higgs boson scientificamerican1186-76

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The Higgs BosonI t could give mathematical consistency to the standard od l- theory that describes the in teractions of fundam ental p rt .The search for the elusive parti e wi require new acc

T e t ly f ndamental p oblemsof p ysics can always be explained in simple te ms wit o t

t e elp of complicated eq ations o

mat ematical a g ments At least t iswas once told to me by Victo Feisskopf, an eminent p ysicist w o

often engages in s c explanationsand e may ve y well be ig t It cetainly olds fo a p oposed b t ndiscove ed pa ticle called t e Higgsboson and t e so called Higgs eld associated wit it

T e Higgs boson, w ic is namedafte Pete Higgs of t e Unive sityof Edinb g , is t e c ief missing ing edient in w at is now called t e standa d model of elementa y p ocessest e p evailing t eo y t at desc ibes t ebasic constit ents of matte and t ef ndamental fo ces by w ic t ey inte act Acco ding to t e standa d model, all matte is made p of q a ks andleptons, w ic inte act wit one anote t oug fo fo ces g avity, elect omagnetism, t e weak fo ce and t est ong fo ce T e st ong fo ce, fo instance, binds q a ks toget e to makep otons and ne t ons, and t e esid alst ong fo ce binds p otons and neut ons toget e into n clei T e elect o

magnetic fo ce binds n clei and elect ons, w ic a e one kind of lepton,into atoms, and t e esid al elect omagnetic fo ce binds atoms into molec les T e weak fo ce is esponsiblefo ce tain kinds of n clea decay T ein ence of t e weak fo ce and t est ong fo ce extends only ove a s o t

ange, no la ge t an t e adi s of anatomic n cle s; g avity and elect omagnetism ave an nlimited angeand a e t e efo e t e most familia oft e fo ces

In spite of all t at is known abo t

t e standa d model, t e e a e easonsto t ink it is incomplete T at is w e et e Higgs boson comes in Speci cally, it is eld t at t e Higgs boson givesmat ematical consistency to t e stan

byMar i usJ G V ma

da d model making it applicable toene gy anges beyond t e capabilitiesof t e cu ent gene ation of pa ticle accele ato s b t t at may soon be

eac ed by f t e accele ato s Mo eove , t e Higgs boson is t o g t togene ate t e masses of all t e f ndamental pa ticles; in a manne of speaking, pa ticles "eat t e Higgs boson togain weig t

T e biggest d awback of t e Higgsboson is t at so fa no evidence ofits existence as been fo nd Insteada fai amo nt of indi ect evidence al

eady s ggests t at t e el sive pa ticledoes not exist Indeed mode n t eo

etical p ysics is constantly lling t evac m wit so many cont aptionss c as t e Higgs boson t at it is amaing a pe son can even see t e sta s on aclea nig t! Alt o g f t e accele ato s may well nd di ect evidence oft e Higgs boson and s ow t at t e motivations fo post lating its existencea e co ect, I believe t ings will not beso simple I m st point o t t at t isdoes not mean t e enti e standa dmodel is w ong Rat e , t e standa dmodel is p obably only an app oximation albeit a good one of eality

Even t o g t e only legitimate eason fo int od cing t e Higgs boson is to make t e standa d modelmat ematically consistent m c attention as been given to t e conceptally easie p oposal t at t e pa ticlegene ates t e masses of all t e f ndamental pa ticles I s all t e efo e begin wit t at topic

Cent al to an nde standing of owt e Higgs boson would gene ate massis t e concept of a eld A eld is simply a quantity, s c as tempe at e,de ned at eve y point t oug o tsome egion of space and time, s c ast e su face of a f ying pan In p ysicst e te m " eld is usually ese ved fosuch entities as t e g avitational eldand the elect omagnetic eld Fields

gene ally make t emse s e t means of t e exc ange m ipa ticle; t pa ticle t t m i telect omagnetic e fo x m is

t e p oton o q ant m li t mediating pa tic es o t e a ial eld, t e weak el n t t

eld a e specti e t e t(w ic as not et e t tt ee weak ect oso s l t e

an p i l s tgl ons In a somew at a o t e Higgs boson i t me iati cle of t e p opose Hi s

