First look into sbottom and gluino
reconstruction
Massimiliano Chiorboli
University and INFN Catania
SUGRA parameters
m0
m1/2
tan b
A0
200 GeV
100 GeV
2
0
sign m
~
g
~
bL
~
bR
~
q
Massimiliano Chiorboli
m (GeV)
299.2
275.0
309.3
> 300
SUSY
 1.3 nb
tot
~g,~q  1 nb
m (GeV)
~
 2
~

1
~
 20
~
10  LSP
273.4
94.5
95.0
44.5
Catania CMS Week 20/06/2001
Decay chain
and event topology
~
pp  ~q  ~g  bb
~ 0 b
2
Event final state:
~
10   
p
• 2 high pt isolated leptons OS

b
~
 20
~g
~
10


• 2 high pt b jets
• missing Et
~
b
p
Massimiliano Chiorboli
b
Catania CMS Week 20/06/2001
Events production
 SPYTHIA (PYTHIA 6.136)
 CMSJET 4.703
3 fb-1
Signal
SUSY bkg
~
g~
g
1’088’000
~
q~
g
~
q~
q
2’005’000
~
~
g
28’000
~
~
q
51’000
Massimiliano Chiorboli
531’000
~
~

65’000
~~
tt
72’000
SM bkg
tt
1’860’000
Catania CMS Week 20/06/2001
Events selection
 at least 2 isolated
leptons with pt>15
GeV and |h|<2.4
 at least 2 b-jets
with pt>15 GeV
and |h|<2
~
q~
g
~
g~
g
~
q~
q
~
~
q
~
~
g
~
~

~~
tt
tt
Massimiliano Chiorboli
Events
27’228
54’216
3’765
48
165
10
400
1’302
%
1.4
5.0
0.7
<0.1
0.6
10-4
0.5
<10-4
Catania CMS Week 20/06/2001
Reconstruction of
~
20  ~
10   
 invariant mass of e+e- and
m+m
 due to kinematics,
the distribution shows an
edge

SUSY
tt

~ 0
2
~ 0
1

Massimiliano Chiorboli
~ 
0
~
2     ~
10     is forbidden
Catania CMS Week 20/06/2001
Reconstruction of
~
20  ~
10   
85929
Subtracting invariant
mass of OSOF pairs
eliminate SM and
combinatorial bkg
Massimiliano Chiorboli
SUSY
tt
Catania CMS Week 20/06/2001
0
0
~
~
M( 2 )  M( 1 )
estimation
~0
~0
Mmax
   M( 2 )  M( 1 )

M( ~
20 )  M( ~
10 )  50.90  0.39 GeV (50.5 GeV)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Sbottom reconstruction
signal
bkg
 M ~10

p~ 0  1 
2
 M
 


p
 

45 GeV  M      52 GeV
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Sbottom reconstruction (II)
reconstructed
neutralino combined
with the most
energetic b-jet,
assuming M1 known
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Sbottom reconstruction (III)
Assuming M(10) = 44.5 GeV
~
M( brec )  265.0  37.0 GeV
(275.0)
At the moment,
no jet energy correction
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction
 combination of the reconstructed sbottom and a bjet
 ~ 10 % of the selected events have >2 b-jets
the b-jet closest to
the reconstructed
sbottom is chosen
~
  angle (bb)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction (II)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction (III)
~
  angle (brec b - jet)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction (IV)
 Cut on this angle to select the b-jet coming
from the gluino
cos   0.4
cos   0.8
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction (V)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Sbottom and gluino after cuts
(cos  > 0.8)
M(~
grec )  295.2  39.8 GeV (299.2)
~
M(brec )  263.1  31.7 GeV (275.0)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
~
~
M( g ) - M( b )
evaluation
no cut
cos   0.4
Massimiliano Chiorboli
cos   0.8
Catania CMS Week 20/06/2001
~
~
M( g ) - M( b )
evaluation (II)
~
~
M(grec )  M(brec )  21.5  4.5 GeV (24.2)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Dependence
from
1
M(  )
~0
10 mass assumed to be known
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Results within 3 fb-1
M(~
20 )  M(~
10 )  50.90  0.39 GeV
~
M(brec )  263.1  31.7 GeV
for M(~ ) 
0
1 true

~
~
M(brec )  M(b) true  1.6 M(~
10 )assumed  M(~
10 ) true
M(~
grec )  295.2  39.8 GeV

for M(~ ) 
0
1 true
M(~
g rec )  M(~
g ) true  1.6 M( ~
10 ) assumed  M( ~
10 ) true
~
~
M(grec )  M(brec )  21.5  4.5 GeV
Massimiliano Chiorboli


indipenden t from M(~
10 )
Catania CMS Week 20/06/2001
Future plans
 Scanning the mSUGRA parameters plane
 Including the jet energy correction
 Improving the cuts
 Studying this decay chain as a benchmark channel
for the b-tagging
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Gluino reconstruction
M(~
g rec )  295.2
  39.8 GeV
(299.2)
Massimiliano Chiorboli
Catania CMS Week 20/06/2001
Sbottom reconstruction
Assuming M(10) = 44.5 GeV
~
M( brec )  265.0
  37.0 GeV
(275.0)
At the moment,
no jet energy correction
Massimiliano Chiorboli
Catania CMS Week 20/06/2001