Periodic Reporting for period 1 - FIXEDTARGETLAND (The ALICE fixed-target programme layout using bent crystals at the CERN Large Hadron Collider.)
Reporting period: 2020-09-01 to 2022-08-31
Advancements in the knowledge of fundamental constituents of matter and their interactions are usually driven by the development of experimental techniques and facilities, with a significant role of particle accelerators. The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is the world's largest and most powerful particle accelerator colliding opposite beams of protons (p) and lead ions (Pb), allowing for unprecedentedly high centre-of-mass energies of up to 14 TeV and 5.5 TeV, respectively. Its research potential can be extended by implementing a fixed-target experiment. One proposed idea is to perform a fixed-target experiment at ALICE (A Large Ion Collider Experiment), one of four main detectors at the LHC being optimised to register products of heavy-ion collisions, which provides appropriate apparatus to host such an experiment.
The general research objective of the project is to perform a feasibility study of the dedicated machine layout that would allow for the fixed-target programme at ALICE (ALICE-FT). The concept is based on steering onto a solid internal target a fraction of the beam halo split by bent crystals, similar to crystals being developed for beam collimation in the LHC. Splitting the beam is performed by exploiting the channelling process occurring inside a bent crystal, resulting in a trajectory deflection equivalent to the geometric bending angle of a crystal body. The problem to address was to design the machine layout that provides a number of protons on target high enough to exploit the full capabilities of the ALICE detector acquisition system without affecting the LHC availability for regular beam-beam collisions.
A significant innovation of the project is to bring particles of high energy collider to collisions with the fixed-target by deflecting them using the bent crystal. This technique allows profiting from the circulating beam halo particles that are usually considered useless, or even harmful, from the collider perspective. Another important novelty is to operate the LHC both in the collider mode and in the fixed-target mode simultaneously, substantially extending its scientific potential without significant investments into the new equipment. Moreover, due to collisions geometry and ALICE detector configuration, such a setup allows reaching far backward regions of pseudo-rapidity, uncharted with head-on collisions and not accessible with other similar experiments, like LHCb (also in a potential fixed-target mode), PHENIX, STAR.
The successful implementation of the ALICE-FT programme would also be a significant step forward in crystal applications for accelerators as crystals so far were rather used to remove or extract particles from the beam. Experience collected may lead to further crystal-based applications with a big potential in, e.g. crystal-based collimation systems, considered a possible upgrade in the LHC.
The general research objective of the project is to perform a feasibility study of the dedicated machine layout that would allow for the fixed-target programme at ALICE (ALICE-FT). The concept is based on steering onto a solid internal target a fraction of the beam halo split by bent crystals, similar to crystals being developed for beam collimation in the LHC. Splitting the beam is performed by exploiting the channelling process occurring inside a bent crystal, resulting in a trajectory deflection equivalent to the geometric bending angle of a crystal body. The problem to address was to design the machine layout that provides a number of protons on target high enough to exploit the full capabilities of the ALICE detector acquisition system without affecting the LHC availability for regular beam-beam collisions.
A significant innovation of the project is to bring particles of high energy collider to collisions with the fixed-target by deflecting them using the bent crystal. This technique allows profiting from the circulating beam halo particles that are usually considered useless, or even harmful, from the collider perspective. Another important novelty is to operate the LHC both in the collider mode and in the fixed-target mode simultaneously, substantially extending its scientific potential without significant investments into the new equipment. Moreover, due to collisions geometry and ALICE detector configuration, such a setup allows reaching far backward regions of pseudo-rapidity, uncharted with head-on collisions and not accessible with other similar experiments, like LHCb (also in a potential fixed-target mode), PHENIX, STAR.
The successful implementation of the ALICE-FT programme would also be a significant step forward in crystal applications for accelerators as crystals so far were rather used to remove or extract particles from the beam. Experience collected may lead to further crystal-based applications with a big potential in, e.g. crystal-based collimation systems, considered a possible upgrade in the LHC.
The work was mostly focused on delivering the design of the machine layout for the ALICE fixed-target experiment that will meet the requirements. This was mostly done by performing numeric simulations of the accelerator operation that allowed me to estimate the system's performance and perform optimisation of its parameters.
The machine layout for fixed-target experiments at ALICE, based on crystal-assisted HL-LHC beam halo splitting is the main result of the project. The main conclusions are that the project is well feasible, providing the expected performance without jeopardizing the regular operation of the LHC. Moreover, the project was optimized in terms of cost (one crystal instead of two, easy integration of the hardware) and machine operation flexibility (insensitive to changes in machine optics).
The results are exploited in the following ways:
1. The Letter of Intent for the ALICE fixed-target experiment is currently in preparation. It will be submitted soon to the ALICE collaboration. The results of this project are an important contribution to this Letter of Intend.
2. The promising results of this project, together with other crystal-based studies for the LHC, are a strong motivation for the deployment of the dedicated experimental test-stand that is planned to be installed in the Insertion 3 of the LHC. Such a test-stand will serve for experimental verification of concepts used in planned crystal-assisted fixed-target experiments in the LHC.
