Current Knowledge ofNeutrino Cross-Sections

and Future Prospects

D. CasperUniversity of California, Irvine

OutlineWhy do we care?What do we know from past experiments?What are current experiments telling us?Outlook for future experiments

Neutrino Oscillation: GoalsProbe fundamental parameters of Standard Model:

Precision measurement of |m223|

Precision measurement of 23

Measurement of unknown angle 13

Determination of mass hierarchy sgn(m223)

Search for leptonic CP violating phase Measurements involve probabilities

Need number of oscillated neutrinos and number of starting neutrinos

Next generation experiments, starting with MINOS, will have impressive statistical power from high luminosity beams and massive detectors

Systematic uncertainties must be controlled at a level comparable to the statistical errors to take full advantage

12

312

3

“Normal” “Inverted”

Expt. DatesBeamPower(MW)

Det.Mass(kt)

K2K1998-2005

0.005 22.5

MINOS 2005+ 0.25 3.3

J-PARC I 2008+ 0.7 22.5

NOA ? 0.4 ~35

Neutrino Oscillation: Requirements

Neutrino energy resolution for CC interactions

K2K/T2K: Quasi-elastic channelMINOS/NOA: Calorimetry (Evis E)

Control energy-scale systematics for high E-resolution sample at few percent level

EfficiencyContamination

Control near/far beam flux and energy spectrum differences at few percent levelControl background for e appearance signature at few per-mille level

Beam e, CC, NC contributionsControl neutrino/anti-neutrino systematics at percent level for mass hierarchy and CP studies

C. Walter, NUINT02

K2K

NOA(13 nearCHOOZ bound)

NormalHierarchyInverted

Hierarchy

Neutrino Oscillation: RealitiesOnly well-known neutrino interaction cross-section is for electron scattering

Unfortunately useless for oscillation experiments with accelerators

Available data for few-GeV reactions:Old (Early ’70s to mid 80’s)

Normalized to quasi-elastic measurements, using obsolete form factor parameters, and introducing complicated correlated errorsBeam spectrum and flux based on dubious hadron production modelsUndocumented and inconsistent corrections for nuclear targets

SparseEnergy, hadronic mass reach limitedNuclear targets not applicable to common detector materialsAlmost no data on > 1 exclusive channelsAnti-neutrino data even worse

Low-statisticsNeutral current 1 data based on a few dozens of events

Mutually inconsistent

What About a Near Detector?Near detectors are important, but not a panacea flux and spectrum differs far vs. near

Not identical even without oscillation, due to extended sourceCC backgrounds and contamination extrapolate differently than NC+beam, due to oscillationOptimal sensitivity dictates that far detector is at oscillation maximum, making the difference as large as it can be

Near/Far detectors usually not identicalFar detector must be large, coarse-grainedIf identical, near detector has similar resolution and not suited to measure cross-sectionsK2K/T2K solution: two near detectors…

Maximum physics reach requires:Near detector similar in composition, performance and resolution to far detectorGood model/measurements of parent hadron beamGood understanding of exclusive neutrino cross-sections

NOAP()

Nuance

K2K Near Detectors

Extrudedscintillator(15t)

Multi-anodePMT (64ch)

Wave-lengthshifting fiber

EM calorim

eter

1.7m

3m

3m

SciBar SciFi

E (GeV)

MiniBooNE

(H. Tanaka, WG2)

CC Quasi-Elastic ScatteringDominant reaction up to ~1 GeV energyEssential for E measurement in K2K/T2KThe “well-measured” reaction

Uncertain to “only” 20% or so for neutrinosWorse in important threshold region and for anti-neutrinos

Axial form-factor not accessible to electron scattering

Essential to modeling q2 distributionRecoil proton reconstruction requires fine-grained design - impractical for oscillation detectorsRecent work focuses on non-dipole form-factors, non-zero Gn

E measurements

K2K and MiniBooNE CCQE RatesK2K and MiniBooNE rates agree with MC for CCQEOnly shape is measured, not absolute cross-sections

Same data is used to measure the neutrino flux!

