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Sebastian White

Publications and source records attributed to Sebastian White.

At least 19 recordsLinked to original sources
arXiv2025

Design, simulation and performance of the resistive-anode PICOSEC Micromegas detector

The PICOSEC Micromegas detector is a Micro-Pattern Gaseous Detector concept developed to achieve tens of picosecond timing resolution for charged particle detection by combining a Cherenkov radiator with a two-stage Micromegas amplification structure. To improve operational robustness, a resistive anode has been implemented using a DLC layer deposited on a Kapton substrate. While this design enhances detector stability, the resistive layer may influence rate capability, signal formation, and detector capacitance, altering timing performance. This work presents a comprehensive study of a resistive design, including an analytical model and finite-element simulations to quantify rate-dependent gain reduction due to ohmic voltage drop on the resistive layer. An analytical solution for the voltage across a finite-size resistive layer is derived, and a numerical model is developed to evaluate gain suppression under intense particle fluxes. The impact of the resistive layer on signal formation is investigated using time-dependent weighting fields and the Garfield++ simulation framework. The contribution of signal components induced by the resistive layer is quantified, and preservation of the signal leading edge is found for surface resistivities above 100 kohm per square. Single-channel resistive-anode prototypes were designed, constructed, and experimentally characterized. Laboratory measurements using single photoelectrons and power spectral density analysis show the predicted reduction in signal amplitude while preserving the leading edge. Muon beam tests with CsI and DLC photocathodes demonstrate a time resolution of 11.5 ps for CsI, comparable to 11.9 ps for the metallic-anode device, showing the suitability of the resistive design for precision timing applications.

physics.ins-det↗
arXiv2025

Amplitude Walk in Fast Timing: The Role of Dual Thresholds

We apply lessons from fast timing detector R$\&$D to strategies for initial calibration of large timing arrays at future colliders. Detector R$\&$D often benefits from detailed information about the sensor and front-end signal (waveform capture) as well as a quality time reference and tracking. On the other hand, the systems for charged particle (MIP) timing under construction for the CERN High Luminosity LHC log only limited information for each timing channel -- usually amplitude and the time of the leading edge. Furthermore the high event rates certainly present a challenge for \textit{in situ }calibration of the large (compared to intrinsic) time jitter of the leading edge with pulse amplitude -- amplitude walk. In the examples presented here we find a simple linear dependence of walk on the inverse of the pulse slope at threshold for the dynamic range (in amplitude) suitable to charged particle timing. We present a straightforward calibration method for the small variation in the corresponding coefficient from channel-to-channel.

physics.ins-det↗
arXiv2024

Initial Calibration of Large Timing Arrays for the LHC

In preparation for HL-LHC operation a number of new detector systems are being constructed with timing precision on physics objects of <50 picoseconds. These time stamps will reduce the level of pileup induced backgrounds in this LHC phase where the number of interactions per crossing will reach of order 100-200. In the case of CMS, three new systems have initially to be corrected for the usual amplitude walk resulting from the effect of variations in signal size on leading edge timing. In these systems the resulting timing spread (ie walk) ranges from one to four nanoseconds. In the following note we advocate approaching this initial calibration for walk as a calculable correction given early calibration during commissioning -- rather than depending on special collider data to perform the calibration. We derive a simple analytic expression for the walk correction and confirm its effectiveness with lab data.

hep-ex↗
arXiv2023

A large area 100 channel Picosec Micromegas detector with sub 20 ps time resolution

The PICOSEC Micromegas precise timing detector is based on a Cherenkov radiator coupled to a semi-transparent photocathode and a Micromegas amplification structure. The first proof of concept single-channel small area prototype was able to achieve time resolution below 25 ps. One of the crucial aspects in the development of the precise timing gaseous detectors applicable in high-energy physics experiments is a modular design that enables large area coverage. The first 19-channel multi-pad prototype with an active area of approximately 10 cm$^2$ suffered from degraded timing resolution due to the non-uniformity of the preamplification gap. A new 100 cm$^2$ detector module with 100 channels based on a rigid hybrid ceramic/FR4 Micromegas board for improved drift gap uniformity was developed. Initial measurements with 80 GeV/c muons showed improvements in timing response over measured pads and a time resolution below 25 ps. More recent measurements with a new thinner drift gap detector module and newly developed RF pulse amplifiers show that the resolution can be enhanced to a level of 17~ps. This work will present the development of the detector from structural simulations, design, and beam test commissioning with a focus on the timing performance of a thinner drift gap detector module in combination with new electronics using an automated timing scan method.

