This document describes the particle identification and mass selection criteria used to study the decay chain Ξ0b→ Ξc+ π- → Ξ- π+π- → Λπ- → pπ-. Histograms of the Lambda, Xi-, and Xi+c masses are shown with different selection cuts applied to isolate the signal from background events. An optimal set of cuts is chosen based on removing most of the background while retaining as much of the signal as possible. These include restrictions on track types, particle lifetimes, ghost probabilities, and mass windows.

1. Ξc
+
→ Ξ−
ππ
Ξ−
→ Λπ−
Λ → pπ−
1
Mass
measurement
study
by:
Evan
Cornuelle

2. 2
Λ Selec8ons
The
top
Histogram
is
all
mass
entries
vs.
Lambda
LL
and
Lambda
DD
combined.
The
boBom
is
neither
Lambda
LL
nor
Lambda
DD
(LL
is
Long
Stream
Pion
and
Proton.
DD
is
downstream
proton
and
Pion.)
This
selec8on
was
made
because
a
good
lambda
is
produced
from
the
same
track
type
of
proton/pion.

3. 3
Ξ− Selec8ons
The
top
histogram
shows
the
subsets
of
Ximinus
masses.
Separated
into
DD
and
LL
Lambdas
with
a
long-­‐stream
or
down-­‐
stream
pion.
The
boBom
histogram
shows
the
mass
entries
that
do
not
fit
in
any
of:
LL,L;
DD,L;
DD,D.
This
selec8on
was
made
because
true
Ximinus
par8cles
are
made
from
LL
and
DD
lambdas
with
longstream
or
downstream
pions.

4. 4
Selec8ons
Ξ+
c
These
are
histograms
of
XiCplus
with
different
restric8ons
on
Ghost
probability
(The
probability
that
a
hit
is
noise).
Top:
Pass
the
restric8on.
BoBom:
Fail
the
restric8ons.

5. 5
.1
.133
.166
.2
.1
.133
.166
.2
These
histograms
are
also
of
ghost
probabili8es.
The
ranges
here
are
to
op8mize
the
value
used
in
the
selec8on
criteria.
A
value
of
.133
is
chosen
as
the
final
value
because
it
is
similar
in
signal
amounts
compared
to
higher
ghost
probability
values,
but
contains
more
signal
than
a
value
of
.1.
This
removes
as
much
background
as
possible
without
removing
too
much
signal.

6. 6
This
plot
shows
a
par8cle
iden8fica8on
selec8on
criteria.
Less
than
zero,
the
more
likely
the
par8cle
is
a
pion.
Greater
than
zero,
the
less
likely.
Less
than
zero
was
used
as
the
final
value
for
the
selec8on
because
there
is
background
removed
from
PIDK
values
greater
than
zero
as
seen
by
the
orange
line.
Where
as
the
signal
remains
in
the
red
histogram.

7. 7
This
shows
different
set
of
XiCplus
life8me
selec8ons.
The
values
chosen
are
those
greater
than
.45
picoseconds
(units
of
values
in
the
legend
are
in
nanoseconds)
as
mostly
background
is
removed
from
values
less
than
.45
picoseconds.

8. 8
The
final
mass
distribu8on
with
all
of
the
selec8ons.

9. 9
Ξ0
b
→ Ξc
+
π −
Ξc
+
→ Ξ−
ππ
Ξ−
→ Λπ −
Λ → pπ

10. 10
Λ Selec8ons
On
the
top:
Lambda
mass
selec8ons
in
LL
and
DD
subsets.
DD
and
LL
have
the
same
defini8on
as
before.
The
boBom:
All
of
the
entries
that
are
not
LL
or
DD.

11. 11
Ξ− Selec8ons
On
the
top:
Ximinus
mass
selec8ons
in
LL,L;
DD,D
and
DD,L
subsets.
DD,D
;
DD,L
have
the
same
defini8on
as
before.
The
boBom:
All
of
the
entries
that
are
not
LL,L;
DD,D
or
DD,L.

