Periodic Reporting for period 2 - FASERnu (Studying Neutrinos at the High Energy Frontier)
Periodo di rendicontazione: 2023-03-01 al 2024-08-31
Humanity discovered that this Universe is made of particles and has developed particle physics over more than a century. To date we know this universe is made of fundamental particles, which are called Leptons and Quarks. Neutrino is a group of particles belongs Leptons. Since they don't interact with electromagnetic force nor with strong force, they can penetrate even the earth easily. However, physicists have found ways to catch them by means of various neutrino sources and huge detectors with kilo-tons of masses.
Particle physics has been greatly progressed with an employment of particle collider. The state-of-the-art collider is the Large Hadron Collider (LHC) at CERN with a collision energy of 13.6 TeV. At the colliders, wide range of particles can be studied from quarks to hypothetical dark matter, but they miss neutrino physics. In 50 years of history of particle colliders, no neutrino had been detected. This is due to the elusive nature of neutrinos and also the high radiation environment at the colliders. Neutrinos have been regarded as invisible at colliders. While, neutrinos from the LHC is expected to be at the highest energies that human can produce, and no data is currently available at the energies around 1 TeV. This can be a great opportunity for new discoveries.
This ERC-FASERnu project aims to detect and study high energy neutrinos at the LHC. We identified a suitable experimental location 480-m downstream of the proton-proton interaction point, where we can mitigate the problem of high background radiation. We then employ a 1.1-tons nano-resolution neutrino detector with a sensitivity to separate different neutrino species (electron-, mu- and tau-neutrinos) and heavy quark species (charm, beauty). By taking data in the LHC operation in 2022-2025, we can collect about 10000 neutrino interactions. This data samples allows us to study the Lepton Flavor Universality, which has doubted due to recently identified anomalies, with neutrinos. Furthermore, by studying heavy quark production channels, FASERnu can study time-reversal process of heavy meson decays, in which a hint of beyond-standard-model phenomena is observed. This project not only contribute in neutrino physics, but also has implications in QCD and cosmic-ray physics. It is worth noting also that FASERnu will be the only neutrino experiment performed in Europe in this decade using an accelerator.
In the last years, the European strategy of particle physics was reported. The key message was to exploit the LHC as much as possible and plan for the Future Circular Collider. So far, the LHC and neutrino experiments are two separate lines of research, however, FASERnu will bring them together and pioneer a new research domain. Therefore, FASERnu will perfectly fit with the European strategy, and extend the discovery potential of the LHC in a new direction.
Particle physics has been greatly progressed with an employment of particle collider. The state-of-the-art collider is the Large Hadron Collider (LHC) at CERN with a collision energy of 13.6 TeV. At the colliders, wide range of particles can be studied from quarks to hypothetical dark matter, but they miss neutrino physics. In 50 years of history of particle colliders, no neutrino had been detected. This is due to the elusive nature of neutrinos and also the high radiation environment at the colliders. Neutrinos have been regarded as invisible at colliders. While, neutrinos from the LHC is expected to be at the highest energies that human can produce, and no data is currently available at the energies around 1 TeV. This can be a great opportunity for new discoveries.
This ERC-FASERnu project aims to detect and study high energy neutrinos at the LHC. We identified a suitable experimental location 480-m downstream of the proton-proton interaction point, where we can mitigate the problem of high background radiation. We then employ a 1.1-tons nano-resolution neutrino detector with a sensitivity to separate different neutrino species (electron-, mu- and tau-neutrinos) and heavy quark species (charm, beauty). By taking data in the LHC operation in 2022-2025, we can collect about 10000 neutrino interactions. This data samples allows us to study the Lepton Flavor Universality, which has doubted due to recently identified anomalies, with neutrinos. Furthermore, by studying heavy quark production channels, FASERnu can study time-reversal process of heavy meson decays, in which a hint of beyond-standard-model phenomena is observed. This project not only contribute in neutrino physics, but also has implications in QCD and cosmic-ray physics. It is worth noting also that FASERnu will be the only neutrino experiment performed in Europe in this decade using an accelerator.
