Editing Barn (unit) (section)

==Inverse femtobarn==
The inverse femtobarn (fb<sup>−1</sup>) is the unit typically used to measure the number of [[Event (particle physics)|particle collision events]] per femtobarn of [[Cross section (physics)|target cross-section]], and is the conventional unit for time-integrated [[Luminosity (scattering theory)|luminosity]]. Thus if a detector has accumulated {{val|100|u=fb<sup>−1</sup>}} of integrated luminosity, one expects to find 100 events per femtobarn of cross-section within these data.

Consider a [[particle accelerator]] where two streams of particles, with cross-sectional areas measured in femtobarns, are directed to collide over a period of time. The total number of collisions will be directly proportional to the luminosity of the collisions measured over this time. Therefore, the collision count can be calculated by multiplying the integrated luminosity by the sum of the cross-section for those collision processes. This count is then expressed as inverse femtobarns for the time period (e.g., 100&nbsp;fb<sup>−1</sup> in nine months). Inverse femtobarns are often quoted as an indication of [[particle collider]] productivity.<ref name="Metropolis">{{cite news
 | author = Kate Metropolis
 | date = July 21, 2004
 | title = Understanding luminosity through 'barn', a unit that helps physicists count particle events
 | url = http://news-service.stanford.edu/news/2004/july21/femtobarn-721.html
 | publisher = [[Stanford University|Stanford]] News Service
 | access-date = 2009-03-13
 | archive-date = 2009-05-10
 | archive-url = https://web.archive.org/web/20090510020557/http://news-service.stanford.edu/news/2004/july21/femtobarn-721.html
 | url-status = dead
 }}</ref><ref name="Inman">{{cite web
 |author      = Mason Inman, Emily Ball
 |date        = April 16, 2004
 |title       = PEP-II's luminous life
 |url         = http://www2.slac.stanford.edu/tip/special/PEP-II-04-16-04.htm
 |publisher   = [[SLAC National Accelerator Laboratory|SLAC]]
 |access-date  = 2009-03-13
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20090602222519/http://www2.slac.stanford.edu/tip/special/PEP-II-04-16-04.htm
 |archive-date = June 2, 2009
}}</ref>

[[Fermilab]] produced {{val|10|u=fb<sup>−1</sup>}} in the first decade of the 21st century.<ref>{{cite web|url=http://www.science20.com/quantum_diaries_survivor/10_inverse_femtobarns_celebration_time_fermilab |title=10 Inverse Femtobarns: Celebration Time At Fermilab! |publisher=Science20.com |date=December 12, 2010 |access-date=2011-04-08}}</ref>  Fermilab's [[Tevatron]] took about 4 years to reach {{val|1|u=fb<sup>−1</sup>}} in 2005, while two of [[CERN]]'s [[Large Hadron Collider|LHC]] experiments, [[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]], reached over {{val|5|u=fb<sup>−1</sup>}} of proton–proton data in 2011 alone.<ref>{{cite web|url=http://www.quantumdiaries.org/2011/10/17/what-will-we-do-with-all-this-data/ |title=What will we do with all this data? |publisher=Pauline Gagnon, Quantum Diaries |date=October 17, 2011}}</ref><ref>{{cite web|url=http://www.fnal.gov/pub/today/archive_2008/today08-09-26.html |title=CDF, DZero reach 5 inverse femtobarns of luminosity |publisher=Fermilab Today |date=September 26, 2008 |access-date=2011-07-23}}</ref><ref>{{cite web|url=http://www.symmetrymagazine.org/breaking/2011/06/17/lhc-experiments-reach-record-data-milestone/ |title=LHC experiments reach record data milestone |publisher=Symmetry magazine |date=June 17, 2011 |access-date=2011-07-23}}</ref><ref>{{cite web|url=https://twitter.com/CERN/status/99405126694993920|title=Thanks to recent fine tuning, the LHC has delivered 2 inverse femtobarns of data already this year; peak luminosity is now over 2x10^33.|publisher=[[CERN]] |date=August 5, 2011 |access-date=2011-08-05}}</ref><ref>{{cite web|url=http://cdsweb.cern.ch/record/1372204 |title=LHC Report: 2 inverse femtobarns! |publisher=CERN Bulletin |date=2011-08-05 |access-date=2011-08-06}}</ref><ref>{{cite web|url=http://www.interactions.org/cms/?pid=1031152|title=LHC proton run for 2011 reaches successful conclusion|publisher=CERN Press Office|date=2011-10-31|access-date=2011-10-31}}</ref> In April 2012, the LHC achieved the collision energy of {{val|8|u=TeV}} with a luminosity peak of 6760 inverse microbarns per second; by May 2012, the LHC delivered 1 inverse femtobarn of data per week to each detector collaboration. A record of over 23&nbsp;fb<sup>−1</sup> was achieved during 2012.<ref>{{cite web|url=http://lpc.web.cern.ch/lpc/lumiplots_2012.htm |title=LHC luminosity plots |publisher=CERN |date=2012-12-17 |url-status=dead |archive-url=https://archive.today/20130219192316/http://lpc.web.cern.ch/lpc/lumiplots_2012.htm |archive-date=2013-02-19 }}</ref> As of November 2016, the LHC had achieved {{val|40|u=fb<sup>−1</sup>}} over that year, significantly exceeding the stated goal of {{val|25|u=fb<sup>−1</sup>}}.<ref>{{Cite web|url=http://home.cern/about/opinion/2016/11/lhc-smashes-targets-2016-run-0|title=LHC smashes targets for 2016 run {{!}} CERN|website=home.cern|access-date=2016-11-02}}</ref> In total, the second run of the LHC has delivered around {{val|150|u=fb<sup>−1</sup>}} to both ATLAS and CMS in 2015–2018.<ref>{{Cite web|url=https://home.cern/news/news/accelerators/lhc-report-final-days-run-2|title=LHC Report: The final days of Run 2 {{!}} CERN|website=home.cern|access-date=2018-12-07}}</ref>

===Usage example ===
As a simplified example, if a [[beamline]] runs for 8 hours (28&nbsp;800 seconds) at an instantaneous luminosity of {{val|300|e=30|u=cm<sup>−2</sup>⋅s<sup>−1</sup>}}&nbsp;{{=}} {{val|300|u=μb<sup>−1</sup>⋅s<sup>−1</sup>}}, then it will gather data totaling an integrated luminosity of {{val|8640000|u=μb<sup>−1</sup>}}&nbsp;= {{val|8.64|u=pb<sup>−1</sup>}}&nbsp;= {{val|0.00864|u=fb<sup>−1</sup>}} during this period. If this is multiplied by the cross-section, then a dimensionless number is obtained equal to the number of expected scattering events.