Dissemination of the results was done by publishing the results in the scientific journal (sent for review in October 2022), and attending important conferences (IPAC'22, HB'21) and workshops. Activities for non-scientific public were also organised for communication of the performed research.
The machine layout for fixed-target experiments at ALICE, based on crystal-assisted HL-LHC beam halo splitting is the main result of the project. The main conclusions are that the project is well feasible, providing the expected performance without jeopardizing the regular operation of the LHC. Moreover, the project was optimized in terms of cost (one crystal instead of two, easy integration of the hardware) and machine operation flexibility (insensitive to changes in machine optics).
The results are exploited in the following ways:
1. The Letter of Intent for the ALICE fixed-target experiment is currently in preparation. It will be submitted soon to the ALICE collaboration. The results of this project are an important contribution to this Letter of Intend.
2. The promising results of this project, together with other crystal-based studies for the LHC, are a strong motivation for the deployment of the dedicated experimental test-stand that is planned to be installed in the Insertion 3 of the LHC. Such a test-stand will serve for experimental verification of concepts used in planned crystal-assisted fixed-target experiments in the LHC.
Dissemination of the results was done by publishing the results in the scientific journal (sent for review in October 2022), and attending important conferences (IPAC'22, HB'21) and workshops. Activities for non-scientific public were also organised for communication of the performed research.
Crystal-based applications for beam splitting are so far rather focused on beam collimation or beam extraction techniques. What pushes this project beyond the state of the art is to propose a crystal-based machine layout, that can be easily and at low cost installed in the LHC to provide fixed-target collisions and therefore significantly extend the research potential of the LHC.
The fixed-target collisions in the LHC are designed to be operated simultaneously with the regular head-on collisions without jeopardising their efficiency. Several unique advantages are offered with the fixed-target mode compared to the collider mode. With a high density of targets, high yearly luminosities can be easily achieved. In terms of collision energy, the ALICE-FT layout would provide the most energetic beam ever in the fixed-target mode with the centre of mass energy per nucleon-nucleon of 115 GeV for proton beams.
The scientific impact of such a fixed-target programme covers an intensive study of strong interaction processes, quark and gluon distributions at high momentum fraction (x), sea quark and heavy-quark content in the nucleon and nucleus and the implication for cosmic ray physics. The hot medium created in ultra-relativistic heavy-ion collisions offers novel quarkonium and heavy-quark observables in the energy range between the Super Proton Synchrotron (SPS) and the Relativistic Heavy Ion Collider (RHIC), where the QCD phase transition is postulated.
The societal impact is expected to be similar to the impact of other high-energy experiments at CERN. Moreover, the project in some sense highlights the importance of reusing the available resources and making use of "waste" - the method developed in this project is based on intercepting particles that populate the beam halo. These particles are considered useless or even harmful from the collider's perspective and are usually removed from the machine. This project allows us to "recycle" these high-energy particles by redirecting them towards the target allowing for interesting experiments based on fixed-target collisions. The economic impact is also evident. Building a new scientific facility is usually related to a significant cost. On the other hand, this project is very efficient in terms of cost, as the proposed machine layout can be operated in parallel to the regular operation of the LHC. Furthermore, the hardware needed for the project is also minimalistic: one crystal system, one target system and a few absorbers of the same design as regular LHC collimators.
The fixed-target collisions in the LHC are designed to be operated simultaneously with the regular head-on collisions without jeopardising their efficiency. Several unique advantages are offered with the fixed-target mode compared to the collider mode. With a high density of targets, high yearly luminosities can be easily achieved. In terms of collision energy, the ALICE-FT layout would provide the most energetic beam ever in the fixed-target mode with the centre of mass energy per nucleon-nucleon of 115 GeV for proton beams.
The scientific impact of such a fixed-target programme covers an intensive study of strong interaction processes, quark and gluon distributions at high momentum fraction (x), sea quark and heavy-quark content in the nucleon and nucleus and the implication for cosmic ray physics. The hot medium created in ultra-relativistic heavy-ion collisions offers novel quarkonium and heavy-quark observables in the energy range between the Super Proton Synchrotron (SPS) and the Relativistic Heavy Ion Collider (RHIC), where the QCD phase transition is postulated.
The societal impact is expected to be similar to the impact of other high-energy experiments at CERN. Moreover, the project in some sense highlights the importance of reusing the available resources and making use of "waste" - the method developed in this project is based on intercepting particles that populate the beam halo. These particles are considered useless or even harmful from the collider's perspective and are usually removed from the machine. This project allows us to "recycle" these high-energy particles by redirecting them towards the target allowing for interesting experiments based on fixed-target collisions. The economic impact is also evident. Building a new scientific facility is usually related to a significant cost. On the other hand, this project is very efficient in terms of cost, as the proposed machine layout can be operated in parallel to the regular operation of the LHC. Furthermore, the hardware needed for the project is also minimalistic: one crystal system, one target system and a few absorbers of the same design as regular LHC collimators.