I. Dutta

Herein, we report the synthesis, magnetic and theoretical studies of a mixed bimetallic and mixed-valence [MnIII2NiII4(N3)4(hep)4(OMe)2(OAc)4]·MeOH (1·MeOH; hep = 2-ethylhydroxypyridine) complex sharing a common MnIII–MnIII vertex between two defect dicubane NiII2MnIII2O4N2 cores. The single-crystal X-ray data were collected at two different temperatures, confirming that two Jahn–Teller axes of two adjacent MnIII ions in 1 are nearly parallel. One MnIII ion possesses an axis of Jahn–Teller elongation, while the other MnIII ion undergoes Jahn–Teller compression. DC and AC susceptibility measurements were carried out to predict the nature of magnetic exchange interactions between the metal ions and to understand the anisotropic behavior to rationalize its SMM behavior. DC measurements suggest that this ferromagnetically coupled Ni–Mn complex possesses a spin ground state (S) = 6–7 at 2 K, showing a maximum in χT vs T plot at 9.5 K. Fitting the susceptibility data using the PHI program yields three ferromagnetic J values and an antiferromagnetic J value between the metal ions and the reasonable magnetic anisotropy (D) for all the Ni(II) and Mn(III) metal ions. The dominant three ferromagnetic interactions, i.e., (i) the exchange interaction between Ni1–Ni4 and Ni2–Ni3 metal ions is +20.2 cm–1 (J1); (ii) the J2 exchange interaction pertains to the interaction between the Mn2 metal ion with all four Ni metal ions is +3.7 cm–1, (iii) the J4 exchange interaction between the Mn1 and Mn2 metal ions is +6.8 cm–1, which align all the metal ions spin in spin-up orientation, and the presence of a small antiferromagnetic exchange (−6.8 cm–1) contribution (J3; Mn1–Ni3/Ni4) aligns the Ni3 and Ni4 ion spin in between the spin-up/down orientation; representing the possible spin frustration and suggesting a possible spin ground state (S) of 6–7. The existence of spin frustration in the MnIII–NiII triangles cannot be completely ruled out since 1 is made of four hetero bimetallic MnIII–NiII triangular units. To fully comprehend the magnetic properties, extensive density functional theory (DFT) calculations were performed by using the B3LYP/TZV functional setup, yielding very good numerical estimates of Js, which are in agreement with the experimental values. Furthermore, high-level ab initio calculations were performed to calculate the zero-field splitting (D) for all Ni and Mn ions. These calculations predict different sign D values for both Mn(III) ions, which further supports the presence of two different JT-distorted Mn ions in this complex.

We present the design and performance characterization results of the novel Fermilab Constant Fraction Discriminator ASIC (FCFD) developed to readout low gain avalanche detector (LGAD) signals by directly using a constant fraction discriminator (CFD) to measure signal arrival time. Silicon detectors with time resolutions less than 30 ps will play a critical role in future collider experiments, and LGADs have been demonstrated to provide the required time resolution and radiation tolerance for many such applications. The FCFD has a specially designed discriminator that is robust against amplitude variations of the signal from the LGAD that normally requires an additional correction step when using a traditional leading edge discriminator. The application of the CFD directly in the ASIC promises to be more reliable and reduces the complication of evolving time-walk corrections throughout the operational lifetime of the detector system. We will present a summary of the measured performance of the FCFD for input signals generated by internal charge injection, LGAD signals from an infrared laser, and LGAD signals from minimum-ionizing particles. The mean time response for LGAD signals with charge ranging between 5 and 26 fC has been measured to vary no more than 10 ps, orders of magnitude more stable than an uncorrected leading edge discriminator based measurement, and effectively removes the need for any additional time-walk correction. The measured contribution to the time resolution from the FCFD ASIC is found to be 10 ps for signals with charge above 20 fC.

The MIP Timing Detector will provide additional timing capabilities for detection of minimum ionizing particles (MIPs) at CMS during the High Luminosity LHC era, improving event reconstruction and pileup rejection. The central portion of the detector, the Barrel Timing Layer (BTL), will be instrumented with LYSO:Ce crystals and Silicon Photomultipliers (SiPMs) providing a time resolution of about 30 ps at the beginning of operation, and degrading to 50-60 ps at the end of the detector lifetime as a result of radiation damage. In this work, we present the results obtained using a 120 GeV proton beam at the Fermilab Test Beam Facility to measure the time resolution of unirradiated sensors. A proof-of-concept of the sensor layout proposed for the barrel region of the MTD, consisting of elongated crystal bars with dimensions of about 3 x 3 x 57 mm$^3$ and with double-ended SiPM readout, is demonstrated. This design provides a robust time measurement independent of the impact point of the MIP along the crystal bar. We tested LYSO:Ce bars of different thickness (2, 3, 4 mm) with a geometry close to the reference design and coupled to SiPMs manufactured by Hamamatsu and Fondazione Bruno Kessler. The various aspects influencing the timing performance such as the crystal thickness, properties of the SiPMs (e.g. photon detection efficiency), and impact angle of the MIP are studied. A time resolution of about 28 ps is measured for MIPs crossing a 3 mm thick crystal bar, corresponding to an MPV energy deposition of 2.6 MeV, and of 22 ps for the 4.2 MeV MPV energy deposition expected in the BTL, matching the detector performance target for unirradiated devices.

