1. Supersymmetric Particle Reconstructions at CMS
Massimiliano Chiorboli
INFN Catania

2. Massimiliano Chiorboli
Up to a couple of years ago, most of attention devoted to inclusive studies
I started working in the Physics group on sparticle reconstruction
Sbottom, squark ad gluino mass peaks in 3 mSUGRA points
7 May 2003
Massimiliano Chiorboli

3. SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets Massimiliano Chiorboli
Decay Chains p b b p
 2 high pt isolated leptons OS
(leptons = e,m)
 2 high pt b jets
missing Et
 2 high pt isolated leptons OS
(leptons = e,m)
 2 high pt non-b jets
missing Et
SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets
7 May 2003
Massimiliano Chiorboli

4. Generation and Simulation
SUSY events generated with ISAJET PYTHIA 6.158
SM bkg events (tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets) generated with PYTHIA
Detector simulated with CMSJET 4.801
7 May 2003
Massimiliano Chiorboli

5. Massimiliano Chiorboli
Benchmark Points
Proposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia et al. (hep-ph/ )
Rather low m0 and m1/2 values in order to have high SUSY cross section
Three different tan b values (tan b = 10, 20, 35) since BR(c20  l+l- c10) depends on tan b
7 May 2003
Massimiliano Chiorboli

6. Reconstruction Method
At the end-point: p b
2 isolated leptons, pT>15 GeV, |h|<2.4
 2 b-jets, pT>20 GeV, |h|<2.4
assuming M(c10) known
Selecting events “in edge”
Combining the c20 obtained from the two leptons with the most energetic b-jet in the event
7 May 2003
Massimiliano Chiorboli

7. Reconstruction Method
Once the sbottom (or the squark) is reconstructed: p b
SM bkg can be reduced cutting on ETmiss
The main problem is combinatorial
7 May 2003
Massimiliano Chiorboli

8. Massimiliano Chiorboli
Point B
sSUSY = pb
→ dilepton edge well visible
Sbottom Chain
Squark Chain
10 fb-1
60 fb-1
300 fb-1
M(sbottom)
500±7
502±4
497±2
M(squark)
536±10
532±2
536±1
s(sbottom)
42±5
41±4
36±3
s(squark)
60±9
36±1
31±1
M(gluino)
594±7
592±4
591±3
592±7
595±2
590±2
s(gluino)
42±7
46±3
39±3
75±5
59±2
gluino
10 fb-1
sbottom chain
10 fb-1
squark chain
10 fb-1
sbottom
1 fb-1
squark
Result of the fit:
Result of the fit:
Squark mass peaks can be reconstructed in the first few weeks (resolution ~12%)
Sbottom and gluino in the first year (resolution ~6÷8%)
Two independent gluino mass measurements
The resolution can be improved with larger statistics (~5÷6% at 300 fb-1)
Generated values
Generated value:
7 May 2003
Massimiliano Chiorboli

9. Massimiliano Chiorboli
Point G
With respect to the Point B:
Lower total SUSY cross section (8.25 pb)
Lower BR’s of useful decays
Higher BR’s of competitive decays
Lower BR of the last decay
300 fb-1
10 fb-1
7 May 2003
Massimiliano Chiorboli

10. Massimiliano Chiorboli
Point G
sbottom
gluino
Sbottom Chain
300 fb-1
M(sbottom)
720±26
s(sbottom)
81±18
M(gluino)
851±40
s(gluino)
130±43
Squark Chain
M(squark)
774±9
s(squark)
84±9
853±11
126±11
squark
gluino
300 fb-1
7 May 2003
Massimiliano Chiorboli

11. Massimiliano Chiorboli
Point I I G
300 fb-1
The tau channel is the main one also in the other points
Tau-pair edge is not as sharp as in the e and m case, but could help to cover points in which the reconstruction is problematic
It could be exploited in regions with too low leptonic BR B
Neutralino BR’s B G I
BR(c20→ll)
16.44
2.26
0.25
BR(c20→tt)
83.22
75.88
98.13
7 May 2003
Massimiliano Chiorboli

12. Massimiliano Chiorboli
Conclusions
Supersymmetric Spectroscopy has been attempted
CMS will be capable to reconstruct sparticles with favourable parameters
Point B
squark in the first few weeks (1 fb-1)
sbottom and gluino in the first year (10 fb-1)
Point G
squark, sbottom and gluino with 300 fb-1
Point I
no recontruction possible with the lepton channel, but it could be useful to investigate other decay chains (e.g. c→tt)
CMS Note in preparation
7 May 2003
Massimiliano Chiorboli

13. Massimiliano Chiorboli
Future perspectives
What can be done…
Re-run the analysis in full simulation
Try to look fo other sparticles in the same points
stop
non-strongly interacting sparticles
Investigate other decay channels
c→tt at Point I (high tan b points)
Explore reconstruction capability at different points
7 May 2003
Massimiliano Chiorboli