BECKER: L3 at LEP is really a
matter of set zero particles.
And set zero particles decay
into everything we think
is truly elementary today,
with one exception, namely,
the top quark.
LEP is the machine in
Geneva, Switzerland, which
with 27 kilometer circumference
has four interaction regions.
L3 being here, where electrons
and positrons collide
with energies up to 100 GV.
L3 surrounds the intersection
region with a vertex chamber
and a huge facet eye of
12,000 crystals of BGO
to detect photons and electrons.
Hydrones go into the 400
tons of uranium color emitter
and muons will
penetrate everything
and be bent under the influence
of the 0.5 Tesla field
and registered and analyzed
in this [INAUDIBLE]..
L3 also is a collaboration
of 500 scientists
from 42 institutions
led by Professor Ting.
Technically L3 is optimized for
position in muons and photons
and electrons.
Such that the resolution is
1% in dimuon mass and delta
P over P 2.5%.
Since resolution goes linear
with B, that's quadratic with L
a very large conventional
magnet was constructed.
The very good unique
photon resolution
was achieved by new
crystals bismuth germinate.
The magnet itself has
140 turns to generate
a five kilo [INAUDIBLE]
field and that
necessitates a large coil
with a hefty wire carrying
30,000 amps.
The magnetic field return is
done by 8,000 tons of iron,
making it the
largest electromagnet
at the present moment,
according to the book
of records from Guinness.
You see it here in the moment
that the support tube was
cantilevered in, which
carries all other components
of the detector.
The muon detector, each
of its wheels is 95 tons,
gently glides on air cushioned
so the alignment of 30 microns
is not upset.
Here you
see it in reality.
And behind this is
an alignment, which
the muons coming from
the intersection region
are measured to 30 microns
accuracy and they're bent.
This was checked and under
better conditions from set
decays where you know
that the muon should
have the momentum of the beam.
And indeed, from
almost 9,000 events
now observed a resolution
of 2.5% as anticipated.
Inside the huge support tube
is the Hadron calorimeter,
which stops the hadrons
and measures the energy.
And inside that, in turn,
is this huge array of BGO
crystals, shown here, one half
finished one half still being
loaded with crystals into
the carbon fiber structure.
These crystals
for the first time
were grown in
equality and length
so that the electromagnetic
showers could be recorded
with 1% accuracy above 2 GV.
It was done in China.
The performance can
best seen from Pi zero
to gamma gamma decays,
which is resolved to 7 MEV.
The sigman to lambda
gamma with wi 4 MEV.
And the eta, which just
was addressed, was 16 MEV.
In 1990, the machine started
in '98 in 1990 130,000
said zeros got collected, which
gave rise to 35 publications.
In 1991, another 300,000
said zeros got recorded.
So the total is
almost half a million
now, which gives rise
to a determination
of precise parameters of the
standard model and measures
lifetimes very accurately,
all in all 60 papers.
Let me address
just a few of them.
We need, as a matter
of fact, very accurate
luminosity measurement to
do precision measurements,
which is done from small
angled Bhabha scattering.
You can see that the
measurements as points
and theory agrees very well.
So that we can
say the luminosity
is known presently
to 0.6% and will
be even better in the future.
With that, we can measure
as a function of energy
of the machine,
the hadronic events
and obtain a line
shape of a Breit-Wigner
here, which, if magnified,
is incredibly accurate.
This shows the
differential of the values.
If you look at events which
have strong energy deposits back
to back in the BGO crystals,
it's E plus E minus.
And you can plot those.
They also follow a
line shape of the
said 0 after T channel
contributions are removed.
If you look for back to back
muons in the muon system here,
again, you can observe
the line shape,
and the peak of
this distribution
gives you the partial width.
Down here you see
towers decaying
into an electron, the
other one and two three
pions, which would enable you
to measure the lifetime, which
was done.
They also followed
the same line shape.
So that we have no
very accurate results
of this partial [INAUDIBLE]
from electrons, muons and taus
down here.
Hadronic widths
is measured here.
The widths of the
said zero was fitted.
And a very accurate measurement
of the mass has been done.
Now we can ask what is missing.
And the missing channels, if
you attribute them to neutrinos,
you'll find there are three
neutrino species in this world,
unless they are
heavier than 45 GV.
So dark matter has to
be searched elsewhere.
One also can measure with
electrons, muons and taus
The electrons, the
forward-backward asymmetry
that an electron scatters
forward or backward.
That symmetry is shown here
as a function of energy going
through the said zero mass.
The reason this is important
is because this is asymmetry,
if you calculate
it from the vector
and axial [INAUDIBLE]
coupling constants.
It expresses itself
in this term.
And you can extract it from this
measurement and a partial width
measurement we have just shown.
They are related to the standard
model of coupling constants
with the Weinberg angle.
The result of this
is shown here.
GV GA on a very
enlarged scale, GA
is close to the expected
value of minus 0.5.
These are the one sigma
and two sigma contours.
And from this we can
evaluate the sine
squared to the effective.