physics.ins-det↗
arXiv2023

Towards robust PICOSEC Micromegas precise timing detectors

The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector consisting of a Cherenkov radiator combined with a photocathode and a MM amplifying structure. A 100-channel non-resistive PICOSEC MM prototype with 10x10 cm^2 active area equipped with a Cesium Iodide (CsI) photocathode demonstrated a time resolution below 18 ps. The objective of this work is to improve the PICOSEC MM detector robustness aspects; i.e. integration of resistive MM and carbon-based photocathodes; while maintaining good time resolution. The PICOSEC MM prototypes have been tested in laboratory conditions and successfully characterised with 150 GeV/c muon beams at the CERN SPS H4 beam line. The excellent timing performance below 20 ps for an individual pad obtained with the 10x10 cm^2 area resistive PICOSEC MM of 20 MOhm/sq showed no significant time resolution degradation as a result of adding a resistive layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B4C) photocathode presented a time resolution below 35 ps; opening up new possibilities for detectors with robust photocathodes. The results made the concept more suitable for the experiments in need of robust detectors with good time resolution.

physics.ins-det↗
arXiv2019

Timing Performance of a Micro-Channel-Plate Photomultiplier Tube

The spatial dependence of the timing performance of the R3809U-50 Micro-Channel-Plate PMT (MCP-PMT) by Hamamatsu was studied in high energy muon beams. Particle position information is provided by a GEM tracker telescope, while timing is measured relative to a second MCP-PMT, identical in construction. In the inner part of the circular active area (radius r$<$5.5\,mm) the time resolution of the two MCP-PMTs combined is better than 10~ps. The signal amplitude decreases in the outer region due to less light reaching the photocathode, resulting in a worse time resolution. The observed radial dependence is in quantitative agreement with a dedicated simulation. With this characterization, the suitability of MCP-PMTs as $\text{t}_\text{0}$ reference detectors has been validated.

physics.ins-det↗
arXiv2018

Digitized Waveform Processing for Fast Timing

The prospect of pileup induced backgrounds at the High Luminosity LHC (HL-LHC) has stimulated intense interest in technology for charged particle timing at high rates\cite{challenge}. In this paper I report on a framework for fast timing sensor and related electronics development used primarily within the context of PICOSEC. Our collaboration accumulated a large ($\sim$fewTbyte) set of waveforms from timing sensors based on MicroChannel Plates(MCP), MicroPattern Gas Detectors(MPGD) and capacitive readout Avalanche Diodes (aka HFS) with typically 20-40 GSa/s waveform sampling. We have reported charged particle time resolutions of 3.6, 24 and 20 picoseconds, respectively for these sensors. In this paper I discuss some of the tools developed during this activity for the processing of waveforms digitized at sampling rates ranging from 40 MHz (ATLAS ZDC) to 40 GHz (PICOSEC).

physics.ins-det↗
arXiv2017

PICOSEC: Charged particle Timing to 24 picosecond Precision with MicroPattern Gas Detectors

The prospect of pileup induced backgrounds at the High Luminosity LHC (HL-LHC) has stimulated intense interest in technology for charged particle timing at high rates. In contrast to the role of timing for particle identification, which has driven incremental improvements in timing, the LHC timing challenge dictates a specific level of timing performance- roughly 20-30 picoseconds. Since the elapsed time for an LHC bunch crossing (with standard design book parameters) has an rms spread of 170 picoseconds, the $\sim50-100$ picosecond resolution now commonly achieved in TOF systems would be insufficient to resolve multiple "in-time" pileup. Here we present a MicroMegas based structure which achieves the required time precision (ie 24 picoseconds for 150 GeV $\mu$'s) and could potentially offer an inexpensive solution covering large areas with $\sim 1$ cm$^2$ pixel size. We present here a proof-of-principle which motivates further work in our group toward realizing a practical design capable of long-term survival in a high rate experiment.

physics.ins-det↗
arXiv2016

Fast Timing for High-Rate Environments with Micromegas

The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate a Micromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkov-radiator front window, which produces sufficient UV photons to convert the ~100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ~50 primary photoelectrons, using a bulk Micromegas readout.

physics.ins-det↗
arXiv2013

Experimental Challenges of the European Strategy for Particle Physics

In planning for the Phase II upgrades of CMS and ATLAS major considerations are: 1)being able to deal with degradation of tracking and calorimetry up to the radiation doses to be expected with an integrated luminosity of 3000 $fb^{-1}$ and 2)maintaining physics performance at a pileup level of ~140. Here I report on work started within the context of the CMS Forward Calorimetry Task Force and continuing in an expanded CERN RD52 R$&$D program integrating timing (i.e. measuring the time-of-arrival of physics objects) as a potential tool for pileup mitigation and ideas for Forward Calorimetry. For the past 4 years our group has focused on precision timing at the level of 10-20 picoseconds in an environment with rates of $~10^6-10^7$ Hz/$cm^2 $ as is appropriate for the future running of the LHC (HL-LHC era). A time resolution of 10-20 picoseconds is one of the few clear criteria for pileup mitigation at the LHC, since the interaction time of a bunch crossing has an rms of 170 picosec. While work on charged particle timing in other contexts (i.e. ALICE R$&$D) is starting to approach this precision, there have been essentially no technologies that can sustain performance at these rates. I will present results on a tracker we developed within the DOE Advanced Detector R$&$D program which is now meeting these requirements. I will also review some results from Calorimeter Projects developed within our group (PHENIX EMCAL and ATLAS ZDC) which achieved calorimeter timing precision< 100 picoseconds.

