Underlying event

Last updated

In particle physics, underlying event (UE) refers to the additional interactions of two particle beams at a collision point beyond the main collision under study. Specifically, the term is used for hadron collider events which do not originate from the primary hard scattering (high energy, high momentum impact) process. [1] The term was first defined in 2002. [2] [3]

Contents

Further explanation

Underlying events can be thought of as the remnants of scattering interactions. [4] [5] The UE may involve contributions from both "hard" and "soft" processes (here “soft” refers to interactions with low p-T, i.e. transverse momentum, transfer [6] ).

These are important both in the simulation of particle experiments (often using event generators); and interpretation and analysis of data so as to filter out the desired signals. [7]

Features

Contents of UE include initial and final state radiation, beam-beam remnants, multiple parton interactions, pile-up, noise. [5]

Related Research Articles

<span class="mw-page-title-main">Tevatron</span> Defunct particle accelerator at Fermilab in Illinois, USA (1983–2011)

The Tevatron was a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory, east of Batavia, Illinois, and is the second highest energy particle collider ever built, after the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. The Tevatron was a synchrotron that accelerated protons and antiprotons in a 6.28 km (3.90 mi) ring to energies of up to 1 TeV, hence its name. The Tevatron was completed in 1983 at a cost of $120 million and significant upgrade investments were made during its active years of 1983–2011.

<span class="mw-page-title-main">Top quark</span> Type of quark

The top quark, sometimes also referred to as the truth quark, is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs Boson. This coupling is very close to unity; in the Standard Model of particle physics, it is the largest (strongest) coupling at the scale of the weak interactions and above. The top quark was discovered in 1995 by the CDF and DØ experiments at Fermilab.

<span class="mw-page-title-main">Large Hadron Collider</span> Particle accelerator at CERN, Switzerland

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.

<span class="mw-page-title-main">ATLAS experiment</span> CERN LHC experiment

ATLAS is the largest general-purpose particle detector experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN in Switzerland. The experiment is designed to take advantage of the unprecedented energy available at the LHC and observe phenomena that involve highly massive particles which were not observable using earlier lower-energy accelerators. ATLAS was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012. It was also designed to search for evidence of theories of particle physics beyond the Standard Model.

A collider is a type of particle accelerator that brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators.

<span class="mw-page-title-main">Compact Linear Collider</span>

The Compact Linear Collider (CLIC) is a concept for a future linear particle accelerator that aims to explore the next energy frontier. CLIC would collide electrons with positrons and is currently the only mature option for a multi-TeV linear collider. The accelerator would be between 11 and 50 km long, more than ten times longer than the existing Stanford Linear Accelerator (SLAC) in California, USA. CLIC is proposed to be built at CERN, across the border between France and Switzerland near Geneva, with first beams starting by the time the Large Hadron Collider (LHC) has finished operations around 2035.

<span class="mw-page-title-main">Two-photon physics</span> Branch of particle physics concerning interactions between two photons

Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear effects. In pure vacuum, some weak scattering of light by light exists as well. Also, above some threshold of this center-of-mass energy of the system of the two photons, matter can be created.

<span class="mw-page-title-main">DØ experiment</span> Particle physics research project (1983–2011)

The DØ experiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments located at the Tevatron Collider at Fermilab in Batavia, Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009, when its energy was surpassed by the Large Hadron Collider. The DØ experiment stopped taking data in 2011, when the Tevatron shut down, but data analysis is still ongoing. The DØ detector is preserved in Fermilab's DØ Assembly Building as part of a historical exhibit for public tours.

Leptoquarks are hypothetical particles that would interact with quarks and leptons. Leptoquarks are color-triplet bosons that carry both lepton and baryon numbers. Their other quantum numbers, like spin, (fractional) electric charge and weak isospin vary among theories. Leptoquarks are encountered in various extensions of the Standard Model, such as technicolor theories, theories of quark–lepton unification (e.g., Pati–Salam model), or GUTs based on SU(5), SO(10), E6, etc. Leptoquarks are currently searched for in experiments ATLAS and CMS at the Large Hadron Collider in CERN.

In particle physics, the parton model is a model of hadrons, such as protons and neutrons, proposed by Richard Feynman. It is useful for interpreting the cascades of radiation produced from quantum chromodynamics (QCD) processes and interactions in high-energy particle collisions.

In experimental particle physics, missing energy refers to energy that is not detected in a particle detector, but is expected due to the laws of conservation of energy and conservation of momentum. Missing energy is carried by particles that do not interact with the electromagnetic or strong forces and thus are not easily detectable, most notably neutrinos. In general, missing energy is used to infer the presence of non-detectable particles and is expected to be a signature of many theories of physics beyond the Standard Model.

In high-energy physics, jet quenching is a phenomenon that can occur in the collision of ultra-high-energy particles. In general, the collision of high-energy particles can produce jets of elementary particles that emerge from these collisions. Collisions of ultra-relativistic heavy-ion particle beams create a hot and dense medium comparable to the conditions in the early universe, and then these jets interact strongly with the medium, leading to a marked reduction of their energy. This energy reduction is called "jet quenching".

