MiniBooNE Update and Extension Request

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MiniBooNE Update andExtension Request

• Richard Van de Water and Steve Brice
• for the MiniBooNE Collaboration
• Nov 2, 2007

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Overview

1. Brief reminder of oscillation result
2. Update on low energy excess
3. Sampling of other analyses
4. Run request for an electron anti-neutrino
   appearance search

MiniBooNE requests an additional 3.0 x 1020 POT
in anti-neutrino mode to give the experiment a
total of 5.0 x 1020 POT in this configuration
and enable a powerful check of the LSND result in
anti-neutrinos. The experiment further requests
that these POT be delivered in FY2008 and FY2009.
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oscillation analysis Results in April 2007
track-based analysis Counting Experiment
475ltE?lt1250 MeV data 380
events expectation 358 ?19 (stat) ? 35
(sys) significance 0.55 ?
Phys. Rev. Lett. 98, 231801 (2007)
No evidence for ?????e appearance in the
analysis region
However, at low energy
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Status of Low Energy ne Candidate Analysis Since
Oscillation Publication

• Have observed a 4 sigma excess down to 200 MeV
  (including systematic errors).
• Confirmed excess is electromagnetic (electron or
  gamma-ray), i.e. particle ID is working at low
  energy. MiniBooNE has no ability to distinguish
  gammas from electrons
• Events have normal reconstruction, e.g. Visible
  energy, radius, x,y,z, beam angle, etc.
• Major sources of backgrounds all look well
  modelled, e.g. dirt, radiative delta decay,
  mis-ID pions and muons.
• Working on possible new sources of single
  gamma-rays.
• Currently analyzing neutrinos from NuMI source,
  horn-off, and anti-neutrino data sets.

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Examination of backgrounds
reconstructed
neutrino energy bin (MeV)
200-300 300-475
475-1250 total background????? 28425
27421 35835 ????eintrinsic
26 67
229 ????? induced 258
207 129
NC ?0 115
76 62 NC
??N??????????????????????20 51
20 Dirt
99 50
17 other 24
30 30 data
37519 36919
38019

• No significant excess at higher E, where??e bkgd
  dominant.
• Largest backgrounds at lower E are ??-induced,
  in particular
• NC ?0
• NC ??N??
• Dirt

Preliminary
New 200-300 MeV bin
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Checking Known ne Backgrounds

• Measure ?0 production rate as a function of ?0
  momentum and compare to MC prediction to
  calculate a correction factor. Correct NC ??
  mis-ID rate using this measured correction factor
• (Also can be used to correct the ??? N ?
  radiative background)
• Dirt background is due to ? interactions outside
  detector creating neutrals that enter tank
• Measured in dirt-enhanced samples
• Before box-opening meas/pred 1.000.15
• After box opening (bigger sample) meas/pred
  1.08?0.12
• Backgrounds with a muon measured using events
  with cleanly time separated electron from muon
  decay
• Includes any background from muon internal
  bremsstrahlung
• Paper on this work arXiv0710.3897 hep-ex
  Submitted to PRD

visible energy (GeV)
dist to tank wall along track (cm)
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Possible Sources of Additional Single Gamma
Backgrounds
Since MiniBooNE cannot tell an electron from
a single gamma, any process that leads to a
single gamma in the final state can be a
background
Preliminary

• Processes that remove/absorb one of the gammas
  from a ??-induced NC ?0 ? ??
• Photonuclear absorption was missing from our
  GEANT3 detector Monte Carlo
• But tends to give extra final state particles.
• Reduces size of excess
• Systematics being calculated
• No effect above 475 MeV

Stat error only
200ltEnlt300 Photonuc adds 27 of
excess 300ltEnlt475 Photonuc adds 13 of excess

• ? processes that produce a final state single
  gamma
• Example Anomaly mediated neutrino-photon
  interactions at finite baryon density.
• Standard Model process
• ? Under active investigation, prediction of
• 140 (g?/10)4 events, where g? is 10 to 30.
• Can use photon energy to check prediction.(Harvey
  , Hill, and Hill, arXiv0708.1281hep-ph)

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NuMI Events in MiniBooNE
Work in collaboration with MINOS
NuMI event composition ?? 81 ?e 5 ???
13 ??e 1
MiniBooNE
?
Decay Pipe
Beam Absorber
MINOS near
The beam at MiniBooNE from NuMI is significantly
enhanced in ?e from K decay because of the
off-axis position.
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NuMI nm and ne Samples
nm Charged Current Quasi Elastic Sample
ne Charged Current Quasi Elastic Sample
Results to be presented at an Upcoming Wine and
Cheese seminar
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Broad Range of Analyses

