RECENT RESULTS FROM TASSO AT PETRATASSO Collaboration

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Submitted on 1 Jan 1982

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RECENT RESULTS FROM TASSO AT PETRATASSO Collaboration

D. Lüke

To cite this version:

D. Lüke. RECENT RESULTS FROM TASSO AT PETRATASSO Collaboration. Journal de Physique

Colloques, 1982, 43 (C3), pp.C3-67-C3-71. �10.1051/jphyscol:1982313�. �jpa-00221866�

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CoZZoque C3, suppb6ment au n o 12, Tome 43, ddcembre 1982 page C3-67

-

14

22 - 30 3200

22388

+ +

In-Fig. 1 we show t h e f r a c t i o n of charged IT-, K-, and

p ( p ) among a l l charged h a d r o n s a s a f u n c t i o n o f momentum. w I G G C V

A t p a r t i c l e momenta o f 0.4 GeV/c more t h a n 90% of t h e

charged hadrons a r e p i o n s . With i n c r e a s i n g momentum t h e ^{O 6} f r a c t i o n of IT' among t h e charged h a d r o n s d e c r e a s e s w h i l e ^O"

t h e f r a c t i o n s o f K' and p ( p ) a r e i n c r e a s i n g . At W=34 GeV 0 2

and a momentum of 5 GeV/c t h e p a r t i c l e f r a c t i o n s a r e 00

a p p r o x i m a t e l y IT' : K' : p ( p ) = 0.55 : 0 . 3 : 0115. I n ⁰³ ^a5 ¹⁰ p 1 G c V Z l ^M ¹⁰⁰

F i g . 2 t h e a v e r a g e m u l t i p l i c i t y of xC, K*,_P(P) and A(Z) Fig. 1 Charged hadron i s shown a s f u n c t i o n o f W. The y i e l d of p ( p ) i s r i s i n g f r a c t i o n f a s t e r w i t h W t h a n t h a t o f nf and K'. A t W=34 GeV t h e

r a t i o p ( p ) : IT+ i s t w i c e a s l a r g e a s a t W=5 GeV. On a v e r a g e a n e v e n t a t W=34 GeV c o n t a i n s 10.3 f 0.4 IT',

2.0

+

0 . 2 K', 0 . 8

+

0.1 p ( p ) and 0 . 3 3

+

0.04 A(A). 0

Note t h a t i n b o t h f i g u r e s t h e IT: s p e c t r a i n c l u d e p a r t i c l e s from K: d e c a y , t h e p ( p ) s p e c t r a i n c l u d e p a r t i c l e s from hyperon decay ( l i k e A,A).

We measured a l s o i n c l u s i v e p0 p r o d u c t i o n 2 . ~ s s u m i n g

z

1

f I -

p O , p f , p- t o have e q u a l p r o d u c t i o n r a t e s we f i n d

• IASS

- * *

=

'

0 %

t ⁺

t h a t 30% of a l l IT' r e s u l t from p decay. ₃

H

b - S c a l e b r e a k i n g i n i n c l u s i v e charged p a r t i c l e p r o d u c t i o n . 2 ^-

9 4

The s c a l e d c r o s s s e c t i o n sdo/dxp ( w i t h x p = ~ ' ~ b e a ~ n ) f o r i n c l u s i v e charged p a r t i c l e p r o d u c t i o n i s shown

i n F i g . 3 f o r c.m. e n e r g i e s between 12.0 and 36.7 GeV. 01

S c a l e b r e a k i n g i s observed. For x p > 0 . 2 t h e c r o s s s e c t i o n d e c r e a s e s by w 20% when W i n c r e a s e s from 14 t o 35 GeV.

k

+

l o ,

t A *

- I +

1

:

r'

When p a r a m e t r i z i n g t h e s-depengence o f t h e s c a l e d c r o s s n m

s e c t i o n a s % 1

+

c l I n (s/lGeV ) a f i t y i e l d s t h e c u r v e s W l G e V l

shown i n F i g . 3. The v a l u e s of c l a r e g i v e n i n F i g . 4 , t o - Fig'Z

g e t h e r w i t h s i m i l a r r e s u l t s o b t a l n e d by t h e PLUTO ex- multiplicity p e r i m e n t

