Interaction point

About: Interaction point is a research topic. Over the lifetime, 650 publications have been published within this topic receiving 4449 citations.

ForwArd Search ExpeRiment at the LHC

Abstract: New physics has traditionally been expected in the high-pT region at high-energy collider experiments. If new particles are light and weakly coupled, however, this focus may be completely misguided: light particles are typically highly concentrated within a few mrad of the beam line, allowing sensitive searches with small detectors, and even extremely weakly coupled particles may be produced in large numbers there. We propose a new experiment, forward search experiment, or FASER, which would be placed downstream of the ATLAS or CMS interaction point (IP) in the very forward region and operated concurrently there. Two representative on-axis locations are studied: a far location, 400 m from the IP and just off the beam tunnel, and a near location, just 150 m from the IP and right behind the TAN neutral particle absorber. For each location, we examine leading neutrino- and beam-induced backgrounds. As a concrete example of light, weakly coupled particles, we consider dark photons produced through light meson decay and proton bremsstrahlung. We find that even a relatively small and inexpensive cylindrical detector, with a radius of ∼10 cm and length of 5–10 m, depending on the location, can discover dark photons in a large and unprobed region of parameter space with dark photon mass mA′∼10–500 MeV and kinetic mixing parameter e∼10-6-10-3. FASER will clearly also be sensitive to many other forms of new physics. We conclude with a discussion of topics for further study that will be essential for understanding FASER’s feasibility, optimizing its design, and realizing its discovery potential.

FASER’s physics reach for long-lived particles

Abstract: The ForwArd Search ExpeRiment (FASER) is an approved experiment dedicated to searching for light, extremely weakly interacting particles at the LHC. Such particles may be produced in the LHC’s high-energy collisions and travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work we briefly describe the FASER detector layout and the status of potential backgrounds. We then present the sensitivity reach for FASER for a large number of long-lived particle models, updating previous results to a uniform set of detector assumptions, and analyzing new models. In particular, we consider all of the renormalizable portal interactions, leading to dark photons, dark Higgs bosons, and heavy neutral leptons; light B-L and Li-Lj gauge bosons; axionlike particles that are coupled dominantly to photons, fermions, and gluons through nonrenormalizable operators; and pseudoscalars with Yukawa-like couplings. We find that FASER and its follow-up, FASER 2, have a full physics program, with discovery sensitivity in all of these models and potentially far-reaching implications for particle physics and cosmology.

Performance of the ALICE VZERO system

Abstract: ALICE is an LHC experiment devoted to the study of strongly interacting matter in proton-proton, proton-nucleus and nucleus-nucleus collisions at ultra-relativistic energies. The ALICE VZERO system, made of two scintillator arrays at asymmetric positions, one on each side of the interaction point, plays a central role in ALICE. In addition to its core function as a trigger source, the VZERO system is used to monitor LHC beam conditions, to reject beam-induced backgrounds and to measure basic physics quantities such as luminosity, particle multiplicity, centrality and event plane direction in nucleus-nucleus collisions. After describing the VZERO system, this publication presents its performance over more than four years of operation at the LHC.

The LHCf detector at the CERN Large Hadron Collider

Abstract: LHCf is an experiment dedicated to the measurement of neutral particles emitted in the very forward region of LHC collisions. The physics goal is to provide data for calibrating the hadron interaction models that are used in the study of Extremely High-Energy Cosmic-Rays. This is possible since the laboratory equivalent collision energy of LHC is 1017 eV. Two LHCf detectors, consisting of imaging calorimeters made of tungsten plates, plastic scintillator and position sensitive sensors, are installed at zero degree collision angle ±140 m from an interaction point (IP). Although the lateral dimensions of these calorimeters are very compact, ranging from 20 mm × 20 mm to 40 mm × 40 mm, the energy resolution is expected to be better than 6% and the position resolution better than 0.2 mm for γ-rays with energy from 100 GeV to 7 TeV. This has been confirmed by test beam results at the CERN SPS. These calorimeters can measure particles emitted in the pseudo rapidity range η > 8.4. Detectors, data acquisition and electronics are optimized to operate during the early phase of the LHC commissioning with luminosity below 1030 cm-2 s-1. LHCf is expected to obtain data to compare with the major hadron interaction models within a week or so of operation at luminosity ~ 1029 cm-2 s-1. After ~ 10 days of operation at luminosity ~ 1029 cm-2 s-1, the light output of the plastic scintillators is expected to degrade by ~ 10% due to radiation damage. This degradation will be monitored and corrected for using calibration pulses from a laser.

Performance of the LHCb Vertex Locator

Abstract: LHCb is a dedicated experiment to study new physics in the decays of beauty and charm hadrons at the Large Hadron Collider (LHC) at CERN. The beauty and charm hadrons are identified through their flight distance in the Vertex Locator (VELO), and hence the detector is essential for both the trigger and physics analyses. The VELO is the silicon micro-strip detector surrounding the LHCb interaction point, and is located only 8 mm from the LHC beam during normal operation. It consists of two retractable detector halves with 21 silicon micro-strip tracking modules each and is moved into position for each fill of the LHC, once stable beams are obtained. The detector operates in an extreme and highly non-uniform radiation environment, and the effects of surface and bulk radiation damage have already been measured. The VELO has been successfully operated for the first LHC physics run. Operational results show a signal to noise ratio of > 17 and a cluster finding efficiency of 99.5%. The small pitch and analogue readout, result in a best single hit precision of 4µm having been achieved at the optimal track angle. The VELO is the highest resolution vertex detector at the LHC.