• Collaboration spent last 2 years sole focused
  on ne appearance analysis
• Collaboration retasked over last 5 months to
  broad range of analyses
• No organizational separation between neutrino
  and anti-neutrino mode
• 15 PhD Students 4 graduated

• CC p
• 2 papers expected
• CC p0
• Reconstruction challenges overcome
• 1 paper expected
• NC p0
• 1 paper about to be submitted to PRD
• Coherent/resonant in nu and anti-nu modes
• Flux averaged cross-section measurement
• 2 further papers expected
• NC Elastic
• About to graduate
• Flux averaged cross-section measurement
• 1 paper expected
• nm-e Elastic
• Nu mag. Mom
• 1 paper expected.

• Oscillation
• Refined Nue appearance
• Nuebar appearance
• Numu and numubar disappearance
• 1 PRL, 3 further papers expected
• Low Energy Excess
• Big effort
• 2 papers expected
• Alternative Oscillations
• Phenomenology
• CP violation, Lorentz violation, ...
• 3 papers expected
• NuMI Events
• Large event rate from NuMI beam
• Check on osc. and Low E
• 1 paper being written
• CCQE
• 1 paper submitted to PRL
• 2 further papers expected

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CCQE Events
nm CCQE Q2 distribution

• Excellent description of ?? CCQE reaction has
  been obtained after adjustment of 2
  Fermi-gas-model parameters
• From Q2 (4-mom. transfer) fits to ?? CCQE data
• MAeff -- Effective axial mass
• k -- Pauli blocking param
• Paper on this work arXiv0706.0926 hep-ex,
  submitted to PRL

nm CCQE En distribution
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Wrong Sign Extraction

• Critical to extract neutrino flux in
  anti-neutrino mode from data and not rely
  entirely on MC
• Use angular distribution of muons from CCQE
  interaction
• All anti-nu analyses depend on this work

Neutrino Mode MC Prediction WS-QE 2 RS-QE 75
Non-QE 23
Anti-Neutrino Mode MC Prediction WS-QE 20 RS-Q
E 50 Non-QE 30
Stat errors only
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NC p0 in Anti-Neutrino Mode
Statistical errors only No fit, just
out-of-the-box Monte Carlo
Coherent contribution evident
Mgg (MeV)
Ep(1-COSqp) (MeV)
This is the worlds only anti-neutrino NC p0
sample below 2 GeV
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MiniBooNE Present and Future

• Taken 5.58 x 1020 POT in neutrino mode
• Making suite of cross-section measurements
• Also searching for neutrino disappearance
• Publications already coming out
• No need to request more neutrino mode running
• Taken 2.33 x 1020 POT in anti-neutrino mode
• Making suite of cross-section measurements
• Searching for anti-neutrino disappearance
• PAC request for extra running for an anti-nue
  appearance search
• LSND result was an indication of anti-nue
  appearance
• CP violating models (e.g. 3N) predict no MB
  signal in neutrino mode, but LSND style signal in
  anti-neutrino mode
• Extra 3 x 1020 POT (making grand total of 5 x
  1020 POT)
• Should take FY2008 and FY2009 running

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Calculating anti-ne Appearance Sensitivity

• Two key features of neutrino mode oscillation
  result
• Backgrounds measured or constrained by MiniBooNE
  data
• Systematics estimated by assessing uncertainty in
  all relevant low level quantities (e.g. pion
  production, detector optical model, etc) and
  propagating these to an error matrix on the final
  histogram.
• This approach carries over directly to an anti-ne
  measurement
• i.e. the vast majority of the work has already
  been done
• Just need to turn the crank on the anti-neutrino
  MC and propagate error matrices to produce
  complete anti-ne sensitivity
• Full set of low level systematics has already
  been assessed
• The major differences from neutrino mode analysis
  are handled automatically
• For example larger wrong sign background in ne
  and nm samples

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Anti-nue Appearance Sensitivity
Region allowed at 90 C.L. by joint analysis of
LSND and KARMEN
Only anti-neutrinos allowed to oscillate
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Conclusion and Request

• MiniBooNE is bringing out a wide range of
  important results in neutrino and anti-neutrino
  oscillation and cross-section physics.
• MiniBooNE requests an additional 3.0 x 1020 POT
  in anti-neutrino mode to give the experiment a
  total of 5.0 x 1020 POT in this configuration
  and enable a powerful check of the LSND result in
  anti-neutrinos. The experiment further requests
  that these POT be delivered in FY2008 and FY2009.