It is now ass me t at t is a costant Higgs eld t o st at is, t e vac m of s not empty b t contai s t i n t t

el T e Higgs el is t t e ate mass by c p i t c s

epending on t e c i st e t pa ticle in space as a ce t in p te ti lene gy y Einste n s famo s eqtion, = m 2(ene gy eq s m ssm ltiplied b t e s a e of t s eof lig t , t e co p ing ene gy s eq iva

ent to a mass T e st n e t pling, t e g eate t e mass

T e way pa ti les a e t t t q i e mass in t i ct s itt e Higgs eld is somew at n l

to t e way pieces of lotti so b ink In s c an a lo t of pape ep esent in ivi icles and t e ink ep esent n mass st as pieces of ap f ing si e an t ickn ss so k p ing amo nts of ink di e ent ti s"soak p va ying amo nts of eo mass T e obse ve mass f cle depends on t e pa ticl s "enabso bing ability and on t e s enof t e Higgs eld in space

Wat a e t e c a a te istics f t

p oposed Higgs el ? In ode to endow pa tic es wit mass tHiggs eld, if it exists wo ld ave toass me a nifo m non e o val e evenin t e vac m Mo eove t e Hi gs

1986 SCIENTIFIC AMERICAN, INC


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eld would be a scalar eld, which isone of two kinds of eld importan indescribing the interac ions of particles.A scalar eld is a eld in which eachpoint has associated with it a singlemagnitude, or number. The other important eld is a vector eld: a eldwhere at each point a vector, or arrow,is drawn. A vector has both a magnitude, which is represented by helength of the arrow, and a direction.The electromagnetic, weak and strong

elds are all vec or elds. (The gravita ional eld is a special entity called atensor eld.)

The proposed Higgs eld must be ascalar eld, because if i were a vector

eld, the mass of a particle would ingeneral depend on the particle's alignment with the eld. Stated in a some-

what oversimpli ed way, the mass ofa person would change if he or sheturned around while standing in thesame place. In o her words, the Higgs

eld is "spinless.Because he Higgs eld is spinless,

he Higgs boson mus also be spinless.Spin, as applied to elementary par icles, is a quantum-mechanical proper

y roughly equivalen o the classicalspin of a rotating ball. Elementary par

icles can take on only integer (0, 1, 2and so on) and half in eger (1/2, 3/2and so on) values of spin. Particles thathave integral spin are called bosonsand particles that have half integralspin are called fermions. Bosons andfermions have sharply di ering properties, bu I shall not delve into thattopic here.

The Higgs boson is called a scalarboson because it has a spin of Mostother bosons associated with elds arethought to be vector bosons: particlesthat have a spin of The photon,gluon and and particles,for instance, are spin 1 bosons.

Since vector bosons are ypically associated wi h the fundamental forcesof nature and the Higgs boson is a scalar boson, the force by which particlescouple to the Higgs e d must be anew force. It is introduced explicitlyand solely as a mechan sm o improvethe mathematical consistency of thestandard model. The Higgs force behaves mathematically in a similarmanner to the recentl pub icized

fth force reported by EphraimFischbach of Purdue University. The

MAGNETIC MONOPOLES should exist if the Higgs boson exists. Classically, of course, magnetic monopoles are not found because when a bar magnet is cut in ha f, two sma er bar magnetsare created-not isolated "north and "south poles Magnetic

monopoles could, however, be formed by sweeping magnetic eldlines under the Higgs "rug The b ttom illustration shows apair of monopoles Although there have been scattere reports of

nding monopoles, none of them has been substantiated to date



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p oposed Higgs fo ce is, oweve ,weake and as a m c s o te anget an t e " ft fo ce

T e Higgs fo ce is not a nive salfo ce, beca se it co ples di e entlyto di e ent pa ticles Speci cally, if apa ticle is obse ved to ave mass, t est engt of t e co pling to t e Higgs

eld is ass med to be w ateve q antity is necessa y to gene ate p eciselyt at mass P es mably t e Higgs elddoes not co ple to t e p oton, sinceexpe iment s ows t e p oton is massless t appa ently it co ples to t e

and pa ticles, beca set ey do ave mass It s o ld pe apsbe noted t at pa ticles co ld ave amass of t ei own, in addition to w att ey a e t o g t to acq i e f om t eHiggs eld C io sly, oweve , int e standa d model not a single pa ticle co ld ave a mass of its own wito t dest oying t e mat ematical com

pleteness of t e t eo y

F om a p ysical point of view little isgained by p oposing t at t e Higgsoson acco nts fo mass It is not