We present the design and performance characterization results of the novel Fermilab Constant Fraction Discriminator ASIC (FCFD) developed to readout low gain avalanche detector (LGAD) signals by directly using a constant fraction discriminator (CFD) to measure signal arrival time. Silicon detectors with time resolutions less than 30 ps will play a critical role in future collider experiments, and LGADs have been demonstrated to provide the required time resolution and radiation tolerance for many such applications. The FCFD has a specially designed discriminator that is robust against amplitude variations of the signal from the LGAD that normally requires an additional correction step when using a traditional leading edge discriminator based measurement. The application of the CFD directly in the ASIC promises to be more reliable and reduces the complication of timing detectors during their operation. We will present a summary of the measured performance of the FCFD for input signals generated by internal charge injection, LGAD signals from an infrared laser, and LGAD signals from minimum-ionizing particles. The mean time response for a wide range of LGAD signal amplitudes has been measured to vary no more than 15 ps, orders of magnitude more stable than an uncorrected leading edge discriminator based measurement, and effectively removes the need for any additional time-walk correction. The measured contribution to the time resolution from the FCFD ASIC is also found to be 10 ps for signals with charge above 20 fC.

presented, reaching simultaneous 18 micron and 32 ps resolutions from strips of 1 cm length and 500 micron pitch. With only slight modifications, these sensors would be ideal candidates for a 4D timing layer at the EIC.

We present the results of studies aimed at developing 4D tracking technology for a wide range of physics experiments, including the Electron Ion Collider (EIC) and future Lepton Colliders. The studies focused on evaluating the performance of centimeter-scale AC-LGAD (AC-Low Gain Avalanche Detector) sensors and a new ASIC (Application-Specific Integrated Circuit) called the Fermilab Constant Fraction Discriminator (FCFD). For the AC-LGADs, we present the resolutions obtained with several prototypes, which reach simultaneous resolutions of 18 microns and 32 ps from strips of 1 cm length and 500 micron pitch. Regarding the FCFD, the mean time response for a wide range of signal amplitudes has been measured to be no more than 15 ps. This is orders of magnitude more precise than an uncorrected leading-edge discriminator-based measurement and effectively eliminates the need for a signal amplitude-based correction. Furthermore, the measured contribution to the time resolution from the FCFD ASIC is found to be 10 ps for signals with charges above 20 fC.

This Technical Memorandum (TM) summarizes the Fermilab Test Beam operations for FY2017. It is one of a series of annual publications intended to gather information in one place. In this case, the information concerns the individual experiments that ran at FTBF and are listed in Table 1. Each experiment section was prepared by the relevant authors, and was edited for inclusion in this summary.

• CMS MTD is important for an expanded physics reach : we expect 20- 25% effective luminosity increase in crucial precision Higgs measurements. • Our project is significantly advanced – the sensor performance is close to specification. • We are heavily involved in efforts to ensure 30 ps time resolution for sensors throughout the HL-LHC run.

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). A new timing layer is designed to measure minimum ionizing particles (MIPs) with a time resolution of 30 ps and a hermetic coverage up to a pseudo-rapidity of $|η|$ = 3. This MIP Timing Detector(MTD) will consist of a central barrel region based on LYSO:Ce crystals read out with SiPMs and two end-caps instrumented with radiation-tolerant Low Gain Avalanche Diodes (LGADs). The precision time information from the MTD will reduce the effects of the high levels of pile-up expected at the HL-LHC, and will bring new and unique capabilities to the CMS detector. We present the current status and ongoing R&D of the MTD, including recent test beam results.

This Technical Memorandum (TM) summarizes the Fermilab Test Beam Faciltiy (FTBF) operations for FY2019. It is one of a series of annual publications intended to gather information in one place. This TM discusses the experiments performed at the Test Beam from November 2018 to July 2019. The experiments are listed in Table 1. Each experiment wrote a summary that was edited for clarity and is included in this report.

At HEP experiments, processing billions of records of structured numerical data can be a bottleneck in the analysis pipeline.This step is typically more complex than current query languages allow, such that numerical codes are used.As highly parallel computing architectures are increasingly important in the computing ecosystem, it may be useful to consider how accelerators such as GPUs can be used for data analysis.Using CMS and ATLAS Open Data, we implement a benchmark physics analysis with GPU acceleration directly in Python based on efficient computational kernels using Numba/LLVM, resulting in an order of magnitude throughput increase over a pure CPUbased approach.We discuss the implementation and performance benchmarks of the physics kernels on CPU and GPU targets.We demonstrate how these kernels are combined to a modern ML-intensive workflow to enable efficient data analysis on high-performance servers and remark on possible operational considerations.