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
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address:
CERN,
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(b) Present
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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
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Cornell
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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