LEPTONS

known, fo example, w y t e Higgseld s o ld co ple mo e st ongly to

some pa ticles t an it does to ot e sNo do investigato s nde stand owt e mass of t e Higgs boson itself(w ic is not known comes abo t, alt o g it is gene ally p es med to bedominantly t o g a self inte actionwit t e Higgs eld In t is sense ig

no ance abo t t e o igin of pa ticlemasses is eplaced by igno ance abo tpa ticle-Higgs co plings, and no ealknowledge is gained

Mo eove , t e int od ction of t eHiggs boson c eates a signi cant p oblem wit espect to t e " oly eld ofg avitation T e eq ivalence of massand ene gy implies t at t e g aviton,w ic co ples to anyt ing t at ca iesmass, s o ld co ple to anyt ing t atca ies ene gy, incl ding t e Higgs

eld T e co pling of t e g avitonto t e Higgs eld eve p esent in all

space wo ld gene ate a ge "cosmological constant it wo ld c ve t enive se into an object o g ly t e si e

of a football If t e Higgs boson is ass med to ave o g ly t e same mass

QUARKS

P RTICLE NAME SYMBOLMASS A RES E RIC

PARTICLE NAME(MeV) HARG

E ECTRON NEUTRINO v ABOUT UPELECTRON e- DOWN

M ON NEUTRINO v/ ABOUT CHARMM ON 6 6 S RANGE

TAU NEUTRINO v LESS THAN 64 TOPfTRUTHT U ,- 7 4

BOTTOM/BEAUTY

STRENGTH AT

as t e weak vecto bosons, t e ene ydensity of t e Hi gs eld in t e vac

m wo ld be 10 t illion times eatet an t e densit of matte in an atomicn cle s f t e ea t we e comp ss dto t is density, its vol me wo ld be app oximately 500 c bic centimet s, oa bit mo e t an t e si e of a soft d i kcan Ne dless to say, t is is cont a y toexpe iment

T e t eo ists way o t is allysomet ing It is ass med t at t e"t e vac m (one wit o t a Hi s

eld is c v d in a n ative sense itas a cosmolo ical constant q al in

magnit de b t opposit i si to t eone gen ated y t e Hi s e d Tint od ction o t e Hi s eld t en

attens o t space to make p ciselyt e nive se as we know it T is soltion is, of co se, not v y satisfacto y,and many ingenio s att mpts avebeen made to solve t e p obl m o t

cosmolo ical constant Nonof t e attempts as s cc ded If anyt ing, matte s av own wo beca se t eo ists ke p d mpin mopa ticles and e ds into t e vac m

SYMBOLM SS T EST ELECT IC(Me C E

u 3 % 3 -

c ,5 %s 5 5t ,5 ; %

HYPO ETIC LP ICLEO 5,

FORCE RANGECENTIM TER IN

ARRIERMASS T REST

SPINELEC IC

MCOMPARISON WI HSTRONG FORCE

RAVITY INFINITE

ELEC ROMAGNETISM INFINITE

WE K LESS HANCENTIME ER

STRONGLESS THAN

CENTIMETER

S ND RD OD f m ntar part c ph s cs h ds that

th r ar 2f ndam nta c nst t nts f matt r (topand f r as c f rc s (bottom c nst t nts f matt r ar d d d nt tgr ps f s : pt ns and q arks. pt ns st nd p nd nt

h r as an nd d a q ark has n r n s at d. Q arks ara a s part f arg r part c s s ch as pr t ns and n tr ns; apr t n f r nstanc s th ght t mad f t p q arks and

(GeV) C E

GRAVITON C NJ C

PHOTON O I CWEAK SECTOR OBOSONS: I C

OI C L

93 O SE EI CTL

GLUONS P M NE LCONFIN

n d n q ark. he partic es interact ith one another means

f th f r f rc s. ach f rc in turn has a partic e assoc ated itht (ca d a s n) that c n s the force. he H ggs force if tsts u d a f h n h ch u d be mediated th Higgs

s n. h mass s f th f ndamenta c nstitu nts are g en nm ns f ctr n ts (M V) and th mass s of th part c esthat c n the f rc s ar g n n ns f ectron o ts (GeV).



