Implementation and First Results of the High-Density Gas Target (SMOG2) at the LHCb Experiment

Core Concepts

The newly installed SMOG2 gas target system at LHCb enables a diverse physics program by providing a high-density gas target within the LHCb detector, allowing for fixed-target collisions concurrently with collider mode operation, and opening new possibilities for heavy-ion, hadron, spin, and astroparticle physics research.

Abstract

• Bibliographic Information: O. Boente Garcia et al. (LHCb Collaboration), "High-density gas target at the LHCb experiment," Phys. Rev. Accel. Beams 27, 111001 (2024).
• Research Objective: This paper describes the implementation and first results of the SMOG2 system, a fixed-target gas target system integrated into the LHCb experiment at CERN. The research aims to demonstrate the system's capabilities for conducting a wide range of physics studies, including heavy-ion physics, nucleon structure, and cosmic-ray physics.
• Methodology: The paper details the technical design and construction of the SMOG2 system, including the storage cell, gas feed system, and considerations for minimizing interference with the LHC beam. It also outlines the physics program enabled by SMOG2, highlighting the unique opportunities it offers for various research areas. The commissioning of the system and initial data collected during the 2022 LHC runs are presented, showcasing the system's functionality and potential.
• Key Findings: The SMOG2 system successfully operates within the LHCb detector, enabling fixed-target collisions without compromising the data acquisition and reconstruction quality of both beam-gas and beam-beam interactions. The commissioning phase demonstrated the system's capability to handle various gases, including helium, neon, argon, and hydrogen, with plans to incorporate deuterium, nitrogen, oxygen, and heavier noble gases. The system's design allows for a high target areal density, leading to an expected integrated luminosity comparable to dedicated fixed-target experiments.
• Main Conclusions: The successful implementation and commissioning of the SMOG2 system at LHCb mark a significant advancement in particle physics experimentation. The system's ability to operate concurrently with the collider mode, its versatility in handling various gases, and its high target areal density open up unique opportunities for a diverse physics program, promising significant contributions to our understanding of heavy-ion physics, nucleon structure, and cosmic-ray physics.
• Significance: The SMOG2 system enhances the research capabilities of the LHCb experiment, enabling it to explore new physics domains and address fundamental questions in particle physics. The system's unique features and the promising results from its commissioning phase position it as a valuable tool for future research at the LHC.
• Limitations and Future Research: The paper acknowledges the need for further studies on the injection of heavier gases and the long-term effects of gas injection on the NEG coating of surrounding components. Future research will focus on exploiting the full potential of the SMOG2 system for various physics analyses, including measurements of charm production, antiproton production, and studies of heavy-ion collisions at large rapidities.

Stats

Beam-gas interactions occur at approximately 4% of the proton–proton (pp) collision rate at LHCb.
The system can collect 100 pb−1 of proton fixed-target data per year with a flow rate as low as 10^15 particles per second.
The storage cell is positioned 34 cm away from the main interaction point of the LHCb detector.
The storage cell is 20 cm long with an inner diameter of 1 cm.
The minimum allowed aperture over the longitudinal range of the SMOG2 storage cell is 3 mm.
The expected beam lifetime with the gas target is 2060, 97, and 22 days for pH, pAr, and PbAr, respectively.

Quotes

"The recently installed internal gas target at LHCb presents exceptional opportunities for an extensive physics program for heavy-ion, hadron, spin, and astroparticle physics."
"The commissioning phase has yielded promising results, demonstrating that fixed-target collisions can occur concurrently with the collider mode without compromising efficient data acquisition and high-quality reconstruction of beam-gas and beam-beam interactions."

Key Insights Distilled From

High-density gas target at the LHCb experiment

by O. Boente Ga... at arxiv.org 11-12-2024

https://arxiv.org/pdf/2407.14200.pdf

Deeper Inquiries

How might the data collected using SMOG2 influence the development of future particle accelerators and detectors, particularly those focused on fixed-target experiments?

The data collected using SMOG2 at LHCb stands to significantly influence the development of future particle accelerators and detectors, especially those designed for fixed-target experiments, in several key ways:

Optimization of Fixed-Target Configurations: SMOG2, by successfully operating concurrently with the collider mode at LHCb, provides a compelling proof-of-concept for integrated fixed-target programs within collider experiments. This could encourage the implementation of similar setups in future colliders, maximizing their physics reach without the need for dedicated fixed-target beamlines.
Advancements in Gas Target Technology: The design and operation of SMOG2's storage cell, with its ability to handle a variety of gases at high densities while maintaining LHC vacuum requirements, pushes the boundaries of gas target technology. The lessons learned from SMOG2, particularly in terms of gas injection, density control, and mitigation of beam-induced effects, will be invaluable for developing more sophisticated gas targets for future experiments.
Development of Advanced Detector Systems: The successful integration of SMOG2 with the LHCb detector, particularly the VELO, offers valuable insights for future detector development. The need to handle the specific challenges posed by fixed-target collisions, such as higher particle rates at forward angles and potential background from beam-gas interactions, will drive innovation in areas like radiation-hard materials, high-granularity tracking, and fast data acquisition systems.
Novel Background Suppression Techniques: Operating a fixed-target experiment within a collider environment necessitates the development of highly effective background suppression techniques. The experience gained from SMOG2 in identifying and mitigating backgrounds, such as those induced by beam-gas interactions or the machine itself (MIB), will be crucial for future fixed-target experiments, enabling cleaner event selection and more precise measurements.
In essence, SMOG2 serves as a valuable testing ground for technologies and methodologies relevant to fixed-target experiments. The knowledge gained from its operation will be instrumental in shaping the next generation of particle accelerators and detectors, paving the way for more precise and wide-ranging explorations of the subatomic world.