And from refinement
of the calculation
of the partial widths, we can
conclude that the top mass
must be around 196 GV.
Let me come to a test of QED.
From E plus E minus
goes to gamma gamma,
which has nothing to
do with the zed 0.
In fact, the gammas are strongly
peaked towards the beamline
and very well described by QED
with cutoff parameters which
are very high and
let you conclude
that electron radius
is less equal then
to the minus 18 meters.
Also, if you consider gammas
from the e star exchange,
there is no room
for it and the mass
must be bigger than
122 GEV, if it exists.
Let me switch from QED to
QCD, which was now calculated
completely to second order.
Looking at three jet events and
looking at the smallest energy
jet scaled to the
beam energy, we
see a strongly
falling distribution,
which happens to agree
to the QCD calculation
for a gluon spin one.
If the gluon spin was
zero this distribution
wouldn't fit at all.
In QCD, we should have
flavor independence
of the coupling constant.
It shouldn't depend on which
kind of working quark you use.
We can single out the
heaviest quarks known now.
Beak works by large PT muons and
measure for those events of S
and it turns out to be the same
then for all the others, which
is a necessary condition.
The thrust distribution, which
is the projecting of energies
on an axis, is known
over four decades now
and agrees with the
theory very well.
This allows to extract this
coupling constant and the value
you find this way 0.118.
However, if you
use other methods
you can get higher results.
Therefore we give
an average of 0.125
and consider a theoretical
uncertainty of 0.08.
Search for the standard Higgs
is done by looking for Zed 0
decaying into a Higgs
and a virtual Zed
0, which in turn decays into
a neutrino anti-neutrino quark
anti-quark lepton anti-leptor.
This is a process which is
completely calculatable.
So if the Higgs
mass were 40 GEV you
should find so many of this
kind of decays and of neutrino
decays.
So this is the prediction
for the various channels.
No such event was seen.
Therefore one can say up
to the 95% confidence level
that the Higgs mass must
be bigger than 52.3 GEV.
There is an event which
is bigger than 52.3 GEV
and which fulfills
the topology which
we expect from such an event,
in that it has a mu plus, a mu
minus, and to rather broad
jets, which could be attributed
to a BB bar and they would
form a mass of about 70 GEV.
But clearly, the likelihood of
such a thing occurring is low
and it needs more events.
Charge takes were searched for
in the tau channels and CS bar.
The result is that up to
45 GEV nothing was found.
The following things are
unique to the L3 detector
and its features.
The eta was always
a little mysterious,
as it was mentioned before.
It can be observed with a
BGO with very good resolution
and high certainty.
The spectrum of eta is
observed in Zed 0 decays.
However, as a function
of the relative energy,
follows exactly to what
you expect and therefore
is nothing mysterious.
Three gammas can be
detected very well
and Zed zeros should not
decay into it, unless there
is a signature for new physics.
One event of this type was seen.
0.5 are expected from QED.
That lets us set a branching
ratio of 10 to the minus 5
for this process not to happen.
Hard photons will explore the
details of the interaction
at short distances.
If you compare the
zero decay and 2 QQ
bar with a gluon emission,
the color string lines
will lead to the gluon.
If you have QQ bar
where the gamma emitted,
the color line goes from
the quark to the quark.
So you expect more
hadronic energy
to be ejected in this part here.
And this is an
energy flow diagram.
And the purple line
gives you this process
and indeed there is
more hadronic energy
ejected for this gamma
events than for gluon events.
And in the other half
it's the other way around,
as it should be.
So this gives insight into the
clustering structure perhaps.
Physics of heavy quarks.
They can be singled out by
muons having a high transverse
momentum with respect
to the general jet
axis of the order of
a quarter of the mass.
That lets us select very well
B mesons from other things.
Because a cut at one
and a half GV and PT
leaves you only
with this red staff,
which is prompt B decays.
That's true for muons
as well for electrons.
Taking only those events
with a high PT muon,
you can again plot
their occurrence.
And they follow bright
richner shape, again,
of the Zed zero with
a partial width of 8
at 385 MEV as expected.
Re-extrapolate the muon, the
decay muon towards the beam,
will since it's a decay,
miss the exact beam point
by a impact parameter delta.
Evaluating that
gives you a measure
for the lifetime, which
is 1.3 picoseconds.
From this lifetime, and
knowing the branching ratio
on how often B's decay
to leptons, together
with low energy
data from Cleo, we
can evaluate the
transition matrix element
from B's to C's to be 0.046.
Looking into the zero decays
with MU plus MU minuses,
the invariant mass peaks at 3.1
GEV showing the J resonance.
And a branching ratio
for this process
is 4 times 10 to the minus 3.
Re-extrapolating the MU plus
MU minus to the decay point
gives us a measure of the
decay time by this distance.
This is a different
method, which
agrees exactly to the first
one in giving 1.3 picoseconds.
Taking this B event and
looking by the charge
of the muon for the
forward backward asymmetry,
we find one, which
is 0.08, which
would allow to
extract the coupling
constants for B mesons.
