10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Zelimir Djurcic Physics Department Columbia University Backgrounds in Backgrounds in neutrino appearance signal at MiniBooNE

10/24/2005 LSND took data from ,000 Coulombs of protons - L = 30m and 20 < E < 53 MeV Saw an excess of  e : 87.9 ± 22.4 ± 6.0 events. With an oscillation probability of (0.264 ± ± 0.045)%. 3.8  significance for excess. Oscillations? Before the MiniBooNE: The LSND Experiment Signal:  p  e + n n p  d  (2.2MeV) Need definitive study of   e at high  m 2 … MiniBooNE

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe magnetic horn: meson focusing decay region:    , K    movable absorber: stops muons, undecayed mesons “little muon counters:” measure K flux in-situ  → e ? 50 m decay pipe magnetic focusing horn FNAL 8 GeV Beamline MiniBooNE detector Search for e appearance in  beam   e ???   e ??? Use protons from the 8 GeV booster  Neutrino Beam ~ 1 GeV 12m sphere filled with mineral oil and 1520 PMTs located 500m from source

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Neutrino Interactions in the Detector e n  e - p We are looking for   e : Current Collected data: 685k neutrino candidates (before analysis cuts) for 6.5 x protons on target (p.o.t.) If LSND is correct, we expect several hundred e (after analysis cuts) from for   e oscillations. - 48% QE - 31% CC  +/- - 1% NC elastic - 8% NC  0 - 5% CC  0 - 4% NC  +/- - 4% multi-  Janet Conrad ’ s talk

10/24/2005 Michel electrons prod from  decay: provide E calibration at low energy (52.8 MeV), good monitor of light transmission, electron PID  0 mass peak: energy scale & resolution at medium energy (135 MeV), reconstruction We have calibration sources spanning wide range of energies and all event types ! 12% E res at 52.8 MeV Energy Calibration cosmic ray  + tracker + cubes: energy scale & resolution at high energy ( MeV), cross-checks track reconstruction provides  tracks of known length → E   e

 0 →  Michel e - candidate beam  candidate beam  0 candidate Čerenkov rings provide primary means of identifying products of interactions in the detector  n   - p e n  e - p  p   p  0 n ring profile → can distinguish particles which shower from those which don ’ t Particle Identification

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Background to e appearance signal Comes from:  ’  -Misidentification of  ’s in charged current  events as electrons. e  -Intrinsic e ’s in  beam.  0  -Misidentification of  0 ’s in neutral current  events as electrons.  -Radiative decays of . Separation of  from e events –Exiting  events fire the veto –Stopping  events have a Michel electron after a few  sec –Also, scintillation light with longer time constant  enhanced for pions and protons (high dE/dx) –Čerenkov rings from outgoing particles Shows up as a ring of hits in the phototubes mounted inside the MiniBooNE sphere Pattern of phototube hits tells the particle type

10/24/2005      e + e   K +   e + e K L  -  e + e Monte Carlo Intrinsic e in the beam e from  decay –Directly tied to the observed  interactions Kaon rates measured in low energy proton production experiments –HARP experiment (CERN) –E910 (Brookhaven) –MiniBooNE Data Small intrinsic e rate  Event Ratio e /   6x10 -3 “ Little Muon Counter ” measures rate of kaons in-situ See Robert Nelson ’ s talk for details !

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Production of the  0 ’s Resonant  0 production  N     N=(p,n)    0 N’ Coherent  0 production  A   A  0  0 →  e appearance:  0 production important because background to  → e signal  0 background In addition to its primary decay  N, the  resonance has a branching fraction of 0.56% to N  final state. if  ’s highly asymmetric in energy or small opening angle (overlapping rings) can appear much like primary electron emerging from a e QE interaction!

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Reconstruction and PID Various algorithms (MLL, ANN, BDT) used to optimize PID, to achieve good: ● Robustness ● Efficiency of PID separation Boosted decision trees: Go through all PID variables and find best variable and value to split events. For each of the two subsets repeat the process Proceeding in this way a tree is built. Ending nodes are called leaves. After the tree is built, additional trees are built with the leaves re-weighted. The process is repeated until best S/B separation is achieved. Reference NIM A 543 (2005) 577.

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Efficiency of PID separation example: muon / electron identification, measured with cosmic ray muons and associated decay electrons, for two PID algorithms under study MuonsElectrons PRELIMINARY PRELIMINARY Neural Network Boosting Decision Tree Boosting PID Algorithm

10/24/2005 Important Cross-check… … comes from NuMI events detected in MiniBooNE detector! See Alexis Aguilar-Arevalo ’ s talk for details ! MiniBooNE Decay Pipe Beam Absorber We get e, ,  0,  +/-, ,etc. events from NuMI inMiniBooNE detector, all Use them to check mixed together Use them to check our e reconstruction and PID separation! Remember that MiniBooNE conducts a blind data analysis! We do not look in MiniBooNE data region where the osc. e are expected … NuMI events serve as gold mine to verify our analysis!

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe Fit to E distribution used to separate background from signal. Look for appearance of e events above background expectation –Use data measurements both internal and external to constrain background rates Signal Mis ID Intrinsic e Appearance Signal Event Class Cross-check K + HARP,LMC,External Data K 0 E910,MiniBooNE Data External Data  MiniBooNE Data  0 NuMI,MiniBooNE Data Other( ,etc) NuMI,MiniBooNE Data

10/24/2005Zelimir Djurcic-PANIC05-Santa Fe MiniBooNE Oscillation Sensitivity  m 2 = 0.4 eV 2  m 2 = 1 eV 2 Oscillation sensitivity and measurement capability –Data sample corresponding to 1x10 21 pot –Systematic errors on the backgrounds average ~5%

At the current time have collected 6.5x10 20 p.o.t. Plan is to “ open the box ” when analysis is ready  Current estimate is not before end of 2005 This leads to the question of the next step –If MiniBooNE sees no indications of oscillations with   Need to run with   since LSND signal was    e –If MiniBooNE sees an oscillation signal  Then ………… (stay tuned). Conclusion and Prospects Background to   e oscillation signal is well understood. Most backgrounds can be constrained with MiniBooNE data. Background will be constrained to allow the signal to be extracted, if present.  Background will be constrained to allow the signal to be extracted, if present.