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982313

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JOURNAL DE PHYSIQUE

F i g . 3 S c a l e d c r o s s s e c t i o n a s f u n c t i o n o f s

0 PLUTO

F i g . 4 c l -.05 a s f u n c t l o n o f x

P

0 0.2 0 4 0.6 0.8 1.0

X P

Df i

p r o d u c t i o n .

P r o d u c t i o n o f charmed h a d r o n s i s of s p e c i a l i n - TA550 ( w l m u x u y l

l I I I : I I I I

t e r e s t s i n c e charmed h a d r o n s ( a s w e l l a s bottom .lL5GeV

h a d r o n s ) c o n t a i n t h e p r i m a r y charm q u a r k ( r e s p .

1

x".,.". , ~5 I . ? L ~ M I K ? ' I ~ I I G C V

bottom q u a r k ) . T h a t i s b e c a u s e a t PETRA e n e r g i e s _{; m} ( f o r o u r d a t a sample, Ww 32 GeV) p r o d u c t i o n o f charmed and bottom h a d r o n s from t h e s e a i s neg- _f l i g i b l e . We d e t e r m i n e d t h e c r o s s s e c t i o n f o r i n - c l u s i v e D** p r o d u c t i o n and i t s p r o d u c t i o n a n g u l a r d i s t r i b u t i o n i n a s e a r c h f o r e l e c t r o m a g n e t i c -

weak i n t e r f e r e n c e e f f e c t s i n charm quark p a i r pro- O .IL 36

.IS .a3 . Y

d u c t i o n . D*+ were i d e n t i f i e d t h r o u g h t h e d e c a y s AM: M 1 K - ~ - ~ J - u ( K-~*I{GCVI

D*+ -t Don+ ( b r a n c h i n g r a t i o 44 f 10%) and F i g .

5

D i s t r i b u t i o n o f AM Do -t K-a+ ( b r a n c h i n g r a t i o 3 . 0

+

0 . 6 % ) . F i g . 5 TASY) ( W W ~ W Y I

shows t h e d i s t r i b u t i o n of t h e mass d i f f e r e n c e

D.* . ~ o ~ r n q

AM = M(K-sCn+) - M(K-v+) f o r M(K-?I+) masses i n t h e Do mass r e g i o n ( 1 . 7 4

-

1.98 GeV) and f o r h i g h e n e r g e t i c D*+ w i t h f r a c t i o n a l e n e r g y x =

-- 2

% z

El

^0.3

EK-.rr+v+ / Ebeam > 0.5, assuming e a c h p a r t i c l e i n

t u r n t o b e a kaon and a pion. The d e c a y DfC + Don+

-

$16

,,

i s i n d i c a t e d by t h e narrow peak c e n t e r e d around

AM = 0.145 GeV. I t s w i d t h a g r e e s w i t h t h e ex- 0.1

p e c t e d rms r e s o l u t i o n o f a b o u t 1 . 5 MeV. F i g . 6

shows t h e s c a l e d c r o s s s e c t i o n s d o / d x f o r i n - ⁰0.2 O L 0 6 a8 1.0

c l u s i v e D%* p r o d u c t i o n , a f t e r c o r r e c t i n g f o r de- .= E ~ . I E-

c a y s o t h e r t h a n D*+ + DOT+ and Do + ~ - v + . The F i g . 6 S c a l e d c r o s s s e c t i o n p r o d u c t i o n a n g u l a r d i s t r i b u t i o n o f D*+ ( F i g . 7)

i s a s m e t r i c . A f i t t o t h e form 1 + a c o s e + c 0 s 2 e ₂₀ ^{TASSO (}relirninor )

(where p a r a m e t e r a i s f i t t e d ) y i e l d s a n asymmetry of A = -0.35 i 0 . 1 4 . F o r comparison, a n asymmetry

of a b o u t -0.14 i s e x p e c t e d f o r p r o d u c t i o n of charm _n _Asym=-0.35=0.14 q u a r k s . Provided s t a t i s t i c s c a n be improved i n t h e f u t u r e , ~5

-

²

- . --_ __-

^_/-

t h e s t u d y o f D*f p r o d u c t i o n w i l l a l l o w t o measure I +cos2 Q t h e weak n e u t r a l c o u p l i n g of t h e charm q u a r k .