In the last years, the European strategy of particle physics was reported. The key message was to exploit the LHC as much as possible and plan for the Future Circular Collider. So far, the LHC and neutrino experiments are two separate lines of research, however, FASERnu will bring them together and pioneer a new research domain. Therefore, FASERnu will perfectly fit with the European strategy, and extend the discovery potential of the LHC in a new direction.
The first work was the analysis of the pilot data taken in 2018. Since the experimental setup was completely new and the condition was very different from that of conventional experiments which uses the same detector technology, a big challenge was to develop analysis codes for this experiment. After quite a bit of efforts, we reported a detection of neutrino interaction candidates, which was well received by the physics community and public.
The knowledge acquired through the pilot run was considered in the design of the actual detector setup. The design of the detector was fixed in 2021, to have 730 tungsten plates (neutrino target) and emulsion films (high precision particle tracker) with a mass of 1.1 tons. The detector components were produced in the same year. The detector assembling scheme was then established in the beginning of 2022. The first detector was delivered in March 2022, in time for the start of Run 3 of the LHC operation. We need to replace the emulsion films several times during the data taking. So far 3 detectors in 2022 and 2 detectors in 2023 were exposed to the neutrino beam from the LHC.
The analysis of detector is ongoing, together with developments of algorithms for reconstruction and kinematical analysis. We have reported the detection of neutrinos with FASERnu detector in Summer 2023, when the statistical significance of electron neutrino charged-current events exceeded 5 sigma. The neutrino cross sections of electron and muon neutrinos were obtained at the end of this reporting period in Feb 2024.
The knowledge acquired through the pilot run was considered in the design of the actual detector setup. The design of the detector was fixed in 2021, to have 730 tungsten plates (neutrino target) and emulsion films (high precision particle tracker) with a mass of 1.1 tons. The detector components were produced in the same year. The detector assembling scheme was then established in the beginning of 2022. The first detector was delivered in March 2022, in time for the start of Run 3 of the LHC operation. We need to replace the emulsion films several times during the data taking. So far 3 detectors in 2022 and 2 detectors in 2023 were exposed to the neutrino beam from the LHC.
The analysis of detector is ongoing, together with developments of algorithms for reconstruction and kinematical analysis. We have reported the detection of neutrinos with FASERnu detector in Summer 2023, when the statistical significance of electron neutrino charged-current events exceeded 5 sigma. The neutrino cross sections of electron and muon neutrinos were obtained at the end of this reporting period in Feb 2024.
Progress beyond the state of the art
1) No neutrino had ever been detected from colliders before this project. However, now we firmly established a detection of neutrinos at the LHC. This is the first observation of neutrinos at any colliders, which opened a new page of neutrino physics in term of methodologies.
2) Neutrino cross section measurements lacked data at TeV energies. We provided measurements at this unexplored energy range for the first time.
Prospect:
1) Neutrino cross section measurements of all three flavor neutrinos as a function of energy
2) Lepton flavor universality test in inclusive neutrino scattering cross section
3) Lepton flavor universality in heavy quark production (charm and beauty quarks)
4) Constraints of hadron production models by neutrino data
1) No neutrino had ever been detected from colliders before this project. However, now we firmly established a detection of neutrinos at the LHC. This is the first observation of neutrinos at any colliders, which opened a new page of neutrino physics in term of methodologies.
2) Neutrino cross section measurements lacked data at TeV energies. We provided measurements at this unexplored energy range for the first time.
Prospect:
1) Neutrino cross section measurements of all three flavor neutrinos as a function of energy
2) Lepton flavor universality test in inclusive neutrino scattering cross section
3) Lepton flavor universality in heavy quark production (charm and beauty quarks)
4) Constraints of hadron production models by neutrino data