Sparticle reconstruction in
final states with di-leptons
M. Chiorboli, M. Galanti, A. Tricomi
University and INFN, Catania
Credits: Luc Pape
Outline


Aim: measurement of sparticle masses
from kinematical end-point analyses in
events containing c20→c10ll (l=e,m)
Feasibility study:
– first step: parton level
– preliminary attempts with FAMOS
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
End-point analysis

c 20
~
q

~

q
c 10


In sequential decays, all the sparticle
masses involved can be extracted from
the measurement of edges and
thresholds in the effective mass
distributions
Maxima and minima of effective masses
correspond to collinear configurations
Only squark chains considered at this
stage
Squark coming from gluino decays or
directly produced
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
Event selection: parton level

50k events @ LM1
–
–
–
–
–



M½=250, sign(μ)=+, M0=60, A0=0, tan(β)=10
total SUSY cross section 41.6 pb
M(~g)>M(~q)
BR(~c20→ ~ll → ~c10ll ) = 11.2%
BR(~c20→ ~c10ll) negligible
Generated processes: ~q~g, ~g~g, ~c~g
Forced decays: ~g→ ~qq, ~q → ~c20q, ~c20 →
~ll, ~l → ~c10l
Pythia 6.224 + Isajet 7.69
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
Dilepton end point

c 20
~
q

c 10
~


Use dilepton signature to tag
presence of c02 in event, then
work back up decay chain
constructing invariant mass
distributions of combinations
of leptons and jets
q
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
(l1q) and (l2q) edges
1
c 20
~
q


~

c 10

2
q
Upper endpoint of
m(l1q) is reached for all
values of m(ll)
Max of m(l2q) varies as
a function of m(ll)
– Two endpoints, for
high and low m(ll)
values
Mario Galanti
University & INFN - Catania
m(ll)

(l2q)max,2 (2nd lepton, l1 flipped)
2
M lmax,

2q
M R max
M l 2q
MX
PRS session, CPT Week
November ‘04
m(l1q) and m(l2q)
(l1q) and (l2q) edges
c 10

c
~
q
0
2
~



q
The two end points can be
separated by cutting on M(ll)
No Mll cut
expected values:
M (l1q )
max
 395 GeV/c
2
M (l 2q ) max, 1  317 GeV/c 2
M (l 2q )
max, 2
Mll < 20 GeV/c2
 210 GeV/c
2
Mll > 70 GeV/c2
 2q
 1q
Mario Galanti
University & INFN - Catania
M(lq)
PRS session, CPT Week
November ‘04
M(lq)
M(lq)
Parameter dependence
LM1
GeV/c2
GeV/c2
m(ll) vs. m(l1q) and m(l2q)
GeV/c2
No Mll cut
Mario Galanti
University & INFN - Catania
Mll < 20 GeV/c2
PRS session, CPT Week
November ‘04
B
GeV/c2
Mll > 70 GeV/c2
(llq) edges

M
 MQ
max, 1
llq
 M X2
1 
 M2
Q

 M 02
1 
 M 2
X





Two upper end points for high and
low m(ll)
Lower threshold depending on
M(ll) (parametrization known)
M
M
max, 2
llq
max, 3
llq
 MQ
 MQ
 M R2  M 02 
1 
1 

2
 M  M 2 
Q 
R 

 M R2
1  2
 MX
m(ll)
M(llq)max,2 or M(llq)max,3
 ( M X M 0 ) 2 

1 
 (M M )2 
Q
R


Mario Galanti
University & INFN - Catania
M(llq)max,1
PRS session, CPT Week
November ‘04
m(llq)
llq edges
expected values:
M (llq ) max, 1  448 GeV/c 2
M (llq )
No Mll cut
max, 3
 404 GeV/c
Mll > 75 GeV/c2
Mario Galanti
University & INFN - Catania
M(llq)
PRS session, CPT Week
November ‘04
M(llq)
2
Mll < 30 GeV/c2
M(llq)
M(l2q)
(llq) edges

Identification of l1
and l2 mandatory
to observe the true
maxima in llq
distribution
Distinction between
the two leptons:
under investigation
Mario Galanti
University & INFN - Catania
M(llq)
M(l1q)

PRS session, CPT Week
November ‘04
M(llq)
First attempt with FAMOS


10k events produced @ LM1
– FAMOS_0_9_0_pre4, CMKIN _3_1_0
– Only ~q ~c10 process, forced decays
Created rootfiles with information on:
– muons: FastMuonLvl3Finder
– jets: FamosPersistentJetFinder
– missing Et: FamosMETfromCaloTower
– No electrons yet
– No mu isolation yet
– No b-tagging
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
Dilepton edge with FAMOS
Event selection:
– 2 muons (Pt>15 GeV/c)
– ≥1 jet
– missing Et > 100 GeV

Dilepton mass distribution
with muons only
M(ll)
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
m(llq)
M(lq)
m(ll)
PARTON LEVEL:
M(lq)
m(ll)
FAMOS:
Mll < 30 GeV/c2
m(llq)
Open questions

How to treat combinatorial in real
analysis
– High jet multiplicity in events

l1 vs. l2 separation
– Under study

Dependence on parameters
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04
Conclusions and
near future plans


From parton level studies, the end point
analysis looks promising
FAMOS:
–
–
–
–

Test release 1_0_0
Electron reconstruction
b-tagging
Muon isolation
More realistic analyses:
– All SUSY samples
– SM background
Mario Galanti
University & INFN - Catania
PRS session, CPT Week
November ‘04