RECENT RESULTS FROM JADE AT PETRA

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RECENT RESULTS FROM JADE AT PETRA

G. Heinzelmann

To cite this version:

G. Heinzelmann. RECENT RESULTS FROM JADE AT PETRA. Journal de Physique Colloques,

1982, 43 (C3), pp.C3-59-C3-62. �10.1051/jphyscol:1982311�. �jpa-00221864�

CoZZoque ~ 3 , suppZBment azl n o 1 2 , Tome 43, dgcembre 1982 page C3-59

RECENT RESULTS FROM J A D E AT PETRA

G. Heinzelmann

II. I n s t i t u t Exp. Physik, UniversitLft Hamburg, F. R. G .

H a d r o n i c c r o s s s e c t i o n u ( e + e - + h a d r o n s ) . A p r e c i s e measurement o f oh t h e h a d r o n i c c r o s s s e c t i o n i n e f e - a n n i h i l a t i o n i n t o h a d r o n s h a s b e e n a c h i e v e d w i t h a s y s t e m a t i c e r r o r o f 3 % . The h a d r o n i c c r o s s s e c t i o n o r t h e r a t i o R = u ~ / u ( ~ ~ ~ ~ ~ ) = oh3s/4na2 i s o f fundamental i m p o r t a n c e . I t i s g i v e n i n p u r e QED f o r p o i n t 11 e a u a r k s , n e g l e c t i n g masses, by t h e sum o v e r t h e q u a r k c h a r g e s s q u a r e d t i m e s a c o l o r f a c t o r t h r e e : R = ~ c Q ' ~ = 1113 = 3.67. T h i s g e t s m o d i f i e d due t o QCD c o r r e c t i o n s and t h e p r e s e n c e o f t h e weak n e u t r a l c u r r e n t t o

2 ) ( l + a s / ~ + ~ ( a ~ ) ) R = 31 ( Q $ - ~ Q £ v ~ v ~ x + (ve+ae) ( v f + a f )

x

w i t h X = ( ~ ~ / 8 f i na) ( s M ~ / ( S - ~ 5 ) ) .

The QED c o r r e c t i o n i n f i r s t o r d e r a s / n changes R by AR1.5% (as=0.18) t h e second o r d e r by AR@.3%. Due t o t h e s dependence o f a s ( r u n n i n g ) R changes from l o w e s t t o h i g h e s t PETRA e n e r g i e s (12

-

37 GeV) by R%1.5%. The change i n R due t o t h e n e u t r a l weak c u r r e n t h a s a s t r o n g s dependence due t o t h e Zo p r o p a g a t o r . At p r e s e n t l y h i g h e s t PETRA e n e r g i e s (37 GeV), assuming s i n 2 0 w = 0 . 2 3 , a change i n R by AR%l% i s e x p e c t e d due t o t h e e l e c t r o - w e a k i n t e r f e r e n c e . A p r e c i s e measurement o f R i s t h e r e f o r e needed t o d e t e r m i n e a s and t o t e s t t h e c o u p l i n g o f t h e n e u t r a l weak c u r r e n t .

F o r t h e measurement of R t h e h a d r o n i c e v e n t s from t h e one photon a n n i h i l a t i o n have t o b e s e p a r a t e d from QED p r o c e s s e s such a s e+e- + e+e-, + e f e - y , + U U , + TT,

...

^and

a l s o from two photon p r o c e s s e s e+e- + e+e- + h a d r o n s which a r e c h a r a c t e r i z e d by m i s s i n g e n e r g y and momentum i n t h e d e t e c t o r . The main s e l e c t i o n c r i t e r i a r e q u i r e d n 5 4 c h a r g e d t r a c k s , v i s i b l e energy Evis > Ebeam and a n o r m a l i z e d momentum b a l a n c e a l o n g t h e beam d i r e c t i o n

