Martin Lewis Perl

Martin Lewis Perl
Born	(1927-06-24)June 24, 1927 New York City,New York
Died	September 30, 2014(2014-09-30)(aged 87) Palo Alto, California
Nationality	American
Alma mater	New York University Tandon School of EngineeringandColumbia University
Known for	Tau lepton
Children	Jed Perl
Awards	Nobel Prize in Physicsin 1995
Scientific career
Fields	Physics
Institutions	University of Michigan Stanford Linear Accelerator Center(SLAC) University of Liverpool
Doctoral advisor	I. I. Rabi
Doctoral students	Melissa Franklin,Samuel C. C. Ting

Martin Lewis Perl(June 24, 1927 – September 30, 2014) was an Americanchemical engineerandphysicistwho won theNobel Prize in Physicsin 1995 for hisdiscoveryof thetau 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, wereJewishimmigrantsto the US from thePolisharea ofRussia.

Perl was a 1948chemical engineeringgraduate of Brooklyn Polytechnic Institute (now known asNYU-Tandon) in Brooklyn. After graduation, Perl worked for theGeneral 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 atUnion CollegeinSchenectady, New York,which led to his growing interest in physics, and eventually to becoming a graduate student in physics in 1950.

He received his Ph.D. fromColumbia Universityin 1955, where his thesis advisor wasI.I. Rabi.Perl's thesis described measurements of the nuclear quadrupole moment ofsodium,using the atomic beam resonance method that Rabi had won the Nobel Prize in Physics for in 1944.

Following his Ph.D., Perl spent 8 years at theUniversity of Michigan,where he worked on the physics ofstrong interactions,usingbubble chambersandspark chambersto study the scattering ofpionsand laterneutronsonprotons. While at Michigan, Perl andLawrence W. Jonesserved as co-advisors toSamuel C. C. Ting,who earned the Nobel Prize in Physics in 1976.

Seeking a simpler interaction mechanism to study, Perl started to considerelectronandmuoninteractions. He had the opportunity to start planning experimental work in this area when he moved in 1963 to theStanford Linear Accelerator Center(SLAC), then being built inCalifornia.He was particularly interested in understanding themuon: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 chargedleptons.In addition, he considered the possibility of finding a thirdgenerationof lepton through electron-positroncollisions.

Perl is one of the 20 American recipients of the Nobel Prize in Physics to sign a letter addressed to PresidentGeorge W. Bushin 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 theDepartment of Energy'sOffice of Science,theNational Science Foundation,and theNational Institute of Standards and Technology.

He died after a heart attackat Stanford University Hospital on September 30, 2014, at the age of 87.His son,Jed Perl,is an author and art critic forThe New Republic.

Discovery of the tau particle

Thetaulepton (τ, also called the tau particle, tauon or simply tau) is anelementary particlesimilar to the electron, with negativeelectric chargeand aspin of1⁄2,but with 3477 times the mass. Together with theelectron,themuon,and the threeneutrinos,it is classified as alepton.

The tau was first detected in a series of experiments between 1974 and 1977 by Perl with his colleagues at theSLAC-LBLgroup.Their equipment consisted ofSLAC's then-new
e⁺
–
e⁻
colliding ring, calledSPEAR,and theLBLmagnetic detector. They could detect and distinguish between leptons, hadrons andphotons.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.The tau has a lifetime of only2.9×10⁻¹³sand so these particles decayed within a few millimetres of the collision.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:

We have discovered 64 events of the form

e⁺
+
e⁻
→
e^±
+
μ^∓
+ 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:

e⁺
+
e⁻
→
τ⁺
+
τ⁻
→
e^±
+
μ^∓
+ 4
ν

This was difficult to verify, because the energy to produce the
τ⁺

τ⁻
pair is similar to the threshold forD mesonproduction. Work done atDESY-Hamburg, and with the Direct Electron Counter (DELCO) atSPEAR,subsequently confirmed the discoveryand established the mass and spin of the tau.

The symbol τ was derived from the Greekτρίτον(triton,meaning "third" in English), since it was the third charged lepton discovered.

Nobel Prize and later career

Perl won the Nobel Prize in 1995 jointly withFrederick 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 theneutrino".In 1996 he publishedReflections on Experimental Science,which consists of "comments, scientific reprints, reflections, and a memoir...".

He joinedUniversity of Liverpoolas a visiting professor.He served on the board of advisors ofScientists and Engineers for America,an organization focused on promoting sound science in American government. In 1996, he received the Golden Plate Award of theAmerican Academy of Achievement.In 2009, Perl received an honorary doctorate from theUniversity of Belgrade.

See also

• List of Jewish Nobel laureates

External links

• Media related toMartin Lewis Perlat Wikimedia Commons

• Martin L. Perlon Nobelprize.orgincluding the Nobel Lecture, December 8, 1995Reflections on the Discovery of the Tau Lepton
• Nobel Prize press release, explaining the significance of Perl's work
• Personal blog: Reflections on Physics
• U.S. Patent 5943075Universal fluid droplet ejector (Martin Lewis Perl)
• U.S. Patent 5975682Two-dimensional fluid droplet arrays generated using a single nozzle (Martin Lewis Perl)
• Gary Feldman, John Jaros, and Rafe H. Schindler, "Martin L. Perl", Biographical Memoirs of the National Academy of Sciences (2016)