physics.ins-det↗
arXiv2011

Mathematica with ROOT

We present an open-source Mathematica importer for CERN ROOT files. Taking advantage of Mathematica's import/export plug-in mechanism, the importer offers a simple, unified interface that cleanly wraps around its MathLink-based core that links the ROOT libraries with Mathematica. Among other tests for accuracy and efficiency, the importer has also been tested on a large (~5 Gbyte) file structure, D3PD, used by the ATLAS experiment for offline analysis without problems. In addition to describing the installation and usage of the importer, we discuss how the importer may be further improved and customized. A link to the package can be found at: http://library.wolfram.com/infocenter/Articles/7793/ and a related presentation is at: http://cd-docdb.fnal.gov/cgi-bin/DisplayMeeting?conferenceid=522

physics.data-an↗
arXiv2010

Neutron Production and Zero Degree Calorimeter Acceptance at LHC

We calculate cross sections for the far forward LHC detectors to be used for luminosity measurement. A simple model, based on a parametrization of available inclusive neutron data and the assumption that 2 arm rates in non-diffractive events are uncorrelated, is introduced. The calculated rates are in reasonable agreement with preliminary data from RHIC and we are now comparing with rates at 3 LHC energies.

hep-ph↗
arXiv2010

Diffraction at the LHC: a non-technical Introduction

In diffractive interactions of protons or nuclei a violent collision can occur that leaves the forward going particle completely intact -with probability determined by the structure of the proton or nucleus. At very high energies these collisions also occur with both incident particles remaining intact. This is called central exclusive production. If a new particle, such as the Higgs boson, were produced exclusively this process would give a precise measurement of its mass and test for expected properties of the Higgs. Because of its unusual features this process is also a promising discovery tool. In this paper I focus on analogous electromagnetic processes because many aspects apply to both- particularly the role of coherence. Also, topics in diffraction with nuclear beams are based on electromagnetic interactions. I also discuss two proposed measurements in ATLAS with Pb beams and with proton beams (diffractive Higgs production).

nucl-ex↗
arXiv2010

The role of Spectator Fragments at an electron Ion collider

Efficient detection of spectator fragments is key to the main topics at an electron-ion collider (eIC). Any process which leads to emission of fragments or $γ$'s breaks coherence in diffractive processes. Therefore this is equivalent to non-detection of rapidity gaps in pp collisions. For example, in coherent photoproduction of vector mesons their 4-momentum transfer distribution would image the "gluon charge" in the nucleus in the same way that Hofstadter measured its charge structure using elastic scattering of $\sim$100 MeV electrons. Whereas he could measure the $\sim$4 MeV energy loss by the electron due to excitation of nuclear energy levels (Figure 1), even the energy spread of the incident beam would prevent such an inclusive selection of quasielastic events at an eIC. The only available tool is fragment detection. Since, in our example, one finds that $\sim100$ of deexcitations go through $γ$'s or 1 neutron, rarely to 2 neutron and never to protons(due to Coulomb barrier suppression), the eIC design should emphasize their detection.

nucl-ex↗
arXiv2009

Beam Fragmentation in Heavy Ion Collisions and its implication for RHIC triggers at low s

We show that with a realistic treatment of spectator momentum distributions the RHIC detector trigger sensitivity is high even when RHIC is run below injection energies. In particular, a problem region with $\sqrt{s_{NN}}$=10 to 60 or 80 GeV assuming a simple Fermi step model is not found when using a more realistic one. We argue also that production of fast nucleons (with momenta $> p_F$ in the nucleus rest frame) provides complementary information about the collision process.

nucl-ex↗
arXiv2009

Design of a 10 picosecond Time of Flight Detector using Avalanche Photodiodes

We describe a detector for measuring the time of flight of forward protons at the Large Hadron Collider (LHC) up to and beyond the full instantaneous design luminosity of 1034 cm-2 s-1. Our design is based on deep diffused, high gain avalanche photodiodes (APDs) which give a signal of ~6000 e when traversed by 7 Teravolt protons. We observe pulse risetimes of 650 psec and a pulse width of 5 nsec and calculate a time resolution of ~10 psec and a maximum count rate of >100 Mhz.

physics.ins-det↗