Topological Study of Downgoing Muon Events for the Separation of High Energy Single muons from Muon bundles Raghunath Ganugapati(Newt) && Paolo Desiati

Detection With AMANDA-II Extra Terrestrial Neutrinos High energy spectrum hypothesis dF/dE œ E-2 Backgrounds Conventional Atmospheric µ dF/dE œ E-3.7 Conventional Atmospheric n from decay of (π± , K± ) Possible nm components from decay of atmospheric charmed particles. dF/dE œ E-2.7

Charm Mechanism Vs π± , K± Mechanism The interaction of a high energy cosmic ray with air nuclei produces a D± which takes up most of the energy and momentum of the primary. Showering effect and the production of accompanying π± and K± is negligible when required to estimate the flux at the surface of the earth. Ref: Doctoral thesis of Prof.Varieschi

Muon Bundles The multiple muon background goes with the same slope as the signal so the signal will be masked in the fluctuations of the multiple muon background We need to reject this background To improve the sensitivity Of our instrument to prompt muon Singles Multiples Signal log10(energy at cpd) GeV

Timing Pattern Larger distance = > larger time delay (Pandel) Why are we getting more early (less delayed) hits at large distances from track)? Suggests a different time delay structure then the normal Cherenkov cone and it could possibly be exploited for identication

Early Hit Illustration(Idea1) Muon2 Early Hit Reconstructed track A B Cherenkov cone BCD from reconstructed track propagating in time relative to the tracks. Limitations Random Noise hits (3.0 photo electron cut) Misreconstructed single muon ( Good angular resolution vital ) D Δθ C Muon1 snapshot The hit at B is earlier by time length(AB)/cice

EarlyHit From Muon Bundle Reconstructed Track Earlyhit Amplitude>3pe (proximity cut)(Noise Hits suppressed) Distance<50m (proximity cut) timedelay<-15ns

EarlyHit from Mis-Reconstructed Muon These are earlyhits that have high penality and hence unlikely to Occur for a Well reconstructed single muon

64-Iteration Convoluted Pandel Vs 16-fold Patched Pandel The Convoluted Pandel Convoluting gaussian PMT noise smearing with Pandel function using Confluent Hyper geometric functions (George and Mathieu) Much better Angular resolution and description of time delay distributions High energy Muon With nhits>200 Time delay (ns) (16-fold ppandel) “1-fold iterated Convoluted Pandel has approximately same angular resolution Of a 16-fold ppandel” -Mathieu Ribordy (AMANDA collaboration meeting,Mons)

Muon Bundle Filter Efficiency Signal Does retain A decent bit of single muon Singles Multiples Rejected by Factors of 1 in 50 Nhits(true track) Signal Singles Multiples Fraction of muons that pass VS Muon multiplicity @AMANDA depth Nhits(reconstructed track)

Systematics Of the Filter Energy Dependence Muon Multiplicity Degree Of Misreconstruction

Mis-Reconstructed Muon 0 degree 2 degree Notice the loss in signal as we go from 0 to 5 degree point Spread misreconstruction 5 degree Cut these out Misreconstructed single high energy muon are lost in this filter,there is a need to ensure high angular resolution for this method to work optimally EarlyHits

Muon Multiplicity Cut these Earlyhits 10-25 25-50 2 3 4-10 The filter and the method works better when there are more muons Cut these Earlyhits

Energy Dependence Signal Background Cut these Earlyhits Earlyhits Nhits 150-200 200-250 250-300 300-350 At higher energies We get rid of more background while not loosing any signal Cut these Cut these Earlyhits Earlyhits

ENERGY LOSS There are two kinds of processes: Continuous: ionization Energy loss vs. muon energy: There are two kinds of processes: Continuous: ionization Stochastic: Pair production, bremstrahlung, photonuclear interactions Above the critical energy (600 GeV in water) stochastic losses dominate. Very important that this plot only shows the average muon energy loss and no mention of fluctuations

Multiple Muon Event

Single Muon Event The Amplitude in the PMT’S In general saturates well below this limit (the peaks appear compressed When seen through the adc channel) Largest Shot (Energy Release) Still belongs to Single muon

NEW ESTIMATORS y = σ B/<B> An estimator1 is defined, based on a comparison between the light produced by the muon and the light it would have produced if it was a minimum Ionizing muon: An estimator2 is derived from estimator 1 and is y = σ B/<B> B=Number of Observed Photon/Number of Photons expected from MIM

Ice Properties Ice properties themselves introduce some fluctuations into the observed amplitude What the optical properties of a dust layer could do to the Photo Electron recorded? May be need to apply corrections to the PE recorded depending on the layer of ice to retrieve information in original form to undo what ice does (for Horizontal muons this gets tricky!!!)

Reconstruction Errors True track Large Amplitude Seen when lower is expected from reco track hypothesis B Dust Δθ Reco Track Clear Ice A Dust Small Amplitude Seen when large is expected from reco track hypothesis

HIT AND EVENT SELECTION To overcome some of these problems partly I choose only direct hits(-15ns to 75 ns)(less effected by ice properties) Use hits with in 50m radius cylinder around the track(less scattered) Require the event to have at least 6 direct hits(more direct hits means more information to study the fluctuations ) Criteria on Track length and chi square to improve reconstruction quality Take only hits with amplitude greater 3.0 P.E for reconstruction. (No noise hits which will introduce some systematic fluctuations)

SIGNAL-BACKGROUND DISTRIBUTIONS Singles Multiples Keep These y = σ B/<B> y = σ B/<B> Linear scale Log scale Done with Reconstructed track(Con Pandel)

SIGNAL-BACKGROUND DISTRIBUTIONS Singles Multiples Keep These y = σ B/<B> y = σ B/<B> Lin scale Log scale Done with true track

SIGNAL-BACKGROUND DISTRIBUTIONS Singles When all hits are chosen notice what happens? Any possible separation of signal and background through this parameter is masked out by the fluctuations of ice properties Multiples Keep These y = σ B/<B> Done with all hits (not just direct hits)

SYSTEMATICS Multiplicity Energy y = σ B/<B> y = σ B/<B> 2 muon Nhits(150-200) 3 muon Nhits(200-250) 5 muon Nhits(250-300) 5-10 muon Nhits(300-350) 10-25 muon Nhits(350-400) Very Little Correlation ? Nhits(400-450) No correlation Cut these Cut these y = σ B/<B> y = σ B/<B>