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

Executive Summary

The CMS Precision Proton Spectrometer (PPS) underwent a major upgrade for LHC Run 3, focusing on enhanced radiation tolerance and improved timing resolution for Central Exclusive Production (CEP) studies.

Core Upgrade: The PPS system, located 200 m from the CMS interaction point, received substantial upgrades to both its tracking and timing subsystems to handle the higher luminosity and radiation environment of Run 3.
Tracking System: Utilizes new 150 µm-thick, single-sided 3D silicon pixel sensors (FBK production) read out by PROC600 chips, designed for superior radiation hardness compared to Run 2 components.
Radiation Mitigation: A critical innovation is the integration of a miniaturized stepping motor, allowing remote vertical movement (approx. 500 µm steps) of the tracking detectors during beam downtimes. This strategy successfully mitigates efficiency degradation caused by non-uniform irradiation of the readout chips.
Timing System: Upgraded with 500 µm-thick single-crystal CVD diamond sensors (Element Six) arranged in a double-diamond configuration, optimizing the signal-to-noise ratio.
Performance Validation: The vertical movement strategy proved effective, maintaining tracking efficiency across the 2023 data-taking period (26.0 fb^-1 collected).
Timing Improvement: Preliminary results show the vertex longitudinal coordinate resolution (Z_{PPS, timing}) achieved 1.9 cm, representing a significant improvement over the 2.77 cm resolution obtained during Run 2.

Technical Specifications

Parameter	Value	Unit	Context
Tracking Sensor Type	3D Silicon Pixel	N/A	Single-sided processing (Run 3)
Tracking Sensor Thickness	150	µm	Physical thickness
Tracking Active Bulk Thickness	230	µm	Active material depth
Tracking Pixel Pitch	150 x 100	µm²	Pixel geometry
Tracking Readout Chip	PROC600	N/A	Used for Run 3 sensors
Timing Sensor Material	Single-crystal CVD Diamond	N/A	Procured from Element Six
Timing Sensor Thickness	500	µm	Sensor thickness
Timing Configuration	Double-diamond	N/A	Two aligned sensors read by one amplifier
Target Time Resolution	Less than 30	ps	Timing system design goal
Achieved Vertex Z Resolution (Run 3)	1.9	cm	Preliminary result, two-arm timing system
Run 2 Vertex Z Resolution (Comparison)	2.77	cm	Previous performance baseline
Integrated Luminosity Collected (2023)	26.0	fb^-1	PPS Tracker + Timing active time
Vertical Movement Step Size	Approx. 500	µm	Used for radiation damage mitigation
Z_vertex vs Delta t Slope (Observed)	0.048 ± 0.003	ns/cm	Correlation measurement

Key Methodologies

The PPS upgrade and performance validation involved specific material sourcing, assembly, and operational strategies:

Sensor Sourcing and Production:
- Tracking: New 3D silicon pixel sensors were produced at Fondazione Bruno Kessler (FBK, Trento, Italy), leveraging single-sided processing technology for Run 3.
- Timing: 500 µm-thick single-crystal CVD diamond sensors were procured from Element Six (Didcot, UK).
Module Assembly and Integration:
- Tracking sensors were bump-bonded at IZM (Berlin) to four PROC600 readout chips and assembled onto newly designed flex hybrids.
- Timing sensors were integrated into a double-diamond layout (two aligned crystals per channel) to optimize the signal-to-noise ratio.
Radiation Damage Mitigation (Tracking):
- A miniaturized stepping motor was integrated into the detector package mechanics.
- This motor allows for remote, vertical movement of the sensors (in steps of approximately 500 µm) during beam downtimes.
- This movement shifts the region of peak irradiation away from the damaged area of the readout chip, effectively recovering detector efficiency.
Timing Readout Optimization:
- The readout chain was revised, utilizing the NINO comparator and the HPTDC for primary timing measurement.
- An alternative readout path based on the SAMPIC chip was added to provide a precise reference for detector commissioning and calibration.
Performance Characterization:
- Tracking efficiency was evaluated as a function of integrated luminosity (fb^-1) to monitor the evolution of radiation damage and confirm the effectiveness of the vertical movement strategy.
- Vertex longitudinal resolution was derived from low pileup data (average interactions per bunch-crossing µ = 1) by comparing the PPS timing coordinate (Z_{PPS, timing}) with the central CMS tracker coordinate (Z_vertex).

Commercial Applications

The advanced materials and engineering solutions developed for the CMS PPS have direct relevance to several high-tech and industrial sectors:

High-Energy Physics (HEP) and Accelerator Technology:
- Precision tracking and timing detectors for future high-luminosity colliders (e.g., HL-LHC).
- Radiation-hard beam monitoring and diagnostics systems.
Radiation Detection and Dosimetry:
- Single-Crystal CVD Diamond: Used for high-speed, high-resolution radiation detectors in extreme environments due to its wide bandgap, high carrier mobility, and exceptional radiation hardness.
- Applications include medical dosimetry (radiotherapy), neutron detection, and environmental monitoring.
Space and Aerospace Electronics:
- 3D Silicon Pixel Detectors: Their inherent radiation tolerance makes them ideal for imaging and sensing applications in satellites and deep-space missions where components are exposed to high flux of charged particles.
High-Speed Electronics and Data Acquisition:
- Development and testing of ultra-fast readout chips (like PROC600) and timing electronics (NINO, HPTDC) are transferable to high-throughput data processing and telecommunications infrastructure.
Precision Robotics and Remote Handling:
- The miniaturized stepping motor system designed for remote, precise movement in a hazardous environment (Roman Pots) is applicable to remote handling systems in nuclear facilities or other inaccessible industrial settings.

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