ELTE researchers lead the NA61/SHINE experiment at CERN this summer

During the summer of 2024, NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) at CERN Super Proton Synchrotron (SPS) continued its goal of measuring hadron-nucleus interactions for neutrino experiments all over the globe. Researchers from the ELTE NA61/SHINE group participated in the summer data collection period.

The summer 2024 measurements were dedicated to precisely understanding the neutrino flux of the Deep Underground Neutrino Experiment (DUNE), which is the next-generation flagship experiment currently under construction in the US. According to the plans the proton beam at 120 GeV/c is impinged on the first LBNF (Long Baseline Neutrino Facility) prototype graphite target, which is designed for DUNE. Researchers aim to understand the underlying nature of neutrino oscillation, the phenomenon in which neutrino flavor “oscillates” from one (e.g. muon type neutrino) to the other (e.g. electron type neutrino) while traveling. This mysterious neutrino property could give an answer to why the universe is made only of ordinary matter and no antimatter. Two ELTE physicists led the summer data taking campaign, Yoshikazu Nagai (assistant professor) as physics coordinator and Barnabás Pórfy (Ph.D student) as DAQ (Data AcQuisition) expert.

Nowadays, there are several different types of neutrino related studies around the globe. The main difference between them is the type of neutrino source they are using. This could be either natural sources such as solar neutrinos, atmospheric neutrinos or cosmic neutrinos, or we can use artificial sources like reactor neutrinos or accelerator neutrinos. Neutrinos, however, are very difficult to detect due to their weakly interacting nature, therefore, neutrino experiments typically require high intensity neutrino sources. A solution to achieve a high-intensity neutrino beam is to use an accelerator (as shown in Figure 1). Naturally, the next question which scientists need to be addressed is on how many neutrinos have been produced and sent off to the neutrino detector. In other words, it is essential to completely understand the error coming from hadron production, which involves the production of neutrino parents. However, it is not practical for accelerator-based neutrino experiments to conduct ``in situ’’ hadron production measurements of neutrino parents, simply because the intensity of the proton beam is too high to place any detector instruments near the neutrino production target.

Figure 1: A schematic drawing of accelerator-neutrino generation. A high intensity proton beam is impinged on a graphite target to produce a bunch of hadrons. They are focused by the device toroidal magnetic field produced by “magnetic horn” and let them decay to neutrinos.

Thus, accelerator-based neutrino experiments rely on external experiments to measure errors associated with hadron production.

Fortunately, proton beams from SPS can be used to replicate the neutrino experiment energies from various accelerators such as those at Fermilab in the US or J-PARC in Japan. Measurements of hadron production are essential for flux prediction of accelerator-based, long-baseline neutrino experiments like T2K (Tokai to Kamioka) in Japan and DUNE (Deep Underground Neutrino Experiment) in the US. The NA61/SHINE experiment at CERN SPS has served a critical role in such precision measurements since its birth. In 2009-2010, NA61/SHINE took data for the T2K experiment, using a 31 GeV/c proton beam on graphite targets. Since then, NA61/SHINE has published a total of 8 papers in prestigious journals! 

Figure 2: A view from the beam-upstream. The LBNF prototype target and the Long Target Tracker are installed just in front of the NA61/SHINE apparatus.

During the summer of 2024, NA61/SHINE was taking data for DUNE using a secondary proton beam at 120 GeV/c energy.The 150 cm long, LBNF prototype target, along with the newly commissioned LTT (Long Target Tracker) developed by Richárd Nagy, Gergő Hamar, András László, and Dezső Varga at HUN-REN Wigner Research Centre for Physics, for the summer data taking period, is placed downstream of the target, visible on the Figure below. The LTT is a Time Projection Chamber designed to improve forward-going hadron measurements.

Figure 3: Example event from the summer of 2024, showing signals from all detectors in a collision of proton to graphite target (top) and zoomed in to the data from Long Target Tracker (bottom)

Researchers from the NA61/SHINE group at ELTE participated in the full 4 week duration of the summer data taking campaign. Yoshikazu Nagai acted as Physics Coordinator, making all the important decisions related to physics during the whole period of the run. Barnabás Pórfy was, and still is, working with the DAQ team as TPC-DAQ expert managing all TPC-readout related issues be it software or hardware.

Figure 4: Yoshikazu Nagai (left) and Barnabás Pórfy (right) standing next to the NA61/SHINE experiment at CERN.

Important developments during the major shutdown (2019-2022)

To constrain errors on the DUNE neutrino flux, very high-statistics data are necessary, which is at least ten times more proton interactions on graphite compared to the past measurements made for the T2K experiment in 2009-2010. Thankfully, the upgrade of the recent Long Shutdown 2 at CERN allowed NA61/SHINE to increase the data taking rate 15-20 times!

This feat was achieved by several upgrades of the experiment,

notably the replacement of the TPC readout electronics which greatly influenced the data quality and rate. Further implementation of the readout system for non-TPC detectors was also done on an advanced readout chip which allows to digitalize the signals at a much higher rate than before. The introduction of a fully scalable data acquisition system and a new trigger system has further optimized the process, ensuring faster and cleaner data collection. Several Hungarian research groups and researchers also participated in the development of the other detectors. Further information on these can be found on the  CERN Document Server.

This upgrade allowed NA61/SHINE to take 183 millions events in 2022, 232 millions this summer over 4 weeks of data taking. The increase is more visible when we compare it to the 2010 run of 5 weeks, which resulted in 10 millions of events.

Future prospects

In the upcoming years, the NA61/SHINE will continue its operation and data taking until the start of Long Shutdown 3 in 2026. There are already ongoing discussions and investigations for the extension of the NA61/SHINE program post-LS3 (2029-) era. A workshop was organized in December of 2022 on the topic of possible physics programs. Yoshikazu Nagai, as a leader of the NA61/SHINE collaboration, is also leading the proposal for low-energy beamline to measure for short baseline neutrino experiments such as MicroBooNe.

Acknowledgments

The research group was supported by OTKA K-138136, K-138152 and FK-137812 grants of the National Research, Development and Innovation Fund. Barnabás Pórfy was furthermore supported by the DKOP-23 Doctoral Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.