0 - 0.8 - 0.4 0 0.4 0.8

cos 8 0 -

Fig.7 D i s t r i b u t i o n of COSQ $ .;

D

1

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ponding t o a t o t a l i n t e g r a t e d l u m i n o s i t y o f 71.5 pb-l a t c.m. e n e r g i e s between 33 and

2

50%

37 GeV) we f i n d t h a t p r o d u c t i o n of charged

6

_LO%

₆

Higgs and t e c h n i p i o n s i s excluded ( w i t h

;

⁰

95% c . 1 . ) i n t h e mass r a n g e 5

-

^{13 GeV}

.-

3'1. rz

and f o r h a d r o n i c b r a n c h i n g r a t i o s l a r g e r

2 -

t h a n a b o u t 70% f o r t h e decay H+ + c s and

g

^{z o r}

^f

c b ( s e e F i g . 9 ) , provided m m 2

BR(H -+cb)/BR(H+ c s )

<

0 . 5 a s expected go.,, 10.1

g

by t h e o r y . I n F i g . 9 o u r r e s u l t i s shown

-

t o g e t h e r w i t h t h e JADE r e s u l t . Taken t o - loo+ o *I.

4

g e t h e r , t h e two e x p e r i m e n t s e x c l u d e t h e

e x i s t e n c e of a p o i n t l i k e charged s c a l a r threshold reglon c'b rn, l GeVl

p a r t i c l e , w i t h decay modes a s d i s c u s s e d ,

in t h e mass r a n g e between 5 and 13 GeV. Fig.9 on hadronic branching r a t i o a s f u n c t l o n o f mass

L e p t o n i c d e c a y s of b-quarks.

"H

From a s t u d y of i n c l u s i v e

u'

and e' s p e c t r a from h a d r o n i c e v e n t s a t c.m. e n e r g i e s around 34.6 GeV we o b t a i n e d t h e b r a n c h i n g r a t i o s :

BR(b -+ UVX) = 15.0

+

3 . 5 ( s t a t . )

+

3.5 ( s y s t . ) %, and

BR(b + evX) = 13.6

'

4 . 9 ( s t a t . ) i- 4.0 ( s y s t . ) %. The forward-backward c h a r g e asym- m e t r i e s o f t h e l e p t o n s were determined t o A(u) = -0.17+0.10 and A(e) = -0.11f0. 17, compared t o a n asymmetry of -0.084 a s e x p e c t e d from GWS t h e o r y .

Electroweak i n t e r f e r e n c e e f f e c t s have been s t u - ₁₂

-

^{C C 4 F}W . Y ' W

d i e d i n l e p t o n p a i r p r o d u c t i o n e+e- -+ e+e-, u+p-, rcr-. F i g . 8 shows t h e measured d i f f e r e n - t i a l c r o s s s e c t i o n s a t a n a v e r a g e W=34.4 GeV,

- t

' -

-

- .-s-v+s- W - X L W z.4- -+...+--

f-Lj--+ I. -1.:

-

C-c - I - I ~ + , = ~ L L G C ~ -

~ p n t r m ~ w r ~ '

normalized t o t h e QED c r o s s s e c t i o n . I n c a s e of 0 9

'+u-

p r o d u c t i o n a n asymmetric a n g u l a r d i s t r i b u t i o n M

i s s e e n . The measured forward-backward c h a r g e I L

asymmetries AUu and ATT a r e g i v e n i n t h e f o l l o w i n g 5 t a b l e t o g e t h e r w i t h t h e v a l u e s AGWS e x p e c t e d from 2 12

e 1 0 -

t h e s t a n d a r d GWS t h e o r y .

r

;

^{0 8 .}

The d a t a have been 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 . The measured asymmetry A =-'3.104

+

^0.023 ^{0 8 -}

i s i n good agreement w i t h t h e ~ a l u e ' ~ 0 . 0 9 2 e x p e c t e d 06 -

g

.

