Getting the beamline right for CPV sensitivity

Amit Bashyal, Oregon State University

Amit Bashyal

Neutrino flux predictions that rely solely on standard simulations suffer from large uncertainties. Amit Bashyal, a graduate student at Oregon State University since 2015, is working to improve the culprit: poorly modeled hadron interaction cross sections.

After finishing his undergraduate work in Professor Jaehoon Yu’s group at UT Arlington in 2014, Bashyal spent some time at Fermilab as an International Fellow where he studied the uncertainties in CP violation measurements for different candidate LBNF beamline designs, working closely with Fermilab scientists Laura Fields and Alberto Marchionni.

Now at Oregon State, he continues to work with Fields in the DUNE beamline simulations group, and with his advisor, Professor Heidi Schellman. For the past year Bashyal has been using the Package to Predict Flux (PPFX), originally designed by Leo Aliaga for MINERvA, to estimate the systematic uncertainties on different beamline designs due to hadron production.

Visualization of one of the DUNE Optimized Beamline candidates showing Target Baffle, Focusing System and Decay Pipe. Image: A. Bashyar and the Beam Optimization Group

“By implementing PPFX in DUNE, we use the best current hadronic interaction data to further constrain the uncertainties and get a better characterization of the beamline” said Bashyal. “By making the flux prediction reliable, our work is helping the detector design group.”

Bashyal’s early work with Fields helped in deriving the new optimized beamline design and his current work is solidifying the team’s confidence in the expected systematics from this design.

“Amit’s work has already had a major impact on DUNE beamline designs and he is continuing to update the simulation codes as the designs evolve,” said Schellman. “He is now taking his knowledge of neutrino beamlines and systematics back to the NUMI beamline to better understand the flux in the MINERvA experiment for his thesis.”

Rowan Zaki, Radboud University

Rowan Zaki

Also contributing to the beamline optimization effort is Rowan Zaki, a student at Radboud University in Nijmegen, the Netherlands. Currently producing a Master’s thesis on his efforts, Zaki worked with Fermilab scientists Laura Fields and Paul Lebrun for about eight months last year on both the beamline and the spectrometer.

Like Bashyal, Zaki worked on optimizing the LBNF beamline for CP-violation sensitivity, but his efforts focused on simulating in Geant4 the effects of different beamline parameters, such as the initial particle’s momentum, the position of the target, and the position of the third focusing horn, on the neutrino flux at the DUNE far detector. He also performed a study on the new cylindrical graphite target.

“Rowan contributed significantly to the final beam plots that we presented at the Beam Optimization Review in October 2017,” said Fermilab scientist Alberto Marchionni.

Zaki also estimated the effective duty cycle of the LBNF spectrometer for the LBNF beamline.

“For the spectrometer to be operated at its full potential, it can receive only one proton per RF bucket,” he said. “For protons coming from the Main Injector, we have to use the RF bucket frequency of 53 MHz.”

This corresponds to a 19 ns RF bucket.

By constructing a simple counting experiment with the use of PMTs and plastic scintillators, and installing it at the Fermilab Test Beam Facility, Zaki was able to investigate the time of arrival of the protons within a Main Injector long spill, the 4.2 s time window during which protons are slowly extracted from the machine.

“We looked for the ratio of how often there is only one proton in such a RF bucket over the total number of buckets” Zaki said. From this, he was able to extract a rough estimate of the efficiency of data collection expected from the LBNF spectrometer, leading to a better understanding of how well DUNE will be able to measure the LBNF beam content.

Now it’s on to graduate school applications!