The Impossible Experiment
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Incoming energy crucial for your physics
result, but only badly known (~50%)
Beam composition not fully known
Beam diameter ~ 0.5 m at its source
Beamline ~ 300 – 1000 km
Beam diameter ~ 600 m at the detector
Cross sections ~ 10-11 mb
Only a small part of the final state known
Winter Park 2011
Long Baseline Experiments
Soudan Mine,
Nova
770 km
Homestake Mine
Dusel
T2K: JPARC-Kamioka ~ 300 km,
OPERA: CERN –Gran Sasso ~730 km
Winter Park 2011
Long baseline experiments
M. Wascko
Winter Park 2011
Neutrino oscillation search
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neutrino oscillations: probability for 2 flavors:
Ã
P(º¹ !
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º e; t ) = sin 2 2µ sin 2
¢ m2L
!
4E º
Crucial parameter: neutrino energy E
Flux: obtained from Event-Generators
for hadronic production and subsequent
weak decay
Energy must be reconstructed
from hadronic final state
Need to understand ‚classical‘ hadronic interactions
Winter Park 2011
Neutrino nucleon cross section
QE
‚ DIS
¼
N
N'
P. Lipari, Nucl. Phys. Proc. Suppl. 112, 274 (2002)
R+
10-38 cm² = 10-11 mb
QE is used for
energy
reconstruction
Winter Park 2011
Quasielastic scattering
W, Z
axial form factors
• FA  FP and FA(0) via PCAC
• dipole ansatz for FA with
• MA= 1 GeV:
Winter Park 2011
Axial Formfactor of the Nucleon
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neutrino data agree with electro-pion prod. data
MA ¼ 1.02 GeV world average
MA ¼ 1.07 GeV world average
Winter Park 2011
Axial Formfactor of the Nucleon
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Recent Data give significantly larger values for MA
MiniBooNE (2010):
MA = 1.35 GeV
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One difference:
all old data use H (or D) as target
all new data use nuclei (C, O, Fe) as target
Winter Park 2011
MA Problem
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Old neutrino experiments used H and D as
targets
All modern experiments use heavy nuclei
Quasielastic scattering kinematics is used
to reconstruct neutrino energy also in
oscillation experiments
Problem to identify QE on nuclear targets
Winter Park 2011
QE Identification
Need event generator to reduce data to true QE event
Winter Park 2011
GiBUU transport
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what is GiBUU?
semiclassical coupled channels transport model
general information (and code available):
http://theorie.physik.uni-giessen.de/GiBUU/
GiBUU describes (within the same unified theory and code)
 heavy ion reactions, particle production and flow
 Pion, proton and antiproton induced reactions
 low and high energy photon and electron induced reactions
 neutrino induced reactions
……..using the same physics input! And the same code!
Winter Park 2011
CC nucleon knockout: m56Fe  m- N X
p
n
w/o FSI
p
n
w FSI
E = 1 GeV
Winter Park 2011
Detector Types: QE Identification
Cerenkov detector (MiniBooNE, K2K 1kt)
measured
Too high QE: misidentifies
about 20%, pion-induced fakes
Tracking detector (Sci-BooNE, K2K, SciFi)
measured
QE identification is clean, but
30% of total QE cross section is
missed
Winter Park 2011
Detector Sensitivities: T2K
T2K has different detector types:
1. Tracking for near detector
2. Cherenkov for far detector
Near Detector sees only about 50% of all QE events
Winter Park 2011
Energy Reconstruction and
Detector Thresholds
Energy reconstruction sensitive to the detector pion thresholds
Winter Park 2011
Energy reconstruction via CCQE
Rms energy deviations S
~15% energy uncertainty from
quasifree qe kinematics alone
~21% uncertainty for
Cerenkov detectors, error
grows with neutrino energy
~16% uncertainty for
tracking detectors
Errors in reconstructed º energies larger than expected
Winter Park 2011
Energy reconstruction via CCQE
Ã
P(º¹ !
º e; t ) = sin 2 2µ sin 2
¢ m2L
!
4E º
Energy uncertainties affect mixing masses,
Event identification affects mixing angles
Winter Park 2011
±CP with LBNE
Uncertainties at the oscillation maximum due to detector
as large as dependence on CP violating phase
Wilson, LBNE workshop
Event reconstruction hampers determination of CP violating phase
Winter Park 2011
Physics Summary
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Experiments have to rely heavily on event-generators to
identify QE events needed for energy reconstruction
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Quasielastic scattering events contain admixtures of Delta
excitations
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 excitations affect nucleon knockout, contaminate QE experiments
Energy reconstruction good up to 15 – 20%. Combined error
from near and far detectors ~ 20 – 30%. Experiments
want 5%! Challenge for event generators!
Extraction of axial mass (1 GeV) strongly affected by nuclear
structure (RPA correlations), difficult to get
both absolute height and slope.
Winter Park 2011
Need for Low Energy Nuclear Physics
in Neutrino Physics
Low-Energy Nuclear Physics
determines response
of nuclei to neutrinos
Need excellent event generators
To extract fundamental science
Winter Park 2011