^-^u

from GWS t h e o r y . Within t h e GWS t h e o r y a combined f i t 0 8 06 0 6 0 1 a ^{3 2}^{O L} 06 :8

t o t h e e+e- and I,A+~- c r o s s s e c t i o n s gave s i n BW = ^cos^E

0.27

+ .

Assuming; MZ = 90 GeV, a f i t of t h e ~ i ~ . 8 Lepton pair p r o d u c t i o n v p c t o r and a x i a l - v e c t o r c o u p l i n g s r e s u l t e d i n

gv = -0.04

+

^{0.06, g2}⁼^0.26

+

0.07. T h i s i s i n good

2 2

agreemeqt w i t h t h e paredigtion of t h e GUS t h e o p : g: = 0.25 ( I - 4 s i n 0 ) = 0.0016 f o r s i n BW = 0.23, and ga = 0.25. I f we f i x g = 0.0016 and g2 = 0.2!!, we c a n f i t f o r t h e mass of t h e Z0 : t h e 95% c o n f i d e n c e f i m i t s a r e 4 6 ~ e ~ ~ < MZ < 155 GeV.

+ -

5

Hadronic c r o s s s e c t i o n u ( e e -+ h a d r o n s ) .

The r a t i o R = u(e+e- -+ h a d r o n s ) / uuF! was measured f o r c.m. e n e r g i e s W between 12.0 and 36.7 GeV w i t h a p r e c i s i o n of t y l c a l l y e r r o r of

+

2% f o r h i g h e r o r d e r (> a

'3

) QED c o r r e c t i o n s . For W

+

5.2%. The e r r o r i n c l u d e s a s y s t e m a t i c > 14 GeV, R i s c o n s t a n t w i t h a n a v e r a g e R = 4.01 f 0.03 ( s t a t ) f 0.20 ( s y s t ) . Quarks a r e found t o b e p o i n t - l i k e w i t h a mass-parameter d e s c r i b i n g a p o s s i b l e quark f o r m f a c t o r : A+ > 186 GeV. A comparison w i t h R v a l u e s from o t h e r PETRA e x p e r i m e n t s i s done by Heinzelmann6.

S e a r c h f o r charged Higgs and t e c h n i p i o n s . 7

We have s e a r c h e d f o r charged Higgs mesons and t e c h n i p i o n s (denoted a s H+-) i n t h e p r o c e s s e+e- -t H+H-. While t h e l e p t o n i c decay H + T ; ~ f o r masses MH = 4

-

^{13 GeV}

had been e x c l u d e d by o t h e r experiments8, we s t u d i e d t h e p r o c e s s where b o t h H de- c a y i n t o h a d r o n s : H+ -t c s and cb. From o u r sample o f 20000 h a d r o n i c e v e n t s ( c o r r e s -

0 6 1 ' - 1 2 -

IcoseI r 1.0 1 0 . 8 u+p-

T+T-

nb-' 70200 65800 EVTS 2391 577

Ameasured -0.104+0.023 -0.056+0.044

AGlqS -0.092 -0.080

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JOURNAL DE PHYSIQUE

Radiative width of f'(1515). 9

In photon-photon collisions we observed the excitation of the f'(1515) and its decay-into K+K- (Fig. 10a) and into KgKg (Fig. lob). Assuming the f' is produced in a helicity = 2 state, we determined the product of radiative width times branching ratio for the decay into KK : I'(f'f yy)

.