iPbal1

> 0 . 4 . Charged and n e u t r a l p a r t i c l e s have b e e n u s e d i n t h e a n a l y s i s . The o b s e r v e d d i s t r i b u t i o n s of c h a r g e d m u l t i p l i c i t y rich ( F i g . l a ) , v i s i b l e e n e r g y Evis ( F i g . Ib) and momentum b a l a n c e pbal a r e w e l l r e p r o d u c e d by Monte C a r l o c a l c u l a t i o n . The a c c e p t a n c e e r r o r o f +1.5% and t h e e r r o r from two p h o t o n back- ground s u b t r a c t i o n ( 1 . 2 + 0 . 7 ) % h a v e b e e n checked b y v a r y i n g t h e c u t s : The c u t i n t h e v i s i b l e energy Ev;s/Ebeam h a s b e e n r a i s e d from 1 t o 1.6 and f u r t h e r m o r e a c u t h a s b e e n i n t r o d u c e d i n t h e a n g l e between t h e e v e n t t h r u s t a x i s and beam d i r e c t i o n a t cosB=0.6 which s t r o n g l y s u p p r e s s e s two p h o t o n p r o c e s s e s . I n b o t h c a s e s R changed bv l e s s t h a n 1 % . The l u m i n o s i t y was d e t e r m i n e d from Bhabha s c a t t e r i n g e v e n t s o b s e r v e d i n t h e b a r r e l l e a d g l a s s c o u n t e r s w i t h l c o s e l i 0 . 7 6 . T h i s h a s been checked a g a i n s t a l u m i n o s i t y measurement i n t h e end c a p s . The t o t a l l u m i n o s i t y d e t e r m i n e d from t h e end c a p s a g r e e s w i t h i n 0.4% w i t h t h e b a r r e l l u m i n o s i t y .

F i g . l a 0 1 2 3

F i g . Ib E ( v i s i b l e ) / E ( b e a m )

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982311

C3-60 JOURNAL DE PHYSIQUE

Rad. c o r r . a r e a p p l i e d up t o o r d e r a 3 . The measured R v a l u e s a r e shown i n F i g . 2 w i t h t h e s t a t i s t i c a l e r r o r s and a p o i n t

t o p o i n t s y s t e m a t i c e r r o r o f 1.8%. The t o t a l s y s t e m a t i c e r r o r i s 3%. The mean R v a l u e i s given i n Table 1 t o e t h e r w i t h r e c e n t r e s u l t s from TASSO

P

) and MARK J. A f i t t o t h e d a t a t r e a t i n g a s

o r sin2@, a s a f r e e p a r a m e t e r g i v e s t h e ^{1 5 -} v a l u e s a l s o shown i n T a b l e I . I n t h e

f i t t h e quark masses have been t a k e n i n t o a c c o u n t 2, and a l s o t h e s depend- ence o f a s . The TASSO r e s u l t s i n c l u d e 3 0

a q u a d r a t i c a l l y added s y s t e m a t i c e r r o r

:

^JADE

- I* order QCD

,

\ ,rL_____---_-

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^{--- ---}

-

----, ;

- parton modd 1

- OED only

-

-

10 20 30 40

R A R A R

s t a t . s y s t .

N e u t r a l weak c u r r e n t e f f e c t s i n l e p t o n p a i r p r o d u c t i o n e+e- +

,,+,,-

^{and e+e- -t T+T-.}

F i r s t e v i d e n c e f o r t h e p r e s e n c e o f t h e n e u t r a l weak c u r r e n t i n e+e- a n n i h i l a t i o n

of 2% f o r h i g h e r o r d e r ( > a 3 ) QED y'Z GeV

c o r r e c t i o n s .

Table 1 F i g . 2

JADE MARK J TASSO')

was p r e s e n t e d a t t h e Bonn c o n f e r e n c e 1981 i n t h e ,,-pair forward backward asymmetry A,,,,. T h i s h a s meanwhile a l s o been p u b l i s h e d 3 ) . The l e p t o n p a i r forward backward asymmetry A,,,, and A,, i n e+e- a n n i h i l a t i o n due t o t h e e l e c t r o w e a k i n t e r f e r e n c e i s p r o p o r t i o n a l t o t h e a x i a l v e c t o r c o u p l i n g a1 o f l e p t o n s A=3/2 a 1 2 ~ + ~ ( ~ 2 ) where

