Periodic Reporting for period 5 - CHROMIUM (CHROMIUM)
Reporting period: 2022-10-01 to 2023-09-30
The recent discovery of the Higgs particle has left us in no doubt that the Standard Model (SM) of particle physics is correct in very large part.
However, another slightly less recent discovery, that of neutrino mass, is in tension with the SM's successes. In order for the Weak force to be properly described in the theory,
neutrinos were assigned exactly zero mass: however it has been proved that while their masses are very small, they are definitely not zero. Over the last few decades, particle physicists mounted a number of experiments looking for, and finally measuring, a quantity known as Charge Parity (CP) violation in sub-atomic particles called quarks. This manifests itself as a difference in interaction rates between matter and antimatter particles and the reason for looking for this difference was an attempt to explain what happened to the anti-matter which must have existed in the early universe. The simple explanation was that as the Universe expanded, transitions between matter and anti-matter were stopped at some energy density and over time, the small excess of matter that had been produced led to the total annihilation of all the antimatter, leaving just a small amount of matter which is what we see around us in the Universe.
However, the discovery of neutrino mass gives rise to the possibility of a mechanism which can explain the matter that we see.
The overarching goal of this proposal was to demonstrate that a giant water Cherenkov detector could be built at a fraction of the cost, in order to allow enough detector mass to measure the CP violating angle (at a later time).
The novel detector concept was named CHIPS, for Cherenkov detectors In PitS which was located in the Wentworth 2W flooded taconite pit near Aurora, Minnesota. This pit intersects the NuMI neutrino beam. The concept pushes on the costs of the detector by using the natural body of water to support the detector volume, avoiding a very strong and costly mechanical structure. It was designed to use the water overburden to shield from cosmic rays, making use of the time window that the beam is delivered and the knowledge of the neutrinos direction, to avoid having to be positioned under a very large overburden of rock.
The new technical concept was that of a submerged cylinder, providing a light tight, and water tight barrier within which are mounted the PMTs. The internal water would be continuously circulated and cleaned making the water very transparent to the Cherenkov light being produced. The PMTs are traditional, and very well understood, low technical risk, photon detectors. They have been deployed in water Cherenkov detectors before but the technical challenge here is to combine the signals from so many PMTs under the water, and use local computer power also under the water to identify the neutrino events coming from the NuMI beam which arrive at a known time and within a very short time window. The electronic were then transported to shore, up to 300m away, via one fibre cable. This again provides very large cost savings compared to traditional detectors.
However, another slightly less recent discovery, that of neutrino mass, is in tension with the SM's successes. In order for the Weak force to be properly described in the theory,
neutrinos were assigned exactly zero mass: however it has been proved that while their masses are very small, they are definitely not zero. Over the last few decades, particle physicists mounted a number of experiments looking for, and finally measuring, a quantity known as Charge Parity (CP) violation in sub-atomic particles called quarks. This manifests itself as a difference in interaction rates between matter and antimatter particles and the reason for looking for this difference was an attempt to explain what happened to the anti-matter which must have existed in the early universe. The simple explanation was that as the Universe expanded, transitions between matter and anti-matter were stopped at some energy density and over time, the small excess of matter that had been produced led to the total annihilation of all the antimatter, leaving just a small amount of matter which is what we see around us in the Universe.
However, the discovery of neutrino mass gives rise to the possibility of a mechanism which can explain the matter that we see.
The overarching goal of this proposal was to demonstrate that a giant water Cherenkov detector could be built at a fraction of the cost, in order to allow enough detector mass to measure the CP violating angle (at a later time).
The novel detector concept was named CHIPS, for Cherenkov detectors In PitS which was located in the Wentworth 2W flooded taconite pit near Aurora, Minnesota. This pit intersects the NuMI neutrino beam. The concept pushes on the costs of the detector by using the natural body of water to support the detector volume, avoiding a very strong and costly mechanical structure. It was designed to use the water overburden to shield from cosmic rays, making use of the time window that the beam is delivered and the knowledge of the neutrinos direction, to avoid having to be positioned under a very large overburden of rock.
The new technical concept was that of a submerged cylinder, providing a light tight, and water tight barrier within which are mounted the PMTs. The internal water would be continuously circulated and cleaned making the water very transparent to the Cherenkov light being produced. The PMTs are traditional, and very well understood, low technical risk, photon detectors. They have been deployed in water Cherenkov detectors before but the technical challenge here is to combine the signals from so many PMTs under the water, and use local computer power also under the water to identify the neutrino events coming from the NuMI beam which arrive at a known time and within a very short time window. The electronic were then transported to shore, up to 300m away, via one fibre cable. This again provides very large cost savings compared to traditional detectors.
Final design has been verified by detailed simulations. The eventual energy resolution of the detector was shown to be as good as Super-K with much lower density of PMT coverage but with very good timing from each of the small PMTs. This was published in "Neutrino characterisation using convolutional neural networks in CHIPS water Cherenkov detectors" Citation Josh Tingey et al 2023 JINST 18 P06032 DOI 10.1088/1748-0221/18/06/P06032
The description of the construction is available https://arxiv.org/abs/2401.11728(opens in new window)
A design based on the front plane design has been developed using borrowed PMTs from our French colleagues. The electronics for these PMTs has been developed from scratch using innovative design using components that are commercially available and present in many mobile phones. We were lent 500 3" Hamamatsu R6091's from our colleagues from the NEMO-3 collaboration and together with
electronics developed at UW we have developed a novel idea of a distributed readout system for particle physics based on commercially available electronic components. There are three distinct aspects of this hardware development: a small-format Cockroft-Walton (CW) positive HV generator base (based on a design from the COUPP experiment at FNAL) to drive the PMTs; a "microdaq" board which contains a STM32F446 microprocessor and sits on the PMT, delivering self-triggered time-over-threshold information to the single-board computer as well as control signals to the CW board; and the WR signal fan-out board to deliver the absolute time to every \microdaq. The CW is controlled via PWM signals which adjust the resonant frequency to change the overall magnitude of the HV. The advantage of the positive HV base is that the PMTs can be submerged in water without loss of functionality which is often observed with a negative HV. Miniature negative HV CW bases are much easier to build, without the need for a large transformer which typically must be specially fabricated. We have innovated on this by using two commercially available inductors on either side of the base board.
