815:
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
245:
on a project using a particle accelerator to measure the cross sections of certain nuclear reactions. According to an account of theirs from a couple years later, they were dining in a cafeteria in
December 1942 and discussing their work. They "lamented" that there was no name for the unit of cross
606:
In SI, one can use units such as square femtometers (fm). The most common SI prefixed unit for the barn is the femtobarn, which is equal to a tenth of a square zeptometer. Many scientific papers discussing high-energy physics mention quantities of fractions of femtobarn level.
816:
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 fb in nine months). Inverse femtobarns are often quoted as an indication of
862:
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 fb was achieved during 2012. As of
November 2016, the LHC had achieved
246:
section and challenged themselves to develop one. They initially tried to find the name of "some great man closely associated with the field" that they could name the unit after, but struggled to find one that was appropriate. They considered "
270:", which also worked because the unit was "really as big as a barn." According to the authors, the first published use of the term was in a (secret) Los Alamos report from late June 1943, on which the two originators were co-authors.
1019:
The initial published report to feature the unit was C.P. Baker, M.G. Holloway, L.D.P. King, and R.E. Schreiber, "Cross section for the reaction 20(230, 240)10," (
975:
206:
1042:
922:
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.
185:, and is best understood as a measure of the probability of interaction between small particles. A barn is approximately the cross-sectional area of a
1126:
948:
1160:
1156:
943:
1263:"Thanks to recent fine tuning, the LHC has delivered 2 inverse femtobarns of data already this year; peak luminosity is now over 2x10^33"
1096:
1185:
1073:
1241:
801:
38:
266:. But this latter association, combined with the "rural background" of one of the scientists, suggested to them the term "
1420:
262:, another scientist associated with their work, but considered "Manley" too long and "John" too closely associated with
190:
1329:
938:
194:
1425:
1020:
996:
1206:
793:
797:
504:
470:
198:
166:
808:
of integrated luminosity, one expects to find 100 events per femtobarn of cross-section within these data.
1415:
1347:
851:
843:
247:
1371:
1134:
250:" too long (in retrospect, they considered an "Oppy" to perhaps have been allowable), and considered "
238:
812:
1130:
1220:
1164:
1069:
1063:
967:
817:
259:
242:
234:
222:
1127:"Understanding luminosity through 'barn', a unit that helps physicists count particle events"
1104:
1010:
858:
of proton–proton data in 2011 alone. In April 2012 the LHC achieved the collision energy of
847:
210:
178:
174:
43:
162:
465:
Calculated cross sections are often given in terms of inverse squared gigaelectronvolts (
510:
475:
170:
1409:
968:"Non-SI units accepted for use with the SI, and units based on fundamental constants"
500:
1262:
932:
516:
481:
466:
230:
146:
104:
1333:
226:
1308:
1034:
792:
The inverse femtobarn (fb) is the unit typically used to measure the number of
251:
209:
acknowledged it in the 8th SI Brochure (superseded in 2019) due to its use in
182:
158:
129:
17:
1021:
https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-00002-MS
935:", a unit of time created by the same people at the same time as the barn
887:
runs for 8 hours (28 800 seconds) at an instantaneous luminosity of
884:
831:
823:
1400:
995:
M.G. Holloway and C.P. Baker, "Note on the origin of the term 'barn'"],
1287:
186:
1014:
278:
The unit symbol for the barn (b) is also the IEEE standard symbol for
263:
1397:
999:(submitted 13 September 1944, issued 5 March 1947). Reprinted as
1266:
899:, then it will gather data totaling an integrated luminosity of
839:
267:
255:
254:" to be too easily confused with the commonly-used Greek letter
150:
71:
1023:) (June 28, 1943), which also defines the unit in its abstract.
279:
1001:
Holloway, M.G.; Baker, C.P. (1972). "How the barn was born".
282:. In other words, 1 Mb can mean one megabarn or one megabit.