x

c o n t a i n s a p r o p a g a t o r o f ZO. The t o t a l l e p t o n p a i r c r o s s s e c t i o n ~ ( e + e - + , , + ~ - ) i s s e n s i t i v e t o t h e v e c t o r c o u p l i n g R,,,, = U , , , , / U ~ ~ ; , ~ = 1 + 2 v I z X + 0 ( x 2 ) . I n t h e s t a n d a r d GSW-model a2=1 and v12= ( 1 - 4 s i n ~ 0 ~ ) ~ = 0.006 u s i n g s i n 2 @ , = 0.23. I n t h i s model a d e v i a t i o n from QED due t o t h e weak n e u t r a l c u r r e n t i s t h e r e f o r e ex- p e c t e d i n t h e forward backward asymmetry whereas i n t h e l e p t o n p a i r c r o s s s e c t i o n no d e v i a t i o n i s e x p e c t e d due t o t h e s m a l l v e c t o r c o u p l i n g .

(sin20,=0.23 a s f i x e d )

15 A,,,, w i t h t h e s t a t i s t i c s p r e s e n t l y a v a i l a b l e from JADE

(I

~ t d = 4 8 ~ b - l ) i s shown i n F i g . 3 . A c l e a r d e v i a t i o n from QED (dashed c u r v e ) i s s e e n . A f i t t o t h e d a t a g i v e s a n asymmetry e x t r a p o l a t e d t o t h e f u l l @-range

and c o r r e c t e d f o r h i g h e r o r d e r QED p r o c e s s e s

23

(A(QED)%+I%) o f A,,,, = -(10.8 f 2.2 ( s t a t . )

+

^{1.0 '23}

( s y s t . ) ) . This c a n b e compared t o A,,,,= -9.2% p r e -

l 3

d i c t e d by t h e s t a n d a r d GSW model. From t h e lneasured

u

\

asymmetry a2=1.17 f 0.24 i s o b t a i n e d i n good a g r e e - 0.5

*- ^'

ment w i t h t h e GSW t h e o r y . The measured asymmetry of

$

t h e T - p a i r s A,, =-(7.9 f 3.9) a g r e e s w i t h t h e ex-

p e c t a t i o n b u t i s a l s o c o m p a t i b l e w i t h p u r e QED w i t h i n

cos 8

2 s t a n d a r d d e v i a t i o n s due t o t h e l i m i t e d s t a t i s t i c s . 0.0

No d e v i a t i o n from QED i s s e e n i n t h e ,,-pair t o t a l -0.5 0.0 0 5 c r o s s s e c t i o n a s e x p e c t e d f o r t h e s m a l l v e c t o r F i g . 3

c o u p l i n g . A f i t t o t h e d a t a g i v e s v2=0.20

+

0 . 3 2 .

s i n 2 0 w

3.93

*

^{0 . 0 3 f 0.09}

3.84 t 0.05 f 0.22 4.01 f 0 . 0 3 f 0.20

Four j e t s t r u c t u r e . I n e+e- a n n i h i l a t i o n i n t o hadrons t h e e x i s t e n c e o f b o t h m o and t h r e e j e t s h a s b e e n demonstrated and a r e i n t e r p r e t e d a s a m a n i f e s t a t i o n of t h e under- l y i n g q u a r k s and g l u o n s . Here t h e o b s e r v a t i o n of a 4 - j e t s t r u c t u r e i s r e p o r t e d . T h i s i s e x p e c t e d t o show up a t h i g h e n e r g i e s . Two measures , b o t h s e n s i t i v e t o t h e p r e s e n c e

0.14 5 0.08

0 . < a s < .22 (95%C.L.) 0.24 f 0.05 t 0 . 1 3

0.25

+

^0.05 (a,=O. 18)

0.41 + 0.12-0.15 (as=0.17) 0 . 4 0 t 0.15+0.02 (as=O. 17)