12. 12
This
is
a
histogram
of
different
end
vertex
chi2
values.
The
end
vertex
chi2
values
expresses
the
“goodness”
of
the
Ximinus
end
vertex.
This
selec8on
is
not
used
as
all
of
the
subsets
have
significant
background.

13. 13
Ξ+
c
Selec8ons
This
shows
different
ranges
of
mass
cuts
on
the
allowed
Ximinus.
The
mass
range
chosen
is
the
red
(1315,1327).
Background
is
reduced
with
only
a
liBle
loss
of
signal.
Red:
(1315
MeV,1327
MeV)
Green:
(1310
MeV,
1332
MeV)
Blue:
(1300
MeV,
1342
MeV)

14. 14
These
are
histograms
of
Ghost
Probability
selec8ons.
Top
two
plots::
Red:
Ghost
P
<
.1
Green:
Ghost
P
<
.2
Blue:
Ghost
P
<
.3
These
are
histograms
of
Ghost
Probability
selec8ons.
Resolved
between
.1
and
.2
BoBom
two
plots::
Red:
Ghost
P
<
.1
Green:
Ghost
P
<
.133
Blue:
Ghost
P
<
.166
A
value
of
.133
is
chosen
to
reduce
ghosts
and
background
as
well
as
to
keep
as
much
signal
as
possible

15. 15
These
are
histograms
of
Neural
Network
Ghost
Probability
selec8ons.
Resolved
between
.1
and
.2
BoBom
two
plots::
Red:
Ghost
P
<
.1
Green:
Ghost
P
<
.133
Blue:
Ghost
P
<
.166
A
value
of
.166
is
chosen
to
reduce
ghosts
and
background
as
well
as
to
keep
as
much
signal
as
possible
These
are
histograms
of
Neural
Network
Ghost
Probability
selec8ons.
Top
two
plots::
Red:
Ghost
P
<
.1
Green:
Ghost
P
<
.2
Blue:
Ghost
P
<
.3

16. 16
This
histogram
shows
different
ranges
of
the
pion’s
track
type
Chi2
value.
When
coupled
with
a
degrees
of
freedom,
this
value
gives
a
probability
that
the
track
is
a
pion.
A
value
of
.01
is
used
as
it
reduces
a
fair
amount
of
background
and
not
as
much
signal
as
higher
values.

17. 17
The
par8cle
iden8fica8on
for
the
pion
that
goes
with
the
XiCplus
is
taken
as
less
than
zero

18. 18
This
histogram
shows
a
life8me
selec8on
of
the
XiCplus
mass
ad
different
sub-­‐sets.
Most
of
the
entries
removed
from
values
less
than
.45
picoseconds
appear
to
be
background,
as
the
distribu8ons
look
flat.
The
value
chosen
is
greater
than
.45
picosecnds.

19. 19
This
is
the
final
fiBed
mass
distribu8on
the
the
XiCplus
that
will
be
used
to
look
for
a
XiBzero.

20. 20
A
histogram
of
the
entries
that
do
not
pass
the
selec8ons
on
the
XiCplus

21. 21
Ξ0
b
Selec8ons
Distribu8ons
of
the
XiBZero
mass
are
shown
here.
On
the
boBom
is
the
distribu8on
without
any
selec8on
criteria.
The
top
includes
a
selec8on
criteria
on
the
XiCplus
that
will
be
paired
with
the
pion.
This
includes
all
prior
criteria,
along
with
a
mass
cut
from
2457
MeV
to
2477
MeV.
(Shown
in
orange)
The
green
histogram
shows
a
par8cle
iden8fica8on
of
less
than
zero
selec8on
on
the
pion
aBributed
with
the
XiBzero.
There
does
not
appear
to
be
any
signal
in
the
distribu8on

22. 22
A
life8me
selec8on
criteria
was
aBempted
with
the
XiBzero
to
remove
background.
This
was
not
effec8ve
as
the
background
remains
in
all
of
the
subsets.

23. Conclusion
A
mass
measurement
is
found
for
the
with
promising
errors.
The
would
something
to
look
into
further.
There
is
not
a
result
found
for
the
Mass
23
Ξ+
c
Ξ+
c
Ξ0
b