**CHARGED TRACKS ANALYSIS**

(PR D65, 072005 04/01/2002)

See CDF-notes __
5288__ (physics analisys) and __
5575__ (complementary studies and efficiency corrections).

In this study we try to characterize soft interactions (whatever they are)
and to find any peculiar behavior which

exhibit specific properties that may help us to understand them.

We start working with a sample of events which are collected without requiring
any particular "a priori" condition

("minimum bias" events). Out of minimum-bias events we select the "soft"
ones by applying the only selection

criterium that we know to be valid for them: we require that they do not
show up as jets (jets are spreads of collimated

fast particles that are typical of head-on parton collisions). In our particular
definition of "soft" events we include all

events with no jets of energy greater than 1.1 GeV. This number is suggested
by the detector ability to measure a jet

energy, but we show that the results do not critically depend on this particular
value.

Finally we study the properties of selected soft events as compared to all the others. In particular we analyze:

- the charged multiplicity distribution. This is the probability for an event to produce a given number of final particles in the central region.
- the transverse momentum distribution. This is the probability for particle produced in the central region to have a given transverse momentum
- the fluctuation (from event to event) of the event average transverse momentum. This is an indication of what is the spread of the mean energy released transversally to the colliding axis.

We observe that in the sample of "soft" collisions all these properties are independent from the c.m.s. energy for

events that produce the same number of particles. In other words, the production mechanism of soft events seems

to depend only on the number of produced particles. Their mean number increases with increasing c.m.s. energy,

but their probability distribution around the mean is invariant.

Once fixed the number of the final state particles, all the other properties of these particles are the same,

independently from the total initial energy available in the collision.

This is an unexpected and new result, and the analysis is the first one
of this kind ever published.

__Part of the plots blessed for this analisys:__

1. primary charged particles multiplicity
distributions, in KNO form (MB)

2. primary charged particles multiplicity distributions,
in KNO form (soft)

3. primary charged particles multiplcity distributions,
in KNO form (hard)

4. average charged particles pT vs multiplcity
(MB)

5. average charged particles pT vs multplicity
(soft)

6. average charged particles pT vs multiplcity
(hard)

**ANALYSIS OF K ^{
0}_{s} AND Lambda^{ 0}^{
}**

See CDF-notes__
6075__ and __
6043__ (pick latest versions).

Besides the lighter quarks ** u** and

multiparticle interactions to be statistically significant and experimentally accessible with a

Minimum-Bias trigger. It is also a valid probe to investigate the transition of soft hadron

interactions to the high-pT QCD perturbative region.

This paper describes an analysis of k and Lambda (V0) production in pp
interactions. It is part of

a low-pT multiparticle production systematic study structured in comparative
analyses of

statistical distributions and particle correlations at different c.m.s. energies.

Specific emphasis is given to the dependence of the particle correlations
on charged multiplicity

and to the ``hardness'' of the interaction.

In analogy with the paper described above the whole analysis was repeated
on two different types

of events that have been selected by dividing MB data into soft and hard
sub-samples.

Inclusive distributions of multiplicity and transverse momentum of K and
Lambda are presented

first. The high statistics of the data sample collected at sqrt(s)=1800 and
630 GeV and accurate

efficiency corrections, allow to extend the range of these measurements and
their precision with

respect to previous ones.

Studies of the dependence of the average pT of V0 and of their mean number
on the event charged

multiplicity are also presented. It is not possible to enphasize any difference
of the <pT> dependence

with multiplicity at the two energies, even in the full MB sample. This is
even more so for the soft

and hard sub-samples. Nevertheless the behavior of the three sub-samples is
clearly different.

__The kinematic selection of K and Lambdas (described
in note 6075)__

- look for opposite sign CTC track pairs converging to a secondary vertex;
- fit secondary vertex with both K and L0 hypotheses and keep best fit;
- secondary vertex 3-C fit must have probability >5%;
- fitted mass must be within 3 sigmas from k/L0 mass;
- vertex displacement projected in x-y plane (Lxy) >1 cm;
- decay products in pT>0.300 GeV/c and |eta|<1.5;
- | Z(V0) - Z(event) | < 6 cm;
- d0(V0) < 0.7 cm;
- pT(V0) > 0.4 GeV/c;
- | eta(V0) | < 1.0

Includes efficiency + "fakes" + acceptance + contamination.