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Pe haps somehow the unive se became at f om the dynamics of thebig bang explosion, which is believedto have c eated the unive se some 15to 20 billion yea s ago

The theo y as it stands, with oneHiggs eld, does not explicitly cont adict obse vation, even if one must accept the inc edible disappea ance of

the cosmological constant Ce tain extensions of the theo y p oposed ovethe past decade often involve the int oduction of additional Higgs elds Although the a guments fo such extensions a e often compelling, the phenomena associated with these ext aHiggs elds have eithe neve beenseen o cont adict obse ved facts

To account in an elegant way foce tain symmet ies obse ved in thest ong inte actions, fo example, a second Higgs eld was p oposed by Helen R uinn of the Stanfo d LineaAccele ato Cente SLACand Robe to Peccei of the eutsches Elect onen Synch ot on DESYthe elect on accele ato in Hambu g) Theensuing theo y p edicted a new andp esumably ve y light pa ticle calledthe ax ion So fa , in spite of extensivesea ches, the ax ion has not been foundIn addition the theo y has d amaticcosmological consequences conce ning a phenomenon known as "domainwalls In gene al a domain wall ma kswhe e two egions of di e ing p ope

ties meet each othe omain wallsa e, fo instance, found in pe manentmagnets, whe e one egion of atomswhose spins a e aligned in one di ection meets anothe egion of atomswhose spins a e aligned in a di e entdi ection

t is believed that ce tain Higgs eldswould have given ise to domain

walls in the ea ly unive se hen theunive se was young, the tempe atu ewas ext emely hot and no Higgs eldis thought to have existed At sometime the unive se would have cooledsu ciently to allow a backg oundHiggs eld to come into being Unlessthe cooling we e completely unifo m,the Higgs eld would quite likely haveexhibited di e ent p ope ties f omone egion in space to the next Towhat extent the clash of such egionswould esult in visible o even violentphenomena depends on detailed p ope ties of the Higgs elds, but onewould expect some kind of clash inconnection with the suggestive p oposal of uinn and Peccei

The question is why domain wallsbetween such egions have not beenobse ved It could mean that the e isno Higgs eld, o that natu e has beenca efu in i s use of the eld Alte -

natively, the walls could have disappea ed ea ly in the histo y of the unive se This is athe typical one sta tswith an excellent a gument, d ags in aHiggs eld and then things go w ongIt ce tainly inspi es little faith in themechanism altogethe .

The int oduction of an ext a Higgsboson also c eates di culties in amodel that is att acting conside ableattenti n called the SU(5) g and uni

ed theo y The goal of uni ed theoies in gene al is to account fo the

fou fo ces in te ms of one fund amen-

SC R F ELD

VECTOR F ELD

" '. ' < iH t\t ij f 1

t l/ f \t tl /!

I / k - ' , / / " ' \I / . - ' \I k - "I / k 1 / j I

dil / I1 \\ 1 f tt \ \

! ! ?

- . / !

\ - . -

F D e m t t de g t e te t t e t e t e

e d q t t ( tem e t e) de ed t e e t t g t me eg e d t me ( t e e g ) k d e d e e d

(top d e t e d (bottom e d e d e e t ted t t g e m g t de m e e e e ted e e t e e t e d t e t e d t m g t de e e e ted e e t e e gt

d d e t e e e ted t e e t t t e e d e ee e t m g et e k d t g e d e e m e e t e d ; t e gg e d te t d e e d ( e g t e d e e t t ed te e d )



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tal force. A step toward achieving thatgoal was reached over the past two decades with the introduction and verication of the so-called electroweaktheory. The theory holds that the electromagnetic force and the weak forceare manifestations of the same underlying force: the electroweak force Theelectroweak theory was dramatically

con rmed in 198 3 at CERNthe European laboratory for particle physics,with the detection of the W+, W and

particles.The SU(5) grand uni ed theory

seeks to bind the strong force and theelectroweak force into one commonforce; the designation SU(5) refers tothe mathematical group of symmetrieson which the theory is based. According to SU(5) theory, the strong, weakand electromagnetic forces, which behave quite di erently under ordinarycircumstances, become indistinguishable when particles interact with anenergy of approximately 10 billionelectron volts (GeV)

