GENIE Low Energy

Hi,

I have committed classes to the VLE package which allow inverse beta decay events to be generated using the standard gEvGen.exe.

Before they can be used, some of the global configuration files must be editted (in order to add the IBD Event Generator). I want to check with Constantinos before committing these. I will add a comment to this entry when the configurations have been committed to CVS.

The only other outstanding issue is that there is a hard-coded cutoff on the minimum neutrino energy of 10 MeV when GENIE makes the cross section splines. This issue is being discussed with Costas and will be resolved soon(ish).

Eliminating this cutoff at 10 MeV produces very nice results. Here are some plots, where I've used the neutrino flux given in Eqn 26 of Strumia, with the supernova distance and total energy corresponding to SN1987A (D=51.4 kpc, Etot=3e53 ergs).

Here is the positron energy distribution (compare to Fig 2a of Strumia):

Positron Energy Distribution

Here is the positron angular distribution (compare to Fig 2b of Strumia):

Positron Angular Distribution

As a sanity check, the following plot shows the initial state neutrino energy distribution in green (arbitrary units). This is compared to the neutrino flux (in blue, the functional form from Strumia, and in black circles, the histogrammed flux used internally by GENIE) as well as to the IBD cross section.

And the longitudinal positron momentum as a function of the neutrino energy:

Longitudinal Positron Momentum vs Neutrino Energy

These results can be compared to those coming from the default GENIE with the 10 MeV cut in place:

Neutrino Energy Distribution with 10 MeV cut

Longitudinal Positron Momentum vs Neutrino Energy with 10 MeV cut

Positron Energy Distribution with 10 MeV cut

Positron Angular Distribution with 10 MeV cut

Finally, the cross section spline file including the IBD can be obtained here:

Download ibd_xsec_splines.xml

This contains 200 knots over the of 1 to 400 MeV for both IBD and the inverse reaction.

These splines can be viewed in the following plots. Note that the default quasi-elastic cross section which was already in GENIE already did quite a good job at calculating the cross section! The trick will be getting the neutrino - nucleus xsec's...

IBD Cross Section Splines

The StrumiaVissaniIBDPXSec class has (finally) been committed to GENIE. This class calculates the inverse beta decay cross section based on the Strumia/Vissani paper.

In order to test it, a full update of GENIE must be done, since some of the code outside the VLE package has been modified. On the bright side, GENIE will use a very low Q2 integration minimum for inverse beta decay, so the S-V xsec should be quite accurate.

To update,

cd $GENIE
cvs udpate -P -d
make
cd src/VLE
make

To test the code, you can use the following macros:

loadlibs.C To load the libraries (change the xml2 and log4cpp lines as necessary).

testXsec.C To run the xsec code (run it in un-compiled mode).

drawXsec.C To make the plots from my previous entry.

Coming soon: the code to make a complete IBD event and a bit of documentation on how to go about adding a cross section.

So, I am still a little slow in getting code written for GENIE, I think there are still a few gray areas for me to work out. However, like Corey, I have provided a few nifty plots. Speaking of Corey, if you have successfully added your code to genie, would you be so kind as to send me a brief description of your work?

Getting my information from two papers:

http://arxiv.org/abs/hep-ex/0105068 (LSND Collaboration)

http://arxiv.org/abs/nucl-th/9903022 (K.L.V.)

Experimentally measured values of the exclusive C12(Nue,e-)N12g.s. (that's ground state) reaction, gathered by the LSND Collaboration, match well with K.L.V.’s calculated cross-calculation of the same final ground state reaction. Using the same Random Phase Approximation method K.L.V. has calculated the total cross-section for C12(Nue,e-)N12, which is comparable to GENIE.

GENIE's cross-section for GEVGL=CC -p Nue -t C12, matched with K.L.V.'s total and exclusive cross-section calculations. As an added bonus, I have included the measured values for the exclusive reaction from the LSND Collaboration:
http://minos.phy.tufts.edu/Blogs/GENIELowEnergy/60.60.ps.jpg

Made a correction to this plot, sorry.
http://minos.phy.tufts.edu/Blogs/GENIELowEnergy/compareLast.ps.jpg

http://minos.phy.tufts.edu/Blogs/GENIELowEnergy/Log.140.3.ps.jpg (log version)

http://minos.phy.tufts.edu/Blogs/GENIELowEnergy/2.140.190.ps.jpg (extended version)

http://minos.phy.tufts.edu/Blogs/GENIELowEnergy/1.Log.1000.5.ps.jpg (log extended version)

The neutrino - nucleon cross sections have been coded up and will be added to the VLE directory of GENIE soon (just need CVS permissions).

There are still some open issues. While waiting for responses on them, I thought it would be useful to show the current status. When the issues get resolved, I will plan to document the making of this class, in case it may be helpful to others.

