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{{Short description|American scientist}}
{{Infobox scientist
| name              = Martin Lewis Perl
| image             = Martin Perl - tau.jpg
| image_size        = 150px
| caption           = 
| birth_date        = {{Birth date |1927|6|24}}
| birth_place       = [[New York City]], New York
| death_date        = {{death date and age|2014|9|30|1927|6|24}}
| death_place       = [[Palo Alto, California]]
| residence         = 
| citizenship       = 
| nationality       = American
| ethnicity         = 
| field             = [[Physics]]
| work_institutions = [[University of Michigan]] <br /> [[Stanford Linear Accelerator Center]] (SLAC)<br /> [[University of Liverpool]]
| alma_mater        = [[New York University Tandon School of Engineering]] and [[Columbia University]]
| doctoral_advisor  = [[I. I. Rabi]]
| doctoral_students = [[Melissa Franklin]], [[Samuel C. C. Ting]] [[File:Nobel_prize_medal.svg|20px]]
| known_for         = [[Tau lepton]]
| author_abbrev_bot = 
| author_abbrev_zoo = 
| influences        = 
| influenced        = 
| prizes            = [[Nobel Prize in Physics]] in 1995 <br /> [[Wolf Prize in Physics]] in 1982
| footnotes         = 
| children          = [[Jed Perl]]
| signature         = 
}}

'''Martin Lewis Perl''' (June 24, 1927 – September 30, 2014) was an American [[chemical engineer]] and [[physicist]] who won the [[Nobel Prize in Physics]] in 1995 for his [[Discovery (observation)|discovery]] of the [[tau lepton]].

==Life and career==
Perl was born in New York City, New York. His parents, Fay (née Resenthal), a secretary and bookkeeper, and Oscar Perl, a stationery salesman who founded a printing and advertising company, were [[Jewish]] [[Immigration|immigrants]] to the US from the [[Polish people|Polish]] area of [[Russia]].<ref name="nobelbio">{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/perl-bio.html|title=Martin L. Perl - Biographical|publisher=Nobel Media AB|year=1995|access-date=2013-12-28}}</ref><ref name="Feldman">{{cite journal |last1=Feldman |first1=Gary |last2=Jaros |first2=John |last3=Schindler |first3=Rafe H. |title=Martin L. Perl (1927–2014): A Biographical Memoir |journal=Annual Review of Nuclear and Particle Science |date=12 October 2017 |volume=67 |issue=1 |pages=1–18 |doi=10.1146/annurev-nucl-061317-093426 |doi-access=free |bibcode=2017ARNPS..67....1F }}</ref>

Perl was a 1948 [[chemical engineering]] graduate of Brooklyn Polytechnic Institute (now known as [[New York University Tandon School of Engineering|NYU-Tandon]]) in Brooklyn.  After graduation, Perl worked for the [[General Electric Company]], as a chemical engineer in a factory producing electron vacuum tubes.  To learn about how the electron tubes worked, Perl signed up for courses in atomic physics and advanced calculus at [[Union College]] in [[Schenectady, New York]], which led to his growing interest in physics, and eventually to becoming a graduate student in physics in 1950.<ref name="nobelbio" />

He received his Ph.D. from [[Columbia University]] in 1955, where his thesis advisor was [[I.I. Rabi]].  Perl's thesis described measurements of the nuclear quadrupole moment of [[sodium]], using the atomic beam resonance method that Rabi had won the Nobel Prize in Physics for in 1944.<ref name="nobelbio" />

Following his Ph.D., Perl spent 8 years at the [[University of Michigan]], where he worked on the physics of [[strong interaction]]s, using [[bubble chamber]]s and [[spark chamber]]s to study the scattering of [[pion]]s and later [[neutron]]s on [[proton]]s.<ref name="nobelbio" />
While at Michigan, Perl and [[Lawrence W. Jones]] served as co-advisors to [[Samuel C. C. Ting]], who earned the Nobel Prize in Physics in 1976.

Seeking a simpler interaction mechanism to study, Perl started to consider [[electron]] and [[muon]] interactions.<ref name="nobellecture">{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/perl-lecture.html|title=Reflections on the Discovery of the Tau Lepton|author=Martin L. Perl|year=1995|access-date=2013-12-28}}</ref>
He had the opportunity to start planning experimental work in this area when he moved in 1963 to the [[Stanford Linear Accelerator Center]] (SLAC), then being built in [[California]].  He was particularly interested in understanding the [[muon]]: why it should interact almost exactly like the electron but be 206.8 times heavier, and why it should decay through the route that it does.  Perl chose to look for answers to these questions in experiments on high-energy charged [[lepton]]s.  In addition, he considered the possibility of finding a third [[Generation (particle physics)|generation]] of lepton through electron-[[positron]] collisions.<ref name="Feldman"/>

Perl is one of the 20 American recipients of the Nobel Prize in Physics to sign a letter addressed to President [[George W. Bush]] in May 2008, urging him to "reverse the damage done to basic science research in the Fiscal Year 2008 Omnibus Appropriations Bill" by requesting additional emergency funding for the [[United States Department of Energy|Department of Energy]]'s [[Office of Science]], the [[National Science Foundation]], and the [[National Institute of Standards and Technology]].<ref>{{Cite web|title=A Letter from America's Physics Nobel Laureates|url=https://fire.pppl.gov/nobel_bush_fy08_050808.pdf}}</ref>

