Download Neutrino Generators and Electron Data

Neutrino Generators and Electron Data
In this talk I will try to summarize work that is being
done to improve existing neutrino Monte Carlos by
tuning them to electron scattering data.
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Hugh Gallagher
[email protected]
Tufts University
CIPANP 2003
NYC
A brief overview of neutrino event generators / neutrino MC physics
Calibration of generators using neutrino data
Electron data as a calibration tool for neutrino MCs
Examples:
PWIA and quasi-free kinematics
Validity of resonance models
DIS / resonance overlap region
Final state re-interactions
Incorporates the work and ideas of many people:
Giles Barr, Omar Benhar, Arie Bodek, Will Brooks, Dave Casper, Eric Hawker,
Thea Keppel, Jorge Morfin, Makoto Sakuda, Steve Wood and Sam Zeller.
Partly a spinoff of the NuINT conference series, which brought together for the
first time nuclear and particle physicists, experimentalists and theorists, to discuss
issues related to low energy neutrino-nucleus cross sections.
Neutrino Event Generators
For neutrino simulations, there is no “industry standard”.
Experiments have tended to write their own, often based on
older codes.
Like most generators, are treated largely as black boxes.
Many in use around the world:
• GENEVE (Icarus)
• JETTA / RESQUE (Chorus)
• NEUGEN (Soudan-2 / MINOS)
• NEUT (SuperK / K2K)
• NUANCE (SuperK / K2K / miniBoone)
• NUX (Icarus / Nomad)
Neutrino Generators
Atmospheric Neutrino Event Rates
NuMI Event Rates on and off axis
(+ high energy tail)
One of the biggest challenges is getting
the physics right over a large range of
energies: 100s of MeV to 100s of GeV.
A. Para, M. Szleper, hepex/0110032
Physics Overview (NEUGEN)
Quasi-Elastic: C.H. Llewellyn-Smith formula in terms of nucleon weak form factors,
vector form factors related to electromagnetic, axial vector form factors measured.
Resonance / single pion production: Rein-Seghal model. Uses the Feynman-KivlingerRavndal model of the nucleon to solve explicitly for the bound states. These are then
identified with the measured resonances and the transition amplitudes are calculated
directly. ~16 resonances in the model, predictions dominated by the D(1232).
DIS: Standard parton model calculation.
Nuclear physics: Modified Fermi Gas Model, nucleons are considered to fill states in a
3-d infinite square well potential. States with p<pF (~220 MeV/c for iron) are filled.
(Actually uses a distribution by Bodek & Ritchie which includes a tail). Also takes
into account Pauli blocking by requiring |q+p|>pF. Intranuclear scattering simulation for p.
Hadronization: based on the KNO model <n> = a + b ln W. JETSET also widely used
for higher energy experiments.
Coherent Production: Rein-Seghal PCAC-motivated prediction.
Generator Physics Overview
Contained Atmos n
100
MINOS
NuTeV
101
102
QEL, RES,
DIS
Predominantly deep
inelastic scattering (DIS)
En(GeV)
Physics
Process:
Primarily
Quasi-Elastic
Target:
Single Nucleon
?
‘free’ quarks
Good: free nucleon
Nuclear Physics..
?
Good: quark parton model
perturbative QCD
Theory:
Data:
Low En bubble
chamber data: ANL,
BNL, Gargamelle
Bubble Chamber:
BNL, ITEP, BEBC
Good: High Statistics
CCFR,NuTeV, CHARM...
Neutrino Data
Much of the data at low energy comes from
low statistics bubble chamber experiments that
ran in the 1960s-1970s.
E ~ 1 GeV:
ANL12’: D2/H2 exposures, n WBB
BNL 7’: D2 ( n WBB) and Neon (n NBB)
CERN: Gargamelle (n propane / freon)
E ~ 10 GeV:
BEBC: H2/D2/Neon exposures (n/n)
FNAL 15’: H2/Ne/D2 exposures (n/n)
In the 30-200 GeV energy range there is high statistics data from a variety of
counter experiments: Nomad, CDHS, CHARM, CCFR, NuTEV.