Three j e t d i f f e r e n t i a l c r o s s s e c t i o n du/dx, 0.1 A c o p l a n a r i t y 0.3 and a i n 2nd o r d e r QCD. The t h r e e j e t c r o s s

s e c t i k h a s been c a l c u l a t e d i n second o r d e r Q C D ~ ) . I n o r d e r t o compare t h e d a t a t o a t i o n w i t h and w i t h o u t 4 j e t s (5% 4 - j e t s w i t h A > 0 . 0 5 ) n o r m a l i s e d t o t h e same number

o f e v e n t s a s t h e d a t a . F i g . 4 shows t h a t t h e J

t h i s c a l c u l a t i o n and d e t e r m i n e a s , two d i f f e r e n t j e t f i n d i n g a l g o r i t h m s have been used matched t o t h e j e t d e f i n i t i o n s of t h e c o r r e s p o n d i n g t h e o r e t i c a l c a l c u l a t i o n s : one b a s e d o n a Sterman Weinberg t y p e o f j e t d e f i n i t i o n and t h e o t h e r one b a s e d on a n i n v a r i a n t mass c o n d i t i o n between p a r t i c l e s . Both g i v e s i m i l a r r e s u l t s . N e u t r a l a s w e l l a s charged p a r t i c l e s have been used i n t h e a n a l y s i s . F o r e v e n t s where 3 j e t s have been found t h e 3 j e t a x e s a r e p r o j e c t e d o n t o t h e e v e n t p l a n e and t h e p a r t o n

t h r u s t ~ ~ = 2 s i n ~ ~ ~ / ( s i n 0 ~ ~ + s i n 0 ~ ~ + s i n O ~ ~ ) i s c a l c u l a t e d from t h e a n g l e s between t h e j e t a x e s . T h i s observed x l d i s t r i b u t i o n i s

c o r r e c t e d f o r d e t e c t o r i n f l u e n c e , photon brems- s t r a h l u n g i n t h e i n i t i a l s t a t e and t h e e f f e c t from

2-parton e v e n t s u s i n g t h e LUND f r a g m e n t a t i o n scheme. , I n F i g . 5 t h e c o r r e c t e d d i s t r i b u t i o n i s compared

2 -

t o t h e t h e o r y which d e s c r i b e s t h e d a t a v e r y w e l l

2

1

f o r a v a l u e of a S ( l s t + 2 n d ) = 0 . 1 6

+

O . Z ( s t a t . )

+

^{0 . 3}

₂

r(x1<0885) ( s y s t . ) . For t h e d e t e r m i n a t i o n o f a s o n l y t h e d a t a

'g ₁

w i t h X I < 0.85 h a v e been u s e d i n o r d e r t o keep t h e c o r r e c t i o n s f o r 2 p a r t o n i n i t i a t e d e v e n t s s m a l l . Comparing t h e d a t a t o a f i r s t o r d e r c a l c u l a t i o n g i v e s ~ ~ ~ ( 1 s t ) = 0 . 2 0 f 0 . 2 ( s t a t . )

+

0 . 3 ( s y s t . ) . The j e t f i n d i n g a l g o r i t h m s a r e supposed t o b e r a t h e r i n s e n s i t i v e t o t h e d e t a i l s o f t h e f r a g m e n t a t i o n p r o c e s s . Using t h e A l i e t a l .

Monte C a r l o program ( 1 s t o r d e r ) f o r t h e c o r r e c t i o n 0.5 0.6 0.7 0.8 0.9 1.0 o f t h e d a t a t h e v a l u e o f a s o b t a i n e d a g r e e s with-

i n t h e s y s t e m a t i c e r r o r w i t h t h e above v a l u e . I t

F i g . 5

XI

i s a l s o i n t e r e s t i n g t o compare t h e d a t a t o t h e ex-

--

p e c t a t i o n f o r a n A b e l i a n Vector t h e o r y ( d o t t e d

c u r v e ) ; however t h i s i s u n a b l e t o d e s c r i b e t h e d a t a f o r any v a l u e of t h e c o u p l i n g s t r e n g t h . F u r t h e r i n f o r m a t i o n can b e found i n Ref. 7 .

