High-luminosity Collider Research Articles

Baryonic dark forces in electron-beam fixed-target experiments

New GeV-scale dark forces coupling predominantly to quarks offer novel signatures that can be produced directly and searched for at high-luminosity colliders. We compute the photon-proton and electron-proton cross sections for producing a GeV-scale gauge boson arising from a U(1)B gauge symmetry. Our calculation relies on vector meson dominance and a phenomenological model for diffractive scattering used for vector-meson photoproduction. The parameters of our phenomenological model are fixed by performing a Markov Chain Monte Carlo fit to existing exclusive photoproduction data for ω and ϕ mesons. Our approach can be generalized to other GeV-scale dark gauge forces.

On a new environment-friendly gas mixture for Resistive Plate Chambers

The standard gas mixture for the Resistive Plate Chambers (RPC), composed of C2H2F4/i-C4H10/SF6, allows the detector operation in avalanche mode, as required by the high-luminosity collider experiments. The gas density, the low total charge delivered inside the gas and the comfortable avalanche-streamer separation guarantee high detection efficiency, rate capability and slow detector aging. The standard RPC gas mixture is mostly based on Hydrofluorocarbons, HFCs, extensively used in the refrigeration industry. The Hydrofluorocarbons are now considered to be non-eco-friendly gases for their high Global Warming Potential (GWP). The SF6 has the largest GWP, 22900, but, due to its low concentration, it contributes only with few tens of units to the total value. The major contribution comes from the main standard gas mixture component, the C2H2F4 (GWP ≈ 1300). These gases are not recommended for industrial uses anymore, thus their availability will be increasingly difficult over time and the search for an alternative gas mixture with low-GWP is then of absolute priority within the RPC community. We report the performance of the RPC working with new environment-friendly gases which could replace the standard mixture. In this work the standard mixture main component, the C2H2F4, is replaced by a proper mixture of CO2 (GWP = 1) and Tetrafluoropropene (C3H2F4, GWP≈6). The other high-GWP component, the SF6, is replaced by a molecule, the Chloro-Trifluoropropene (C3H2ClF3, GWP ≈ 5) never tested in RPC detectors. The mixtures studied have a total GWP ≈ 10. We report, for several eco-gas mixtures, the detection efficiency, streamer probability, electronic and ionic charge as a function of the high voltage. Moreover, the timing properties are studied and the detector time resolution is measured. We also focus the attention on a new category of signals having intermediate properties between avalanche and streamer, called ”transition events”. This category is negligible for the standard gas mixture but relevant for HFO/CO2-based gas mixtures. We show a direct comparison between SF6 and C3H2ClF3 to study in depth the possibility to replace the SF6.

Neutron radiation induced effects in 4H-SiC PiN diodes

Silicon carbide (SiC) is a wide band gap semiconductor and an attractive candidate for applications in harsh environments such as space, fusion, or future high luminosity colliders. Due to the large band gap, the leakage currents in SiC devices are extremely small, even after irradiation to very high fluences, enabling operation without cooling and at high temperatures. This study investigates the effect of neutron irradiation on 50 μm p-n 4H-SiC diodes using current-voltage, capacitance-voltage, and charge collection efficiency (CCE) measurements up to neutron fluences of 1 × 1016 n eq/cm2. The leakage currents of the investigated devices remained extremely small, below 10 pA at 1.1 kV reverse bias. In the forward bias, a remarkable drop of the current was observed, which was attributed to an increased epi resistivity due to compensation of the epi layer doping by deep-level defects. The CCE was evaluated for alpha particles from a radioactive source, a 62.4 MeV proton beam at the MedAustron ion therapy center and using UV-TCT. The charge collection efficiency in reverse bias was shown to scale directly with the 1 MeV equivalent fluence Φeq as CCE∝Φeq -0.63±0.01. A CCE better than 50% was able to be obtained for fluences up to 1 × 1015 n eq/cm2. Because of the low currents in the forward direction, particle detection was also possible in forward bias, where the CCE was found to be increased relative to reverse bias. Furthermore, a significant dependency on the amount of injected charge was observed, with the CCE surpassing 100% in alpha and UV-TCT measurements, requiring further systematic investigation.

Characteristics of thin p-MCz Si Microstrip Detector Irradiated upto a mixed fluence of 1017neq./cm2for the FCC

Silicon microstrip detectors can be used for the precise particle tracking in the inner tracking region of the detector used in the future high luminosity collider experiment. In the future experiments, hadron collider provides higher luminosities on the strip detector, and therefore, a detector requires very high radiation hardness. Within CERNRD50collaboration, MCz Si is identified as a prime radiation hard material for the fabrication of the p-Si microstrip detector. In this paper, we have used the experimentally verified four level deep-trap mixed irradiation model for p-MCz Si to investigate the effect of heavy irradiations up to a mixed fluence of 1017n eq./cm2 on the full depletion voltage, leakage current, and charge collection efficiency using SRH and CCE modelling.The changes in the characteristics were evaluated, and effect of the traps on the macroscopic performance of the detectors and possible improvement in the design and semiconductor technology of the p-Mcz silicon microstrip detector.

Measured and projected beam backgrounds in the Belle II experiment at the SuperKEKB collider

The Belle II experiment at the SuperKEKB electron–positron collider aims to collect an unprecedented data set of 50ab−1 to study CP-violation in the B-meson system and to search for Physics beyond the Standard Model. SuperKEKB is already the world’s highest-luminosity collider. In order to collect the planned data set within approximately one decade, the target is to reach a peak luminosity of 6 × 1035cm−2s−1 by further increasing the beam currents and reducing the beam size at the interaction point by squeezing the betatron function down to βy∗=0.3mm. To ensure detector longevity and maintain good reconstruction performance, beam backgrounds must remain well controlled. We report on current background rates in Belle II and compare these against simulation. We find that a number of recent refinements have significantly improved the background simulation accuracy. Finally, we estimate the safety margins going forward. We predict that backgrounds should remain high but acceptable until a luminosity of at least 2.8 × 1035cm−2s−1 is reached for βy∗=0.6mm. At this point, the most vulnerable Belle II detectors, the Time-of-Propagation (TOP) particle identification system and the Central Drift Chamber (CDC), have predicted background hit rates from single-beam and luminosity backgrounds that add up to approximately half of the maximum acceptable rates.

Timespot1: a 28 nm CMOS Pixel Read-Out ASIC for 4D Tracking at High Rates

We present the first characterization results of Timespot1, an ASIC designed in CMOS 28 nm technology, featuring a 32 × 32 pixel matrix with a pitch of 35 μm. Timespot1 is the first small-size prototype, conceived to readout fine-pitch pixels with single-hit time resolution below 50 psrms and input rates of several hundreds of kilohertz per pixel. Such experimental conditions will be typical of the next generation of high-luminosity collider experiments, from the LHC run5 and beyond. Each pixel of the ASIC includes a charge amplifier, a discriminator, and a Time-to-Digital Converter with a time resolution indicatively of 22.6 psrms and maximum readout rates (per pixel) of 3 MHz. To respect system-level constraints, the timing performance has been obtained keeping the power budget per pixel below 40 mW. The ASIC has been tested and characterised in the laboratory concerning its performance in terms of time resolution, power budget and sustainable rates. The ASIC will be hybridized on a matched 32 × 32 pixel sensor matrix and will be tested under laser beam and Minimum Ionizing Particles in the laboratory and at test beams. In this paper we present a description of the ASIC operation and the first results obtained from characterization tests concerning its performance.

Analysis of Bulk and Surface Radiation Damage in n+ in p SFz Si Micro Strip Detectors for the Future High Luminosity Collider Experiments: TCAD Simulation and Measurements

Within the framework of CERN RD50 collaboration, several radiation damage models for n/p-SFz, n-MCz Si have been explored for the better understanding of the experimental results in radiation damage analysis of the irradiated Si detectors. In the present paper, the important review on the microscopic radiation damage model for the p-type SFz Si detector combining the surface and radiation damage effects that can be used to simulate radiation damages effects in the heavily irradiated detectors for the good comparison of the experimental data and simulation result. The surface radiation damage models were extracted from the experimental measurements on the p-MOS capacitor and Gate-Controlled Diodes irradiated by Gamma or X-ray radiations in the range of 10 to 500 Mrad (Si). Whereas, the bulk damage model microscopic parameter was extracted from the experimental (TSC, DLTS) measurements on the n in p-SFz Si microstrip detector. The radiation damage (surface and bulk) models can be fed into the commercial Synopsys TCAD device simulator program for the designing and optimization of the detector, which can be used in the very harsh radiation environment of the HL-LHC, or FCC experiment. The objective of this analysis was to verify the experimental results using the new microscopic radiation damage models on the p-SFz Si for the radiation damage analysis of p- SFz Si detectors irradiated by proton, neutron or mixed at very high fluences. The results were verified by comparison of the experimental data with TCAD simulation.

