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Dec 19, 1984 - PHY82-15414. (NU), and No. .... resolution ~E/E = 20%/d- in the SC. .... (d) Permanent address: CERN, Geneva, Switzerland. (e) Present ...
SLAC -PUB - 3520 December 19, 1984 P/E)

Search for Single Photons from Supersymmetric Particle Production E. Fernandez, W. T. Ford, N. Qi, A. L. Read, Jr., and J. G. Smith Department of Physics, University of Colorado, Boulder, Colorado 80309 and T. Camporesi, R. De Sangro, A. Marini, I. Peruzzi, M. Piccolo, and F. Ronga I. N. F. N., Laboratori Nazionali di Frascati, Frascati, Italy and H. T. Blume, R. B. Hurst, J. P. Venuti, H. B. Wald, and Roy Weinstein Department of Physics, University of Houston, Houston, Texas 77004 and H. R. Band, M. W. Gettner, G. P. Goderre, 0. A. Meyer,‘“] J. H. Moromisato, R. 0. Polvado, W. D. Shambroom, J. C. Sleeman, and E. von Goeler Department of Physics, Northeastern University, Boston, Massachusetts 02115 and W. W. Ash, G. B. Chadwick, S. H. Clearwater,[*’ R. W. Coombes, H. S. Kaye,‘“] K. H. Lau, R. E. Leedy, H. L. Lynch, R. L. Messner, L. J. Moss, F. Muller,IJ1 H. N. Nelson, D. M. Ritson, L. J. Rosenberg, D. E. Wiser, and R. W. Zdarko Department of Physics and Stanford Linear Accelerator Center, Stanford University, Stanford, California 94305 and D. E. Groom, and H. Y. Lee[“’ Department of Physics, University of Utah, Salt Lake City, Utah 84112 and M. C. Delfino, B. K. Heltsley,[fl J. R. Johnson, T. L. Lavine, T. Maruyama, and R. Prepost Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 Submitted

to Physical

Review

Letters

This work was supported in part by the U. S. Department of Energy under contracts No. DE-AC02-81ER40025 (CU), No. DE-AC03-76SF00515 (SLAC), and No. DE-AC02-76ER00881 (UW); by the National Science Foundation under contracts No. NSF-PHY82-15133 (UH), No. NSF-PHY82-15413 and No. NSFPHY82-15414 (NU), and No. NSF-PHY83-08135 (UU); and by the Institute Nazionale di Fisica Nucleare.

ABSTRACT A search in e+eenergetic

photon

for supersymmetric photons

is m,- > 37 GeV/c’

the supersymmetric

photon

states which

at fi

limit, on an anomalous

of either supersymmetric (Z) this limit

for final

has been performed

at PEP. The upper of mass limits

annihilation

contain

= 29 GeV with

particles

assuming

or neutrinos.

radiative

2

11.30.Pb,

detector in terms

pair production

For the supersymmetric

at the 90% confidence

14.80.Pb,

the MAC

signal has been interpreted

electron

level if mgL = rnzR and

(7) has rn? = 0.

PACS numbers:

only a single

13.1O.+q

The method ing weakly

of using a radiative

interacting

count the number

neutral

photon

particles

of light neutrino

The experimental

signature

photon.

Several

discover

light neutral

sneutrino

authors2

e+e-

was first proposed

families

e+e-

to identify

+

interactions

by Ma and Okada’

to

via the reaction

vD7.

(1)

of this reaction

is a final state containing

have suggested

that this technique

supersymmetric

produc-

particles

only a single

could

such as the photino

be used to (5) and the

(fi) in the reactions

e+e-

+

q57

(2)

e+e-

+

t67.

(3)

and

Unlike

previous

searches3

for the ;i or b, a search for reactions

not require

that the 5 or fi decay within

search with

the MAC

annihilation

in the PEP storage ring at SLAC.

Reaction

detector

(2) proceeds

for single photon

by the exchange

(Z). The cross section is a function &.

Similarly,

partner

have been limited

(3) have similar

describes

final states produced

of a virtual

supersymmetric

(3) is a function

of the W boson.

distributions 3

a

by e+e-

electron to m,- >

of both mg and m@.

Searches for real Z495’6 0rF’

to masses less than &.

energy and angular

This report

of both rn? and m,-, and is sensitive

the cross section for reaction

@ is the supersymmetric production

the detector.