K2K SciBar2-ring QE(70% purity)

MiniBooNE

(88% purity)

CC Resonant Single-Pion Production

Existing data inconsistent (factor 2 variations)Treatment of nuclear effects unclearRenewed theoretical interest with JLAB data

Sato et al. Dynamical Model

K2K/MiniBooNE CC Pion Production

1-kton: Study of 0 proton decay backgroundMiniBooNE: 85% purity for CC ± sample(no results, in progress)

1-kton0 candidates

Normalizedto total events

NC Single-Pion ProductionHistorical samples of NC single pion production:

ANL p n + (7 events) n n 0 (7 events)

Gargamelle p p 0 (240 evts) n n 0 (31 evts)

Crucial background for e appearance searches!

K2K/MiniBooNE NC 0 ProductionK2K(Preliminary)

( )( ) ( )

( )( )

0

0

K2K 1-kton cross-section measurement:

(NC 1 )0.065 0.001 stat 0.007 syst

(NC 1 )0.064 NEUT

For K2K beam spectrum ( E =1.3 GeV)MC

CC

CC

m

m

n

s p

s n

s p

s n

= ± ±

=

MiniBooNE:Shape comparison only

Deep-Inelastic ScatteringOne area with lots of data and a clear theoretical framework, but uncertainties remain:

Nuclear effects?Low-q2 regimeConnection/overlap with resonant production

Quark/Hadron DualityRecent JLAB data have revived interest in quark/hadron dualityBodek and Yang have shown that DIS cross-sections can be extended into the resonance regime, and match the “average” of the resonant cross-section

Bodek and Yang

Nuclear Effects (QE/Resonant)

1ktonSciFi

SciBar MiniBooNE

All currently running detectors seeanomalous suppression at low-Q2

One anomaly or two?

Nuclear Effects (DIS)

0.7

0.8

0.9

1

1.1

1.2

0.001 0.01 0.1 1

EMCNMCE139E665

shadowing

original

EMC finding

Fermi motion

x sea quark valence quark

-

LH on

LH off

+

Hadron formation lengtheffects

E = 5 GeV(NEUGEN)

Bound nucleon structure functions

Final-State Interactions

Renewed theoretical interest, plus new data from JLAB

NEUTMC

“Hope is on the way…”HARP data (next talk)

Hadron production measured with K2K, MiniBooNE targets at CERNWill provide essential data for neutrino fluxes, aid absolute cross-section measurements

MINERA at NuMI (2006?)T2K Near Detectors (2009?)

280m: Fine-grained (design not finalized)2km: Water Cherenkov + fine-grained (not yet approved)Potential to measure cross-sections around few GeV, if independent flux prediction available

MINERA at a GlanceScintillating strip design leverages DZERO, K2K, MINOS experience

Modular construction, good spatial resolution, 3d-tracking, fast timing and dE/dx measurement at attractive cost

Fully-active central volume surrounded by magnetized “calorimeters”

Inner fiducial mass > 3 tonsIron + Lead planes upstream to vary nuclear target

Parasitic operation within current NuMI/MINOS run-plan yields 1.25M neutrino events/ton

Broad neutrino energy reachMINOS near detector can substitute for downstream muon rangerMIPP will measure NuMI hadron production within ~few percent, allowing precision absolute cross-section measurements

MINERA CCQE Measurements

Full simulated analysis, including realistic detector simulationand reconstruction

MINERA Resonant Pion Production

Errors statistical only, assuming 50% efficiency

Coherent Pion ProductionNeutral-current reaction important background for e appearance search

Realistically, 100% uncertainties in rate for oscillation experimentsTheoretical models vary significantlyCC reaction (easier to measure) closely related to NC

No data on light nuclei in energy region of relevance

K2K and MiniBooNE may help at low energies, but NC background to e appearance feeds down from high energiesEasier to distinguish with proton reconstruction and (for CC reaction) dE/dx

MINERASimulatedMeasurements

ConclusionsFew-GeV neutrino interaction physics is (finally) leaving the “Dark Ages”Multiple, synergistic lines of attack are beginning to peel back our ignorance:

Data from K2K and MiniBooNEElectron scattering dataHEP/Nuclear collaboration (NUINT workshops)Revived theoretical attention to different questions

MINERA and T2K can provide another quantum leapIndependent knowledge of fluxes are vital for absolute measurements

Continued progress on cross-sections will be invaluable for future oscillation experiments