PHYSICS WITH THE MAC DETECTORColorado-Frascati-Northeastern-SLAC-Utah-Wisconsin Collaboration

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Submitted on 1 Jan 1982

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PHYSICS WITH THE MAC DETECTORColorado- Frascati-Northeastern-SLAC-Utah-Wisconsin

Collaboration

D. Ritson

To cite this version:

D. Ritson. PHYSICS WITH THE MAC DETECTORColorado-Frascati-Northeastern-SLAC- Utah-Wisconsin Collaboration. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-52-C3-56.

�10.1051/jphyscol:1982309�. �jpa-00221862�

JOURNAL DE PHYSIQUE

CoZZoque C3, suppze'ment au n 0 2 2 , Tome 43, de'cembre 1 9 8 2 page c3-52

P H Y S I C S W I T H THE MAC DETECTOR

Colorado-Frascati-Northeastern-SLAC-Utah-Wisconsin Collaboration Presented b y D.M. P,itson

SLAC, S t a n f o r d U n i v e r s i t y , S t a n f o r d , CA 94305, U. S.A.

The data from the MAC detector presented here are based on integrated luminosities of between 20 and 30 pb-l.

1. Properties of Tau-Leptons a. Lifetimes

Our results are based on a sample of 280 tau decays into three-charged parti- cles. Our best lifetime value (fig. l(a) and l(b)) are :

b. Tau-Branching Ratios

With an integrated luminosity of 24.8 pb -1

,

583 tau pairs were observed decaying into one-charged prong and three-charged prongs, respectively. This corresponded to BB(T + 3-prong + neutrals)= (15.3 f 0.7 f 1.O)X

.

118 events were found-with a muon decay plus a three-charged prong decay, corres- ponding to B R ( r + pvv) = (17.6 f 1.5 f 1.O)W

.

Only two candidates were observed to decay into a muon and a five-charged prong jet. At least one of these events was consistent with two of the charged prongs arising from a photon con-

ul c version in the beam pipe leading to

>

w BR(T+~-prong+neutrals)<0.7% with a 95% C.L.

Fig. 1. (a) Distribution of tau- .A = 1.20

+

^0.080

+

^{0.15 GeV.}

le~ton decay paths for fitted

vertices relative to the beam Al = 2.5

+

^0.20

+

0.4 GeV.

lo

^- 2. QCD Determinations

a. Energy-Energy Correlations

0 Figure 2 shows the calorimetrically

interaction point. (b) Distri- bution of decay paths for tau- leptons statistically weighted.

300-

ul

$ 200 2

W 3 I00

0 -

b . K-Value for Annihilation into Multi-

Hadrons

--

-30 -20 -10 0 10 20 30 we obtained

DECAY PATH ( m m ) a, = 0.16 f O.OOb(stat) f O.OZ(sys).

( b )

-

-

- -

-

-

-

I - n L -

determined full energy-energy correlation using 9 7 % x 4~ solid-angle coverage. The data is corrected for detector biases, radiative ef- fects and weak decays. Fitting to the perturb- ative QCD result to order as2, a qq fragmenta- tion term

sin-^,

^{and a}

qqg

fragmentation term (as~l/&) [ ~ i n - ~ x (X < ~ / 2 ) ;siq (X > */2)

1

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982309

D.M. R i t s o n

- P i g . 2. The f u l l e x p e r i m e n t a l energy- energy c o r r e l a t i o n a s a f u n c t i o n o f c o s x , t h e c o r r e l a t i o n a n g l e . Also shown a r e t h e f i t t e d c o n t r i b u t i o n s from QCD, t h e q{

-

and t h e

qqg

f r a g m e n t a t i o n terms.

-0.60 -0.30 0 0.30 0.60

7 82 COSX .28#AS

R was determined from two methods. The f i r s t method used n e a r l y t h e f u l l a c c e p t a n c e of t h e d e t e c t o r and removed two photon backgrounds w i t h c u t s on E v i s 9 El and energy imbalance. Thesecond method a c c e p t e d o n l y e v e n t s whose t h r u s t a x i s , a s determined from t h e i n n e r d r i f t t r a c k s , l a y i n t h e r a n g e 55'-125O t o t h e beam a x i s . F i g u r e 3 shows s c h e m a t i c a l l y t h e method used t o e s t i m a t e two-photon c o n t r i b u t i o n s t o t h e c r o s s s e c t i o n u s i n g t h e energy d i s t r i b u t i o n h i s t o g r a m . The r e s u l t s a r e

P r e d i c t e d

R = 3 . 6 7 - ( 1

+

a s / r ) = 3.9 Observed w i t h f u l l - a c c e p t a n c e

R = 3.93

+

0.04

+

0.12

+

[0.12 ( r a d i a t i v e s y s ) ] Observed w i t h f i d u c i a l l y c u t - a c c e p t a n c e

R = 3.87 k 0.04 f 0.10

+

10.10 ( r a d i a t i v e s y s ) ]

R a d i a t i v e c o r r e c t i o n s were made t o t h e l u m i n o s i t y and m u l t i h a d r o n c r o s s s e c t i o n s t o a 3 o n l y . An e s t i m a t e o f t h e s y s t e m a t i c e r r o r s a r i s i n g from t h e omission of t h e h i g h e r o r d e r r a d i a t i v e terms i s i n c l u d e d i n t h e e r r o r a s s i g n m e n t s .

3 . Two Gamma P h y s i c s a . Muon P a i r P r o d u c t i o n

F i g u r e 4 shows t h e d i s t r i b u t i o n of two photon produced mu-mu e v e n t s . The s e c t i o n c r i t e r i a were b a s e d o n a c o l l i n e a r muon p a i r s w i t h e a c h muon momentum g r e a t e r t h a n 1 . 5 GeV/c. 2,374 e v e n t s were o b s e r v e d i n 25 pb-l. The d a t a a g r e e w e l l w i t h t h e a b s o l u t e p r e d i c t e d Monte C a r l o d i s t r i b u t i o n and g i v e

w i t h i = 4.02 f 0.50 w i t h a

x

Z /df = 1 2 - 9 / 1 8

.

b . R a t i o of M u l t i h a d r o n Events t o Muon P a i r s , w i t h E l e c t r o n Tags

Events were s e l e c t e d by r e q u i r i n g a n i s o l a t e d e l e c t r o n a t 2 18O t o t h e beam a x i s and a n a s s o c i a t e d e l e c t r o m a g n e t i c shower i n e x c e s s of 6 GeV. 'Muon e v e n t s

7 - - 7'--

- -

800

W -

:

a s d e t e r m i n e d from c a l o r i m e t r y , f o r e v e n t s

:Background

:

w i t h momentum t h r u s t - a x e s 8 i n t h e r a n g e

Z

T)

:

55O-125O. The d o t t e d r e g i o n shows t h e

1 m u l t i h a d r o n c o n t r i b u t i o n f o r e n e r g i e s below

:

1 6 G e V , a s e s t i m a t e d from t h e m u l t i h a d r o n

:

sample w i t h 7 8 prongs. The h a t c h e d a r e a

:

i s t h e e s t i m a t e d c o n t r i b u t i o n from two photon

:

e v e n t s and o t h e r backgrounds.

20 40 60

ENERGY ( G e V ) u.e ,

- -

:

F i g . 3. The d i s t r i b u t i o n o f e v e n t e n e r g i e s ,

C3-54 JOURNAL DE PHYSIQUE

F i g . 4. The d i s t r i b u t i o n of two photon produced mu-mu e v e n t s a s a f u n c t i o n of p L 2

.

The h i s t o g r a m i s t h e Monte C a r l o

> - MONTE CARL0 p r e d i c t i o n and shows t h e e x c e l l e n t a g r e e -

W EXPERIMENT ment of p r e d i c t i o n and t h e o r y .

30 pb-l. 90% of t h e e v e n t s had i n v a r i a n t masses > 2 GeV, and t h e s q u a r e d f o u r momen- tum t r a n s f e r s were i n t h e r a n g e o f 20 - 100 (GeV/c) 2

.

A f t e r s u b t r a c t i n g backgrounds from i n e l a s t i c Compton s c a t t e r i n g (9%) and t a u p a i r s (8%) and f o l d i n g i n t h e d e t e c t i o n e f f i c i e n c i e s a v a l u e o f R' i n terms of N

had r e q u i r e d a t l e a s t o n e i d e n t i f i e d muon and

2 0

and N t h e c o r r e c t e d numbers of m u l t i h a d r o n UP

'

m u l t i h a d r o n e v e n t s 2 3 charged t r a c k s . 1 3 3 e u ~ and 104 e-hadron e v e n t s were found i n

and muon p a i r s , was o b t a i n e d , namely,

I I I

(0)

( I

Expt Results

R' = N / N = 0.95

+

^0.12

+

0.20 Monte C a r l o for

had

uu

i n good agreement w i t h t h e q u a r k model pre- d i c t i o n of 3Ce4 t a k i n g i n t o a c c o u n t t h r e s h o l d

q

e f f e c t s f o r charm p r o d u c t i o n .

4 . I n c l u s i v e Muon D e t e c t i o n and F l a v o r Tagging a . P a r t i c l e S e a r c h e s and t h e I n c l u s i v e

Lepton Spectrum

Surrounding t h e MAC c a l o r i m e t r i c d e t e c - t o r s a r e f o u r s e p a r a t e d l a y e r s of d r i f t c o u n t e r s t h a t d e t e c t and measure a n g l e s and p o s i t i o n s of emerging muons. Combined w i t h t h e magnetized s t e e l o f t h e d e t e c t o r , t h e s e l a y e r s p r o v i d e momentum and p o s i t i o n v e c t o r s f o r d e t e c t e d muons. R e s t r i c t i n g muon momenta t o v a l u e s

2 GeV/c r e d u c e d t h e backgrounds from punch- through p r o c e s s e s t o low l e v e l s . C u t s c a n b e made i n b o t h t h e pl of t h e muon r e l a t i v e t o t h e c a l o r i m e t r i c t h r u s t a x i s and t h e j e t mass of t h e non-muon a s s o c i a t e d j e t . The j e t mass, ? I I - , , is

JET MASS IN GeV -..*., F i g . 5. The o b s e r v e d d i s t r i - b u t i o n o f m u l t i h a d r o n e v e n t s c o n t a i n i n g a muon w i t h pl > 1 GeV/c and p > 2 GeV/c a s a f u n c t i o n of t h e mass of t h e

" r e c o i l i n g " jet i n GeV. ( a ) Shows t h e observed h i s t o g r a m and t h e a b s o l u t e l y n o r m a l i z e d Monte C a r 1 0 p r e d i c t i o n f o r m u l t i -

J e L

d e f i n e d i n terms of h e m i s p h e r i c t h r u s t , TlI2, hadron p r o d u c t i o n through 2) s t a n d a r d q u a r k f l a v o r s

.

^{( b )}

and beam e n e r g y , Eb, a s Mjet = E b ( l

-

T

.

Shows t h e observed d i s t r i b u t i o n F i g u r e 5 ( a ) shows t h e h i s t o g r a m f o r muons w i t h and the predicted distribution pl

>

1 GeV/c v e r s u s t h e observed j e t mass f o r p r o d u c t i o n v i a t h e s t a n d a r d o p p o s i t e t o t h e r e c o i l i n g muon. The t h e o r e t i c a l l y quark and an

c a l c u l a t e d and a b s o l u t e l y n o r m a l i z e d Monte C a r l o quark with charge and a d i s t r i b u t i o n assuming o n l y u, d , s , c , and b mass o f 1 0 GeV.

D.M. R i t s o n C3-55

q u a r k s is i n e x c e l l e n t agreement w i t h t h e o b s e r v e d d i s t r i b u t i o n . F i g u r e 5 ( b ) shows t h e same e x p e r i m e n t a l d i s t r i b u t i o n compared w i t h t h a t e x p e c t e d from m u l t i h a d r o n p r o d u c t i o n b a s e d on u, d , s , c , b, and a 1 1 3 charged t quark of mass 1 0 GeV and a 10% b r a n c h i n g r a t i o f o r decay i n t o muons. C l e a r l y t h e p r o d u c t i o n of a n a d d i t i o n a l 1 1 3 charged q u a r k w i t h t h i s mass and b r a n c h i n g r a t i o is r u l e d o u t by t h e d a t a . A l t e r n a t i v e l y t h e d a t a c o n f i r m s t h e b r a n c h i n g r a t i o i n t o muons f o r t h e B-meson observed by t h e C o r n e l l CLEO d e t e c t o r .

b. a s f o r Flavor-Tagged Samples

D e t e c t e d muons c a n b e used t o p r o v i d e f l a v o r - t a g g i n g . With c u t s of

Pl

u

^< 1 GeV/c t h e e v e n t sample s h o u l d c o n t a i n 11% bg, 69% c c and 20% n / K decay, and w i t h p > 1 GeV/c i t s h o u l d c o n t a i n 44% bb, 41% c c and 15% n / K decay. M u l t i -

1 u

p l i c i t y d i s t r i b u t i o n s were c l o s e l y s i m i l a r f o r t a g g e d and untagged e v e n t s . Energy- energy c o r r e l a t i o n measurements made o n muon-tagged m u l t i h a d r o n e v e n t s shows a s t o b e i d e n t i c a l , w i t h i n e r r o r s (- 20%), t o t h a t o b t a i n e d from t h e t o t a l m u l t i h a d r o n sample, t h u s c o n f i r m i n g t h e independence o f a o f q u a r k f l a v o r .

c . L i f e t i m e Measurements on Muon Tagged Events

Using t h e d i s p l a c e m e n t of t h e muon from t h e j e t v e r t e x and t h e d i s p l a c e m e n t s of t h e j e t v e r t i c e s l i m i t s o n B - l i f e t i m e s h a v e b e e n o b t a i n e d . The v a l u e i s

r < 3.7 1 0 - l 2 s e c w i t h a 95% c o n f i d e n c e l e v e l . b

5. Weak-EM I n t e r f e r e n c e s

a . Muon and Tau P a i r Charge-Asymmetry i n P r o d u c t i o n

A t o t a l of 1 , 8 7 6 muon p a i r s s u i t a b l e f o r charge-asymmetry measurements have b e e n observed. The r e s u l t a n t charge-asymmetry A a t

6

= 29 GeV i s

u1-1

A = -0.044

+

^0.024 w i t h a

x

2 / d f = 21/18

vu

and compares w i t h -0.063 e x p e c t e d from t h e s t a n d a r d model.

A t o t a l of 1 , 2 4 7 t a u p a i r e v e n t s s u i t a b l e f o r asymmetry measurements were o b s e r v e d . The measured charge-asymmetry i s

Arr = -0.013

+

^0.029 w i t h a

x

2 ^{/ d f = 22/16} w i t h -0.063 e x p e c t e d from t h e s t a n d a r d model.

b

.

Bhabha S c a t t e r i n g

The a n g u l a r d i s t r i b u t i o n f o r Bhabha s c a t t e r i n g h a s b e e n found t o b e i n good agreement w i t h t h a t p r e d i c t e d from t h e o r y . Prom t h e r e s u l t s t h e Weinberg-Salam a n g l e

'aw

i s found t o b e

s i n Ow 2 = 0.24

+

^0.10

0.05 _< s i n 2 e w 5 0.44 w i t h a 95% c o n f i d e n c e l e v e l . 6. L i m i t s f o r t h e P r o d u c t i o n of New P a r t i c l e s

The c h a r a c t e r i s t i c s of o u r e v e n t samples a r e c o m p l e t e l y c o n s i s t e n t w i t h produc- t i o n of known l e p t o n and q u a r k f l a v o r s v i a one photon a n n i h i l a t i o n and two photon p r o c e s s e s .

T a b l e I summarizes t h e p r e s e n t s t a t u s of a number of o u r p a r t i c l e s e a r c h e s . Method A r e f e r s t o a s c a n o f e v e n t s c o n t a i n i n g one i s o l a t e d muon and a j e t . T h i s e v e n t c l a s s would c o n t a i n e v e n t s r e s u l t i n g from p r o d u c t i o n of a p a i r o f heavy l e p t o n s and o r supersymmetric-tau p a i r s , o r t e c h n i p i o n s , o r charged Higgs produc- t i o n . The jet-mass, m u l t i p l i c i t y d i s t r i b u t i o n and unbalanced momenta i n t h e p l a n e p e r p e n d i c u l a r t o t h e beam have b e e n used t o p r o v i d e l i m i t s f o r t h e p r o d u c t i o n of t h e s e p a r t i c l e s .

Method B u s e s a c o l l i n e a r muon p a i r s s e l e c t e d w i t h a c o l l i n e a r i t y a n g l e s >

l o 0 ,

C3-56 JOURNAL DE PHYSIQUE

p I > 3 GeV, and no photon d e t e c t e d . 3 1 e v e n t s were o b s e r v e d i n 1 4 ~ b - 1 . F i g u r e 6 shows t h e o b s e r v e d a c o p l a n a r i t y d i s t r i b u t i o n compared w i t h t h e two p h o t o n Monte C a r l o p r e d i c t i o n s . The d o t t e d c u r v e shows t h e d i s t r i b u t i o n of t h e a d d i t i o n a l 4 3 e v e n t s t h a t would b e e x p e c t e d from t h e p r o d u c t i o n o f supersymmetric-muons w i t h masses of 1 0 GeV.

Method C h a s b e e n d e s c r i b e d i n S e c t i o n 4a and o b t a i n s l i m i t s from t h e jet-mass d i s t r i b u t i o n s a s s o c i a t e d w i t h muon-tagged m u l t i h a d r o n e v e n t s . The l i m i t s , based on a n a l y s i s of t h e s e jet-mass d i s t r i b u t i o n s , o n t h e p r o d u c t i o n of new q u a r k f l a v o r s , c h a r g e d Higgs and t e c h n i p i o n s a r e t a b u l a t e d under Method C i n T a b l e I.

T a b l e I p r o v i d e s s t r o n g e v i d e n c e a g a i n s t t h e p r o d u c t i o n o f new c h a r g e d p a r t i c l e s t a t e s i n t h e PEP e n e r g y domain.

-t

-

We h a v e o b s e r v e d 1 5 4

u u

y e v e n t s . T h e i r a n g u l a r d i s t r i b u t i o n and momentum d i s t r i b u t i o n s a r e e n t i r e l y c o n s i s t e n t w i t h t h e p r e d i c t i o n s o f QED, and t h e r e i s no e v i d e n c e f o r p r o d u c t i o n of pu* p a i r s b e i n g produced. A l s o 17 ~ ' u - ~ y e v e n t s h a v e b e e n a n a l y z e d and r u l e o u t p r o d u c t i o n o f e x c i t e d

u*u*

p a i r s w i t h masses < 1 4 GeV.

F i g u r e 7 shows t h e r a t i o of efe- + yy d i v i d e d by t h e p r e d i c t e d c r o s s s e c t i o n v e r s u s a n g l e . The l u m i n o s i t y c a l i b r a t i o n s f o r t h i s measurement w e r e b a s e d on Bhabha s c a t t e r e d e v e n t s s e l e c t e d w i t h i d e n t i c a l c r i t e r i a t o t h e two photon a n n i h i - l a t i o n e v e n t s . The f i n a l r e s u l t s a r e v i r t u a l l y f r e e of s y s t e m a t i c e r r o r s and a r e s t a t i s t i c s l i m i t e d . With a 95% c o n f i d e n c e l e v e l , t h e mass of a n e x c i t e d e*

p r o p a g a t o r i n e l e c t r o n - p o s i t r o n a n n i h i l a t i o n i n t o two p h o t o n s i s r e s t r i c t e d t o mass > 55 GeV.

Z

I l l I I I

-

Two Photon Monte Corlo Predtct~on -

---

Monte Carlo Pred~ct~on for a 10 GeV -

Supersyrnmetr~c muon ji (43 events1 -

-

\

0 I \ I I I I

Technipion and Charged Higgs

3 - 5 GeV and

8

-

10 GeV 95%

f o r 5 - 10 GeV Supersymmetric Muon

-

Supersymmetric Tau

0

F 2

u

n

W .

[r a

0 .

W .

0

\ X +

7

a , .

L

LL 0

0 5 0 100 150 200 250 300 350 9

+

ACOPLANARITY ANGLE A + [degrees] .,,,,,,

+Methods A , B , and C a r e des..-;hed i n the body of t h e t e x t .

+ u

+

Photino

? + T

+

Photino

- ^{I 7 1}

-

- - -

-

+

^,

* -

+ '

⁺

'

9

-

-

-

-

-

I

B A

2

OO

I I I

0.4 0.6

F i g . 6. The d i s t r i b u t i o n of a c o p l a n a r COSe

-."

^{. 2 .}

muon p a i r s as a function of t h e acopla- ^{F i g . 7 .} The e x p e r i m e n t a l l y o b s e r v e d r a t i o n a r i t y a n g l e . o f a n n i h i l a t i o n i n t o two p h o t o n s a s a

f u n c t i o n of t h e c o s i n e of t h e p r o d u c t i o n a n g l e , 8 .

TABLE I : Summary o f P a r t i c l e S e a r c h e s

2 - 13 GeV 7

-

13 GeV

Confidence Limit

95%

9 5%

9 5%

95%

9 5%

95%

P a r t i c l e Charge 213 t Quark Charge 113 t Quark Heavy Charged Lepton

Methodt C C A C Decay Mode(s)

2 t + (u+Jet) + J e t 2 t + (v+Jet) + J e t 2L + (uvv) + J e t 2n*(or 2H) -+ 2(bc) J e t s

Mass Range Excluded 3 - 1 3 GeV 5 - 1 2 GeV 4 - 14 GeV 7 - 12 GeV