RECENT RESULTS FROM THE CELLO COLLABORATION AT PETRA

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Submitted on 1 Jan 1982

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RECENT RESULTS FROM THE CELLO COLLABORATION AT PETRA

H.-J. Behrend

To cite this version:

H.-J. Behrend. RECENT RESULTS FROM THE CELLO COLLABORATION AT PETRA. Journal

de Physique Colloques, 1982, 43 (C3), pp.C3-72-C3-74. �10.1051/jphyscol:1982314�. �jpa-00221867�

JOURNAL DE PHYSIQUE

CoZZoque 6 3 , suppldment a u n o 12, Tome 43, ddcembre 1982 page

H.-J. Behrend

DESY,

N o t k e s t r a s s e 85, 2000 Hamburg 52, F.R.G.

+ - + -

I . e e

The reaction was measured using a l l possible decay channels except e+e-v; and

V + ~ - V V

f i n a l s t a t e s by triggering t h e detector on '2 charged p a r t i c l e s with trans- verse momentum of

200 MeV/c. With JLdt = 11.3 pb-l 434 events were collected.

Table 1: Branching Fractions f o r T-lepton 0.84

0.02 0.15

0.02 0.01

0.004 The t o t a l cross section i s consistent with the point cross section

RT = aT/u - 1.03

0.05

0.07 ( s t a t . , s y s t . ) (standard model

1.003). The P t -

cutoff parameters

a r e determined from or = a p t ( l

s / ( s - A "

to

A- >

111 GeV,

149 GeV with 95% c.1. -

The asymmetry of the forward-backward production i s < A T T >

- ( 1 0 . 3 r 5 . 2 ) - 1 0 - ~ compared t o the standard GWS-theory of -9.2.10-2. The l i f e t i m e of the T-leptons was determined my measuring the decay vertex t o (4.7 + 3.9/-2.9). 10-13 sec.

2 . Coupling Strengths of Weak Neutral Currents

Using a l l three leptonic reactions e+e-

e'e-,

the weak neutral coupling constants a , v were determined from a common f i t of the t h e o r e t i c a l d i f f e r e n t i a l cross ection expressionsto the experimental d i s t r i b u t i o n s yielding a2 = 1.22

0.41, vq = -0.12

0.33 (standard model: a2 = 1,

0.008)

(see Fig.1).

Fig.1: The 95% c.1.-contours a s determined from ve-scattering

(shaded a r e a s ) and t i s ex- periment in a v2 - a e p l a n e .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982314

H.-J. Behrend

i\ssuming t h e v a l i d i t y o f t h e standard GWS-model t h e simultaneous f i t g i v e s s i n 2 0

0.21 + 0.14/-0.09.

W

3. Systematic E r r o r s i n a, - Determination from e'e- Reactions

The p r o p e r t i e s o f hadronic a n n i h i l a t i o n events were compared t o two models f o r t h e f r a g m e n t a t i o n i n t o hadrons:

a ) Hoyer model, which uses independent f r a g m e n t a t i o n o f quarks and gluons a l a Feynman-Field.

b ) Lund model, u t i l i z i n g a c o l o u r s t r i n g model where q q - p a i r s and qqg events a r e produced along the s t r i n g between the o r i g i n a l qq p a i r .

The study was done w i t h charged hadrons o n l y and i s based on a s t a t i s t i c s o f 3021 events (11.6 pb-1). Three d i f f e r e n t methods were used f o r t h e d e t e r m i n a t i o n of as:

- from t h e f r a c t i o n f3 o f 3 j e t events determined by 3 d i f f e r e n t methods

- from t h e t h r u s t d i s t r i b u t i o n o f 3 j e t events determined b y a c l u s t e r method

- from t h e a s y n e t r y o f energy weighted angular c o r r e l a t i o n s .

Experimental r e s u l t s were compared t o Monte-Carlo p r e d i c t i o n s a d j u s t i n g

t o g e t agreement i n b o t h d i s t r i b u t i o n s . F o r o t h e r parameters i n t h e models t h e standard values were used. The r e s u l t s a r e g i v e n i n Table 2.