The surface Resistive Plate Counter: An RPC based on resistive MPGD technology

The surface Resistive Plate Counter (sRPC) is a revolutionary RPC based on surface resistive electrodes realized with Diamond-Like-Carbon sputtered on Apical® foil. Exploiting high granularity current evacuation schemes developed for resistive MPGD and using electrodes with low surface resistivity (down to ∼100MΩ/□), sRPCs standing particle fluxes up to several hundreds kHz/cm2 should be easily developed. The scalability of the technology allows the construction of detectors for large area applications at future high luminosity colliders.

Possibility of experimental study on nonleptonic weak decays* *Supported by the National Natural Science Foundation of China (11705047, 12275068, U1632109, 11875122), the Natural Science Foundation of Henan Province, China (222300420479) and the Excellent Youth Foundation of Henan Province, China (212300410010)

The ground vector meson has not yet been experimentally discovered until now. Besides the dominant electromagnetic decays, nonleptonic weak decays provide another choice to search for the mysterious mesons. Inspired by the potential prospects of mesons in future high-luminosity colliders, nonleptonic weak decays induced by bottom and charm quark decays are studied within the SM by using a naive factorization approach. It is found that for , , , , , , , and decays, a few hundred and even thousands of events might be observable in CEPC, FCC-ee and LHCb@HL-LHC experiments.

The surface Resistive Plate Counter: A new RPC based on resistive MPGD technology

The surface Resistive Plate Counter (sRPC) is a new RPC based on surface resistive electrodes realized with Diamond-Like-Carbon (DLC) sputtered on Apical\\protect \\relax \\special {t4ht=®} foil. Exploiting the high rate resistive MPGD technology, detectors able to stand several tens of kHz/cm2 can be easily developed. The scalability of the technology allows the construction of detectors for large area applications at future high luminosity colliders.

Dark sector production via proton bremsstrahlung

Experiments using proton beams at high luminosity colliders and fixed target facilities provide impressive sensitivity to new light weakly coupled degrees of freedom. With these experiments in mind, we revisit the production of dark vectors and scalars via proton bremsstrahlung, making use of a model that describes the underlying nucleon scattering cross-section in the forward direction due to pomeron exchange. We compare the resulting distributions and rates with those obtained via variants of the Fermi-Weizsacker-Williams approximation, and provide production rate distributions for a range of beam energies, including those relevant for the proposed Forward Physics Facility at the High Luminosity-LHC.

Development of a compact test board for silicon sensors IV/CV characterization

To build silicon trackers of modern and future high-luminosity collider experiments, thousands of silicon strip modules have to be produced and tested. The modules in new trackers must reliably work usually during 5–10 years or more under harsh irradiation conditions, as it will be impossible to replace a failing module once installed inside the detector. It means that reliable and rigorous testing of strip modules and its components is mandatory. To sustain the production throughput we should be able to test several modules in parallel. For this reason a fast, reliable, scalable and cost effective production QC test bench has to be designed and implemented. For the CV and IV measurements of sensors and modules we are developing a low-cost (less than 500 €) integrated electronic board which will be scaled up to ten channels to measure DUTs in parallel. In the current work the design of the IV/CV board and the calibration procedure to increase the accuracy of the current and capacitance measurements, for which a special calibration dipole board based on tight tolerance capacitors and resistors has been designed, as well as future development plans are described.

Radiation Hardness Property of Ultra-Fast 3D-Trench Electrode Silicon Detector on N-Type Substrate.

The radiation fluence of high luminosity LHC (HL-LHC) is predicted up to 1 × 1016 1 MeV neq/cm2 in the ATLAS and CMS experiments for the pixel detectors at the innermost layers. The increased radiation leads to the degradation of the detector properties, such as increased leakage current and full depletion voltage, and reduced signals and charge collection efficiency, which means it is necessary to develop the radiation hard semiconductor devices for very high luminosity colliders. In our previous study about ultra-fast 3D-trench electrode silicon detectors, through induced transient current simulation with different minimum ionizing particle (MIP) hitting positions, the ultra-fast response times ranging from 30 ps to 140 ps were verified. In this work, the full depletion voltage, breakdown voltage, leakage current, capacitance, weighting field and MIP induced transient current (signal) of the detector after radiation at different fluences will be simulated and calculated with professional software, namely the finite-element Technology Computer-Aided Design (TCAD) software frameworks. From analysis of the simulation results, one can predict the performance of the detector in heavy radiation environment. The fabrication of pixel detectors will be carried out in CMOS process platform of IMECAS based on ultra-pure high resistivity (up to 104 ohm·cm) silicon material.

Improving the Luminosity Burn-Off Estimate by Considering Single-Diffractive Effects

Collisions in a high-luminosity collider result in a continuous burn-off of the circulating beams that is the dominant effect that reduces the instantaneous luminosity over time. In order to obtain a good estimate of the luminosity evolution, it is imperative to have an accurate understanding of the burn-off. Typically, this is calculated based on the inelastic cross-section, as it provides a direct estimate of the number of protons that participate in inelastic collisions, and are hence removed. Likewise, protons that participate in elastic collisions will remain in the machine acceptance, still contributing to luminosity. In between these two regimes lie diffractive collisions, for which the protons have a certain probability to remain in the machine acceptance. Recent developments of the SixTrack code allow it to interface with Pythia, thus allowing for more precise simulations to obtain a better estimate of the diffractive part of the cross-section. In this paper, we will mainly concentrate on slowly-drifting protons that are close to the acceptance limit, resulting from single-diffractive scattering.

Influence of surface damage and bulk defects on the interstrip isolation of p-type silicon strip sensors

Silicon strip sensors of upcoming tracking detectors in high luminosity colliders usually consist of a p-doped bulk with n-type strip implants. The general consensus is that such a design requires an additional interstrip isolation structure such as a p-stop implant. If there is no additional implant between the strips, it is expected that the strip isolation will be insufficient. Before irradiation, impurities and defects in the material lead to positive charge in the oxide and Si/SiO_2 interface which attracts electrons from the bulk. Those electrons accumulate just beneath the surface and between the n+ strip or pixel implants, which decreases the interstrip resistance significantly. Ionising radiation introduces even more charge inside the silicon dioxide, which further decreases the interstrip resistance. Contrary to that expectation of a decreasing interstrip resistance due to irradiation, a high interstrip resistance was sometimes observed after proton irradiation. Hence, bulk defects induced by proton irradiation seem to have a non-negligible impact on the strip isolation. Therefore, an irradiation campaign with sensors without any interstrip isolation implant has been performed. The use of sensors without isolation structures provides deeper insight into the dominant isolation effects. The sensors' performance is first evaluated before irradiation. Afterwards, a set of sensors is irradiated with different particles in order to systematically introduce a mixture of surface and bulk defects. This enables the distinction and leads to a better understanding of the different effects. Finally, a combined TCAD model is derived which is able to describe the beneficial effect of bulk defects and the complicated interplay between surface and bulk damage.

Forbidden dark matter annihilations into Standard Model particles

We present kinematically forbidden dark matter annihilations into Standard Model leptons. This mechanism precisely selects the dark matter mass that gives the observed relic abundance. This is qualitatively different from existing models of thermal dark matter, where fixing the relic density typically leaves open orders of magnitude of viable dark matter masses. Forbidden annihilations require the dark matter to be close in mass to the particles that dominate its annihilation rate. We show examples where the dark matter mass is close to the muon mass, the tau mass, or the average of the tau and muon masses. We find that most of the relevant parameter space can be covered by the next generation of proposed beam-dump experiments and future high-luminosity electron positron colliders. Forbidden dark matter predicts large couplings to the Standard Model that can explain the observed value of (g − 2)μ.

Cryogenic Electronics Development for High-Energy Physics: An Overview of Design Considerations, Benefits, and Unique Challenges

In the quest to study the fundamental nature of matter and the universe, high-energy physics (HEP) experiments often operate in extreme conditions that lie well outside the standard operating range of integrated circuits (ICs). Two prominent examples of such extreme environments are 1) the irradiation levels experienced at high luminosity colliders and 2) operation at cryogenic temperatures [1]. Cryogenic electronics is a broad term that encompasses circuits operating at temperatures below the standard operating limit (−55 °C in the case of military grade electronics), all of the way down to millikelvin, as in the case of superconducting circuits. Cryogenic circuits have a long history [2] and have found applications in a broad spectrum of applications, such as infrared focal plane arrays, positron emission tomography, and quantum science. While CMOS circuits have been reliably operated at deep-cryogenic temperatures (<; 4.2 K), this article focuses on applications down to liquid nitrogen (77 K) and provides an overview of the design considerations, benefits, and unique challenges pertaining to cryogenic CMOS ICs for large HEP experiments.

