The CMS Precision Proton Spectrometer in Run 3 - upgrade and performance

At a Glance

Metadata	Details
Publication Date	2024-12-17
Authors	Andrea Bellora
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for High Energy Physics Timing Detectors

This document analyzes the requirements and achievements detailed in the paper “The CMS Precision Proton Spectrometer in Run 3: upgrade and performance” and maps them directly to 6CCVD’s advanced MPCVD diamond capabilities, positioning 6CCVD as the premier supplier for next-generation radiation-hard timing and tracking systems.

Executive Summary

The CMS Precision Proton Spectrometer (PPS) upgrade for LHC Run 3 demonstrates the critical role of high-purity Single-Crystal Diamond (SCD) in achieving state-of-the-art timing resolution in extreme radiation environments.

Core Application: Time-of-flight measurement and vertex reconstruction in the CMS PPS at the CERN LHC.
Critical Material: 500 µm-thick Single-Crystal CVD (SCD) diamond sensors, utilized in a radiation-hard double-diamond configuration.
Performance Achievement: The upgrade resulted in a substantial improvement in vertex z resolution, achieving a preliminary result of 1.9 cm, significantly better than the 2.77 cm achieved in Run 2.
Engineering Innovation: Implementation of a vertical movement system (≈ 500 µm steps) to mitigate efficiency degradation caused by non-uniform irradiation damage.
Material Requirement: Ultra-high purity, high charge collection efficiency (CCE) SCD is mandatory to meet the target time resolution of < 30 ps.
6CCVD Value Proposition: 6CCVD specializes in delivering custom, high-purity SCD wafers (0.1 µm to 500 µm thickness) with precision laser segmentation and custom metalization required for advanced HEP detector assembly.

Technical Specifications

The following hard data points were extracted from the analysis of the CMS PPS Run 3 upgrade:

Parameter	Value	Unit	Context
Diamond Sensor Material	Single-Crystal CVD (SCD)	N/A	Timing system detectors
Diamond Sensor Thickness	500	µm	Required thickness for time-of-flight measurement
Target Time Resolution	< 30	ps	Goal for the upgraded timing system
Achieved Vertex Z Resolution (Run 3 Preliminary)	1.9	cm	Significant improvement over Run 2 performance
Previous Vertex Z Resolution (Run 2)	2.77	cm	Baseline performance
Detector Configuration	Double-diamond	N/A	Two aligned SCD sensors per plane
Detector Movement Step	≈ 500	µm	Vertical movement for radiation damage mitigation
Integrated Luminosity (2023)	26.0	fb^-1	Collected by PPS timing detectors
LHC Collision Energy	13.6	TeV	Operating environment for Run 3

Key Methodologies

The successful upgrade and preliminary performance validation relied on precise material specification and advanced mechanical integration:

Material Procurement: New production of 500 µm-thick single-crystal diamond sensors, segmented into two or four channels, was sourced for high radiation tolerance.
Detector Layout: All new detector planes utilized a double-diamond layout (two aligned SCD sensors) to optimize the signal-to-noise ratio (SNR) for precise timing.
Readout Optimization: The timing readout chain was revised, utilizing the NINO comparator and HPTDC, with an alternative SAMPIC readout added for precise commissioning reference.
Radiation Damage Mitigation: A miniaturized stepping motor was integrated into the detector package mechanics, allowing for remote vertical movement (≈ 500 µm steps) during beam downtimes.
System Expansion: The total number of timing stations was increased, bringing the total to two stations (8 diamond planes) per side of CMS, enhancing redundancy and coverage.
Performance Validation: Preliminary results were derived from low pileup data analysis, confirming the effectiveness of the upgrades in improving vertex z resolution.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification MPCVD diamond materials required for the next phase of high-energy physics instrumentation, offering custom solutions that exceed standard catalog offerings.

Applicable Materials for HEP Timing Detectors

To replicate or extend the performance achieved in the CMS PPS Run 3 upgrade, researchers require ultra-high purity, low-defect SCD.

6CCVD Material	Specification	Relevance to PPS Upgrade
Optical Grade SCD	High Purity, Low Nitrogen (N) Concentration, High CCE	Essential for achieving < 30 ps time resolution and maximizing radiation hardness.
Custom Thickness SCD	0.1 µm to 500 µm (Standard)	Direct match for the 500 µm thickness used in the PPS timing system.
Polycrystalline Diamond (PCD)	Up to 125 mm diameter plates	Suitable for large-area tracking or dosimetry applications where single-crystal size is limiting.

Customization Potential for Advanced Detector Design

The PPS upgrade utilized segmented crystals and specific mechanical integration. 6CCVD offers full customization to meet these complex engineering demands:

Custom Dimensions & Segmentation: 6CCVD provides precision laser cutting services to segment SCD wafers into the required 2- or 4-channel layouts, ensuring perfect alignment for double-diamond configurations.
Thickness Control: We guarantee thickness uniformity across the wafer, critical for minimizing time-walk effects and ensuring consistent charge collection efficiency (CCE) across all detector channels.
Surface Preparation: Our SCD wafers are polished to an industry-leading surface roughness of Ra < 1 nm, which is crucial for minimizing surface leakage current and optimizing metalization adhesion for reliable electrical contacts.
Integrated Metalization: 6CCVD offers in-house deposition of standard and custom metal stacks (including Au, Pt, Pd, Ti, W, Cu) required for bump-bonding or wire-bonding to front-end electronics like the NINO comparator or PROC600 chips.

Engineering Support for Radiation-Hard Systems

The challenge of non-uniform irradiation and radiation damage mitigation highlights the need for expert material selection.

Radiation Hardness Optimization: 6CCVD’s in-house PhD team specializes in optimizing the growth parameters of SCD to maximize intrinsic radiation tolerance, ensuring stable performance even after collecting high integrated luminosity (e.g., > 26 fb^-1).
Material Selection Consultation: We assist engineers in selecting the optimal diamond grade (SCD vs. PCD, doping levels) based on specific application requirements, such as high-rate tracking versus ultra-precise timing.
Global Logistics: We offer reliable global shipping (DDU default, DDP available) to major research facilities and universities worldwide, including CERN collaborators.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The CMS Precision Proton Spectrometer is designed for studying Central Exclusive Production in pp collisions at the LHC. It consists of tracking and timing detectors to measure protons that escape along the LHC beam line after the interaction in CMS. Both tracking and timing systems underwent a substantial upgrade for Run 3. The tracking detector employs new single-sided 150 $\mu$m-thick silicon 3D pixel sensors, read out with the PROC600 chip. An innovative mechanical solution was adopted to mitigate the radiation effects caused by the non-uniform irradiation of the readout chip, allowing for moving the detectors during beam downtimes. The time-of-flight measurement system uses 500 $\mu$m-thick single-crystal CVD diamond sensors in double-diamond configuration and was upgraded with the aim of improving the radiation tolerance and obtaining a time resolution of less than 30 ps. In this contribution the new apparatuses installed for Run 3 and their preliminary performance will be presented.

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.476.0870