871:. In total, the second run of the LHC has delivered around
867:
over that year, significantly exceeding the stated goal of
202:
27:
Unit for cross sectional area used in high-energy physics
1309:"LHC proton run for 2011 reaches successful conclusion"
1186:"10 Inverse Femtobarns: Celebration Time At Fermilab!"
1221:"CDF, DZero reach 5 inverse femtobarns of luminosity"
830:
in the first decade of the 21st century. Fermilab's
1209:. Pauline Gagnon, Quantum Diaries. October 17, 2011.
800:, and is the conventional unit for time-integrated
189:nucleus. The barn is also the unit of area used in
118:
100:
78:
65:
57:
49:
37:
32:
1103:. Scientific Digital Visions, Inc. Archived from
197:to quantify the interaction of a nucleus with an
1039:How Many? A Dictionary of Units of Measurement
1242:"LHC experiments reach record data milestone"
8:
1372:"LHC Report: The final days of Run 2 | CERN"
1068:. Routledge Kegan & Paul. p. 487.
1043:University of North Carolina at Chapel Hill
1155:Mason Inman, Emily Ball (April 16, 2004).
29:
1348:"LHC smashes targets for 2016 run | CERN"
177:, today it is also used in all fields of
678:
613:
533:
284:
959:
258:. They then considered naming it after
1207:"What will we do with all this data?"
949:List of humorous units of measurement
804:. Thus if a detector has accumulated
181:to express the cross sections of any
7:
1223:. Fermilab Today. September 26, 2008
944:List of unusual units of measurement
875:to both ATLAS and CMS in 2015–2018.
1288:"LHC Report: 2 inverse femtobarns!"
1332:. CERN. 2012-12-17. Archived from
1244:. Symmetry magazine. June 17, 2011
1188:. Science20.com. December 12, 2010
1033:Russ Rowlett (September 1, 2004).
25:
1401:citation for this usage of "barn"
1125:Kate Metropolis (July 21, 2004).
1062:Green, Jonathon (December 1987).
82:
1311:. CERN Press Office. 2011-10-31
274:Commonly used prefixed versions
883:As a simplified example, if a
201:. While the barn never was an
1:
766:0.1 ym = 100000 rm
750:0.1 zm = 100000 ym
734:0.1 am = 100000 zm
715:0.1 fm = 100000 am
1133:News Service. Archived from
834:took about 4 years to reach
286:Multiples and sub-multiples
191:nuclear quadrupole resonance
1290:. CERN Bulletin. 2011-08-05
1101:The Language of the Nucleus
1442:
939:Orders of magnitude (area)
195:nuclear magnetic resonance
972:SI brochure (8th edition)
794:particle collision events
615:Conversion from SI units
515:= 1), this simplifies to
96:
1157:"PEP-II's luminous life"
680:Conversion to SI units
199:electric field gradient
1330:"LHC luminosity plots"
1095:Craig A. Stone, Ph.D.
838:in 2005, while two of
469:), via the conversion
233:, American physicists
161:). Originally used in
1065:Dictionary of Jargon
813:particle accelerator
798:target cross-section
602:SI units with prefix
70:the broad side of a
1421:Non-SI metric units
681:
616:
287:
179:high-energy physics
165:for expressing the
91:... is equal to ...
679:
614:
285:
183:scattering process
126:
120:
110:
102:
1015:10.1063/1.3070918
818:particle collider
796:per femtobarn of
788:Inverse femtobarn
785:
784:
781:
780:
675:
674:
599:
598:
458:
457:
243:Purdue University
235:Marshall Holloway
223:Manhattan Project
207:SI standards body
175:nuclear reactions
135:
134:
79:Conversions
16:(Redirected from
1433:
1426:Particle physics
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1269:. August 5, 2011
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1163:. Archived from
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241:were working at
239:Charles P. Baker
225:research on the
211:particle physics
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1167:on June 2, 2009
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167:cross sectional
163:nuclear physics
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1392:External links
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1336:on 2013-02-19.