(2) and (3) does

Photons

from reactions

and cannot be distinguished

(l)on

an event-by-event

basis. The total cross section for reaction

w h ere N,, is the number

to (l+N,/4),

rng = 50 GeV/c2 reaction

the cross sections for reactions

families.

to differentiate

signal at present

sensitivities

Experimental

acceptance.

(1) for m,- > 50 GeV/c2.

would

either

particles

The processes e+e-

escaping

detector,

can produce

the observed

either

photon

If efficient

beam axis, then El, is the energy undetected

down

backgrounds.

Other

halo interactions.

---) e+e-7,

m,- < 50 GeV/c2

at angles outside

777,

and p+p-7,

However,

the transverse

in these cases must, be balanced particle

detection

is kinematically

extends limited

photon

to within

or NV > 3.

by: El,

backgrounds

unobserved

regions

of the

energy Elr

5 (&

- Er) sin t&to. polar

< 2.3 GeV for the above

result from beam-gas

for the photon

and beam

was chosen well removed

Results from two data samples are presented

The first sample

of 36 pb-’

had eveto N 10” with

El,., > 4.5 GeV.

The second data sample of 80 pb-’

the search region

to include

With

nearly

and minimal

47r sr coverage

dead regions,

tion and study of reactions

E,

angle of

from the above backgrounds.

El,

of

a small angle from the

and eveto is the maximum

A search region in Elr

A strong

by that of the unobserved

A veto angle t&t,, = 5’ limits El, single photon

= 29 GeV,

the detector

with

pipe or into inefficient

such backgrounds.

Since

search arise from processes with a

produced

the beam

of the detected

particles.

indicate

to the photon

and other

particles

as rnr3 at fi

from reaction

backgrounds

large angle photon

For NY = 3 and

(1) and (2) are comparable.

(2) has a cross section which decreases roughly

it is difficult

particles.

of light neutrino

(1) ‘I8 is proportional

the search region

here.

chosen as

had eveto = 5’, expanding

> 3.0 GeV. from both

the MAC

tracking

detector9

with missing energy. 4

and calorimetric

is well suited The detector

detectors,

for the identificaconsists of a central

drift

(CD) with

chamber

10 layers of drift cells covering

17” from the beam axis with onal barrel

of electromagnetic

and hadronic counters

calorimeters

extend

from

information

calorimeters

for calorimeter

coordinate,

obtained

5’ segmentation dially

into three layers. determine

resolution

~E/E

After

= 20%/d-

evetofrom

between

The trigger

radial

angle 4 and 4 cm resolution

energy

energy

and in the endcap length

and electrons calibration

the CD and endcap

e+e-7

ra-

Bhabha

3% and an energy

calorimeters

of the veto calorimeter

lengths

of

in order to reduce was measured

to be

The photon

must

final states.

> 0.3 GeV.

and 0.25 GeV for the second data sample. with energy

elsewhere.4

At, least two of the three

These thresholds The trigger

> 3 GeV by studying

is required

were lowered

efficiency e+e-7

The data analysis searches for events with a single photon The photon

from

SC is segmented

from radiative

within

> 2.0 GeV in one of the SC sextants.

layers must have energy

other particles.

calorimeters

planes and 8.5 radiation

for this search has been described

be > 95% for photons

in the axial

was taken, small angle veto calorime-

chamber

100 to 5O. The inefficiency

5 1 x 10d4 by studying

in the SC and HC

in the SC.

from proportional

lead, were installed

and tracking.

is determined

the first data sample of 36 pb-’

ters, constructed

identification

showers

Studies of photons

an absolute

and scintillation tubes outside

muon

from charge division,

counters,

layers of drift

provide

in both 8 and 4. The 14 radiation

scattering

deposit

in azimuthal

the CD is a hexag-

calorimeters

Several

to 0 N 10’.

angles more than

(SC), scintillation

Pl anar endcap

(HC).