G l u o n j e t b r o a d e n i n g . F i r s t e v i d e n c e h a s been r e p o r t e d a t t h e Bonn c o n f e r e n c e 1981 t h a t hadrons from gluon j e t s have h i g h e r mean t r a n s v e r s e momenta a s compared t o h a d r o n s from quark j e t s . T h i s h a s been f u r t h e r i n v e s t i g a t e d . Three j e t e v e n t s , i n t e r - p r e t e d a s gluon b r e m s s t r a h l u n g q?g a r e u s e d a s a s o u r c e f o r g l u o n s . For 3 - j e t e v e n t s (Ecm=33GeV) Monte C a r l o c a l c u l a t i o n s show, t h a t t h e l e a s t e n e r g e t i c j e t ( j e t o p p o s i t e d a t a a r e s i g n i f i c a n t l y b e t t e r d e s c r i b e d t a k i n g

f o u r j e t s i n t o a c c o u n t . T r i p o d i t y shows s i m i l a r e v i d e n c e . At low energy (Ecm=22GeV) t h e d a t a a r e w e l l d e s c r i b e d w i t h o u t 4 j e t s a s e x p e c t e d s i n c e 4 j e t s a t t h a t e n e r g y a r e s t i l l u n r e s o l v e d from 2 and 3 j e t s . The comparison o f h i g h and low energy d a t a d e m o n s t r a t e s t h a t n e i t h e r t h e method used nor b-decays s i m u l a t e t h e o b s e r v e d d i s - t r i b u t i o n s a t 33 GeV. F u r t h e r e v i d e n c e i s ob- t a i n e d i f t h e t r a n s v e r s e momentum o f t h e p a r t i c l e s w i t h r e s p e c t t o t h e e v e n t j e t a x e s

i s c o n s i d e r e d f o r d i f f e r e n t subsamples i n t h e ^lo Q p l o t . The observed d i s t r i b u t i o n s i n p t c a n c o n s i s t e n t l y b e d e s c r i b e d o n l y i f 4 - j e t s a r e ^u ro

t a k e n i n t o a c c o u n t . Without 4 - j e t s t h e Monte C a r l o c a l c u l a t i o n s f o r d i f f e r e n t p a r t s of t h e

2

Q p l o t need d i f f e r e n t uq t o d e s c r i b e t h e d a t a . Also t h e Q p l o t population i t s e l f i s b e t t e r d e s c r i b e d w i t h 4 - j e t e v e n t s . F u r t h e r r e s u l t s a r e r e p o r t e d i n Ref. 5 .

0.3

JADE

- ³³ Gev, events w ~ t h D3 ^e 0.01

I

Data

- L 2 3 1

:

^{-C --123}

1

2+3+4 j e t s .

,'1.__-_. ^/

i

1 2 + 3 / j e t s I

- - L - - -

-

1

^-

I c - - -

C3-62 JOURNAL DE PHYSIQUE

t o t h e b i g g e s t o p e n i n g a n g l e between t h e j e t a x e s ) i n a n e v e n t h a s t h e h i g h e s t prob- a b i l i t y ( ~ 5 0 % ) t o o r i g i n a t e from t h e gluon. On t h e o t h e r hand a n a l m o s t c l e a n sample o f q u a r k j e t s i s o b t a i n e d by a n a l y s i n g a l l d a t a a t Ecm=14GeV a s 2 - j e t e v e n t s . Fig. 6 shows t h e d i f f e r e n t i a l p t - d i s t r i b u t i o n of t h e l e a s t e n e r g e t i c j e t (50% gluon) a t ECm=33GeV compared t o t h e p t - d i s t r i b u t i o n o f quark j e t s r e c o r d e d a t Ecm=14 GeV.

These quark and gluon j e t s h a v e s i m i l a r j e t e n e r g i e s . P a r t i c l e s , n e u t r a l and c h a r g e d , have been used i f t h e y a r e w i t h i n a cone o f 50 d e g r e e o o e n i n g a n g l e around t h e r e - c o n s t r u c t e d j e t a x e s . F i g . 6 shows t h a t t h e