He died after a heart attack<ref name=":0">{{Cite news|url=https://www.nytimes.com/2014/10/04/science/martin-perl-physicist-who-discovered-electrons-long-lost-brother-dies-at-87.html|title=Martin Perl, 87, Dies; Nobel Laureate Discovered Subatomic Particle|newspaper=The New York Times|date=3 October 2014|last1=Overbye|first1=Dennis}}</ref> at Stanford University Hospital on September 30, 2014, at the age of 87.<ref>{{Cite web|url=http://news.stanford.edu/news/2014/october/martin-perl-obit-100114.html|title = Stanford's Martin L. Perl, winner of 1995 Nobel Prize for discovery of tau lepton, dead at 87|date = October 2014}}</ref> His son, [[Jed Perl]], is an author and art critic for ''[[The New Republic]]''.<ref name=":0" />

===Discovery of the tau particle===
<!-- The following paragraphs copied from [[Tau (particle)]] -->
The [[Tau (particle)|tau]] lepton (τ, also called the tau particle, tauon or simply tau) is an [[elementary particle]] similar to the electron, with negative [[electric charge]] and a [[spin-½|spin of {{frac|1|2}}]], but with 3477 times the mass. Together with the [[electron]], the [[muon]], and the three [[neutrino]]s, it is classified as a [[lepton]].<ref name="Feldman"/><ref name="Woolfson">{{cite book |last1=Woolfson |first1=M. M. |title=Materials, Matter & Particles: A Brief History |date=2010 |publisher=World Scientific |isbn=978-1-84816-461-1 |url=https://books.google.com/books?id=MQmPWnTkB2kC&pg=PA268 |language=en}}</ref>

The tau was first detected in a series of experiments between 1974 and 1977 by Perl with his colleagues at the [[SLAC]]-[[Lawrence Berkeley National Laboratory|LBL]] group.<ref name="Perl1975">
{{cite journal|last1=Perl|first1=M. L.|last2=Abrams|first2=G.|last3=Boyarski|first3=A.|last4=Breidenbach|first4=M.|author-link4=Martin Breidenbach|last5=Briggs|first5=D.|last6=Bulos|first6=F.|last7=Chinowsky|first7=W.|last8=Dakin|first8=J.|last9=Feldman|first9=G.|display-authors=8|year=1975|title=Evidence for Anomalous Lepton Production in {{SubatomicParticle|Positron}}{{SubatomicParticle|Electron}} Annihilation|journal=[[Physical Review Letters]]|volume=35|issue=22|page=1489|bibcode=1975PhRvL..35.1489P|doi=10.1103/PhysRevLett.35.1489}}</ref> Their equipment consisted of [[SLAC]]'s then-new {{SubatomicParticle|Antielectron}}–{{SubatomicParticle|Electron}} colliding ring, called [[SPEAR]], and the [[Lawrence Berkeley National Laboratory|LBL]] magnetic detector. They could detect and distinguish between leptons, hadrons and [[photon]]s. SPEAR was able to collide electrons and positrons at higher energies than had previously been possible, initially at up to 4.8 GeV and eventually at 8 GeV, energies high enough to lead to the production of a tau/antitau pair.<ref name="nobellecture" /> The tau has a lifetime of only {{val|2.9|e=-13|u=s}} and so these particles decayed within a few millimetres of the collision.<ref name="nobelPR">{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/press.html|title=The Nobel Prize in Physics 1995 - Press Release|publisher=Nobel Media AB|year=1995|access-date=2014-01-01}}</ref> Hence Perl and his coworkers did not detect the tau directly, but rather discovered anomalous events where they detected either an electron and a muon, or a positron and an antimuon:<ref name="Halyo">{{cite journal |last1=Halyo |first1=Valerie |title=Martin L. Perl (1927–2014) |journal=Nature |date=December 2014 |volume=516 |issue=7531 |pages=330 |doi=10.1038/516330a |pmid=25519123 |s2cid=4405993 |language=en |issn=1476-4687|doi-access=free |bibcode=2014Natur.516..330H }}</ref>

{{blockquote|We have discovered 64 events of the form

:{{SubatomicParticle|Positron}} + {{SubatomicParticle|Electron}} → {{SubatomicParticle|Electron+-}} + {{SubatomicParticle|Muon-+}} + at least two undetected particles

for which we have no conventional explanation.}}

The need for at least two undetected particles was shown by the inability to conserve energy and momentum with only one. However, no other muons, electrons, photons, or hadrons were detected. It was proposed that this event was the production and subsequent decay of a new particle pair:

:{{SubatomicParticle|Positron}} + {{SubatomicParticle|Electron}} → {{SubatomicParticle|Antitau}} + {{SubatomicParticle|Tau}}  → {{SubatomicParticle|Electron+-}} + {{SubatomicParticle|Muon-+}} + 4{{SubatomicParticle|Neutrino}}

This was difficult to verify, because the energy to produce the {{SubatomicParticle|Antitau}}{{SubatomicParticle|Tau}} pair is similar to the threshold for [[D meson]] production. Work done at [[DESY]]-Hamburg, and with the Direct Electron Counter (DELCO) at [[SPEAR]], subsequently confirmed the discovery<ref name="Feldman"/> and established the mass and spin of the tau.

