Underlying event explained

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]}

Further explanation

Underlying events can be thought of as the remnants of scattering interactions.^[4] 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^[5]).

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.^[6]

Features

Contents of UE include initial and final state radiation, beam-beam remnants, multiple parton interactions, pile-up, noise.^[7]

External links

• CMS measures the ‘underlying event’ in pp collisions

Notes and References

1. Web site: Underlying Event – a definitive study by CDF - Collider Blog. Collider Blog.
2. Barnaföldi . Gergely Gábor . Agócs . András G. . Lévai . Péter . Underlying Event Studies for LHC Energies . AIP . 2011 . 10.1063/1.3579440 . 1348. 124. 1101.4155v1.
3. Affolder . T. . Akimoto . H. . Akopian . A. . Albrow . M. G. . Amaral . P. . Amidei . D. . Anikeev . K. . Antos . J. . Apollinari . G. . Arisawa . T. . Artikov . A. . Asakawa . T. . Ashmanskas . W. . Azfar . F. . Azzi-Bacchetta . P. . Bacchetta . N. . Bachacou . H. . Bailey . S. . de Barbaro . P. . Barbaro-Galtieri . A. . 5. CDF Collaboration . Charged jet evolution and the underlying event in proton-antiproton collisions at 1.8 TeV . Physical Review D . American Physical Society (APS) . 65 . 9 . 2002-04-22 . 0556-2821 . 10.1103/physrevd.65.092002 . 092002. 1969.1/181493 . free .
4. http://www2.ph.ed.ac.uk/~vjm/Lectures/SH_IM_Particle_Physics_2013_files/Jets-Lecture10.pdf Lecture 10: QCD at Colliders
5. Aad . G. . Abbott . B. . Abdallah . J. . Abdelalim . A. A. . Abdesselam . A. . Abdinov . O. . Abi . B. . Abolins . M. . Abramowicz . H. . Abreu . H. . Acerbi . E. . Acharya . B. S. . Ackers . M. . Adams . D. L. . Addy . T. N. . Adelman . J. . Aderholz . M. . Adomeit . S. . Adragna . P. . Adye . T. . 5. The ATLAS Collaboration. Measurement of underlying event characteristics using charged particles inppcollisions at \sqrt{s} =900 GeV and 7 TeV with the ATLAS detector . Physical Review D . 83 . 11 . 2011-05-31 . 1550-7998 . 10.1103/physrevd.83.112001 . 112001. free. 1012.0791v2.
6. Web site: Underlying Events. Jon Butterworth. ucl.ac.uk. London. 2006. Jon. Butterworth. Wilhelm and Else Heraeus-Seminar on “New Event Generators for Particle Physics Experiments”
7. Web site: Mazumdar . Kajari . Underlying events in p-p collisions at LHC . tifr.res.in . 23 March 2022.