Dedication to Nathan Isgur

View metadata, citation and similar papers at core.ac.uk brought to you by CORE

provided by Caltech Authors

Mark B. Wise

California Institute of Technology, 452-48 Caltech, Pasadena 91125,CA USA

Nathan passed away in July after a lengthy illness. I am sure most of you are familiar wit mans hhi y contribution heavo st y quark certainls i physic t i d ysan fitting thae w t minute w beginnintake fe th ea t honoa o st m f thigo hi r s meeting. Actually Nathan's main physics interest was the strong interactions rather than heavy quark physics per se. He was already very well known for work he did with Gabriel Karl and others on the nonrelativistic quark model before the work that he did on heavy quark symmetry and its applications. However, Nathan understood the limitations of the nonrelativistic quark model, and was thrilled that the methods he helped develop allowed one to derive systematically from the theory of the strong interactions many properties of hadrons that contain a heavy quark. familiae b t no Sincry witma e h u manNathan'yo f yo s work outsid aree th f ao f eo heavy quark physics givI , e below lis mosa s somf to hi f te o importan heavn tno y quark physics papers. They are not in any particular order and might not even be the most citedthinI t k .Bu least a the particularls e t y onear e som wa th e sh f eo y proud of: • "Wh e pseudoscalar-mesoth y n mixing angl s —10°"i e , Phys. Rev. D12, 3770 (1975). In this paper Nathan gave a simple explanation based on quark model mixing for the observed T| — T|/ mixing angle. It is a beautiful piece of simple physics that still form understandinr basie ou s th f so value th thif r eo g fo s angle. • "P-wave baryon quare th n ksi model", (wit Karl. hG ) Phys. Rev. D18,4187 (1978); "Positive-parity excited baryon quara n si k model with hyperfine interactions", (with G. Karl) Phys. Rev. D19, 2653 (1979). These two papers form the basis of the Isgur-Karl quark model for baryons. It is shocking how many properties of the baryons this nonrelativistic quark model approac abls hi explaino et . • "KK molecules", (wit Weinstein. hJ ) Phys. Rev. D41, 2236 (1990). This paper gave some very simpl t powerfuebu l arguments that what e useb o dt calle 5(980e dth ) shoul interprete e usuade b th s la typt quarf dno eo k model state but rather as a weakly bound kaon-anti-kaon state. • "Perturbativ Exclusivn i D eQC e Processes", (wit . LewellyhC n Smith) Phys. Lett. B217, 535 (1989). Here Nathan argues that the perturbative predictions for exclusive processes made by Brodsk Lepagd yan egooa shoule b d t approximatiodno n until very large Q2.

Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp This was a very important paper because at the time it was written much of the

community thought that these predictions are relevant at quite low Q. 2 • "Flux-tube model for hadrons in QCD", (with J. Paton) Phys. Rev. D31, 2910 (1985). Ther mane ear y propertie energ w thaD lo tf ysQC o canno describee b t d wite hth non relativistic quark model, for example, the properties of exotic mesons. Also one would lik havo et deepeea r understandin nonrelativistie th y wh f go c quark model work allt sa . Nathan mad starea thin to s proble thimn i s paper. When I called my wife Jackie from Rome to tell her that Nathan passed away she was saddenet "suci t hgooa pu gentld e ddan sh tha es a tI manneve . lefd us "tha r heard Nathan raise his voice or get angry during any discussion, physics or otherwise. always t wa It'tha criticale coule b e sno h s t h t composet dno bu , neved dan r felte th nee mako dt e someone feel smalt appreciateno thef i ld yha propee dth r reasonina n gi particular argument stilt havlBu .I harea d time viewing Natha "gentle"s na thin.I k this is because most of my interactions with him centered on physics. He was fiercely driven understano t physice dth s issue puzzlins s wa tha e h t gcoule h over d d an ,perfor m even mose th t bruising calculation thef si y would helgai m intuitioe pafterns hi th n wa I . e nh physics bein greaga t calculato littla s ri e like bein ggreaa t athlete taket ,i s disciplind ean perseverance as well as natural talent. Just as it is hard to picture professional athletes as gentle souls when they are off the field it is sometimes hard for me to see Nathan in that light. t NathaI firsme t sophomora n s whe wa Universite nI th t ea f Torontoyo d ha e H . recently com Toronto et graduata s oa eteachins studenwa d undergraduatn ga an t e seminar class on statistical mechanics. He chose as the book Kittel's thermal physics, greaf o whice t undergraduaton hs i marvelouea s textswa t .I s course. Natha giftea s ndwa teacher both in the seminar style of that course and in the more conventional lecture style as well. Canadians are not as daring as Americans. Like most of my friends I lived at home during my undergraduate years and was more than a little nervous about leaving home to graduato d e Unitee worth n ki d lookin s timStatese wa th eI y gB . into graduate schools Natha professoa s Universite nwa th t ra Torontof yo tol e thae .H woulde m th happe db y graduats S hi U s hava e o t e th e e m o student o g insistet o t tbu s bese dwa th te thinm r gfo and get my PhD there. The first time I tried, I didn't get into any of the US graduate schools that I wanted to attend stayeI o s , t Universitda Torontf yo mastersa r ofo e t endeI .th f beino p du e gon best movecareery m f s o tooI . kgraduata e coursquare th n keo model from Nathad nan he also supervised my reading of Bjorken and Drell Volume 1.1 have often thought what Nathan taugh thae tm t yea radvantagn gava e em e over contemporariemany m f yo o swh had more experience with tools from field theory but lacked some of the intuition that came from the type of quark model calculations that Nathan had exposed me to. After that tim ewoulI d work with Nathan wheneve camrI e hom visi o efamilt y tm y durin summere gth weeo tw . k Usualla woulI visis d into wa an td g t yoi Universitf yo Toronto to talk with Nathan almost every weekday. That's how our collaboration on heavy quark physics started. Actually, it might have started off with a phone call before

Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp visia t home certainlt ,bu y serioumuce th f ho s wor dons kwa e durin visity gm s homeI . remember vividl ypapee tha th idee r rtth a fo wher treatee ew d semileptonid an D o t cB D W decays away from zero recoil came on the last day of one of my visits to Toronto. I hourw fe sa onl beford y ha fligh y em t idelefte aTh . camwhils u were o et e w fronn ei f o t the blackboard shor.o Tims s didn'tI ewa t havrestrooe th ee timus m o e t before heading ou rathe a airporte ts th int rwa o ot t uncomfortabl t I .traffi ge o t c makd edi drivI e t ebu flighe satisfd th othean ty ym r needairporte th t sa . I have very fond memorie togethed wore di th e heavkf n w o so r y quark physics. Intellectuall mose th s t excitinwa t yi g periocareey m physicsf n di ro . Even aftee th r early 1990's and well into the period when Nathan was not well we continued to talk about particle physics nevee H . r los passios subjece hi t th continued r nfo an t o dt publish important work. Few particle theorists have been as influential as Nathan and so universally well liked. I miss him and think about him often, as I am sure many of you also do.

Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp