1. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) C. Mariani (INFN Rome) May 19 th, 2005 @ LNF Spring School “ Bruno Touschek ”

2. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) K2K Collaboration 250km JAPAN: High Energy Accelerator Research Organization (KEK) / Institute for Cosmic Ray Research (ICRR), Univ. of Tokyo / Kobe University / Kyoto University / Niigata University / Okayama University / Tokyo University of Science / Tohoku University KOREA: Chonnam National University / Dongshin University / Korea University / Seoul National University U.S.A.: Boston University / University of California, Irvine / University of Hawaii, Manoa / Massachusetts Institute of Technology / State University of New York at Stony Brook / University of Washington at Seattle POLAND: Warsaw University / Solton Institute Since 2002 JAPAN: Hiroshima University / Osaka University U.S.A.: Duke University CANADA: TRIUMF / University of British Columbia ITALY: Rome FRANCE: Saclay SPAIN: Barcelona / Valencia SWITZERLAND: Geneva RUSSIA: INR-Moscow

3. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005)  1995 Proposed to study neutrino oscillation for atmospheric neutrinos anomaly.  1999 Started taking data.  2000 Detected smaller number of neutrinos than the expectation at a distance of 250 km. Disfavored null oscillation at the 2 level.  2002 Observed indications of neutrino oscillation. The probability of null oscillation is less than 1%.  2004 Confirm neutrino oscillation with both a deficit of  and the distortion of the E spectrum. Confirm neutrino oscillation with both a deficit of  and the distortion of the E spectrum. 1. Introduction and history of K2K

4. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 2. K2K experiment  monitor  monitor Near detectors (ND) ++  Target+Horn 200m decay pipe SK 100m ~250km  12GeV protons ~10 11   /2.2sec (/10m  10m) ~10 6   /2.2sec (/40m  40m) ~1 event/2days  Signal of oscillation at K2K Reduction of  events Distortion of  energy spectrum (monitor the beam center)

5. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Accumulated POT (Protons On Target) protons/pulse (×10 12 ) Accumulated POT (×10 18 ) K2K-I K2K-II 10.5x10 19 POT, 8.9×10 19 POT for Analysis Jan 03 Oct-Nov 04 K2K-I K2K-II

6. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) SK Events (BG: 1.6 events within  500  s 2.4×10 -3 events in 1.5  s) T SK T spill GPS SK TOF=0.83msec 107 events Decay electron cut.  20MeV Deposited Energy No Activity in Outer Detector Event Vertex in Fiducial Volume More than 30MeV Deposited Energy Analysis Time Window  500  sec  5  sec T DIFF. (s) - 0.2  T SK - T spill - TOF  1.3  sec

7. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 3. Analysis Overview Observation #, p  and   interaction MC Measurement  (E ), int. KEK Far/Near Ratio (beam MC with  mon.) Observation # and E  rec. Expectation # and E  rec. (sin 2 2 ,  m 2 ) SK

8. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 4. Near detector measurements  1KT Water Cherenkov Detector (1KT)  Scintillating-fiber/Water sandwich Detector (SciFi)  Lead Glass calorimeter (LG) before 2002  Scintillators Bar Detector (SciBar) after 2003  Muon Range Detector (MRD) Muon range detector LG calorimeter

9. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 4.1 1KT Flux measurement  The same detector technology as Super-K.  Sensitive to low energy neutrinos. Far/Near Ratio (by MC)~1×10 -6 M: Fiducial mass M SK =22,500Kton, M KT =25ton : efficiency  SK-I(II) =77.0(78.2)%,  KT =74.5% exp SK N =150.9 N =107 +12 -10 obs SK

10. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 4.2 SciBar neutrino interaction study  Full Active Fine-Grained detector (target: CH). Sensitive to a low momentum track. Identify CCQE events and other interactions (non-QE) separately.  p CCQE Candidate CCQE non-QE 25  p (degree)  p =  obs - CCQE  DATA CC QE CC 1  CC coherent-  CC multi-  2 track events p

11. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 4.3 Near Detectors combined measurements (p    ) for 1track, 2trackQE and 2track nQE samples  (E), nQE/QE  Fitting parameters (E ), nQE/QE ratio Detector uncertainties on the energy scale and the track counting efficiency. The change of track counting efficiency by nuclear effect uncertainties; proton re-scattering and  interactions in a nucleus …  Strategy  Measure (E ) in the more relevant region of   20 for 1KT and   10 for SciFi and SciBar.  Apply a low q 2 correction factor to the CC-1 model (or coherent ).  Measure nQE/QE ratio for the entire   range.

12. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 5. Super-K oscillation analysis  Total Number of events  E rec spectrum shape of FC-1ring- events  Systematic error term f x : Systematic error parameters Normalization, Flux, and nQE/QE ratio are in f x Near Detector measurements, Pion Monitor constraint, beam MC estimation, and Super- K systematic uncertainties.

13. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) K2K-SK events K2K-all (K2K-I, K2K-II) DATA (K2K-I, K2K-II) MC (K2K-I, K2K-II) FC 22.5kT 107 (55, 52) 150.9 (79.1*, 71.8) 1ring 67 (33, 34) 93.7 (48.6, 45.1 ) -like 57 (30, 27) 84.8 (44.3, 40.5) e-like 10 (3, 7) 8.8 (4.3, 4.5) Multi Ring 40 (22, 18) 57.2 (30.5, 26.7) for E rec (56) * Updated from the previous analysis

14. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 150.9 107 #SK Events Expected shape (No Oscillation) E rec [GeV] KS probability=0.08% V: Nuclear potential Toy MC CC-QE assumption

15. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005)  N SK obs =107  N SK exp (best fit)=150.9 E rec [GeV] Best Fit KS prob.=36% m 2 [eV 2 ] sin 2 2 Data are consistent with the oscillation. Based on lnL preliminary

16. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Null oscillation probability K2K-IK2K-IIK2K-all  disappearance 2.0%3.7%0.26% (3.0) E spectrum distortion 19.5%5.4%0.74% (2.6) Combined 1.3% * (2.5) 0.56% (2.8) 0.0050% (4.0) K2K confirms neutrino oscillation discovered in Super-K atmospheric neutrinos. Disappearance of  and distortion of the energy spectrum as expected in neutrino oscillation. The null oscillation probabilities are calculated based on lnL. *: The value is changed from the previous one.

17. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 6. Summary has confirmed 4.0 ( Phys.Rev.Lett.94:081802,2005 )  With 8.9×10 19 POT, K2K has confirmed neutrino oscillations at 4.0 ( Phys.Rev.Lett.94:081802,2005 ). 3.0 Disappearance of  3.0 2.6 Distortion of E spectrum2.6 - 68% - 90% - 99% 0.006 0.0 0.2 0.4 0.6 0.8 1.0 0.002 0.004 m 2 [eV 2 ] sin 2 2

18. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Backup slide

19. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Neutrino beam and the directional control ~1GeV neutrino beam by a dual horn system with 250kA. <1mrad The beam direction monitored by muons Y center X center ≤  1 mrad ~5 years

20. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Neutrino spectrum and the far/near ratio beam 250km 10 -6 1.0 2.0 Far/Near Ratio E  (GeV) beam MC w/ PION Monitor E (GeV)  energy spectrum @ K2K near detector

21. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) NEUT: K2K Neutrino interaction MC  CC quasi elastic (CCQE) Smith and Moniz with M A =1.1GeV  CC (resonance) single (CC-1) Rein and Sehgal ’ s with M A =1.1GeV  DIS GRV94 + JETSET with Bodek and Yang correction.  CC coherent  Rein&Sehgal with the cross section rescale by J. Marteau  NC + Nuclear Effects  /E (10 -38 cm 2 /GeV) E (GeV)

22. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Neutrino energy reconstruction

23. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 4.3 Near Detector Spectrum Measurements  1KT Fully Contained 1 ring  (FC1R) sample.  SciBar 2 track nQE ( p >25  ) 1 track, 2 track QE ( p ≤25 ), 2 track nQE ( p >25  ) where one track is   SciFi 1 track, 2 track QE ( p ≤25 ), 2 track nQE ( p >30  ) where one track is  After applying the low q 2 suppression of nQE observed in SciBar, the angular distributions of all other samples are reasonably reproduced.

24. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) A hint of K2K forward  deficit. SciBar non-QE Events K2K observed forward  deficit. A source is non-QE events. For CC-1,  Suppression of ~q 2 /0.1[GeV 2 ] at q 2 <0.1[GeV 2 ] may exist. (0.1GeV 2 value comes from fitting 2 track nonQE sample in SciBar) For CC-coherent ,  The coherent may not exist. We do not identify which process causes the effect. The MC CC-1 (coherent ) model is corrected phenomenologically. Oscillation analysis is insensitive to the choice. q 2 rec (Data-MC)/MC DATA CC 1  CC coherent-  Preliminary q 2 rec (GeV/c) 2

25. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Flux measurements  2 =638.1 for 609 d.o.f  ( E< 500) = 0.78  0.36  ( 500 E < 750) = 1.01  0.09  ( 750 E <1000) = 1.12  0.07  (1000 E <1500) = 1.00  (1500 E <2000) = 0.90  0.04  (2000 E <2500) = 1.07  0.06  (2500 E <3000) = 1.33  0.17  (3000 E ) = 1.04  0.18 nQE/QE = 1.02  0.10 The nQE/QE error of 10% is assigned based on the sensitivity of the fitted nonQE/QE value by varying the fit criteria.  >10(20 ) cut: nQE/QE=0.95 0.04  standard(CC-1 low q 2 corr.): nQE/QE=1.02 0.03  No coherent: =nQE/QE=1.06 0.03 (E ) at KEK E preliminary

26. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 1KT:  momentum and angular distributions. with measured spectrum   (deg.) 0 20 90 flux measurement low q 2 corr. p  (MeV/c) 0 1600 800 1Kt -like sample Quasi elastic Single pion

27. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) 0-0.5 GeV 0.5-0.75GeV 0.75-1.0GeV 1.0-1.5GeV E QE (MC) nQE(MC) MC templates KT data P  (MeV/c)  (MeV/c) flux  KEK (E ) (8 bins) interaction (nQE/QE)

28. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) SciFi (K2K-IIa with measured spectrum) P  1trk P  2trk QE P  2trk non-QE   1trk   2trk QE   2trk non-QE 02(GeV/c)040(degree) flux measurement 10

29. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) SciBar (with measured flux) P  1trk P  2trk QE P  2trk nQE   1trk   2trk QE   2trk nQE flux measurement 10

30. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005)  disappearance versus E shape distortion sin 2 2 m 2 [eV 2 ] N SK (#  ) E shape Both disappearance of  and the distortion of E spectrum have the consistent result.

31. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005)  Best fit values. sin 2 21.51 m 2 [eV 2 ] = 2.1910 -3  Best fit values in the physical region. sin 2 21.00 m 2 [eV 2 ] = 2.7910 -3 logL=0.75 Results sin 2 2  =1.51 can occur due to a a statistical fluctuation with 12.6%. A toy MC sin 2 2 m2m2 1.00 2.79 1.51 12.6%

32. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) Log Likelihood difference from the minimum.  m 2 <(1.87~3.58)×10 -3 eV 2 at sin 2 2=1.0 (90% C.L.) lnL - 68% - 90% - 99% - 68% - 90% - 99% m 2 [eV 2 ] sin 2 2

33. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) K2K-I vs K2K-II

34. C.Mariani@LNF Spring school “Bruno Touschek” (19 th May 2005) The change of N SK exp in K2K-I (Bugs)  The detector position 295m  294m -1%  MC difference between KT and SK KT; M A (QE)=1.1 (NC el ) KT =1.1×(NC el ) SK SK; M A (QE)=1.0  Efficiency change! -1% N SK exp Change ~2% 295m 294m