^BR(f' ⁺^KK) ⁼0.11 f 0.02 (stat.) f 0.04 (syst.) keV. The decay f' + KK is dominant. Using the limits0.5 c

BR(£' + KK) < 1 and the radiative width of the f0 meson, r(fO + yy) = 2.9520.40 keV (Ref. 19) we estimated the mixing angle 8 of the .JPC = 2" nonet within the framework of SU(3) to be within the 95% confidence limits: 25.4O c 8 < 34.7'.

This agrees with the value 8 = 28O f '3 obtained from the quadratic Gell-Mann Okubo mass formula. The small radiative width r(ff + yy) constrains the fraction of non-strange quarks in f' to be c 3% (95% c.1.).

Fig. lOa Fig. lob

Distribution Distribution

of effective of effective

mass M(K+K-)

12 1 1 16 18 20 12 1' 15 4 8 2 0 mass M(K:

M IK+K-ICMI UIK;K;)CWI

+ - + -

Observation of a narrow structure at 2.1 GeV in yy + IT n IT n.

A narrow structure has been observed in the four ^{A -}

pion system of the reaction yy + IT+=-n+~-. The IbU - " ' " ' ~ " ' " " ' " ' " ' " " " " -

data correspond to a total integrated luminosity: T A W 1 of about 84 pb-l, most of them taken at a beam

2

¹²⁰ ^-

energy of 18.3 GeV. The exclusive n+n-n+n-

-

^w

channel was separated from events with addi-

"

tional, undetected particles by requiring a low

%

^-

net momentum transverse to the beam: ^{( C}

^hT(

^<0.070 GeV/c. Assigning pion masses to

- ^"

6 0

i t '

- all particles there are a total of 3955 events

:

t

with a nfn-r+ir- mass M4Ac 4 GeV. The M4, mass

2

distribution (Fig. 1 1) shows a narrow structure near 2.1 GeV. A smooth background of the shape

(a + b

-

^M) ^exp(-c

-

^M)was fitted to the data Mba [ GeV

1

between 1.65 and 3.00 GeV, including the signal Fig.11 Four pion mass spectrum region near 2.1 GeV. In the mass interval

2.05

-

2.15 GeV the fit predicts 190 f 14 events, whereas 250 events are observed. This deviation

from the smooth curve corresponds to an effect of 4.3 standard deviations.

Interpreting the structure as a resonance we fitted a non-relativistic Breit- Wigner shape plus a smooth background to the data, folding the Breit-Wigner with a Gaussian distribution in order to account for our mass resolution (a FJ 25 MeV).

The fit gave Mo = 2.100 f 0.020 GeV for the mass (the error includes a systematic uncertainty of 0.020 GeV),

r

= 0.030

+

0.034 GeV for the width of the Breit-Wigner, and No = 97 f 40 events under the Breit-Wigner curve. After correcting for

acceptance (which is 4% on average) the coupling strength to yy is determined to

r~~

⁼^[1.25^f0.5 (stat.) f 0.5 (syst.)] / (2J+I) (keV) where 3 is the spin of the assumed resonance.

References:

1. TASSO Collaboration, M.Althoff et al., DESY-Report No. 82-070 (1982).

2. TASSO Collaboration, R-Brandelik et al., DESY-Report No. 82-046 (1982).

3. TASSO Collaboration, R.Brandelik et al.,Phys.Lett. 114B (1982) 65.

4. TASSO Collaboration, R-Brandelik et al., DESY-Report No. 82-032 (1982).

5. TASSO Collaboration, R.Brandelik et al., Phys.Lett. 113B (1982) 499.

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8. JADE Collaboration, W.Barte1 et al., Phys.Lett. 114B (1982) 211, CELLO Collaboration, H.J.Behrend et al., DESY 82-021 (1982),

MARK J Collaboration, A.Adeva et al., LNS Technical Report Number 125 (1982), MARK I1 Collaboration, C.A.Blocker et al., SLAC-PUB-2923 (1982).

10.Particle Data Group, Phys.Lett. lllB (1982) 1.