Current cross section calculations:

or on log scale:

View cross sections on log scale.

The IBD x-sec agrees very well with the table displayed in the paper:

View ratio of IBD cross section: GENIE to values in the paper.

However, this agreement is only achievable with:

• The proton anomalous magnetic moment being 1.793, as given in the paper. PDG (and GENIE) have k_p = 2.793. I have emailed Strumia regarding this issue, but so far haven't received a response. Update: After talking with the authors, the parameter used is the anomalous magnetic moment, which is k_p-1 for the proton (and k_n for the neutron).
• The minimum q^2, used for the integral to calculate the total cross section, is limited in GENIE to not be smaller than 10^-4. For the plots above, this limit had been changed to 10^-10.

The limit of q^2 >= 10^-4 (default in GENIE) can cause some trouble for very low energy neutrinos:

View ratio (GENIE to paper) with default q^2 >= 10^-4

I've contacted Constantinos to talk about possible solutions.

Here are some links to relevant cross-section papers.

General

Neutrino–electron scattering theory
William J Marciano and Zohreh Parsa

http://iopscience.iop.org/0954-3899/29/11/013

Precise quasielastic neutrino/nucleon cross section
Alessandro Strumia, Francesco Vissani

http://arXiv.org/abs/astro-ph/0302055

Neutrino nucleus cross sections for low energy neutrinos at SNS facilities
M. Sajjad Athar, Shakeb Ahmad, S.K.Singh

http://arxiv.org/abs/nucl-th/0506046

Neutrino-nucleus reactions and nuclear structure
E Kolbe, K Langanke, G Martínez-Pinedo and P Vogel

http://iopscience.iop.org/0954-3899/29/11/010/

Carbon

Neutrino C-12 reactions and the LSND and KARMEN experiments on neutrino oscillations.
C. Volpe, N. Auerbach, G. Colo, T. Suzuki, N. Van Giai, (Orsay, IPN & Tel Aviv U. & Milan U. & Nihon U., Tokyo) .

http://www.springerlink.com/content/9v5883v7t742w4p4/

Inclusive C-12(nu/mu,mu)N-12 reaction in the continuum random phase approximation.
E. Kolbe, F.K. Thielemann, (Basel U.) , K. Langanke, P. Vogel, (Caltech)

http://prola.aps.org/abstract/PRC/v52/i6/p3437_1

Weak reactions on C-12 within the continuum random phase approximation with partial occupancies.
E. Kolbe, (Basel U.) , K. Langanke, (Aarhus U.) , P. Vogel, (Caltech) .

http://dx.doi.org/10.1016/S0375-9474(99)00152-9

Argon

Neutrino Capture Cross Sections for Ar-40 and beta-decay of Ti-40
W.E. Ormand, P.M. Pizzochero, P.F. Bortignon, R.A. Broglia

http://arxiv.org/abs/nucl-th/9405007

nu/e (anti-nu/e) - Ar-40 absorption cross sections for supernova neutrinos
M. Sajjad Athar, S.K. Singh

http://dx.doi.org/10.1016/j.physletb.2004.04.025

Supernova Neutrino Detection in a liquid Argon TPC
A. Bueno, I. Gil-Botella, A. Rubbia

http://arXiv.org/abs/hep-ph/0307222

Oscillation effects on supernova neutrino rates and spectra and detection of the shock breakout in a liquid argon TPC
I. Gil-Botella and A. Rubbia

http://iopscience.iop.org/1475-7516/2003/10/009/

Neutrino absorption efficiency of an 40Ar detector from the β decay of 40Ti
M. Bhattacharya et al.

http://prc.aps.org/abstract/PRC/v58/i6/p3677_1

Inverse β- decay of 40Ar: A new approach for observing MeV neutrinos from laboratory and astrophysical sources
R. Raghavan
http://prd.aps.org/abstract/PRD/v34/i7/p2088_1

Oxygen

Nuclear response of water Cherenkov detectors to supernova and solar neutrinos
W.C. Haxton

http://prd.aps.org/abstract/PRD/v36/i8/p2283_1

Weak Interaction Rates in 16-O
W.C. Haxton

http://prl.aps.org/abstract/PRL/v65/i11/p1325_1

Estimates of weak and electromagnetic nuclear decay signatures for neutrino reactions in Super-Kamiokande
E. Kolbe, K. Langanke, P. Vogel

http://prola.aps.org/abstrac/PRD/v66/i1/e013007

Signal for Supernova νμ and ντ Neutrinos in Water Čerenkov Detectors
K. Langanke, P. Vogel, and E. Kolbe

http://prl.aps.org/abstract/PRL/v76/i15/p2629_1

Iron, lead

The role of $\nu$-induced reactions on lead and iron in neutrino detectors
E. Kolbe, K. Langanke

http://arXiv.org/abs/nucl-th/0003060

Supernova neutrino induced reactions on iron isotopes.
J. Toivanen, E. Kolbe, K. Langanke, G. Martinez-Pinedo, P. Vogel

http://dx.doi.org/10.1016/S0375-9474(01)00992-7

Coherent elastic neutrino-nucleus scattering:

Supernova observation via neutrino - nucleus elastic scattering in the CLEAN detector.
Charles J. Horowitz, K.J. Coakley, D.N. McKinsey

http://arxiv.org/abs/astro-ph/0302071

DATA

Measurement of the weak neutral current excitation C-12(nu(mu) nu'(mu))C*-12(1+,1,15.1-MeV) at E(nu(mu)) = 29.8-MeV.
By KARMEN Collaboration (B. Armbruster et al.).

http://dx.doi.org/10.1016/S0370-2693(98)00087-2

Measurements of charged current reactions of muon neutrinos on C-12.
By LSND Collaboration (L.B. Auerbach et al.).

http://arXiv.org/abs/nucl-ex/0203011

Measurements of charged current reactions of nu(e) on 12-C.
By LSND Collaboration (L.B. Auerbach et al.).

http://arXiv.org/abs/hep-ex/0105068

Notes from the June 18 phone meeting :

In attendance: Kate Scholberg, Alec Habig, Corey Reed, Costas Andreopoulos, Cully Little, Hugh Gallagher, Diane Markoff, Ryan Schmidt

A: Goals of the project and summary of interaction channels (Kate)

Goals of the project: To make GENIE useful for supernova, reactor, and stopped pion beam experiments.

Interaction channels of interest (in order of descending priority):

1) Inverse beta decay. Well known cross section, including electroweak corrections (e.g. Strumia and Vissani).

2) Elastic scattering on electrons (already in GENIE).

3) CC and NC reactions on O16 and C12. Theory predictions good to around 20%.

4) CC and NC on Argon.

5) Coherent elastic scattering. Theoretically straightforward.

6) CC and NC on heavy nuclei (eg. Cl, Fe, Pb).

B: Extending GENIE (Costas)

Recommends reviewing the NIM paper for an overview of the GENIE architecture. Suggests starting with a simple channel - inverse beta decay. Extending GENIE means creating a new event generation thread. For an example of an event generation module of comparable simplicity, review the code in the ${GENIE}/src/NuGamma directory.

Adding a new interaction type involves three new classes, which handle:
*) the cross section calculation
*) the event generation module (the thing that modifies the event record by adding new particles)
*) and the interaction list generator, which determines if this process can occur for a specified initial state

Suggests starting with the cross section calculation. With this one can create cross section splines, a good intermediate step for validation. A question came up about the spacing of knots on the splines - these can be specified on the command line of gmkspl as well as the maximum energy and would certainly need to be changed for low energy usage by an experiment.

Costas will create a new package ${GENIE}/src/VLE for this work. Developers are encouraged to commit to it freely, it will not be built as part of the GENIE default build and will thus not interfere with any other users.

Cully reported on attempts to install GENIE at Duke. Build was failing at the PYTHIA step, will send details to Costas.

C: Validation

Costas and Hugh described the GENIE validation philosophy:

1) Be thinking about validation throughout the development process.
2) Validation programs and procedures (including external data) should be documented and included as part of GENIE.
3) Validation exercises should be, if possible, carried out by independent groups from those doing the model development work.

Diane has experience with validation for nuclear pile codes, and would be willing to take this on for the inverse beta decay channel.

Kate pointed out that for most of the reactions we are talking about, external data does not exist. While validation with external data is the ideal, in this context validation means "whatever the model developers do to convince themselves that the code is doing the right thing".

Costas pointed out that another aspect of the GENIE philosophy is that the code should produce something sensible (i.e. not crash) for all nuclei in the energy range of validity.

D: Other Items

The issue was raised of nuclear de-excitations, how important these are for the reactions / detectors of interest and whether the models currently in GENIE are sufficient for certain nuclei. Possible correlations (e.g. from shell model calculations) of reaction cross sections and de-excitation gamma energies?

Kate will call the next meeting, when sufficient progress has been made. Costas will be in Greece for the next 3 weeks but will do his best to respond to questions.

E: Action Items

Costas will set up a shell GENIE package - VLE - for this work.
Kate will post a list of relevant theory papers.
Costas will get cvs write access for those who need it.
Hugh will set up the GENIE low energy blog.

Welcome to the blog for GENIE Low Energy. This site is devoted to discussion and information sharing about efforts to extend the validity of GENIE to lower energies (10s of MeV). The goal is to make GENIE applicable for reactor, supernova, and stopped pion beam neutrino experiments.