The uni cation of the strong forcewith the electroweak force requires theexistence of an additional set of vectorbosons, whose masses are expected tobe several orders of magnitude greater than the masses of the weak vectorbosons Since the new vector bosons

ELECTR N

PR N

PH T N PH T N

ELECTR N

EL CTR N LECTR N

are so heavy, they essentially need aHiggs eld of their own. In SU(5) theory, therefore, the vacuum containstwo Higgs elds that couple with different strengths to di erent particles

The most important consequenceof the SU(5) theory is that quarks,through the new set of vector bosons,can change into leptons s a result the

proton that "immortal conglomeration of three quarks could decay intolighter particles such as a positron (atype of lepton that can be thought of asa positively charged electron) and aparticle called a pion Given the existence of two Higgs elds, the decayrate can be computed. Experimentsdone in recent years have not, however, found any such deca [see "TheSearch for Proton Decay, by J. M.LoSecco, Frederick Reines and DanielSinclair; C ENT F C MER CANJune,

985] It would seem that there issomething wrong with the SU(5) theory or the Higgs eld or both I believethe main concepts of the SU(5) theorywill survive over the long r n.

Moreover, if the S (5) grand unied theory is correct and the Higgseld does exist, magnetic monopoles

should have been created in the rst10 second of the universe An example of a magnetic monopole is an

ELEC R N

PR N

LECTR N L CTR NF Y R

( ); k

(bottom

k :

; k

8

isolated pole of a bar magnet (Classically, of course, such objects are notfound, because when a bar magnetis cut in half, two smaller bar magnets are created rather than isolated"north and "south poles ) Proponents of the SU(5) theory di er overthe internal composition of the monopole and over how many monopoles

should exist; it is generally agreed thatthe monopole should have an enormous mass for an elementary particle,perhaps from 10 6 to 10 7 times themass of the proton Although therehave been scattered reports of nding monopoles, none of the reportshas been substantiated; nature seemsto dislike anything involving Higgs

elds The search for monopoles continues see "Superheavy MagneticMonopoles, by Richard A Carrigan,Jr., and Peter Trower; C ENT F

MER CANApril, 1982]A further smattering of evidence

suggests that nature has been sparingin its use of the Higgs elds if theyhave been used at all As it happens, inthe electroweak theory the employment of only the simplest type ofHiggs eld leads to a relation betweenthe masses of the W bosons and theboson. The relation is expressed interms of a factor called the rho-parameter, which is essentially the ratio ofthe mass of the W bosons to the massof the boson. (There are correction

factors that need not bother us here.)The expected value of the rho-parameter is 1; experimentally it is found to be1.0 3, with an estimated error of 5 percent If there is more than one Higgs

eld, the rho parameter can take onvirtually any value Assuming that theagreement between theory and experiment is not accidental, the implicationis that only one Higgs eld exists

At this point it becomes necessaryI to question seriously whether theHiggs boson exists in nature I mentioned above that the only legitimatereason for postulating the Higgs bosonis to make the standard model mathematically consistent. Historically theintroduction of the Higgs boson togive such consistency had nothing todo with its introduction to account formass. The introduction of the Higgsboson to account for mass came out ofa "model building line, in which theories were explicitly constructed tomodel nature as closely as possible.

orkers in this line include Sidney A.

Bludman of the University of Pennsylvania, who proposed the bulk of themodel containing Wbosons, and Sheldon Lee Glashow of Harvard niversity, who incorporated electromagnetism into Bludman's model teven



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einberg of the niversity of Texas atAustin, using methods deve oped byThomas . B. Kibb e of the ImperiaCo ege of Science and Techno ogy inLondon, rep aced the part of the mode concerning partic e masses with theHiggs mechanism for generating mass.The integration of quarks into the vector-boson theory was achieved by Nico a Cabibbo and Luciano Maiani ofthe niversity of Rome, Y. Hara ofthe niversity of Tsukuba, G ashowand ohn I iopou os of the co e Norma e Sup rieure in Paris.

