Upward Showering Muons in Super-Kamiokande

Transcription

1 Upward Showering Muons in Super-Kamiokande Shantanu Desai /Alec Habig For Super-Kamiokande Collaboration ICRC 5 Pune

2 Upward Going Muons in Super-K.5 THRU STOP dφ/dloge υ ( 1-13 cm - s -1 sr -1 ) E υ (GeV) Thrugoing Stopping

3 Muon Energy loss as a function of Energy Non-Showering muon Showering Muon < de/dx (MeV cm g -1 ) > 1 1 Total Loss Radiative Loss Ionization Loss Average < de/dx > from M.C. E i L E f de/dx = (E i - E f )/L Distribution asymmetric for each muon energies Muon energy (GeV) (Groom et al 3) Reasonably good agreement of Monte-Carlo with PDG Aim of this analysis is only to separate a given muon into showering/non-showering

4 Corrections to raw PMT charge Muon track d wat PMT Apply following correction for every PMT in Cherenkov Cone q corr = q raw d wat exp(d wat /L atten ) F(θ) where L atten = Water attenuation length, d wat = Distance from PMT to point of projection to µ track F(θ) = PMT acceptance + shadowing Divide the muon track into 5 cm bins. For each bin, calculate average corrected charge and its error as follows: i Q corr N pmt 1 q corr N pmt where N pmt = No of pmts within the given projected distance corresponding to each bin i Qcorr 1 N pmt N pmt 1 q corr q raw

5 Corrections to raw PMT charge Muon track d wat PMT Apply following correction for every PMT in Cherenkov Cone q corr = q raw d wat exp(d wat /L atten ) F(θ) where L atten = Water attenuation length, d wat = Distance from PMT to point of projection to µ track F(θ) = PMT acceptance + shadowing Divide the muon track into 5 cm bins. For each bin, calculate average corrected charge and its statistical error as follows: i Q corr i Qcorr N pmt 1 1 N pmt N pmt q corr N pmt q corr 1 q raw where N pmt = No of pmts within the given projected distance corresponding to each bin

6 Corrected Charge Distribution Comparison of ionizing vs showering muon Mean corrected photo-electrons /.5 m Muon Energy = GeV Muon Energy = 1 TeV Projected Distance Along Track (m) Mean corrected photo-electrons /.5 m Projected Distance Along Track (m) de/dx =.16 MeV/cm de/dx = 8.5 MeV/cm Both simulated muons have same entry point and direction

7 { { Variables used for showering/non-showering separation n i3 where and i Q corr Q corr i Qcorr Shape Comparison n3 4 Q corr n3 4 qlq corr i Q corr i Qcorr 1 i Qcorr Q corr ql Absolute Corrected Charge Comparison (Average corrected charge averaged over entire muon length) for a ionizing muon as a function of path-length Difference in average corrected charge of given muon same for ionzing muon

8 No of events Data M.C. Variables when applied to 1yr upmu NEUT Monte-Carlo χ comparison for data and monte-carlo log1 (Σ {(de/dx) i - mean} /dof) Data Monte-Carlo No of events [ mean q corr - Q(L) ] comparison for data and monte-carlo

9 SHOWERING CUT USED χ /DOF >4 and >1. OR χ /DOF >3 and >. OR χ /DOF> and >.5 OR χ /DOF>5 and >.5 OR > 4.5 Total no of showering events = 5575 (out of 3731) in 1 year upmu NEUT Monte-carlo Efficiency = 71 % where, Efficiency = No of events Identified by algorithm No of events with E / X >.85 MeV/cm E = Energy deposited by muon in inner detector X = Length of muon in inner detector

10 NEUTRINO ENERGY SPECTRA dφ/dloge υ ( 1-13 cm - s -1 sr -1 ) Showering Non-showering Stopping <E υ > ~ 1 GeV <E υ > ~ 1 GeV <E υ > ~ 1 TeV E υ (GeV)

11 Event Display of upward showering muon Super-Kamiokande Run 11 Sub 3 Ev :1:46:37 13 dee4 66 Inner: 1877 hits, pe Outer: 49 hits, 863 pe (in-time) Trigger ID: xb D wall: 169. cm Upward-Going Muon Mode Charge(pe) > < Times (ns)

12 Angular Resolution of showering muons 4 Angular resolution of Showering thrumus Shaded region contains 68 % of total area µ true µ fit Angular resolution = 1.5 No of events Angle between precision fit and truth fit Thrugoing muons : Angular resolution ~ 1 Stopping muons : Angular resolution ~ 1

13 Zenith-angle distribution of showering muons 1 No Oscillation m =.5 sin Θ =1. 8 No of events cosθ Showering muons relatively insenstive to oscillation ==> For this dataset chi-square for null -oscillation should be very good fit

14 Background Subtraction Applied the showering algorithm to horizontal thrugoing muon with < cos(θ)<.8 Azimuth distribution of all showering muons (1) () (1) / 14 P P P No of Events Number of Events 1 1 Region (1) Φ < 6, Φ > 4 Region () 6 < Φ < Φ (degrees) cosθ Fit to thin rock zenith angle distribution: f[cos(θ)] = p1+ exp [p+p3 cos(θ)] N bkgd = for cos(θ)> -.1 (Asymmetric distribution because of bump near horizon)

15 Showering Muon Oscillation Results Best-fit (physical region) : χ = 4.68 / 7 dof for ( m, sin θ) = (.14 ev,.9) Best-fit (null oscillation) : χ = 6.51/9 dof 1 9 No of showering muons cosθ Zenith angle comparison at best fit point Null oscillation normalized by livetime

16 Projections of chi-square distributions for showering muons % C.L. 9% C.L. 68% C.L % C.L. 9% C.L. 68% C.L. χ - χ min 6 4 χ - χ min m (ev ) sin θ Null oscillation allowed even at 68 % confidence level as expected for this high energy ν µ with mean energy of ~ 1 TeV

17 Comparison with all upward thrugoing muons % C.L. 9% C.L. 68% C.L. 8 99% C.L. 9% C.L. 68% C.L. χ - χ min 6 4 χ - χ min m (ev ) sin θ Best-fit : χ = 7.64 / 7 dof for ( m, sin θ) = (.4 ev,.96) Best-fit at null oscillation : χ = 19.6/9 dof Upward thrugoing muons sensitive to neutrino oscillation

18 CONCLUSIONS A sample of upward thrugoing muons which lose energy through radiative processes have been identified. Mean energy of parent neutrinos of upward showering muons ~ 1 TeV showering muons in 1yr neut Monte-carlo and 39 events in days data Zenith angle distribution of upward showering muons consistent with null oscillations This dataset will now be used for oscillation analysis with all datasets by providing an extra energy bin at highest energies. A variety of astrophysical searches with upward showering muons done. Nothing found. (S. Desai thesis 3. Also A. Habig poster)