Partially Contained Atmospheric Neutrino Analysis Andy Blake + John Chapman Cambridge University January 2004

ν νμ μ UPWARD-GOING MUONSDOWNWARD-GOING MUONS “direction” problem“containment” problem Two Categories of PC Event main background : stopping muons with mis-reconstructed direction main background: through-going muons that appear contained shield helps this analysis

Selecting PC Events (1) CONTAIN DIGITS ( 2) CONTAIN TRACKS Cambridge DemultiplexerCambridge Track Reconstruction Combine digits in adjacent views + select events with non-contained hits beside 1 detector edge Select tracks with > 8 planes + 1 contained vertex Select events with hits < 0.5m from 1 detector edge bottom vertex contained top vertex contained upward-going candidate downward-going candidate

Event Rates ( kT yr ) -1 MC atmosMC cosmicdata TOTAL FLUX4004,500,000 DIGITS > 91602,500,0003,900,000 PC DIGITS90450,000550,000 PLANES > ,000380,000 TRACK RECO25240,000 PC TRACKS1548,00043,000 PC UP746,00041,000 PC DOWN72,1001, ,000 MC events 1,000,000 MC events September 2003 r (~0.12 kT-yr) stopping muons

Upward-Going PC Events

Upward-Going Muons – Aim Track DirectionTrack Topology Likelihood Analysis

Upward-Going Muons – Timing (1) (1) Timing S CT U view V view 1/β = -11/β = +1 Fit S-CT with time slope ± 1 Calculate RMS for each fit Consider RMS up - RMS down MC atmos97.2 % MC cosmic99.8 % data99.1 % Percentage success rate …

Upward-Going Muons - Timing (2) Timing appears worse for data Resolution ~ 60cm ~ 2ns Can also make use of absolute values of RMS …

Upward-Going Muons - Timing (3) RMS up / RANGE RMS from fitting wrong time slope fit track 0 S

Upward-Going Muons - Timing Cuts RMS up – RMS down < -0.2 m RMS up < 2.0 m RMS down > 1.0 m RMS up / RANGE < < 1/β < -0.6 RMS up – RMS down < 0.0 m 1 st pass timing cuts 2 nd pass timing cuts 3.69 (2 evts) 15 (2 evts) MC atmos MC cosmic data 7.346,00041,000 PC digits / tracks BKG / SIG ~ 1.0

Upward-going Candidates (1) data events: (1) run 19135, snarl CRATE 15 !

Upward-Going Candidates (2) data events: (2) run 18902, snarl NEUTRINO CANDIDATE

Upward-Going Candidates (3) MC events: (1) run 231, snarl Large Angle Scattering E μ = 6 GeV ? ? ?? ? ? ? ? ??

Upward-Going Candidates (4) MC events: (1) run 242, snarl Large Scattering Again !!!

Upward-Going Muons – Showers (1) (2) Vtx Showers Mop up remaining hits in event Calculate distance from each track vertex to centre of hits: Δ VTX = VTX shw - VTX trk Consider Δ VTX up - Δ VTX down MC atmos89.6 % MC cosmic38.1 % data45.6 % Percentage success rate … Δ VTX up Δ VTX down for cosmics, showers are distributed roughly evenly between track vertices, but slightly more vertex showers are found at BOTTOM of track

Upward-Going Muons – Showers (2) Vertex Shower Reconstruction showers reconstructed in two passes 1 st pass – dense “primary” showers ( ≥ 4 planes, ≥ 10 strips) 2 nd pass – diffuse “secondary” showers select the dense showers eliminates many “fake” muon showers … … but some still found on steep tracks with multiple strips per plane

Upward-Going Muons - Showers (3) Δ VTX up Δ VTX = VTX shw - VTX trk Quality Cuts W ρ ~ N strips / W 3 shower vertex position: shower density:

Upward-Going Muons - Shower Cuts BKG / SIG ~ 40.0 shower planes > 4 Δ VTX up < 0.7 m density > 5.0 strips plane -3 (kT-yr) -1 MC atmosMC cosmicdata PC UP7.346,00041,000 UP-GOING SHOWER 3.612,00010,000 DENSE SHOWER QUALITY CUTS (6 evts) 50 (6 evts)

Upward-Going Candidates example data events neutrino

Downward-Going PC Events

Downward-Going Muons 0.5m containment cut on top track vertex removes 99% through-going muons most remaining events are steep muons that sneak between the planes remove clean background using trace/direction cuts track containment

Downward-Going Muons – Direction Cuts P y /P P z /P p y /p < 0.9 p z /p > 0.2

Downward-Going Muons – Trace Cuts TRACE Zextrapolate track to detector edge + calculate Z component Trace Z > 6 plns

Next Background Layer Remaining background dominated by very steep muons: muons travelling significant distances down a single plane muons turning back on themselves

Downward-Going Muons – Very Steep Muons Distances of digits from track vertex Combine digits in adjacent views around track vertex Calculate distance between track vertex and furthest digits Charge around track vertex Plane with maximum charge close to track vertex ΔR < 1.1 mQ < 500 PE

Downward-Going Muons – Timing Quality Steep muon events have poor timing 0.5 < | 1/β | < 1.5

Downward-Going Muons - Containment Cuts (kT-yr) -1 MC atmosMC cosmic data PC DOWN7.22,1001,800 DOWN- GOING TIMING 5.42,1001,800 ANGLE + TRACE Q max, ΔR + TIMING (6 evts) 70 (8 evts) P y /P < 0.9 P z /P > 0.2 Trace Z > 6 plns Q max < 500 PEs ΔR < 1.1 m 0.5 < 1/β < 1.5 RMS down < 2.0 m BKG / SIG ~ 10.0

Downward-Going Candidates 6 MONTE CARLO EVENTS 3 demux errors 1 tracking error 1 missing detector 1 only just contained 8 DATA EVENTS 1 demux error 2 tracking errors 3 missing detector 2 coil hole … 0 neutrinos

Demultiplexing Errors these hits should be higher

Tracking Errors

Missing Detector swallowed by LI ?

Conclusion Analysis is progressing … … but still need to peel away some more layers of background Need detailed MC/data comparison e.g. high muon scattering MC timing resolution tracks/showers Need another round of tagging/fixing reconstruction errors … but it’s good that neutrinos can be extracted from the data!