pt f o r t h e "gluon" j e t i s s i g n i f i c a n t l y ^{v I I}

-

h i g h e r t h a n f o r t h e quark j e t . The c u r v e i s

a f i t t o t h e d a t a t o g u i d e t h e e y e . T h a t t h i s -

-

_-

observed d i f f e r e n c e i s n o t due t o t h e method -

-

o f comparing a j e t o u t o f a 3 - j e t e v e n t w i t h a j e t from a 2 - j e t e v e n t h a s b e e n checked w i t h Monte C a r l o c a l c u l a t i o n s assuming t h e gluon fragments l i k e a quark. I t h a s a l s o been checked t h a t u n r e s o l v e d gluonbremsstrah-

l u n g p r e s e n t a t 14 GeV and 4 - j e t e v e n t s a t -,

aG

- - 33 GeV does n o t change t h e r e s u l t . S i m i l a r

5

- d i f f e r e n c e s a r e o b s e r v e d i f t h e "gluon" j e t 0 . 1

=

i n a 3 - j e t e v e n t i s compared t o t h e o t h e r z -

-

2 jets o f t h e s e e v e n t s i n t r a n s v e r s e momentum - - -

w i t h r e s p e c t t o t h e j e t a x i s o r t r a n s v e r s e 0 0.5 I .O 1.5 momentum o u t o f t h e e v e n t p l a n e .

p t (GeV)

F l a v o u r changing n e u t r a l c u r r e n t s o f t h e F i g . 6 type b + ( s , d ) + Zo + ( h a d r o n s ) +

u u

have

been s e a r c h e d f o r . Out o f 10500 m u l t i h a d r o n i c

e v e n t s 20 c a n d i d a t e s were found w i t h t h e s i g n a t u r e o f h a v i n g two o p p o s i t e l y charged muons i n t h e same j e t . From background s o u r c e s 16 e v e n t s a r e e x p e c t e d due t o punch through and charged c u r r e n t d e c a y s . T h i s l e a d s t o a n upper l i m i t f o r f l a v o u r changing n e u t r a l c u r r e n t of BR(B + u+u-/B + a l l ) < 2%. (95% C.L.).

Two photon p h y s i c s . The JADE r e s u l t on t h e photon s t r u c t u r e f u n c t i o n i s r e p o r t e d by ~ e h r e n d ~ ) . Here t h e p r o d u c t i o n of f ( 1 2 7 0 ) and Az(1310) i n t h e two photon p r o c e s s e s e+e- + e f e - f , e+e- + e+e-A2 i s r e p o r t e d . The f i s o b s e r v e d ( F i g . 7) i n t h e decay mode

f + nOnO + 4y and t h e A2 i n t h e decay A2 + p r + r+n-2y.

For t h e f a r e c e n t l y i n s t a l l e d low energy t r i g g e r (2x180 MeV) has been used. Assuming h e l i c i t y 2 t h e r a d i a t i v e w i d t h s a r e T(f ) = ( 2 . 3 f 0 . 2 f 0 . 5 ) keV

and r(A2 ) = ( 0 , 6 3 f

o.%

^k 0 , l l ) keV. The r a t i o 10 r(A2 )/?Tf ) = 0.28 f 0.09 can b e compared t o 0.36

f o r Yxeal YY Su(3) mixing.

0 1 2 3

R e f e r e n c e s :

m (GeV1

1. TASSO C o l l a b o r a t i o n , R . B r a n d e l i k e t a l . ,

P h y s . L e t t . (1982) 499 F i g . 7

2. J. J e r s a k e t a l . , P h y s . L e t t .

98B

(1981) 363

3 . JADE C o l l a b o r a t i o n , W. B a r t e l e t a l . , P h y s . L e t t . 108B (1982) 140 4 . 0 . Nachtmann and A . R e i t e r , Z . Physilc

-

C14 (1982)

47

5 . JADE C o l l a b o r a t i o n , W . B a r t e l e t a l . , DESY 82-016 (1982)

6 . K. F a b r i c i u s , G. Kramer, G. S c h i e r h o l z , I . S c h m i t t , 2.. P h y s i k (1982) 315 7. G. Kramer DESY 82-029 (1982)

JADE C o l l a b o r a t i o n , W. B a r t e l e t a l . , DESY 82-060 (1982) 8 . J . Behrend, t h e s e p r o c e e d i n g s .