1.9’ segmentation

Surrounding

shower calorimeters

the coverage

the central -and endcap Position

at least 5 layers.

polar

to 1.5

is measured

to

final states. unaccompanied

by

to be more than 40’ from the beam axis. 5

This requirement calorimeter

ensures

with

best energy

nent of the detector particles.

shower

and angular

is contained

resolution.

showers are identified

SC, HC, and endcap energy

the photon

calorimeters.

hits from

both single photons

and additional

or neutral

from hits in the

procedure

calorimeters,

allows showers

and can efficiently

low energy showers.

energy E, and angles 8 and 4 computed

charged

and reconstructed

The reconstruction

adjacent

in the SC, the

Signals from each compo-

are used to reject events with additional

Calorimeter

to contain

that

identify

Each shower is assigned

from the vector sum of the energy vectors

of its hits. Candidate pointing

showers are required

consistent

with showers produced

Hits in showers from beam-related as scattering a wider

to have energy deposition

from an upstream

spread of polar

Cuts on the width

enough

to be single

without

vertex

~0 with

the beam

mask, beam halo, or beam-gas

ormin

constraint

= 3.3 cm.

noise have a wider

of each shower

photons

containing

of closest approach

to the beam axis are measured Showers

are required

and analysis

and 0, using radiative

point.

Bhabha

point,

interactions,

point. such have

of azimuthal

showers

A straight Its point

the beam

and

Hits in showers

spread

events with

to the hits in each shower.

narrow

line is fit

of intersection

axis and the shower

rmin to the interaction with resolution

point

in the

a,,, = 12 cm and

to have lzol < 30 cm and rmin < 15 cm.

Showers passing these cuts are identified The detection

retain

from the interaction

axis in the plane

and its distance

plane transverse

from the interaction

angles than those from single photons.

angles.

width,

sources far from the interaction

from cosmic rays or bursts of electronic

centroid,

by photons

depth,

as single photons.

efficiency

was studied

scattering,

as a function

and was found 6

to rise with

of E,, Elr, increasing

Elr,

from (67 f 5)% at, El,

due to trigger,

detector,

in the beam pipe. reaction

= 3 GeV to (73 f 5) % at El,

and event selection

The efficiency,

folded

(1) in the search region,

the second data sample.

= 10 GeV.

inefficiencies, with

and photon

the expected

Elr

for reactions

conversions

dependence

is 71% for the first data sample

The efficiencies

Losses are

of

and 69% for

(2) and (3) differ by less

than 2%. The El7

distributions

of the selected single photons

ples are shown in Fig. 1. No events are observed data sample.

sistent with

other beam-related An estimate

was made

spectrum

e+e-

background

other backgrounds populate

The El,

that of the reaction

of the number

only through

0.05 event

is expected

and two charged

Monte

simulations

Carlo

search regions.

Remaining

mimic

single photons

ton events with selecting

these sources.

from

is carried

of background

originating

from e+e-

are beam-gas

events consistent

photons.

and 777 or veto in-

and veto efficiency background

leav-

of 0.05 event in the is less than 0.1

or beam halo interactions

Both

is

down the beam pipe.

-+ p+p-7

with these origins 7

and

by decay neutrinos,

from the interaction

very soft undetected

QED

-+ e+e-7

Another

tracks which may disappear

backgrounds

background

energy resolution

of this process give an estimate

The estimate

event,.

from

from e+e-

from

energy mismeasurement

most of the energy

ing a photon

of

is con-

a small contribution

of events expected

photon

less than

in which

with

Photons

On the basis of the experimental

+ ~‘-7-7

in the search region

processes.

efficiency.

e+e-

of the first

below each search region

+ e+e-7

in the search regions.

these regions

in the search region

= 5.3 GeV is observed

One event with Elr

the second data sample.

from the two data sam-

point,

which

and multiple

pho-

sources were studied and extracting

by

an El,.,

dependence.

These sources are estimated

search regions.

The probability

of the backgrounds from reaction

that the observed

discussed

above is small.

(1) is expected

event. The reactions

to contribute

event was produced

by any

If N,, = 3 is assumed,

in the search regions,

producing

less than 0.1 event in the

supersymmetric

consistent

particles

0.5 event

with the observed

can not be excluded

as

the source of the event. The observed production fidence

event,

cross section level.

This

regardless

in the detector

corresponds

cross section for radiative authors

10

the limit

photino

ther single e”production4’5

section

11

of the radiative

in this calculation,

is obtained

a limit

for the MAC

acceptance,

continued

and J. Schroeder

reliable

operation

by several

The result

at

mgR, the limit

is m,-, > 30 GeV/c2.

those obtained

from

searches for ei-

The calculation

neutrino

pair production

For the range

< 29 GeV/c2,

by Ware

the limit

of E

cross masses

rn; > 10 GeV/c2

level. the calculations

J. Ellis, V. Barger,

and M. A. Sher for useful discussions, C. T. Pulliam,

The

For m;l = 0 and m,-, = mzR,

for the fi mass.

