Jan 5th 2006 Oxford Mark Thomson, Cambridge 1

A New Approach to searching for e Events in MINOS

Mark Thomson University of Cambridge

This talk:• Motivation

• Basic Idea

• Technicalities

• First attempt

• “Results”

• Outlook

Jan 5th 2006 Oxford Mark Thomson, Cambridge 2

Introduction

Number of reco variables ≈ Number of strips in event

To date all e analysis have used multi-variate techniques

using reconstructed quantities to separate e and NC events. Is this the best approach ? Maybe not…. This analysis is a “special” case:

Motivation:

Basic Idea:

Try to perform event ID using strip information alone NOTE: This is a pure pattern recognition problem

Adopt Nearest Neighbour approach Compare each event to “libraries” of MC events (e and NC) Select N best matches Fraction of N best matches which are e gives a measure of the likelihood of the event being a e

Jan 5th 2006 Oxford Mark Thomson, Cambridge 3

Issues and Technicalities In principle, this approach is optimal + has the “advantage” of being largely reconstruction free But only optimal if phase space fully sampled by MC Need VERY LARGE MC samples

don’t yet know what I mean by very large… (107-8 ?) CPU/memory/disk implications

Disk: NC Ntuples

NC Events

e Ntuples

e NtuplesMemory:

CPU:

MakeLibraries

CompareEvent

for(int i =0;i<nData;++i){

}

Events reduced to bare minimum: strips + somereco info + some MC info

Loop over data, compareevent to MC events in libraries

“Event Likelihood”

Find best matches and construct PID likelihood

Jan 5th 2006 Oxford Mark Thomson, Cambridge 4

Pre-feasibility Study

500k CC e (0-10 GeV) 350k NC (all energies)

Current (small) MC Samples:

Event Processing: Events passed through (nearly) Standard Reco chain with a couple of modifications

Use Atnu strip maker (faster+removes Xtalk) Use new SRCam Track fitter (much faster) Write out simplified Atnu ntuples (fairly compact)

Basically only interested in strips Reco information (e.g. tracks) could be used in event preselection + rejection of CC events, etc.

Have developed code to investigate this approach BUT currently insufficient MC events for full analysis Gained better feel for how things will work Some short cuts, e.g.

strips ganged together in 3s

Jan 5th 2006 Oxford Mark Thomson, Cambridge 5

Event ComparisonNeed a figure of merit for how well two events match

Ask question “what is the probability come from same hit pattern at PMTs ?”

Data are stored as PEs in discrete coordinates of strip/plane

Loop over all planes/strips and compare number of PEs

P = ∫ P(n1,)P(n2,)dplanes strips 0

∞1st try:

Poisson probs

UZ UZ

VZ VZ

Jan 5th 2006 Oxford Mark Thomson, Cambridge 6

Event Comparison cont

“data” eventTrial MC event

Events distributed throughout detector First centre events based on charge weighted mean plane/U Strip/V strip When matching shift whole trial event by ±1 plane, U strip, V strip

Code written for speed – 50000 event comparisons/second hard to speed this up significantly

Jan 5th 2006 Oxford Mark Thomson, Cambridge 7

Example Matches

MC e Best match e Best match NC

Jan 5th 2006 Oxford Mark Thomson, Cambridge 8

Example Matches

MC e Best match e Best match NC

Jan 5th 2006 Oxford Mark Thomson, Cambridge 9

Example Matches

MC e Best match e Best match NC

Jan 5th 2006 Oxford Mark Thomson, Cambridge 10

Example Matches

MC e Best match e Best match NC

Jan 5th 2006 Oxford Mark Thomson, Cambridge 11

Sanity Check

Good correlation, although matched event tends to be slightly lower in energy (due to finite MC stats)

For MC electron neutrino events look at energy of best match electron neutrino event

Jan 5th 2006 Oxford Mark Thomson, Cambridge 12

First “Results”

e

NC

Although low MC stats – performance good Can’t be perfect as high y CC events look like NC events too early to quote FoM – but looks very promising

m2 = 0.0025 eV2

Take sample of 1000 electron neutrino events Find 10 best matches (from e and NC libraries) Plot fraction of top 10 matches which are true e Repeat for sample of 1000 NC events

Jan 5th 2006 Oxford Mark Thomson, Cambridge 13

Conclusions

Outlook

New idea for electron neutrino appearance analysis Based only on strip information In the limit of infinite statistics this should be OPTIMAL With limited MC statistics have demonstrated basic idea Performance already rather good However will do better:

More MC will allow better matching Currently gang together strips in 3s (due to MC stats) (this degrades performance)

Actively pursuing this analysis Currently generating large MC samples for proper feasibility study (5M e + 10M NC)

approx. 250k/day generated and processed Aim for FoM for next collaboration meeting Aim for full analysis + ND check for Boston

…….. it might just work