Heavy Quarks

7/24/2019 Heavy Quarks

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PHY-306 EPP Heavy Quarks Slide

Heavy Quarks

In this section we will cover the followin to!ics"

# $he %har& Quark

# $he 'otto& Quark

# $he (atio (

# $he $o! Quark

# )ny *ore Quarks+


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The Charm Quark

! to 1./ there were 3 uarks u2 dand s

)t S)%4SPE)( e+eStorae (in5

e+ e

7 hadronse+ e7 + e+ e7 e+ e

8ery narrowresonance

4s&all width 5 with a lare

&ass of 391 :e8;c,


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J/Particle

)lso at 'rookhaven< 30 :e8!roton

synchrotron

! 'e7 e+ e anythin

=ne rou! called it - the other J< now known as J/


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J/Width

)ctual widths are s&aller than o>served >ecause of&easure&ent errors and the s!read of the >ea& enery

$he true width ? 0906/ *e8;c,< verynarrow

width @ lifeti&e ? c9f9 Et?

I&!lies lon lifeti&e < so&ethin inhi>itsthe decay9 Aould

eB!ect so&ethin this heavy to decay very ra!idly to !ions

via Stron Interaction

Cew uark flavour < char&

*ass of char& uark? 19D :e8;c,


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J/Decay

$he &ost o>vious decay of the J/is a direct decay

to two char&ed &esons2 D+

and D

%har&ed &esons

'ut we now know the &ass of the Dis 19F/ :e8;c,

$he &ass of the J/is 3910 :e8;c,i9e9 less than twice the G&ass

J/ D+ D


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J/Decay

$he other !ossi>ility is a wei su!!ressed decay to !ions

$his is inhi>ited >y the 3 luon cou!lin

7 lon lifeti&e 7 narrow width


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Other States

$here is also a first eBcited state which is also narrow9

Hiher states with hiher &ass are wide as they can decay to D+ D

( nor&alised

cross section


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Charmed Hadrons

$he 4J

P

5 char&ed &esonsare"

D+ cd D cd

D0 cu D0 cu

DS+ cs DS

cs

)lso eBcited states

D!7 G etc

%har&ed >aryons"C

+ cudetc

Since the char&uantu&

nu&>er is conservedin

stron interactions2 the

!redo&inant decays are viathe weak interaction

G07 J- "+


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The #ottom Quark

In 1.// at Ker&ila> 4KC)5 saw narrowstructure in +&ass s!ectru& in &ass

reion near 10 :e8;c,in reaction

! nucleus7 + anythin

'e2 %u2 9 9 9

Carrow structure

%ontinuous >ackround


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The $%silon

Since then !recise eB!eri&ents at e+e&achines4G=(IS2 Ha&>ur2 %ES(2 %ornell CY5

!silon && *ass of >uark ? D :e8;c,

Ka&ily of ' &esonsand > >aryonsfound"

#+ &u # &d #s &s &

&ud


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The Char'e o( the & Quark

$he chare of the >uark of -eis

confir&ed >y &easurin the ratio ("

as a function of %* 4e+e5 enery

$he rates are deter&ined >y the

strenths of the E* cou!lins at

the two vertices iven >y the

chares of the !articles


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The )atio )

Su& over allcontri>utin uarks

%hare of

L @ so&e threshold

kine&atics factorsM

)s uarks co&e in 3 colours"

$he fact that the factor of 3 is necessary is very stron

evidence in su!!ort of the colour hy!othesis


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The )atio )

*lavour u d s c & t

Char'e, -., -., -., -., -., -.,

*or EC01 , 2e3have uu4 dd4 ss

5 )6 7 -8/9 + :/9 + :/9. 6 ,

*or EC01 ; 2e3have uu4 dd4 ss4 cc

5 )6 7 -8/9 + :/9 + :/9 + 8/9. 6 7

*or EC01 :: 2e3have uu4 dd4 ss4 cc4 &&

5 )6 7 -8/9 + :/9 + :/9 + 8/9 + :/9. 6 7


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The )atio )

u d s 7 ,

u d s c 7 393

u d s c > 7 39/

colour factor of 3


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The To% Quark

)fter 1.// we had"

Quarks

u c

d s >

e!tons

e

e

=>viously one&issin to! t

)lso ood theoretical

reasons for co&!lete

dou>lets

Searched in vain at e+e&achines2 PE$()2 PEP2 EP etc< rulin out any new uarks at their eneries 7 to! &ass

N D :e8;c,4half EP1 enery5


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=Hints= o( the To% Quark

In early 1..0s < !recise &easure&ents of 0decayat EP suest

that the to! &ass ? 1/0 :e8;c,

$hese involve su>tle corrections to >decay !ara&eters due to virtual to!

uark corrections

$hese ive a sliht chane to the

>decay width which de!endson the to! &ass

Kirst order

%orrection

%orrection


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The Discovery o( the To% Quark

In 1.. ru&ours that to! &ay have >een discovered at Ker&ila>

4near %hicao5

In *arch 1..D >oth %GKand G0

%olla>orations clai& < =>servation of the

$o! Quark

$hese are realAs"

A7 e

A7 A7 ?

$he sinaturesare"

e Oets eOets

e eOets Oets

Oets

$a>Oets >y reuirin

a finite decay distance$o! &ass 1/ D :e8;c,


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The Discovery o( To% Quark

G0 EB!eri&ent

%GK EB!eri&ent


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The Discovery o( To% Quark

Gata !oints

Ahat it would

look like

without to!

uarks

Esti&ated to!

uark

contri>ution

)ree&ent

>etween data

and theory for

different to!

&asses


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The To% Quark

$o! Quark %andidate

in )$)S


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@ny 0ore QuarksA

Ae have 3full enerations9 Ae only need one 4u2 d2 e2 e5 for everyday life

So if 3 why not &ore+ Since it is not understood why there are 3

enerations there is no theoretical reason why there shouldnt >e &ore

4Periodic $a>le aain+5

However2 eB!eri&ental evidence now suests only 3

In early 1..0s EP &easured the width of the >to very hih!recision9 $he >can decay into any fer&ion !airs with a co&>ined&ass less than the >&ass 4?.0 :e8;c,5

f u2 d2 s2 c2 >2 e2 2 2 e2 2

$he &ore ways the >can decay2 theshorterits lifeti&eand the larerits

width4@ ? 5


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@ny 0ore QuarksA

:eneration

1 , 3 9 9 9

u c t h 9 9 9

d s > l 9 9 9

e 9 9 9

e B 9 9 9

$he >can decay into all these

> ttsince*>R ,*t

$he >would decay into anynew neutrinos assu&in they

were &assless 4or liht

co&!ared with *>5


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Each of theuuetc

are know as !artial

widths

EPP


The Width o( the >

Ae know how &uch each uark;le!ton !air contri>utes to >

>6 uu+ dd + ss+ cc+ &&

+ e+e+ ++ +

+ is euivalent to &easurinthe nu&>er of neutrino s!ecies er of enerations

(esult fro& EP" ut they cannot >e too

heavy or they would contri>ute too &uch &ass to the niverse 7

)stro!hysical constraint on neutrino &asses


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PHY 306 EPP H Q k Slid

The Width o( the >

Gata !oints

$he red curve 4

Heavy Quarks

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