The LHCf (Large Hadron Collider forward) is a special-purpose

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

experiment for astroparticle (

cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...

) physics, and one of nine detectors in the LHC accelerator at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

. LHCf is designed to study the particles generated in the forward region of collisions, those almost directly in line with the colliding proton beams. LHCf_experiment

Purpose

The LHCf is intended to measure the energy and numbers of neutral

pions In particle physics, a pion (, ) or pi meson, denoted with the Greek letter pi (), is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, mo ...

() produced by the collider. This will hopefully help explain the origin of

ultra-high-energy cosmic ray In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray with an energy greater than 1 EeV (1018 electronvolts, approximately 0.16 joules), far beyond both the rest mass and energies typical of other cosmic ray part ...

s (UHECRs). Detecting UHECRs is performed through observations of secondary

particle shower In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these t ...

s produced when a UHECR interacts with the atmosphere. The LHCf experiment is designed to measure the very-forward region, where most of the energy flow of secondary particles is contained. The results produced by the LHCf experiment complement other high-energy cosmic ray measurements from the

Pierre Auger Observatory The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond . In Earth's atmosphe ...

in Argentina, and the Telescope Array Project in Utah.

Experimental setup

The LHCf setup consists of two independent detectors on either side of the LHC, both 140 m from the

ATLAS An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

interaction point. The detectors are referred to as Arm 1 and Arm 2 and are installed inside target neutral absorbers (TAN), which protect cryo-magnets from neutral particle debris from the interaction region. The two detectors have a common structure of two independent

calorimeter A calorimeter is a device used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters ...

towers, for

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

and

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

measurements. The towers are made from

tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...

absorber layers and

scintillator A scintillator ( ) is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the ab ...

layers, with a difference in the size of transverse sections for the two arms. The calorimeter towers are used to measure incoming particle energy and to identify families of particles. Each detector has a tracking system: the Arm 1 system consists of four double-layers os scintillating fibres; Arm 2 consists of

microstrip Microstrip is a type of electrical transmission line which can be fabricated with any technology where a conductor is separated from a ground plane by a dielectric layer known as ''substrate''. Microstrip lines are used to convey microwave-freq ...

silicon layers. The energy resolution for the detectors is over 3% for photons above 100 GeV and around 40% for neutrons. The position resolution for Arm 1 and Arm 2 is 200 μm and 40 μm for photons respectively, and is around 1 mm for neutrons for both the detectors.

Results

The first phase of data using the LHCf detectors was recorded in 2009–2013, as part of the LHC's Run 1. The LHCf results at 7 TeV centre-of-mass energy showed good agreement with theoretical models for forward photon and neutral pion production. However, the results did not agree for the forward neutron production. LHCf was able to measure how the number of forward photons and neutrons varies with energy at new high energies. The results of the experiment agree with some theoretical models but disagree with other. The current focus of the LHCf is to look out for neutral kaons and neutral eta mesons, particles that include a strange quark. The theoretical models describing this interaction predict secondary muons, but the predicted numbers disagree with experimental data. The LHCf experiment hopes to resolve the "muon puzzle".

References

External links

*
LHCf experiment
record on

INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1 ...

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