MiniBooNE Low Energy Analysis

H. RayLos Alamos National Laboratory

H. Ray 2

Oscillation Fit Reporting

The final fit for e oscillations was performed using 2 different analysesTrack Based : E

QE 475 MeV to 3 GeVBoosting : E

QE 300 MeV to 3 GeV

Increased from 300 MeV due to 2 fit of 1% in Evis variable during 1st step of unblinding process

H. Ray 3

Oscillation Fit Reporting

We felt that we had checked everything to our full ability, and to our best knowledge could not further constrain processes in the low E region

MC studies of potential LSND oscillation signals indicated we could tighten the E requirement with a negligible loss in sensitivity

Prior to unblinding, we agreed to also examine events with E

QE > 300 MeV in the Track Based analysis

H. Ray 4

Observed Event Distribution

H. Ray 5

Observed Event Distribution

Counting Expt :300 MeV < E

QE< 1.250 GeV749 observed evts631 ± 25 ± 45 expected eventsExcess over background : 2.3

Background-subtracted

475 MeV to 3 GeV

H. Ray 6

Observed Event DistributionBackground-subtracted

475 MeV to 3 GeV

Counting Expt : 300 MeV < E

QE< 475 MeVExcess over background : 3.7

H. Ray 7

Observed Event DistributionBackground-subtracted

Best Fit (sin22, m2) = (1.0, 0.03 eV2)

300 MeV to 3 GeV

Only 4% Compatible w/LSND

Excluded by Bugey!

2 Probability: 18%, Null Hypothesis= 3%

H. Ray 8

What are the Low-E Events?

These low Energy events could be many things

We saw these events for the first time on Monday, March 26th (2007)

The following presents our very preliminary investigations to date

H. Ray 9

Fit Energy Event Composition

Boost Analysis 300 MeV to 3 GeV

Other12%

NCpi018%

Rad. Delta4%

K+26%

Ko6%

Mu+33%

Pi+1%

Other37%

Rad. Delta4%

K+10%

Ko3%

Mu+13%

Pi+0%

NCpi033%

Likelihood Analysis 475 MeV to 3 GeV

intrinsic e

mis-id

H. Ray 10

Low Energy Event Composition

Other30%

NCpi029%

Rad. Delta18%

K+5%

Ko1%

Mu+17%

Pi+0%

Other28%

Rad. Delta18%

K+7%

Ko2%

Mu+19%

Pi+0%

NCpi026%

Boost Analysis 300 MeV to 475 MeV

Likelihood Analysis 300 MeV to 475 MeV

intrinsic e

mis-id

H. Ray 11

Fundamental Information

Shutdowns

Low E events show no bias in event time

369 events 369 events

Not normalized to POT

H. Ray 12

Cosmic RaysMeasured from our strobe data

Cosmic events populateupper region of tank

Low E events show no bias in Y (vertical) position

2 expected evts in osc. analysis

369 events

H. Ray 13

Radiative Delta and NC0

Constrain our NC0

production rate using data from our detector Reduces error on mis-id 0 (<2%!)

This also constrains the radiative resonance rate, thus constraining rate of N

H. Ray 14

What we know so farLow E events pass EM Particle ID

Gamma or electronThe evts do not appear to be biased in

run range or event timeThe evts do not appear to be due to

cosmic ray backgroundRadiative Delta : unlikely = need x3

increase NC0 : unlikely = measure very well with

our data

H. Ray 15

SummaryA two-neutrino appearance only

model systematically disagrees with the shape of the excess as a function of E

Need to investigate non-oscillation explanations of the low E excess

Investigation of these low E events is underway

H. Ray 16

Final Results

Any conclusions drawn about the low E events will have no effect on our oscillation result