Overview of CMOS Sensors for Future Tracking Detectors

Depleted Complementary Metal-Oxide-Semiconductor (CMOS) sensors are emerging as one of the main candidate technologies for future tracking detectors in high luminosity colliders. Their capability of integrating the sensing diode into the CMOS wafer hosting the front-end electronics allows for reduced noise and higher signal sensitivity, due to the direct collection of the sensor signal by the readout electronics. They are suitable for high radiation environments due to the possibility of applying high depletion voltage and the availability of relatively high resistivity substrates. The use of a CMOS commercial fabrication process leads to their cost reduction and allows faster construction of large area detectors. In this contribution, a general perspective of the state of the art of CMOS detectors for High Energy Physics experiments is given. The main developments carried out with regard to these devices in the framework of the CERN RD50 collaboration are summarized.

Exploiting Cross-Luminescence in BaF2 for Ultrafast Timing Applications Using Deep-Ultraviolet Sensitive HPK Silicon Photomultipliers

Time resolution of scintillation-based detectors is becoming continuously more important. In medical applications, especially in positron emission tomography (PET), better time of flight (TOF) information of the emitted gammas leads to a higher signal-to-noise ratio in the reconstructed image. Benefits are lower doses applied to and/or shorter scanning times for the patient. In high energy physics (HEP) ultrafast timing becomes increasingly important for reducing pile up effects in future high luminosity colliders and therefore increasing the detector sensitivity in the search for rare events and new physics. This article is an initial study on exploiting the fast cross-luminescence emission in the inorganic BaF2 scintillator with deep ultraviolet-sensitive silicon photomultipliers (SiPMs) from Hamamatsu for precise timing in PET and HEP. Using BaF2 read out by these photodetectors with a photon detection efficiency (PDE) of only about 15% in the desired 200nm emission region, a time resolution of 94±5ps FWHM is achieved when coupling with air. This figure improves to 78$±4ps FWHM when coupling the BaF2 crystal with UV transparent optical grease, Viscasil, to the photodetector. This CTR performance obtained with BaF2 is already better than that measured with LYSO:Ce, a commonly used state-of-the-art inorganic scintillator in PET, when coupled to another Hamamatsu photodetector (S13360) and coupled with Meltmount. Assuming that one could increase the PDE in the ultraviolet to values of 60% obtained today at 420nm, the emission wavelength of LYSO, one could ultimately achieve CTRs below 40ps FWHM. Further improvements in CTR beyond these values could be envisaged if also the single photon time resolution (SPTR) of the ultraviolet sensitive SiPM could be enhanced. Studying the emission of BaF2 more in detail, a very fast decay component of less than 100ps has recently been observed, being of high interest in the domain of ultrafast timing. Hence, in depth investigation of this decay component would give an additional handle to improve time resolution. In view of the prospects in advancing technologies for ultraviolet sensitive SiPMs, with high PDE and SPTR, and further advancements in producing high quality BaF2, one could imagine the development of sub-30ps FWHM TOF-PET systems.

Time Projection Chamber as Inner Tracker for Super Charm-Tau factory at BINP

At present time Budker INP is developing a Super Charm-Tau factory project, which consists of a high-luminosity collider with the luminosity of 1035 cm−2s−1 and a universal magnetic detector. The tracking system of the detector will comprise of an Inner Tracker (IT) and a Drift Chamber (DC). One of the options for IT is Time Projection Chamber (TPC). The advantages of the TPC are high spatial resolution and particle identification capabilities by registration of dE/dx losses. However, using a Time Projection Chamber implies serious challenges. For example, the TPC have to simultaneously deal with tracks from several thousands events and maintain the enormous data rate. This work describes the results of the Monte-Carlo studies of the transport characteristics in various gas mixtures proposed for TPC. Besides of this, the simulation of the ion back flow and its effect on spatial resolution will be reported.