Download CERN/LAA/96-03

CERN/LAA/961.4.1996
A STUDY OF THE MULTIHADRONIC SYSTEMS
PRODUCED AT LEP: THE RATIO OF CHARGED
OVER TOTAL ENERGY.
Authors and Institutions
ABSTRACT
In the early 80's the multihadronic systems produced at ISR were
shown to have the same properties as those produced in (e +e) annihilation
at equivalent energies. Using these data as a starting point we study the
multihadronic systems produced at LEP. The accuracy of the data is such
that, it is possible to disentangle the "gluon dominated" processes from the
"quark dominated" processes. The chosen variable is the ratio of charged
over total energy. Extensions to HERA studies are discussed.
1 — Introduction.
One of the most interesting results obtained with the first high energy
(pp) collider (ISR) was the universality features of the multihadronic
systems produced. The ISR data allowed to discover that the nature of the
interaction — purely hadronic (such as (pp), or electromagnetic (such
as e+e) or weak (such as neutrino production on fixed target experiments),
did not matter. The multihadronic final states produced in all processes
showed the same basic features, within the experimental uncertainty.
The reason why these universality features had never been found
before was due to the fact that a basic mechanism at work in hadronic
processes — the leading effect — was ignored. As a consequence, the
multiparticle systems produced in the very many different hadronic
processes such as (πp), (Kp), (pp), ( p p), and in photoproduction, (e +e)
annihilation and DIS, appeared to have nothing in common. But, once the
leading effect was correctly taken into account, the basic parameters,
describing the multihadronic systems in all the very many different
processes, appear to be the same, within the  20% level of experimental
uncertainty.
A detailed and systematic analysis was done at ISR [Ref] using for the
comparision (e+e) data at equivalent energies from PETRA [Ref]. The
agreement — after so many years of apparent drastic differences — was
well within the experimental errors. Nertheless at ISR (pp) interactions
were gluon-hadronization dominated processes while (e +e) annihilation
were quark-hadronization dominated. A direct comparison between the (pp)
and (e+e) charged multiplicity distributions [Ref] showed that, in this
variable there was indeed a difference between ISR (pp) data and (e +e)
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PETRA results. The difference was following the expectation: gluon jets
appeared flatter than quark jets in the charged multiplicity distribution.
Purpose of the present paper is to extend our (ISR-PETRA) comparison at
the higher energies now available.
This study will take the ISR and the PETRA results as the starting
point. The purpose is to see if it is possible to disentangle some properties
in the multihadronic systems produced in (pp) and (e +e) processes which
are different and therefore connected with the source of these multihadronic
systems: i.e. gluon versus quark hadronization.
There is a collider where both hadronization processes do take place.
This is the (ep) HERA collider at DESY. The "electron" vertex and the
"proton" vertex can be disentangled and provide important information once
the differences could be well established. Differences can be studied if the
starting point is equalities.
From our ISR experiment and subsequent comparition with (e+e) data
two quantities emerged as being not exactly the same. The one already
quoted (the charged multiplicity distribution) and the ratio of charged over
total energy, a quantity called "" [Ref].
This quantity — the ratio  of the total energy associated with the
charged particles over the total energy carried by the charged, the neutral
and the undetectable particles, such as neutrinos — was considered as the
index for “new physics”.
It is in fact using  that the multihadronic systems produced in (e +e)
annihilation gave rise in 1974 [1] to the so called “energy crisis”.
Measuring the total energy associated with charged particles, <E charged>
and knowing the total energy, of the produced final state, from the colliding
beams energies
 se+e-, it was found that
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E
e+e-
ch arg ed
E

total



If (e+e) interactions were to produce π+ππ0, the e+e- value should have
been
e+e-
The interest in the value of e+e-was based on the fact that some
new unknown channels could contribute to the “missing” charged
component of the total energy available for particle production. Even more
interesting was the hypothesis that some unknown neutral channels could
have carried away the excess of neutral energy.
The basic point was, and still is, that the value of e+e-characterizes
the multiparticle hadronic systems produced in (e +e) annihilation. It was
therefore of great interest to determine the value of the same quantity in
purely hadronic interactions. There were no experiments designed for this
purpose and the only available indication seemed to show a large
discrepancy with the (e+e) value. As mentioned before, the reason for the
apparent large discrepancy was understood when the multiparticle systems
studied at ISR were proved to agree with (e +e) data, provided the
“leading” hadron effect was subtracted out [Ref]. In fact, a world analysis
of all multiparticle systems produced in purely hadronic interactions,
showed that the “leading” hadron effect was present in all processes and
needed to be correctly taken in due account. Once this is done, as already
mentioned, universality features [Ref] emerge in the properties of the
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multiparticle hadronic systems produced, in hadronic, electromagnetic, or
even weak interactions.
Purpose of the present paper is to start from the (ISR) and (HERA) data
and extrapolate this knowledge to LEP and HERA.
2 — The Basic Quantities.
The basic quantities will be:
1) the leading effect;
ii) the fractional energy distribution;
iii) the transverse momentum distribution;
iv) the average charged multiplicity;
v) the distribution of the charged multiplicity;
vi) the ratio of charged over total energy.
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