J. D. Ware for providing detector

(1).

has been calculated

supersymmetric

20 < rng

at the 90% confidence

We thank

than

photon

to < 57 fb at the 90% con-

or e”+e”- pair producti0n.e

is used to obtain

assumed

in Fig. 2.

higher

the single

for the e” and q masses.

For rngL >

are significantly

and Machacek

limits

limits

of NV < 41 for reaction

pair production

level is shown

is rng > 37 GeV/c2.

These limits

acceptance

to a limit

and is used to obtain

the 90% confidence

of interpretation,

N. Erickson,

for technical

(2) and (3)

J. S. Hagelin,

S. Rudaz,

J. Escalera,

assistance,

of the PEP storage ring.

a

of reactions

M. J. Frankowski,

and the SLAC

staff for

REFERENCES (a) Present

address:

CERN,

Geneva, Switzerland.

(b) Present

address:

LANL,

Los Alamos,

(c) Present

address:

LBL,

(d) Permanent (e) Present

address: address:

Daejeon,

Berkeley,

CERN,

New Mexico

California

87545.

94720.

Geneva, Switzerland.

Department

of Physics,

Chungnam

National

University,

Korea.

(f) Present address: New York

Laboratory

of Nuclear

Studies,

Cornell

University,

41,287

(1978); Phys.

Ithaca,

14853.

1. E. Maand

J. Okada, Phys.

Rev.

Lett.

Rev.

Lett.

41, 1759 (1978). 2. J. A. Grifols,

X. Mor-Mur,

P. Fayet, Phys.

Lett.

117B,

Lett.

122B,

303 (1983);

Phys.

B241,

638 (1984).

3. W. Bartel

et al. (JADE

4. E. Femandez 5. L. Gladney

and J. Sol&, Phys. 460 (1982);

J. S. Hagelin,

et al. (Mark

Phys.

Collaboration),

114B,

35 (1982);

J. Ellis and J. S. Hagelin, G. L. Kane,

Collaboration),

et uZ. (MAC

Lett.

II Collaboration),

and S. Raby, Nucl.

Lett.

Phys.

Rev.

Phys.

Phys.

139B,

327 (1984).

Lett.

52,22

Rev.

Lett.

(1984). 51, 2253

(1983). 6. H. J. Behrend

et al. (CELLO

Collaboration),

Phys.

Lett.

114B,

287

(1982). 7. B. Adeva et al. (Mark 8. K. J. F. Gaemers,

J Collaboration),

R. Gastman,

Phys.

Rev.

and F. M. Renard,

(1979). 9

Lett. Phys.

53,1806 Rev.

DlQ,

(1984). 1605

9. W. T. Ford, Conf. Report

“The

MAC

Calorimeters

on Instrumentation

and Applications”,

for Colliding

Beams,

in Proc.

Int.

ed. by W. Ash, SLAC

No. 250, p. 174 (1982).

10. J. Ware and M. E. Machacek, and M. Kuroda, dita, Phys.

Rev.

Phys. D30,

Lett.

Phys.

Lett.

142B,

300 (1984); T. Kobayashi

139B,

208 (1984); K. Grassie and P. N. Pan-

22 (1984).

11. J. D. Ware and M. E. Machacek,

Phys.

10

Lett.

147B,

415 (1984).

FIGURE CAPTIONS 1. (a) The observed

E l7 spectrum

8 veto = 10’ and search region spectrum region

El7

for the first data sample of 36 pb-’ El,

> 4.5 GeV/c2.

for the second data sample of 80 pb-’

(b) The observed

with &to

with El,

= 5’ and search

> 3.0 GeV/c2.

2. The lower limit for rng as a function

of mq. The solid curve is for rnzL = mZR.

The dashed curve is for rnEL >> m,-,. The limits level.

11

are at the 90% confidence

I

100

IO

0

I

d ? E > w

I

0.1 100

1

I

(b) .

IO

“r Jl

I

0.1

0 12-84

I

I I

I

+

2 r

qr

Fig. 1

I

I

I

3

4

5

(GeV)

6 4989Al

12 IO

% 25

8 6

7x 4 E ‘2 0 IO 12-84

20 mz

30 ( GeV/c2)

Fig. 2

40 4989A2