaction model) data obtained in the LAr with the WC reconstruction, these beam data will be extrapolated to the far detector

31. A full systematic analysis has not been completed at the moment neither for the 280m nor for the 2Km LAr+WC (using assumption like 10% syst…) • b) WC alone vs SK is nevertheless based on some MC+flux assumptions, what if in reality they are wrong ? We need absolutely the LAr to cross-check the flux*interaction model • c) In real life it may take many years before reaching a good understanding of the systematics (e.g. NOMAD numu  nue analysis ~ 5 years) • d) The WC detector has never been used at this level of precision, we absolutely need all the handles for the systematics, the LAr will be precious

32. Real QE events in the 50l LAr chamber exposed at WANF