NC Pion Production
Example: NC pion production at low energies,
an important background for future experiments
searching for sub-dominant nm ne mixing.
n p p0
240 events
n n p+
104 events
n n p0
31 events
n p p-
94 events
Data in the 1-3 GeV range from
Gargamelle (at right),
ANL (<100 events), and
BNL (200 events bc +
~200 events in Al counter
experiment).
New data from K2K and
miniBoone will certainly
produce major advances.
NC
NC
From a re-analysis of Gargamelle data by Eric Hawker
Plots provided by Sam Zeller. http://www.ps.uci.edu/~nuint
Neutrino Data
Existing programs have primarily been
tuned against neutrino data.
Recent work by Sam Zeller to compare all
available generators with all available data:
•Quasi-elastic scattering
•Elastic scattering
•CC Single pion
•NC single pion
•2 pion channels
•Coherent pion production
•Associated strangeness production
•Total cross sections
+ some differential distributions
http://www.dpf2003.org/xx/neutrino/zeller.ps
Has turned up several interesting
disagreements.
Tuning to Neutrino Data
Elastic / quasi-elastic s
GOOD. Form factors…
CVC
Bubble chamber: SKAT
BNL,ANL,GGM, FNAL
Resonance Production /
Single p s
Several different models,
Rein-Seghal is one.
Bubble chamber: SKAT,
BNL,ANL,GGM,FNAL
Deep Inelastic Scattering
GOOD. Parton model.
Many experiments…
Combining 1-3 above to get
stotal?
Variety of models
(emperical vs. dualitymotivated)
Little n data analyzed
inclusively in the overlap
region
Coherent Scattering
Variety of models
(Rein-Seghal, BelkovKopeliovich, Marteau…)
Very little at low energy
Nuclear Physics: initial
state effects (fermi
motion…)
Variety of models: choice
depends on A and En
none
Nuclear Physics: final
state effects(rescattering…)
Variety of models: choice
depends on A and En
Limited.
Neutrino Data
Efforts are underway to re-analyze
old data with new inputs…
nm p  m p
p+
A useful outcome of this work would
be a database of neutrino data
that could be used to quantitatively
test generators.
Requires:
•Correlated systematic errors
•Experimental cuts
•Proper fluxes
Similar issues faced by all attempts
at “global fits”.
Suggestions / volunteers welcome.
nm n  m n p+
nm n  m p p0
Neutrino vs. Electron Scattering
Similarities
Differences
Parton model
Duality holds for DIS/resonance overlap
Probing identical nuclear structure
Identical nuclear final state interactions
g vs. Z/W (1/Q4 propagator)
V vs. V-A currents
Radiative corrections
Similar kinematics (SLAC / JLab)
CLAS is very similar to a n detector
Spectrometers vs. 4p detectors
Precise knowledge of electron beam
Precision on p/E measurements
High statistics vs. low statistics
MCs are used in different ways
Q: How to use electron data to improve our neutrino simulations in a way that takes
advantage of the similarities (nuclei, kinematics) while minimizing the problems due
to the differences (radiative corrections…).
PWIA and Quasi-Free Kinematics
The treatment of kinematics for n-A scattering in
neutrino Monte Carlos has not been particularly
uniform. A variety of theoretical treaments: Fermi
Gas models, shell models, RPA models…
Fermi gas models most commonly used because of
their simplicity and the ease with which they can be
incorporated into Monte Carlos. “Neutrino Reactions
on Nuclear Targets”, Smith and Moniz, Nucl. Phys.
B43, (1979) 350 is one approach.
Take into account 3 of the main nuclear effects:
•Fermi motion of struck nucleon
•Pauli blocking of final states
•Nuclear binding energy
Not all models are easily implementable in Monte Carlos. Many give predictions for A(e,e’) only.
Monte Carlos need to generate events over all of phase space, which often means applying
models beyond their stated ranges of validity!
PWIA and Quasi-Free Kinematics
Quasi-free kinematics have been studied for
many years in electron scattering. The Plane
Wave Impulse Approximation (PWIA) is directly
relevant to neutrino scattering in the same regime.
Description of intial nucleon in terms of a spectral
function S(p,Es) calculated in nuclear many-body
theory with inputs from scattering experiments.
Consistent treatment of kinematics and “off-shell”
cross sections.
O. Benhar et al. Nucl Phys A579
(1994) 493, and talks at NuINT.
standard prescription due to
DeForest (Nucl Phys A392
(1983) 232. )
PWIA and Quasi-Free Kinematics
Generate n NC events at the same kinematics as an electron A(e,e’) experiment.
(in practice, generate a large sample and apply spectrometer-like cuts)
Directly probes details of the nuclear model (fermi motion, binding energy) to the level of 5 MeV.
Weight MC events by the ratio of the electron scattering cross section to the neutrino
scattering cross section for those kinematics.
Use distributions that have radiative corrections already applied.
Compare to data on:
electron energy loss at fixed scattering angle
missing energy
proton transparency (+probe of final state interactions)
Methods applied by Makoto Sakuda (Nucl. Phys. B, Proc. Suppl. 112 (2002) 298 p), and
Steve Wood (http://home.fnal.gov/~dharris/xsec_agenda.html). All the following plots are
from Steve’s work testing NUANCE with 500 MeV data on Mg and Ca (Whitney et al.
PRC, 9 (1974) 2230) and 700 Mev data on Ca (Zeziani et al. PRL 54 (1985) 1233).
PWIA and Quasi-Free Scattering
d2s / dW / dE (10-5 mbarn/(sr-MeV))
Ee = 500 MeV
Data from Whitney et al (PRC 9 (1974) 2230).
d2s / dW / dE (10-5 mbarn/(sr-MeV))
NUANCE with spectometer-like cuts
properly normalized
250
Steve Wood
350
450
E(e’) (MeV)
E(e’) (MeV)
PWIA and Quasi-Free Kinematics
d2s / dW / dE (10-5 mbarn/(sr-MeV))
Ee = 500 MeV
Data from Whitney et al (PRC 9 (1974) 2230).
q2/2M + eB
s ~ kF
250
Steve Wood
350
d2s / dW / dE (10-5 mbarn/(sr-MeV))
NUANCE with spectometer-like cuts
properly normalized
450
E(e’) (MeV)
E(e’) (MeV)
PWIA and Quasi-Free Kinematics
Data on A(e,e’p) also gives information about the modeling of
final state interactions.
0.6 GeV^2
Yield
Nuance
Proton yield relative to q.
1.3 GeV^2
Final State Reinteractions
At low energies, final state interactions in the nucleus have a large effect on the observed
final state. Although neutrino experiments often did use heavy targets, nuclear effects
were generally considered a nuisance to be corrected for rather than a subject of study.
Neutrino Monte Carlos tend to use intranuclear cascade models to determine the effect
of intranuclear scattering of hadrons.
pion multiplicity
From a comparison of D2 and Neon
Bubble chamber exposures at atmospheric
neutrino energies,
(Merenyi et al., PRD45 (1992) 743.)
Pp(abs) = 0.22 +- 0.05
Pp(cex) = 0.10 +- 0.08
3 GeV nm (CC + NC)
black – intranuke off
red – intranuke on
100k events
Final State Reinteractions
From a FLUKA / Peanut simulation shown by P. Sala at NuInt 02
http://www.ps.uci.edu/nuint/slides/Sala.pdf
Final State Reinteractions
Useful electron scattering data:
Spectrometer data:
A(e,e’p) proton transparency on different targets – but also if interest
to us is where the unseen protons turn up (if anywhere).
CLAS data on different nuclei
charged particle multiplicities
pion energy and angle distributions for different A
correlated low-energy particles
angle between q and proton in elastic events
There is a tremendous abundance of data from CLAS that can address these
questions, the issue will be how much of it will be fully analyzed or what can be
tune generators to “raw data” samples.
Conclusions
Electron scattering data in the same kinematic range as current / near future
neutrino experiments provides an opportunity to significantly improve the quality
of our simulations which have been, to this point, tuned on relatively low statistics
neutrino data.
Areas where improvements are possible include:
1. PWIA and quasi-free kinematics
2. Validity of resonance models and resonance / DIS overlap
3. Final state interactions – intranuclear rescattering of hadrons
Work is underway to modify neutrino generators to also produce electron events,
MC samples can then be directly compared to analyzed and published data.
Published data is only the tip of the iceberg, comparisons to unpublished data
may also be possible but would require a dedicated program to understand
detector acceptances, radiative corrections, etc…
Much work to be done and more effort is needed !
Resonance Model