Could the presence of the gas target, even with its minimal impact, introduce unforeseen systematic uncertainties in the measurements of other LHCb experiments running concurrently?

While SMOG2 is designed to minimize interference with LHCb's primary collider program, its presence could potentially introduce subtle systematic uncertainties in concurrent measurements. These uncertainties, though likely small, warrant careful consideration and dedicated studies:

Luminosity Determination: The presence of the gas target, even at low densities, could slightly alter the beam profile and luminosity at the LHCb interaction point. This effect, if not accurately accounted for, could introduce systematic uncertainties in luminosity-dependent measurements, such as cross-section determinations.
Trigger and Reconstruction Biases: The additional particles produced in beam-gas interactions, though largely mitigated by LHCb's trigger and reconstruction algorithms, could introduce subtle biases. For instance, they might marginally affect track reconstruction efficiency or introduce spurious vertices, potentially impacting specific analyses, particularly those sensitive to rare processes or requiring high track multiplicities.
Material Budget Variations: The opening and closing of the SMOG2 storage cell, though carefully designed, could lead to minute variations in the material budget traversed by particles originating from beam-beam collisions. These variations, if not properly modeled, could affect particle identification and momentum reconstruction, introducing systematic uncertainties in certain measurements.
To mitigate these potential uncertainties, dedicated studies are crucial. These might involve:

Data-Driven Corrections: Analyzing control samples of beam-beam collisions with and without the gas target to quantify and correct for any systematic differences in luminosity, trigger efficiency, or reconstruction performance.
Simulation Validation: Rigorously validating Monte Carlo simulations that incorporate the SMOG2 system to ensure accurate modeling of beam-gas interactions, material budget effects, and their impact on LHCb measurements.
Dedicated Calibration Runs: Performing specific calibration runs with the gas target to precisely characterize its influence on the detector response and develop dedicated corrections for sensitive analyses.
By meticulously addressing these potential systematic effects, LHCb can ensure the high precision and reliability of its measurements, even with the concurrent operation of the SMOG2 fixed-target system.

If we could create a "telescope" to directly observe the internal interactions within the SMOG2 system during a collision, what fundamental insights about the nature of matter and energy might we gain?

A hypothetical "telescope" capable of directly observing the internal interactions within SMOG2 during a collision would be a revolutionary tool, potentially unveiling profound insights into the fundamental nature of matter and energy:

Real-Time QCD Dynamics: We could witness the intricate dance of quarks and gluons in unprecedented detail. Observing the initial parton-parton interactions, the subsequent hadronization process where quarks and gluons combine to form observable particles, and the evolution of the resulting particle shower would provide invaluable data to refine our understanding of Quantum Chromodynamics (QCD), the theory governing the strong force.
Three-Dimensional Nucleon Tomography: By tracking the trajectories and energies of particles emerging from the collisions, we could reconstruct the three-dimensional momentum distribution of quarks and gluons within the nucleons of the target gas. This would be akin to performing a "CT scan" of the proton or nucleus, revealing its internal structure with unprecedented clarity and providing crucial insights into the origins of nucleon spin, mass, and other fundamental properties.
Exotic Particle Searches: The high energies involved in LHC collisions, coupled with the unique kinematic conditions of the fixed-target configuration, could potentially create exotic particles not previously observed. Our "telescope" would allow us to directly search for these elusive particles, such as those predicted by supersymmetry or other theories beyond the Standard Model, potentially revolutionizing our understanding of the universe's fundamental constituents.
Nuclear Matter Under Extreme Conditions: By using heavier gases like xenon or krypton in SMOG2, we could create tiny, extremely dense fireballs of nuclear matter, mimicking the conditions that existed in the very early universe. Observing the properties and evolution of these fireballs could shed light on the phase transitions of nuclear matter, the formation of heavy nuclei, and the dynamics of the quark-gluon plasma, a state of matter thought to have existed shortly after the Big Bang.
Such a "telescope," though currently beyond our technological reach, represents the ultimate dream for particle physicists. It would provide an unparalleled window into the subatomic world, allowing us to directly observe the fundamental processes that govern the universe at its most fundamental level. The knowledge gained would undoubtedly revolutionize our understanding of physics and potentially lead to groundbreaking technological advancements.