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BackUp Slides
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Anti-Neutrino Low Energy Excess Scenarios

• Predictions for the excess of nue(bar) candidate
  events in anti-neutrino mode under 3 scenarios-
• The excess is due to nue CC interactions
• The excess is due to a mis-estimation of the numu
  NC D rate
• The excess is due to some other NC process whose
  cross-section is the same for neutrinos and
  anti-neutrinos
• With 5.0 x 10 20 POT in anti-neutrino mode the
  excesses in these scenarios are not significantly
  different from each other
• Alternatively if one naively scales the neutrino
  mode excess down by the ratio of anti-neutrino
  mode to neutrino mode backgrounds then one
  predicts an excess of 6716.7(sys)16.4(stat) for
  5.0 x 1020 POT.

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CP Violating Models

• Adding two (or more) sterile neutrinos brings a
  CP violating phase (f45) into the mixing matrix
• Fits of such models to world data allow the
  possibility for MiniBooNE to see no signal in
  neutrino mode, but a visible signal in
  anti-neutrino mode

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Particle Identification
No major discrepancy in Particle Identification
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NC ?0 and Radiative ??N? Backgroundsare
Constrained by Identified NC ?0 Events
M?? Mass Distribution for Various p?0 Momentum
Bins

• Using PID variables isolate a very pure sample ?0
  events from ?????N ? ???? N ?0 (mainly from
  ??? N ?0 )
• Purity 90 or greater
• Measure ?0 production rate as a function of ?0
  momentum and compare to MC prediction to
  calculate a correction factor.
• Correct NC ?? mis-ID rate using this measured
  correction factor(Also can be used to correct
  the ??? N ? radiative background)

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Dirt background
- Dirt background is due to ? interactions
outside detector creating neutrals that enter
tank - Measured in dirt-enhanced samples -
before box-opening, fit predicted 1.000.15 -
in different (open) sample, a fit says that
meas/pred is 1.08?0.12. - Shape of visible E
and distance-to-wall distributions are
well-described by MC
results from dirt-enhanced fits
76 ?0 ? ??
dist to tank wall along track (cm)
visible energy (GeV)
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Muon Misidentification(including muon internal
bremsstrahlung)
-Misidentified Muons not a problem.
Paper on this work arXiv0710.3897
hep-ex Submitted to PRD
Data-MC excess, but note the scale!
Apply reconstruction and particle identification
to clean sample muon CCQE events (muon decay
visible). Then scale normalization to account
for how often the second subevent is
missing What results is a direct measurement and
MC prediction for almost all the rate at which
events with a final state muon enter the ne
background
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Detector Anomalies or Reconstruction Problems
No Detector anomalies found - Example rate of
electron candidate events is constant (within
errors) over course of run
No Reconstruction problems found - All low-E
electron candidate events have been examined
via event displays, consistent with 1-ring
events
Signal candidate events are consistent with
single-ring neutrino interactions ? But
could be either electrons or photons
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energy/angle distributions in En bins
475 ltEnlt3000 MeV
300 ltEnlt475 MeV
200lt Enlt300 MeV
visible energy distributions
200lt Enlt300 MeV
475lt Enlt3000 MeV
300lt Enlt475 MeV
cos q distributions
At higher energy, data are well-described by
predicted background
Excess distributed among visible E, cos q bins
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Other DistributionsUZ, Radius, RtoWall, etc.
gt Events distributed throughout tank, no
indication of edge effects.
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Logistics

• Survey of collaborating institutions on ability
  to staff shifts in new two years
• Recent past 54 FTE
• FY2008 44 FTE
• FY2009 37 FTE
• FY2008 shared with SciBooNE so filling shifts
  should not be an issue
• FY2009 will need to increase peoples shift quota
  and perhaps take measures like pager shifts for
  overnight

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Sensitivity Over LSND Only Regions
Regions allowed at 90 C.L. And 95 C.L. by LSND
alone
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Effect of Statistics and Systematics
Regions allowed at 90 C.L. And 95 C.L. by LSND
alone