2008/07/31 Tomonori Kusano Tohoku University

1. Search for active neutrino disappearance using neutral-current interactions in the MINOS long-baseline experiment 2008/07/31 Tomonori Kusano Tohoku University

2. Disappearance of  • Several experiment shows  disappearance while propagating from the production point. reason: - →toscillation (Super-Kamiokande has reported  appearance.) - →soscillation (s:sterile neutrino) • →soscillation could explain the  disappearance.

3. Number of neutrino flavors indicated from Z boson decay width 3 flavors of neutrino coupling with electro-weak current is indicated. • This is a cross section for the e+e-→(), near the Z resonance. • But existence of sterile neutrino can’t be excluded.

4. Target Process Assuming →oscillation (e,,s ) # of NC event would show us the fraction of →s. and e can couple to Z boson. # of NC events would NOT changed. →e  scan’t couple to Z boson. NC events would be suppressed. →s NC:neutral current

5. 734 km Overview of MINOS experiment • Neutrino beam is provided from 120 GeV protons. • Near Detector at Felmilab,and Far detector,734km away, at Soudan. • Compare the results of the two detectors. Near Far

6. Neutrino Beam 120 GeV protons from the Main injector. neutrino beam components 92.9%anti- 5.8%e and anti-e 1.3% →(99%) →(63%)

7. Neutrino Beam configuration • Beam energy spectrum can be chcanged by adjusting the target position. • Low energy configuration(3.3GeV) is selected for this analysis.

8. 15m 4.8m Near Detector • 0.98kt mass, fiducial mass 27t, 282 steel,153 scintillator plane,(Hadronic shower generate scintillation light), 1.4T Magnetic field(Separation for )

9. 30m 8.0m Far Detector • 5.4kt mass,3.8kt fiducial mass,484 steel / scintillator,1.5T magnetic field.

10. Pre-selection • To reject poorly reconstructed events,Event must be separated 40ns separated 1m in the longitudinal direction within 120ns. • GPS time stamp to reject beam spill from noise, cosmic muons, poorly reconstructed events.

11. Event Reconstruction bkg bkg Sig →missidentified as NC events

12. Selection for NC event • Event topology Event Length < 60 planes Track extension < 5 planes (short event) ← ← (at the Near Detector)

13. Energy distribution at the Near Detector Good agreement between the Data and MC. This is the reconstructed Energy of NC-like events at the near Detector.

14. Prediction of the energy spectrum at the Far detector • Near Detector Data→Correct Near Detector MC→Far detector MC (Estimated from Near Detector)⇆Compare the Data at the Far Detector(BOX)

15. Energy distribution at the far detector This is a reconstructed energy spectrum for NC events at the Far detector. Assuming → ,→e oscillations, CC background are estimated.

16. Calculation of R NData:measured event count at Far Detector BCC:predicted(from Near Detector) CC BG from all flavor SNC:predicted number of NC interactions disappearance of nm occurs for neutrino true energy<6GeV→data is separated to two region R differs from 1 by 1.3

17. Results • kept R= 0.780.03(stat)+0.05-0.04(syst.)for 0<E<120(GeV) • →sfraction(1-R)/(1-R) = fsrate= 0.030.39(stat)+0.27-0.36(syst.)(1-R)/(1-R) <0.80 at90% C.L.

18. Single mass-squared splitting • Assuming single mass-squared splitting, m : atmospheric mass squared splitting L : 735km E : energy of the neutrino s: phenomenological parameters (Energy independent)

19. Including e appearance • fsrate = 0.480.40(stat)+0.17-0.25(syst.)fs = 0.43+0.23-0.27(stat.+syst.) fs <0.80 at90% C.L.

20. Summary