The symbol τ was derived from the Greek ''τρίτον'' (''triton'', meaning "third" in English), since it was the third charged lepton discovered.<ref>
{{cite conference
 |author=M.L. Perl
 |title=Evidence for, and properties of, the new charged heavy lepton
 |url=http://slac.stanford.edu/pubs/slacpubs/1750/slac-pub-1923.pdf
 |book-title=Proceedings of the XII Rencontre de Moriond
 |editor=T. Thanh Van
 |year=1977
 |id=SLAC-PUB-1923
}}</ref>
<!-- end of section copied from [[Tau (particle)]] -->

===Nobel Prize and later career===
Perl won the Nobel Prize in 1995 jointly with [[Frederick Reines]].  The prize was awarded "for pioneering experimental contributions to lepton physics". Perl received half "for the discovery of the tau lepton" while Reines received his share "for the detection of the [[neutrino]]".<ref name="nobelcitation">{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/|title=Nobel Prize in Physics, 1995|year=1995|access-date=2013-12-28}}</ref> In 1996 he published ''Reflections on Experimental Science'', which consists of "comments, scientific reprints, reflections, and a memoir ...".<ref>{{cite book|author=Perl, Martin L.|title=Reflections on Experimental Science|series=World Scientific Series in 20th Century Physics – Vol. 14.|publisher=World Scientific|year=1996|url=https://books.google.com/books?id=3ewT6ZXygHsC&pg=PR9|page=ix|isbn=9810225741}}</ref>
 
He joined [[University of Liverpool]] as a visiting professor.<ref>{{cite web|url=https://www.bbc.co.uk/news/uk-england-merseyside-16018296 |title=Professor Martin Perl joins University of Liverpool |publisher=BBC |date=3 December 2011 |access-date=3 December 2011}}</ref> He served on the board of advisors of [[Scientists and Engineers for America]], an organization focused on promoting sound science in American government.  In 1996, he received the Golden Plate Award of the [[Academy of Achievement|American Academy of Achievement]].<ref>{{cite web|title= Golden Plate Awardees of the American Academy of Achievement |website=www.achievement.org|publisher=[[American Academy of Achievement]]|url=https://achievement.org/our-history/golden-plate-awards/#science-exploration}}</ref> In 2009, Perl received an honorary doctorate from the [[University of Belgrade]].<ref>{{cite web|url=http://www.rtv.rs/sr_lat/drustvo/promovisani-pocasni-doktori-beogradskog-univerziteta-_120094.html |title=Promovisani počasni doktori Beogradskog univerziteta - RADIO-TELEVIZIJA VOJVODINE |publisher=Rtv.rs |date=2009-10-20 |access-date=2011-02-17}}</ref>

==See also==
* [[List of Jewish Nobel laureates]]

==References==
{{reflist}}

==External links==
*{{Commons category-inline}}
{{wikiquote}}
*{{Nobelprize|name=Martin L. Perl}} including the Nobel Lecture, December 8, 1995 ''Reflections on the Discovery of the Tau Lepton''
*[https://www.nobelprize.org/nobel_prizes/physics/laureates/1995/press.html Nobel Prize press release, explaining the significance of Perl's work]
*[https://web.archive.org/web/20130127174717/http://martinperl.com/ Personal blog: Reflections on Physics]
*[https://web.archive.org/web/20120205213113/http://www.patentgenius.com/patent/5943075.html U.S. Patent 5943075] Universal fluid droplet ejector (Martin Lewis Perl)
*[https://web.archive.org/web/20130426062451/http://www.patentgenius.com/patent/5975682.html U.S. Patent 5975682] Two-dimensional fluid droplet arrays generated using a single nozzle (Martin Lewis Perl)
*[http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/perl-martin.pdf Gary Feldman, John Jaros, and Rafe H. Schindler, "Martin L. Perl", Biographical Memoirs of the National Academy of Sciences (2016)]

{{Nobel Prize in Physics Laureates 1976-2000}}
{{1995 Nobel Prize winners}}
{{Wolf Prize in Physics}}

{{Authority control}}

{{DEFAULTSORT:Perl, Martin Lewis}}
[[Category:1927 births]]
[[Category:Nobel laureates in Physics]]
[[Category:American Nobel laureates]]
[[Category:American chemical engineers]]
[[Category:American people of Belarusian-Jewish descent]]
[[Category:Columbia University alumni]]
[[Category:Jewish American physicists]]
[[Category:2014 deaths]]
[[Category:Members of the United States National Academy of Sciences]]
[[Category:American particle physicists]]
[[Category:United States Merchant Marine Academy alumni]]
[[Category:University of Michigan faculty]]
[[Category:Wolf Prize in Physics laureates]]
[[Category:Polytechnic Institute of New York University alumni]]