1

MiniBooNE Update andExtension Request

Richard Van de Water and Steve Bricefor the MiniBooNE Collaboration

Nov 2, 2007

2Overview

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.”

3track-based analysis:Counting Experiment: 475<E<1250 MeV data: 380 eventsexpectation: 358 19 (stat) 35 (sys)significance: 0.55

oscillation analysis: Results in April 2007

No evidence for e appearance in the analysis region

96 ± 17 ± 20 eventsabove background,for 300< E

QE <475MeV

However, at low energy

Phys. Rev. Lett. 98, 231801 (2007)

4Status of Low Energy e 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.

5Examination of backgrounds reconstructed neutrino energy bin (MeV) 200-300 300-475 475-1250 total background 284±25 274±21 358±35

eintrinsic 26 67 229

induced 258 207 129 NC 0 115 76 62 NC →N20 51 20 Dirt 99 50 17 other 24 30 30 data 375±19 369±19 380±19

• No significant excess at higher E, where

e bkgd dominant.

• Largest backgrounds at lower E are -induced, in particular:

• NC 0

• NC →N• Dirt

New 200-300 MeV bin

Preliminary

6Checking Known e 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 = 1.00±0.15• After box opening (bigger sample) meas/pred =

1.080.12

• 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: arXiv:0710.3897 [hep-ex]

Submitted to PRD

visible energy (GeV) dist to tank wall along track (cm)

7Possible Sources of Additional Single Gamma Backgrounds

• 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

• 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 gis 10 to 30.• Can use photon energy to check prediction.

(Harvey, Hill, and Hill, arXiv:0708.1281[hep-ph])

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

200<En<300 Photonuc adds ~27% of excess300<En<475 Photonuc adds ~13% of excess

Stat error only

Preliminary

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NuMI event composition:

: 81% e: 5% : 13% e:

1% Decay Pipe

Beam Absorber

The beam at MiniBooNE from NuMI is significantly enhanced in e from K decay because of the off-axis position.

MINOS near

NuMI Events in MiniBooNE

MiniBooNE

Work in collaboration with MINOS

9

NuMI and e Samples

Charged Current Quasi Elastic Sample

e Charged Current Quasi Elastic Sample

Results to be presented at an Upcoming Wine and Cheese seminar

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• CC +

– 2 papers expected

• CC 0

– Reconstruction challenges overcome– 1 paper expected

• NC 0

– 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

• -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

Broad Range of Analyses• Collaboration spent last 2 years sole focused on e 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

= PhD Student (4 already graduated, not shown)

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• 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

-- Pauli blocking param

• Paper on this work: arXiv:0706.0926 [hep-ex], submitted to PRL

CCQE Q2 distribution

CCQE E distribution

CCQE Events

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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 ModeMC Prediction:WS-QE: ~2%RS-QE: ~75%Non-QE: ~23%

Anti-Neutrino ModeMC Prediction:WS-QE: ~20%RS-QE: ~50%Non-QE: ~30%

Stat errors only

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NC 0 in Anti-Neutrino Mode

Coherent contribution evident

E(1-COS) (MeV)M (MeV)

Statistical errors onlyNo fit, just out-of-the-box Monte Carlo

This is the worlds only anti-neutrino NC 0 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. “3+N”) 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-e 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-e 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-e 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 e and 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:-

1. The excess is due to nue CC interactions2. The excess is due to a mis-estimation of the numu NC D rate3. 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 67±16.7(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 (45) 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

21

Particle Identification

No major discrepancy in Particle Identification

22NC 0 and Radiative N Backgroundsare Constrained by Identified NC 0 Events

• 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)

M Mass Distribution for Various p0 Momentum Bins

23“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: 1.00±0.15- in different (open) sample, a fit says that meas/pred is 1.080.12.

- Shape of visible E and distance-to-wall distributions are well-described by MC

shower

dirt

results from dirt-enhanced fits

visible energy (GeV) dist to tank wall along track (cm)

76% 0

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Muon Misidentification(including muon internal

bremsstrahlung)

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 MCprediction for almost all the rate at which eventswith a final state muon enter the e background

-Misidentified Muons not a problem.

Paper on this work:arXiv:0710.3897 [hep-ex]Submitted to PRD

25

example signal-candidateevent display

Detector Anomalies or Reconstruction Problems

event/POT vs day, 300<Enu<475 MeV

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

26

energy/angle distributions in E bins

200< E<300 MeV

300 <E<475

MeV

475 <E<3000

MeV

cos cos cos

200< E<300

MeV

300< E<475

MeV

475< E<3000

MeV

At higher energy, data are well-described by predicted background

Excess distributed among visible E, cos bins

visible energy distributions:

cos distributions:

27Other Distributions

UZ, Radius, RtoWall, etc.

=> Events distributed throughout tank, no indication of edge effects.

28

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 people’s shift quota and perhaps take measures like pager shifts for overnight

29

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