Efficiency: is computed in two ways: with full MC generation/simulation/reconstruction
and

by embedding fake k/L0 into real min-bias events;

Fakes: we mean by this fake associations of secondary tracks, but also V0
which are

reconstructed
outside of our defined limits for the efficiency and also the

contamination
of K in the L0 sample and viceversa;

Acceptance: originated by our fiducial cuts in Lxy and pT of the V0
decay products

Overall correction is computed as C = (1 - Fakes)/(Efficiency x Acceptance)

__Blessed plots:__

1. invariant mass distributions of pi-pi and p-pi
pairs (MB, 1800 GeV)

Invariant mass distribution of the decay products of k and Lambdas
after kinematical selection.

No correction is applied.

2. lifetime distribution of k, raw and corrected
(MB, 1800 GeV)

The lifetime distribution of k is shown before and after effciency
correction.

The mean value is (0.881+-0.006)E-10 s

3. lifetime distribution for Lambda, raw and corrected
(MB, 1800 GeV)

The lifetime distribution of k is shown before and after effciency
correction.

Te mean value is (2.62+-0.08)E-10 s

4. distribution of multiplicity of k for the MB,
soft and hard data samples (630 and 1800 GeV)

Probability for finding 1,2,3,4 k in a event. MB, soft and hard data
samples are shown.

5. distribution of multiplicity of Lambda for the
MB, soft and hard data samples (630 and 1800 GeV)

Probability for finding 1,2,3 Lambda in a event. MB, soft and hard
data samples are shown.

6. invariant pT distribution of k for the MB, soft
and hard samples (1800 GeV)

The inclusive invariant pT dustributions of k (MB, soft and hard)
at 1800 GeV.

We use the form: A( p0 / (pT+p0))exp(n) to fit MB distribution and
obtain that

<pT>=0.74+-0.07 GeV/c

7. invariant pT distribution of k for the MB, soft
and hard samples (630 GeV)

The inclusive invariant pT distributions of k (MB, soft and hard)
at 630 GeV.

With the same form <pT>=0.70+-0.08 GeV/c

8. invariant pT distribution of Lambda for the MB,
soft and hard samples (1800 GeV)

The inclusive invariant pT distributions of Lambda (MB, soft and hard)
at 1800 GeV.

The above form gives <pT>=0.95+-0.09 GeV/c. An exponential function
fits the

data equally well and gives <pT>=1.03+-0.01 GeV/c

9. invariant pT distribution of Lambda for the MB,
soft and hard samples (630 GeV)

The inclusive inavriant pT distributions of Lambda (MB< soft and
hard) at 630 GeV.

The two functions give respectively: <pT>=0.90+-0.07 and <pT>=0.97+-0.01
GeV/c

10. dependence of the mean pT on the event charged
multiplicity (MB, 1800 GeV)

(the mean pT in figs 10 to 15 is not computed from the fit of the
distribution but

as the mean value of the measured pT of all the k/Lambda observed)

11. dependence of the mean pT on the event charged
multiplicity (Soft, 1800 GeV)

12. dependence of the mean pT on the event charged
multiplicity (Hard, 1800 GeV)

13. dependence of the mean pT on the event charged
multiplicity (MB, 630 GeV)

14. dependence of the mean pT on the event charged
multiplicity (Soft, 630 GeV)

15. dependence of the mean pT on the event charged
multiplicity (Hard, 630 GeV)

16. dependence of the mean number of k on the event
charged multiplicity (1800 GeV)

Average number of k per event and per charged track, plotted as a
function of the

number of charged tracks (event multiplicity).

17. dependence of the mean number of Lambda on the
event charged multiplicity (1800 GeV)

18. dependence of the mean number of k on the event
charged multiplicity (630 GeV)

19. dependence of the mean number of Lambda on the
event charged multiplicity (630 GeV)

__Other plots:__

1. efficiency(pT): the efficiency
for finding K and L0 as a function of their pT

2. efficiency(Lxy): the efficiency
for finding K and L0 as a function the secondary vertex

displacement in the transverse plain

3. efficiency(t): the efficiency for finding K and
L0 as a function of lifetime/<lifetime>

4. efficiency(Nch): the efficiency for finding K
and L0 as a function of the charged

multiplicity of the event

5. efficiency(eta): the efficiency for finding K
and L0 as a function of their pseudo-rapidity