A these papers were prod uced overa rather ong period, from 1959through 19 0. In that same periodmany other suggested attempts atmode bui ding were a so pub ished,but none of them, inc uding the ones Ihave cited, drew any attention in thephysics community. In fact, most ofthe authors did not be ieve their ownwork either, and they did not pursuethe subject any further (with the exception of G ashow and I iopou os).The reason for the disbe ief was obvious: no one cou d compute anything.The methods and mathematics knownat the time ed to nonsensica answers.There was no way to predict experimenta resu ts.

hi e I was considering the body ofavai ab e evidence in 19 8, I decidedthat Yang-Mi s theories (a generac ass of theories of which the standard

mode is a speci c examp e) were re evant in understanding weak interactions and that no progress cou d bemade un ess the mathematica dicu ties were reso ved. I therefore started to work on what I ca the "mathematica theory ine, in which itt e attention is paid to the extent theorycorresponds to experimenta observations. One focuses instead on mathematica content. In this ine I was by nomeans the rst investigator. It wasstarted by C. N. Yang and RobertL. Mi s of the Brookhaven NationaLaboratory. Richard Feynman of theCa ifornia Institute of Techno ogy,L. Faddeev of the niversity of Leningrad, Bryce S. De itt of the niversity of North Caro ina and Stan eyMande stam of the niversity of Ca ifornia at Berke ey had a ready madeconsiderab e inroads in this very dicu t subject.

I did not nish the work either. Theconc uding pub ication was the 19 1thesis of my former student Gerard 'tHooft, who was then at the niversi

ty of trecht. In that period few researchers be ieved in the subject. Morethan once I was to d po ite y or not sopo ite y that I was, in the words of Sidney R Co eman of Harvard niversity, "sweeping an odd c r er o weak

+ B S N + B S N

T NN UT INT N N N T N

+ B S N + B S N

+ B S N + B S N ?

NN U IN

T N T NW K V R B e c e o e e k o ce c c e o e ec o

ome ogou o e c e g o p o o o e ec o (see bottom ofustrat on on oppos te pagee e c o e op g oug m em c

de e ou d equ e e ex e ce o dou c ged eg ve p c e o ucp c e k o o ex e p o em e o ved oduc g eu c gedp c e c ed eZOo o (bottom r ghte ex e ce o e o o ee ve ed

interactions. A noted exception was aRussian group, ed by E S. Fradkin ofthe niversity of Moscow, that madesubstantia contributions.

Interesting y enough, the modebui ding ine and the mathematicatheory ine proceeded simu taneous yfor many years with itt e over ap. Iconfess that up to 19 1 I knew nothingabout the introduction of the Higgsboson in the mode bui ding ine. Forthat matter neither did 't Hooft. At onepoint, in fact, I distinct y remembersaying to him that I thought his workhad something to do with the Go dstone theorem (a concept that cameout of the mode -bui ding ine). Sinceneither of us knew the theorem, westared b ank y at each other for a fewminutes and then decided not to worryabout it. Once again progress arosefrom "Don't know how, a phrasecoined by eisskopf.

Progress in the mathematica -theoryine wou d u timate y show that the

e ectroweak theory becomes betterbehaved mathematica y and has morepredictive power when the Higgs boson is incorporated into it. Speci ca y,the Higgs boson makes the theory re

norma izab e: given a few parameters,one can in princip e ca cu ate experimenta y observab e quantities to anydesired precision. A nonrenorma izab e theory, in contrast, has no predictive power beyo d a certain imit: the

theory is incomp ete and the so utionsto certain prob ems are nonsense.

I must point out, however, that thee ectroweak theory can make power

fu predictions even without the Higgsboson. The predictions concern theforces among e ementary partic es.Those forces are investigated in highenergy-physics aboratories by meansof scattering experiments. In such experiments beams of high-energy partic es are directed at a "target partic e.A beam of e ectrons might, for instance, be scattered o a proton. Byana yzing the scattering pattern of theincident partic es, know edge of theforces can be g eaned.

The e ectroweak theory successfuy predicts the scattering pattern when

e ectrons interact with protons. It a sosuccessfu y predicts the interactionsof e ectrons with photons, with Wbosons and with partic es ca ed neutrinos. The theory runs into troub e,however, when it tries to predict the interaction of W bosons with one another. In particu ar, the theory indicatesthat at su cient y high energies theprobabi ity of scattering one W bosono another W boson is greater than 1.Such a resu t is c ear y nonsense. The

statement is ana ogous to saying thateven if a dart thrower is aiming in theopposite direction from a target, he orshe wi sti score a bu 's-eye.

