The Many Uses of Upward-going Muons in Super-K

1. The Many Uses of Upward-going Muons in Super-K Muons traveling up into Super-K from high-energy nm reactions in the rock below provide a high-energy insight into many different problems. Alec Habig, Univ. of Minnesota Duluth for the Super-K Collaboration

2. Upward-going m SK SK m m Stop-m Through-m nm nm • High energy nm can interact in rock some distance away and still produce a m seen by detector • Higher energy particles, more range, more effective volume! • Increasing target mass at high E offsets falling nm spectra • Down-going entering cosmic ray muons restrict this technique to upward-going entering muons Alec Habig

3. Up-m’s in Super-K • For “SK-I” • 4/96 to 7/01 • 1678 live-days up-thru (1657 up-stop) • More than other SK analyses, this one is insensitive to poor detector conditions • For >7m path (>1.6 GeV): • 1878 thru-m • 456 stop-m Alec Habig

4. Atmospheric nm Thru-m data Stop-m data No-osc MC (best norm.) Osc. MC • Up-m flux is presented as a function of cosq and thus baseline • cosq=-1 (Up) have L~10,000 km • cosq=0 (Horizontal) have L~500 km • Lower E, longer L n’s oscillate more • The data match the oscillated MC far better than the non-oscillated MC • sin22q=1.0, Dm2=2.7x10-3 Alec Habig

5. Energy Lever Arm • For nm seen as up-m: • Typical En ~ 10 GeV for stop-m,~ 100 GeV for thru-m • Compare to contained event energies ~ GeV • From the soft atmospheric n spectrum. A harder n spectrum would produce a larger fraction of high energy parent n • Disadvantage – for any single event, the parent n energy is known only to be larger than the observed m energy Alec Habig

6. nm, nt Oscillation • Even with comparatively small statistics and lousy energy resolution, the observation of nm disappearance at higher energies further refines the oscillation fit • Left – 90% C.L. contours with and without up-m data • Best fit (physical region)*: • sin22q = 1.0 • Dm2 = 2.5x10-3 90% C.L. FC,PC Alone With up-m *(absolute best fit slightly unphysical at sin22q=1.03) Alec Habig

7. nm to nsterile? • High energy n experience matter effects which suppress oscillations to sterile n • Matter effects not seen in up-m or high-energy PC data • Reduction in neutral current interactions also not seen • constrains ns component of nm disappearance oscillations • Pure nm-ns disfavored • ns fraction < 20% at 90% c.l. Alec Habig

8. Unusual Models • Alternative ways to make nm disappear without invoking standard nm,nt flavor oscillations include • Lorentz invariance violation • Neutrino decay, decoherence • Fits using all available SK n data (FC+PC+NC+multiring+ up-m, 190 d.o.f.) strongly constrains many such models • Hard for a model to get a good fit over 5 orders of magnitude in energy and 4 in baseline • Long t nm decay and nm decoherence disfavored but not eliminated Alec Habig

9. Galactic Atmospherics? • Cosmic rays interact with interstellar medium as well as our atmosphere • Would also produce n • ISM most dense at low galactic latitudes • Do we see excess n in the galactic plane? • A search for these n does not see this weak signal Alec Habig

10. Astrophysical n • A hard n spectrum: more likely a n signal will be seen as up-m • n space-time coincidences with GRBs not seen at any energy in SK • AGNs or other astrophysical sources would produce point sources of high-energy n • All sky searches for such point-sources are negative • Unbinned searches for unusual clustering of up-m also negative Alec Habig

11. Pick a Source, Any Source • To test your favorite model of n production at some high energy astrophysical source: • Up-m near sources counted, a sampling shown here • Expected count from atm.n background calculated • No excess seen, flux limits computed Alec Habig

12. WIMP Detection • WIMPs could be seen indirectly via their annihilation products (eventually nm) if they are captured in a gravitational well • WIMPs of larger mass would produce a tighter n beam • Differently sized angular windows allow searches to be optimized for different mass WIMPs Alec Habig

13. WIMP Results • The Sun, Earth, and Galactic center are potential WIMP traps • No excess of n are seen in any angular cone about them • Upper limit of WIMP-induced n calculated • Varies as a function of possible WIMP mass • Lower limits for higher masses are due to the better S/N in smaller angular search windows Alec Habig

14. Probing for WIMPs • Most model dependence in indirect searches lies in the cross-section • Most conservative limits are taken for other uncertainties • Direct-detection experiments also do not know cross-sections • Comparisons can be made between direct and indirect searches • Both spin-dependent (left) and spin-independent (right) WIMP-nucleon interactions can be probed (a la Kamionkowski, Ullio, et al) Alec Habig

15. Summary • The high-energy end of the nm spectrum observed by Super-K is seen as up-going m • The extra lever arm in energy contributes to oscillation parameter estimation out of proportion to the small statistics and poor energy resolution of the sample • The high parent n energies allow probes of unusual areas of physics and astrophysics • Nothing unexpected seen, unfortunately The presenter gratefully acknowledges support for this poster from the National Science Foundation via its RUI grant #0098579, and from The Research Corporation’s Cottrell College Science Award Alec Habig