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

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

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.

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

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. 734 km NearFar

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%)

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

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

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

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.

Event Reconstruction Sig bkg →miss identified as NC events

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

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.

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)

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

Calculation of R N Data :measured event count at Far Detector B CC :predicted(from Near Detector) CC BG from all flavor S NC :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 

Results kept  R  = 0.78  0.03(stat) (syst.) for 0<E  <120(GeV)  → s fraction (1-R)/(1-R  ) = f s rate = 0.03  0.39(stat) (syst.) (1-R)/(1-R  ) <0.80 at90% C.L.

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)

Including e appearance f s rate = 0.48  0.40(stat) (syst.) f s = (stat.+syst.) f s <0.80 at90% C.L.

Summary