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18:Shed (physics)
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1416:Units of area
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1075:0-7100-9919-3
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1003:Physics Today
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897:300 μb⋅s
886:
879:Usage example
878:
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849:
846:experiments,
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501:natural units
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105:SI base units
99:
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1379:. Retrieved
1375:
1366:
1355:. Retrieved
1351:
1342:
1334:the original
1324:
1313:. Retrieved
1303:
1292:. Retrieved
1282:
1271:. Retrieved
1257:
1246:. Retrieved
1236:
1225:. Retrieved
1215:
1201:
1190:. Retrieved
1180:
1169:. Retrieved
1165:the original
1150:
1139:. Retrieved
1135:the original
1120:
1109:. Retrieved
1105:the original
1100:
1090:
1079:. Retrieved
1064:
1057:
1046:. Retrieved
1038:
1028:
1006:
1002:
991:
980:. Retrieved
971:
962:
912:8.64 pb
893:10 cm⋅s
882:
822:
810:
791:
774:100 rm
758:100 ym
742:100 zm
723:100 am
699:100 fm
691:Other names
605:
511:
505:
498:
476:
471:
464:
277:
231:World War II
220:
142:
138:
136:
90:
85:
69:
50:Unit of
873:150 fb
811:Consider a
806:100 fb
671:10 rb
663:10 zb
655:10 fb
647:10 nb
639:10 mb
631:10 kb
594:10 GeV
586:0.389379 pb
576:0.389379 mb
570:10 GeV
461:Conversions
260:John Manley
248:Oppenheimer
227:atomic bomb
147:metric unit
66:Named after
39:Unit system
1410:Categories
1381:2018-12-07
1357:2016-11-02
1315:2011-10-31
1294:2011-08-06
1273:2011-08-05
1248:2011-07-23
1227:2011-07-23
1192:2011-04-08
1171:2009-03-13
1141:2009-03-13
1111:2022-11-22
1097:"Glossary"
1081:2009-12-14
1048:2009-12-14
1035:"Units: S"
982:2009-03-13
978:. May 2006
955:References
869:25 fb
865:40 fb
860:8 TeV
828:10 fb
802:luminosity
771:1 yb
763:1 zb
755:1 ab
747:1 fb
739:1 pb
731:1 nb
726:Outhouse
720:1 μb
712:1 mb
707:1 fm
704:1 cb
668:1 rm
660:1 ym
652:1 zm
644:1 am
636:1 fm
628:1 pm
580:1 GeV
445:yoctobarn
431:zeptobarn
403:femtobarn
361:microbarn
347:millibarn
205:unit, the
157:(100
122:equivalent
1376:home.cern
1352:home.cern
856:5 fb
836:1 fb
826:produced
696:1 b
553: GeV
417:attobarn
389:picobarn
375:nanobarn
319:kilobarn
305:megabarn
217:Etymology
155:10 m
153:equal to
141:(symbol:
128:100
113:10 m
84:1 b
1131:Stanford
1009:(7): 9.
997:LAMS-523
926:See also
920: fb
914: =
910: =
908: μb
895: =
885:beamline
832:Tevatron
824:Fermilab
529: am
494: am
169:area of
503:(where
294:Symbol
264:toilets
229:during
221:During
187:uranium
145:) is a
1072:
685:Barns
623:barns
171:nuclei
86:in ...
58:Symbol
1398:IUPAC
933:Shake
916:0.008
848:ATLAS
777:Shed
563:2.568
549:2.568
333:barn
291:Unit
252:Bethe
1267:CERN
1161:SLAC
1070:ISBN
976:BIPM
850:and
840:CERN
559:1 pb
545:1 mb
540:GeV
537:barn
268:barn
256:beta
237:and
193:and
173:and
151:area
139:barn
72:barn
53:area
33:Barn
1011:doi
906:000
903:640
889:300
852:CMS
844:LHC
842:'s
688:SI
620:SI
527:940
517:GeV
499:In
492:940
482:GeV
467:GeV
454:10
451:10
448:yb
440:10
437:10
434:zb
426:10
423:10
420:ab
412:10
409:10
406:fb
398:10
395:10
392:pb
384:10
381:10
378:nb
370:10
367:10
364:μb
356:10
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