Table 2: Values o f

oeduced from Lund and Hoyer model w i t h d i f f e r e n t neth hods

Method - Lund ^Hoyer

N r . o f 3 n e n t s f 3 by: as as

S 0.25, A 0.1 0.28 + .045 0.19 + ^.03

0 9 . 3 0.255

.050 0.20 + ^.035

0 ' ^0.2 0.260 +- .040 0.19

.02

c l u s t e r - a 1 g o r i thm 0.235

.025 0.145 + .02 c l u s t e r t n r u s t 0.235

.025 0.155 + .015

Energy weighted ang.corr. 0.25 r .04 0.150 +- .020

L

The c o n c l u s i o n from t h i s study i s t h a t t h e Lund model y i e l d s s y s t e m a t i c a l l y h i g h e r r s - v a l u e s by 20-50%, whereas w i t h i n one model t h e v a r i a t i o n s a r e w i t h i n 20%. The reason can be l a r g e l y e x p l a i n e d by t h e d i f f e r e n c e i n t h e f r a g m e n t a t i o n process.

4. Photon S t r u c t u r e Functions

a.) F i n a l s t a t e i s a l e p t o n p a i r (u+u- and e'e-).

The p p t o n s t r u c t u r e f u n c t i o n formalism was used t o analyse events o f t h e t y p e e + -,

^{e + e + +}

^{where v"} i s a v i r t u a l photon w i t h a Q~ o f 2 10 G ~ v ~ . The process can be c a l c u l a t e d on t h e b a s i s o f the p o i n t l i k e c o u p l i n g s and good agree- ment i s found f o r F2 versus x, the Feynman s c a l e v a r i a b l e .

b.) Hadronic f i n a l s t a t e .

Events o f t h e t y p e e + v*

e +

( = hadronic system) were .detected by r e c o r d i n g t h e l a r g e a n g l e s c a t t e r e d e l e c t r o n i n endcap c a l o r i m e t e r s . The r e s u l t s were com- pared t o t h r e e t y p e o f model c a l c u l a t i o n s :

- t h e h a d r o n i c c o n t r i b u t i o n described by VDM

- t h e quark p a r t o n c o n t r i b u t i o n , c a l c u l a t e d on t h e b a s i s o f p o i n t l i k e q-y-coup1 i ngs

- QCD c o r r e c t i o n s t o t h e quark p a r t o n c o n t r i b u t i o n by t h e exchange of gluons

i n t h e box diagram .

C3-74 JOURNAL DE PHYSIQUE

Fig.2:

F 2 ( y ) versus x ( v i s ) and comparisons w i t h d i f f e r e n t model c a l c u l a t i o n s f o r CELLO (Fig.2a) and JADE (Fig.26) ex- periment.

Conclusions f o r t h e CELLO experiment:

- The form f a c t o r i s f a r b i g g e r than the VDM p r e d i c t i o n s g i v i n g evidence f o r p o i n t l i k e c o u p l i n g o f t h e t a r g e t photon t o q and q .

- The experimental p o i n t s can best be described by an u,d,s-contribution from t h e QCD-calculation t o g e t h e r w i t h a c-quark c o n t r i b u t i o n according t o t h e quark-parton model

- t h e QCD s c a l e parameter i s i n t h e range o f

0 . 1 - 0.2 GeV.

Conclusions f o r the JADE-experiment:

- Data a r e c o n s i s t e n t w i t h Leading Order QCD

- C o n t r i b u t i o n o f c-quark n o t necessary t o e x p l a i n data

- Higher o r d e r c a l c u l a t i o n s a r e c o n s i s t e n t w i t h t h e data except a t

S M ~

1 x-val ues

- ^"LO

0.28 + 0.13/-0.09;

0.22 + 0.10/-0.09

t

The CELLO-Collaboration c o n s i s t s o f members o f t h e f o l l o w i n g i n s t i t u t i o n s : DESY, Hamburg, Germany

Kernforschungszentrum Karlsruhe and U n i v e r s i t ' d t Karlsruhe, Germany M a x - P l a n c k - I n s t i t u t f U r Physik und Astrophysik, Munchen, Germany L a b o r a t o i r e de 1 ' AccPlerateur L i n g a i r e , Orsay, France

L a b o r a t o i r e de Physique N u c l e a i r e e t Hautes Energies, U n i v e r s i t P de P a r i s , France

Centre d ' Etudes NuclPaires, Saclay, France.