It is here that the Higgs boson enterss a savior The Higgs boson coup es

1 1986 SCIENTIFIC AMERICAN, INC


7/9

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wit t e W bosons in suc a way t att e probability of scattering falls witin allowable bounds a certain xedvalue between 0 and 1. n ot er wordsincorporating t e Higgs boson in t eelectroweak t eory subtracts o t ebad be avior more t oroug description of t e way in w ic t e Higgsboson makes t e electroweak t eoryrenormali able requires a special notation known as Feynman diagrams

MU N NEUTR N

ELECTR N

B S N B S N

B S N B S N

B S N B S N

B S N B S N

[ ee erie 0/ illu tration beginning onpage80and ending below].

Armed wit t e insig t t at t e Higgs. boson is necessary to make t e

electroweak t eory renormali able itis easy to see ow t e searc for t eelusive particle s ould proceed weakvector bosons must be scattered oone anot er at extremely ig energies at or above one trillion electron

MU N NEU R N

ELECTR N

B S N

B S N

H GGS B S N

B S N

ENO MA IZED E EC WEAK EO Y requ res the ex stence of the H ggsboson A renorma zed theory s one that, g ven a few parameters, can be app ed toca cu ate exper menta y observab e quant t es to any des red prec s on A nonrenorma

zab e theory, n contrast, has no pred ct ve power beyond a certa n m t: the theory sncomp ete, and the so ut ons to certa n prob ems are nonsense W thout the ggs boson

the e ectroweak theory successfu y accounts for the scatter ng of neutr nos o e ectrons

(top he theory runs nto troub e, however, when t tr es to pred ct the nteract on of Wbosons w th one another (middle .Spec ca y, the theory nd cates t hat at energ esabove one tr on e ectron vo ts ( eV ) the probab ty of scatter ng one Wboson o another Wboson s greater than Such a resu t s c ear y nonsense he theory s renorma zed by ntroduc ng the ggs boson (bottom aus b e pred ct ons can be rea zed bye ect ve y "subtract ng the set of ustrat ons at the bottom from the set n the m dd e

volts (Te V T e necessa y ene iescould be ac ieved a e propo e 0Te Superco ductin S per o i e(ssc),w ic is c r en y u e co ieration in t e S [see e S econducting S pe col i e by vid ackson a ry i e Sley o cicki F A

arc f e p e n o e s e epartic es fo lows e p e i io o erenormali ed e ec rowe k eo y et ere mus be com e i o efor w ic t e Hi s bo o o bet e obvious c n i e e p erdoes no fo low e p e i io et e weak vecto boso s wo olikely be in er c i o oforce an an en ire e e o ics ould be opened up

di c lty in se rc i o eHiggs boson is a i s m is i yunconstrained s de e mi e b eperimen t e m ss m be e e

an abo 5 e eo p e e s oc e as o ow e vy e Hi bosocould be excep e i e ogenera e some o e e i ieit s been esi e o o e i i s were 1 Te ic i pp o i e y1,000 imes e m ss o e o o t at point eo y su es s e we k

ector bosons cou no o e beviewed as eleme r p i es eyco ld be composi e s c e e o smaller pa ic es

T e o ion of ompo i e eis of course no i ew in e i o yo p ysics e be i i o e

icle men ioned e k ow eof struct re mo ecu es o inucleons (pro o s e o s quarks an lep ons

n consideri g t e Hi s bo o composi e s ruc re i is o y step to suppose su u mepar icles as quarks ep o ereally composi e s uc es e ostill sma er par icles ee e Sture of Q arks a d ep o b iHarari F A i1 8 3 n a sense e o io o iayer o struct re o e beyo qu kand lep ons bri s me f i e ditionally t e way o c o eeparameters s bee o o o ee elayer of s ruct re e s ess o oposite mo e s i p e i i e e y eels of atoms n nu ei e mass cou d a so be pre i e b oito a deeper layer o s ruc ure e

at in t e stand r mode e iboson is respo sible o l obse emasses implies a e e if i e et ere is o su in as a i bo ot ere is at east a common so ce oall masses Searc in or e i sboson cou d ultimately be e s me ssearc ing for a deeper struc ure o elementary particles

higgs boson scientificamerican1186-76

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