Neutrino Generators and Electron Data

1. 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. Hugh Gallagher gallag@minos.phy.tufts.edu 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.

2. 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)

3. A. Para, M. Szleper, hep-ex/0110032 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.

4. 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-Kivlinger- Ravndal 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. Physics Overview (NEUGEN)

5. Physics Process: Predominantly deep inelastic scattering (DIS) Primarily Quasi-Elastic QEL, RES, DIS Single Nucleon Target: ‘free’ quarks ? Low En bubble chamber data: ANL, BNL, Gargamelle Data: Good: High Statistics CCFR,NuTeV, CHARM... Bubble Chamber: BNL, ITEP, BEBC Generator Physics Overview NuTeV MINOS Contained Atmos n En(GeV) 100 101 102 Good: quark parton model perturbative QCD Good: free nucleon ? Theory: Nuclear Physics..

6. 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) Neutrino Data In the 30-200 GeV energy range there is high statistics data from a variety of counter experiments: Nomad, CDHS, CHARM, CCFR, NuTEV.

7. NC NC NC Pion Production Example: NC pion production at low energies, an important background for future experiments searching for sub-dominant nm ne mixing. 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. From a re-analysis of Gargamelle data by Eric Hawker Plots provided by Sam Zeller. http://www.ps.uci.edu/~nuint

8. 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 • Has turned up several interesting • disagreements. http://www.dpf2003.org/xx/neutrino/zeller.ps

9. Tuning to Neutrino Data

10. nm p  m p p+ nm n  m n p+ nm n  m p p0 Neutrino Data • Efforts are underway to re-analyze • old data with new inputs… • 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.

11. Neutrino vs. Electron Scattering Differences g vs. Z/W (1/Q4 propagator) V vs. V-A currents Radiative corrections 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 • Similarities • Parton model • Duality holds for DIS/resonance overlap • Probing identical nuclear structure • Identical nuclear final state interactions • Similar kinematics (SLAC / JLab) • CLAS is very similar to a n detector 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…).

12. 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!

13. 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. )

14. 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).

15. Ee = 500 MeV Data from Whitney et al (PRC 9 (1974) 2230). NUANCE with spectometer-like cuts properly normalized d2s / dW / dE (10-5 mbarn/(sr-MeV)) d2s / dW / dE (10-5 mbarn/(sr-MeV)) 250 350 450 E(e’) (MeV) E(e’) (MeV) Steve Wood PWIA and Quasi-Free Scattering

16. PWIA and Quasi-Free Kinematics Ee = 500 MeV Data from Whitney et al (PRC 9 (1974) 2230). NUANCE with spectometer-like cuts properly normalized d2s / dW / dE (10-5 mbarn/(sr-MeV)) q2/2M + eB d2s / dW / dE (10-5 mbarn/(sr-MeV)) s ~ kF 250 350 450 E(e’) (MeV) E(e’) (MeV) Steve Wood

17. 0.6 GeV^2 Yield 1.3 GeV^2 PWIA and Quasi-Free Kinematics Data on A(e,e’p) also gives information about the modeling of final state interactions. Nuance Proton yield relative to q.

18. Pp(abs) = 0.22 + 0.05 Pp(cex) = 0.10 + 0.08 - - pion multiplicity 100k events 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. From a comparison of D2 and Neon Bubble chamber exposures at atmospheric neutrino energies, (Merenyi et al., PRD45 (1992) 743.) 3 GeV nm (CC + NC) black – intranuke off red – intranuke on

19. Final State Reinteractions From a FLUKA / Peanut simulation shown by P. Sala at NuInt 02 http://www.ps.uci.edu/nuint/slides/Sala.pdf

20. 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.

21. 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: • PWIA and quasi-free kinematics • Validity of resonance models and resonance / DIS overlap • 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 !

22. Resonance Model