B mesons can mix
first normally, if we
have a B meson it will decay
only in a MU minus and a E
minus, not a MU plus emulous.
The B zero bar however, will
decay into MU plus E plus.
But what may happen with a
probability chi of mixing
is that this B turns
into B zero bar.
In that case, it ought to
decay into MU plus as well
as the other one.
So like sine dileptons indicate
that mixing took place.
Just counting the events
of normal occurrence
plus minus combinations, and
those which have equal sine
and therefore could
be due to mixing,
lets us determine the
mixing parameter to be 11%.
Lepton flavor violation
in Z zero decays
would signify themselves
by Zed decaying
to say a MU plus to a
minus, or vise versa.
In that case, if one
looks for muons only,
one should see muons which
peak at a Beam energy.
And due to the good
muon resolution,
they should be within this
red indicated diagram.
As you can see, you only see
decay muons from tau events.
And therefore, we can
set an upper limit of 10
to the minus 5 for this
process not to happen.
Tau polarization.
Recording top plus
tau minus events,
the taus are polarized
between helecity minus one
and helecity plus one stage.
The measurement of
the polarization
is important because it
determines the Weinberg angle
directly.
The measured spectrum of taus
decaying into a Pi's and K's is
given by this point here.
The analytic helicity
ones amplitudes,
shown down here
and minus one here,
they together explain the data
and measure the polarization.
So from tau to pi decays the
polarization is minus 15%.
But you can do it also from
tau to E and tau to MU decays
with the following results
averaged to a minus 13%
polarization.
Other topic is a model
independent analysis
of the number of
neutrinos, which relies
on the [? following ?] effect.
Although, you create
a Z 0 which decays
in neutrino neutrino bar.
It may have emitted
a gamma beforehand.
And that gives you a signature
that this process took place.
The spectrum of this gammas is
given by this blue histogram
and calculation.
And agrees exactly
with the data.
If the number of
neutrinos is three.
So this gives an
independent confirmation.
This is a very interesting
event we have two of,
which was a hard muon, two
hard muons and two hard gammas,
which are not close to them.
What is surprising about
these two events, measured
with an extremely good
gamma gamma resolution,
the invariant gamma gamma
mass for both of them
is close to 60 GEV.
And then there is nothing before
you have here, QED corrections,
a long distance away.
Let me summarize.
Major results from L3 based on
half million Zed zero events,
number of neutrinos is three.
Lepton radius measured
to be smaller than 10
to the minus 17 centimeters,
and quarks as well.
Mass of Higgs must be
bigger than 53 GEV.
The M zero mass is known
to a very high accuracy.
So is the partial
leptonic widths.
The properties of
heavy quarks have
been measured very precisely.
The decay times of B mesons.
The mixing of B mesons
has been determined
and a precise
determination of the stern
coupling constant to second
order has been achieved.
Unique to L3 are the results
that the B to C transition
matrix element was measured
in four different methods.
The sinus of the [INAUDIBLE]
Weinberg angle was determined.
And independent
confirmation that the number
of light neutrinos is
indeed-- three was given.
Flavor violation of Zed
decays does not take place.
The flavor independence of
QCD is manifested by B's.
The [INAUDIBLE] spectrum
does not show any anomalies.
The unexpected decays like
this, indeed, don't exist.
To hard photon
emotion from quarks
agrees very well
with expectations
and confirms that also
quarks are very pointlike.
The branching ratio
into J particles
was measured as 4 times
10 to the minus 3.
And the mass limit for excited
electrons set to over 122 GEV.
What will be next?
Six million Zed
zero events, which
allow to search
for new phenomenon,
as the last mysterious
events I showed you.
Precision tests of the
electoral week theory.
In 1994 the energy will
raise to 200 GEV or above.
And enable W plus
W minus protection
with this luminosity
in three years.
To test electroweak
theories further.
Make a Higgs search up to
masses of 80 to 90 GEV.
And search for new phenomenon.
The W plus W minus production
is interesting in that it
can proceed with
the following three
diagrams, of which this one is
specific to the non [INAUDIBLE]
nature of the standard model.
Together, they give
the very [INAUDIBLE]
cross-section shown here.
If this graph
wouldn't exist they
would raise to very high values.
This is even demonstrated more
in the angular distribution,
which the decay
muons from these Ws
would have with respect to
the beam axis, cosine here.
And the standard model
you expect a very steeply
rising angular distribution.
Whereas, if this
graph doesn't exist,
it would be very much flatter.
And you see many more events
in the back [INAUDIBLE]
hemisphere.
After all these successors
were the standard model,
let me remind you that
the standard model has
20 undetermined
parameters, which have
to be taken from experiment.
Namely, the coupling
constant, electron masses
and the quark masses and
the mixing parameters.
And 13 of those come from the
so-called Higgs sector, which
has to be explored in future.
And that I will
leave to [INAUDIBLE]..
Because if you plot these
masses on a strongly logarithmic
scale, you'll see that they
are all raising upwards.
And something ought to
happen in this region.
Thank you.