<span class="mw-page-title-main">Safety of high-energy particle collision experiments</span> Safety concerns of high-energy particle collision experiments and particle accelerators

The safety of high energy particle collisions was a topic of widespread discussion and topical interest during the time when the Relativistic Heavy Ion Collider (RHIC) and later the Large Hadron Collider (LHC)—currently the world's largest and most powerful particle accelerator—were being constructed and commissioned. Concerns arose that such high energy experiments—designed to produce novel particles and forms of matter—had the potential to create harmful states of matter or even doomsday scenarios. Claims escalated as commissioning of the LHC drew closer, around 2008–2010. The claimed dangers included the production of stable micro black holes and the creation of hypothetical particles called strangelets, and these questions were explored in the media, on the Internet and at times through the courts.

In particle physics, the odderon corresponds to an elusive family of odd-gluon states, dominated by a three-gluon state. When protons collide elastically with protons or with anti-protons at high energies, even or odd numbers of gluons are exchanged. Exchanging an even number of gluons is a crossing-even part of elastic proton–proton and proton–antiproton scattering, while odderon exchange, i.e. exchange of odd number of gluons, corresponds to a crossing-odd term in the elastic scattering amplitude. It took about 48 years to find a definite signal of odderon exchange.

<span class="mw-page-title-main">Particle accelerator</span> Research apparatus for particle physics

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

<span class="mw-page-title-main">Search for the Higgs boson</span> Effort to prove the existence or non-existence of the Higgs boson

The search for the Higgs boson was a 40-year effort by physicists to prove the existence or non-existence of the Higgs boson, first theorised in the 1960s. The Higgs boson was the last unobserved fundamental particle in the Standard Model of particle physics, and its discovery was described as being the "ultimate verification" of the Standard Model. In March 2013, the Higgs boson was officially confirmed to exist.

<span class="mw-page-title-main">Future Circular Collider</span> Proposed post-LHC particle accelerator at CERN, Geneva, Switzerland

The Future Circular Collider (FCC) is a proposed particle accelerator with an energy significantly above that of previous circular colliders, such as the Super Proton Synchrotron, the Tevatron, and the Large Hadron Collider (LHC). The FCC project is considering three scenarios for collision types: FCC-hh, for hadron-hadron collisions, including proton-proton and heavy ion collisions, FCC-ee, for electron-positron collisions, and FCC-eh, for electron-hadron collisions.

Robin Marshall is an Emeritus professor of Physics & Biology in the School of Physics and Astronomy at the University of Manchester. He currently lives in the village of Castillon-du-Gard in the region of Occitanie, where he writes and paints.

<span class="mw-page-title-main">FASER experiment</span> 2022 particle physics experiment at the Large Hadron Collider at CERN

FASER is one of the nine particle physics experiments in 2022 at the Large Hadron Collider at CERN. It is designed to both search for new light and weakly coupled elementary particles, and to detect and study the interactions of high-energy collider neutrinos. In March 2023, FASER reported the first observation of collider neutrinos.

The MilliQan experiment is a small-scale detector experiment at CERN's Large Hadron Collider (LHC). MilliQan is not a separate CERN experiment but is handled as a CMS sub-detector, with a dedicated memorandum of understanding to define authorship and responsibilities. The goal of the MilliQan experiment is to detect millicharged particles: particles with charges much smaller than that of the electron. These particles are motivated by the existence of a dark photon, and discovery of millicharged particles would provide a first probe into the dark sector. The MilliQan prototype detector collected data during LHC Run 2 in 2018 and set competitive constraints on millicharged particle charges and masses. The upgraded Run 3 MilliQan detectors are scheduled to be installed in 2022.

References

  1. "Underlying Event – a definitive study by CDF - Collider Blog". Collider Blog.
  2. Barnaföldi, Gergely Gábor; Agócs, András G.; Lévai, Péter (2011). Underlying Event Studies for LHC Energies. Vol. 1348. AIP. p. 124. arXiv: 1101.4155v1 . doi:10.1063/1.3579440.
  3. Affolder, T.; Akimoto, H.; Akopian, A.; Albrow, M. G.; Amaral, P.; et al. (CDF Collaboration) (2002-04-22). "Charged jet evolution and the underlying event in proton-antiproton collisions at 1.8 TeV". Physical Review D. American Physical Society (APS). 65 (9): 092002. doi:10.1103/physrevd.65.092002. hdl: 1969.1/181493 . ISSN   0556-2821.
  4. Lecture 10: QCD at Colliders, page 20. Particle Physics, Dr Victoria Martin, Spring Semester 2013.
  5. 1 2 Mazumdar, Kajari. "Underlying events in p-p collisions at LHC" (PDF). tifr.res.in. Retrieved 23 March 2022.
  6. Aad, G.; Abbott, B.; Abdallah, J.; Abdelalim, A. A.; Abdesselam, A.; et al. (The ATLAS Collaboration) (2011-05-31). "Measurement of underlying event characteristics using charged particles inppcollisions at GeV and 7 TeV with the ATLAS detector". Physical Review D. 83 (11): 112001. arXiv: 1012.0791v2 . doi: 10.1103/physrevd.83.112001 . ISSN   1550-7998.
  7. Butterworth, Jon (2006). "Underlying Events" (PDF). ucl.ac.uk. London. Wilhelm and Else Heraeus-Seminar on “New Event Generators for Particle Physics Experiments”