Underlying event
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.{{cite web|url=https://muon.wordpress.com/2010/03/26/underlying-event-a-definitive-study-by-cdf/|title=Underlying Event – a definitive study by CDF - Collider Blog|work=Collider Blog}} The term was first defined in 2002.{{cite conference | last1=Barnaföldi | first1=Gergely Gábor | last2=Agócs | first2=András G. | last3=Lévai | first3=Péter | title=Underlying Event Studies for LHC Energies | publisher=AIP | year=2011 | doi=10.1063/1.3579440 | volume=1348|page=124|arxiv=1101.4155v1}}{{cite journal | last1=Affolder | first1=T. | last2=Akimoto | first2=H. | last3=Akopian | first3=A. | last4=Albrow | first4=M. G. | last5=Amaral | first5=P. | last6=Amidei | first6=D. | last7=Anikeev | first7=K. | last8=Antos | first8=J. | last9=Apollinari | first9=G. | last10=Arisawa | first10=T. | last11=Artikov | first11=A. | last12=Asakawa | first12=T. | last13=Ashmanskas | first13=W. | last14=Azfar | first14=F. | last15=Azzi-Bacchetta | first15=P. | last16=Bacchetta | first16=N. | last17=Bachacou | first17=H. | last18=Bailey | first18=S. | last19=de Barbaro | first19=P. | last20=Barbaro-Galtieri | first20=A. | display-authors=5|collaboration=CDF Collaboration | title=Charged jet evolution and the underlying event in proton-antiproton collisions at 1.8 TeV | journal=Physical Review D | publisher=American Physical Society (APS) | volume=65 | issue=9 | date=2002-04-22 | issn=0556-2821 | doi=10.1103/physrevd.65.092002 | page=092002| hdl=1969.1/181493 | hdl-access=free }}
Further explanation
Underlying events can be thought of as the remnants of scattering interactions.[http://www2.ph.ed.ac.uk/~vjm/Lectures/SH_IM_Particle_Physics_2013_files/Jets-Lecture10.pdf Lecture 10: QCD at Colliders], page 20. Particle Physics,
Dr Victoria Martin, Spring Semester 2013.
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{{cite journal | last1=Aad | first1=G. | last2=Abbott | first2=B. | last3=Abdallah | first3=J. | last4=Abdelalim | first4=A. A. | last5=Abdesselam | first5=A. | last6=Abdinov | first6=O. | last7=Abi | first7=B. | last8=Abolins | first8=M. | last9=Abramowicz | first9=H. | last10=Abreu | first10=H. | last11=Acerbi | first11=E. | last12=Acharya | first12=B. S. | last13=Ackers | first13=M. | last14=Adams | first14=D. L. | last15=Addy | first15=T. N. | last16=Adelman | first16=J. | last17=Aderholz | first17=M. | last18=Adomeit | first18=S. | last19=Adragna | first19=P. | last20=Adye | first20=T. |display-authors=5|collaboration=The ATLAS Collaboration| title=Measurement of underlying event characteristics using charged particles inppcollisions at GeV and 7 TeV with the ATLAS detector | journal=Physical Review D | volume=83 | issue=11 | date=2011-05-31 | issn=1550-7998 | doi=10.1103/physrevd.83.112001 | page=112001|doi-access=free|arxiv=1012.0791v2}}).
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.{{cite web|url=http://www.hep.ucl.ac.uk/~jmb/Talks/dresden2005.pdf|title=Underlying Events|authorlink=Jon Butterworth|website=ucl.ac.uk|location=London|year=2006|first=Jon|last=Butterworth}} Wilhelm and Else Heraeus-Seminar on “New Event Generators for Particle Physics Experiments”
=Features=
Contents of UE include initial and final state radiation, beam-beam remnants, multiple parton interactions, pile-up, noise.{{cite web |last1=Mazumdar |first1=Kajari |title=Underlying events in p-p collisions at LHC |url=https://www.tifr.res.in/~mazumdar/talks/UEDY_IIT.pdf |website=tifr.res.in |access-date=23 March 2022}}
See also
References
{{reflist}}
External links
- [http://cerncourier.com/cws/article/cern/59925 CMS measures the ‘underlying event’ in pp collisions]