The WR system is fast becoming the new standard for 1\,ns absolute timing across Ethernet. Software to be developed on the BB single-board computer will collect up the signals from up to 32 PMTs via LVDS links and deliver buffered data to the network via Ethernet. The ensemble will provided a very inexpensive DAQ+HV system. This work was carried on in the last two years of the grant to a very useful delivery point.
One was the idea to suspend one end-cap structure from the other, using Dyneema strings to attach the endcaps to each other and as the mounting points for the PMT planes, instead of a rigid wall structure. This gave us the opportunity to increase the size of the detector without a large cost increase due to the increased structure cost by increasing the length of the strings.
A total of 16 planes received the WR signals from one WR end node. The WR end node will connect up to the GPS driven master clock on the shore via fiber-optic cable.
We demonstrated that we could use the NuMI spill signal as a trigger. This had not been tried before for the remote detectors, as both MINOS and \nova have utilised a very wide gate and have aligned the beam spill time to the activity in the detector after the fact.
The description of the construction is available https://arxiv.org/abs/2401.11728(opens in new window)
A design based on the front plane design has been developed using borrowed PMTs from our French colleagues. The electronics for these PMTs has been developed from scratch using innovative design using components that are commercially available and present in many mobile phones. We were lent 500 3" Hamamatsu R6091's from our colleagues from the NEMO-3 collaboration and together with
electronics developed at UW we have developed a novel idea of a distributed readout system for particle physics based on commercially available electronic components. There are three distinct aspects of this hardware development: a small-format Cockroft-Walton (CW) positive HV generator base (based on a design from the COUPP experiment at FNAL) to drive the PMTs; a "microdaq" board which contains a STM32F446 microprocessor and sits on the PMT, delivering self-triggered time-over-threshold information to the single-board computer as well as control signals to the CW board; and the WR signal fan-out board to deliver the absolute time to every \microdaq. The CW is controlled via PWM signals which adjust the resonant frequency to change the overall magnitude of the HV. The advantage of the positive HV base is that the PMTs can be submerged in water without loss of functionality which is often observed with a negative HV. Miniature negative HV CW bases are much easier to build, without the need for a large transformer which typically must be specially fabricated. We have innovated on this by using two commercially available inductors on either side of the base board.
The WR system is fast becoming the new standard for 1\,ns absolute timing across Ethernet. Software to be developed on the BB single-board computer will collect up the signals from up to 32 PMTs via LVDS links and deliver buffered data to the network via Ethernet. The ensemble will provided a very inexpensive DAQ+HV system. This work was carried on in the last two years of the grant to a very useful delivery point.
One was the idea to suspend one end-cap structure from the other, using Dyneema strings to attach the endcaps to each other and as the mounting points for the PMT planes, instead of a rigid wall structure. This gave us the opportunity to increase the size of the detector without a large cost increase due to the increased structure cost by increasing the length of the strings.
A total of 16 planes received the WR signals from one WR end node. The WR end node will connect up to the GPS driven master clock on the shore via fiber-optic cable.
We demonstrated that we could use the NuMI spill signal as a trigger. This had not been tried before for the remote detectors, as both MINOS and \nova have utilised a very wide gate and have aligned the beam spill time to the activity in the detector after the fact.
The development of the electronics for the loaned PMTs has produced an unforseen innovation.
The idea is for a distributed system that can be used for large arrays of PMTs based on commercially available electronic components. It can be seen as part of a movement to distribute intelligence towards the detector, a natural way forward as electronic components gets cheaper and smarter. This approach of the microprocessor on the PMT was originally pioneered at UW, but has been further developed at UCL with a replacement of the BB by a Rasberry-Pi compute module. A complete set, seen in the figure, can read out 27 PMTs and is presently taking data at three sites : Prague, London and Quy Nhon, Vietnam.
There were unfortunately no physics results from the Cherenkov detector, owing to a technical hitch during deployment and then the covid pandemic prevented non-US citizens from coming to the US during which time the grant and the lease on the mine site ran out.
The idea is for a distributed system that can be used for large arrays of PMTs based on commercially available electronic components. It can be seen as part of a movement to distribute intelligence towards the detector, a natural way forward as electronic components gets cheaper and smarter. This approach of the microprocessor on the PMT was originally pioneered at UW, but has been further developed at UCL with a replacement of the BB by a Rasberry-Pi compute module. A complete set, seen in the figure, can read out 27 PMTs and is presently taking data at three sites : Prague, London and Quy Nhon, Vietnam.
There were unfortunately no physics results from the Cherenkov detector, owing to a technical hitch during deployment and then the covid pandemic prevented non-US citizens from coming to the US during which time the grant and the lease on the mine site ran out.