1. ADR for Massimiliano Chiorboli Universita’ and INFN Catania
Prospects for sparticle reconstruction at new SUSY benchmark points Status report
ADR for
Massimiliano Chiorboli
Universita’ and INFN Catania

2. Massimiliano Chiorboli
Benchmark Points
Proposed Post-LEP Benchmarks for Supersymmetry (hep-ph/ )
The goal is to try to reconstruct sparticles
Last time we showed gluino and sbottom at point B (isajet, 10 fb-1, 300 fb-1), and point G (pythia, 300 fb-1)
In mSUGRA scenario, Pythia overestimates the BR of the decay chain to be selected
Only ISAJET results in this talk
7/10/2002
Massimiliano Chiorboli

3. Massimiliano Chiorboli
Point B
We use the isajet 7.58 parameters as input parameters to pythia 6.152
95.6
c10 = LSP
173.8
c1±
136.2 lR
361.6
c2±
196.5 lL
174.4
c20
520 qR
339.9
c30
540 qL
361.1
c40
524.0 bR
575.9 tR
496.0 bL
392.9 tL
595.1 g
ISAPYTHIA masses and BR’s
(17% bL, 10% bR)
(37 % bL, 25% bR)
(0.04 %)
PYTHIA
(16.4%)
(60%)
(83.2%)
(38%)
7/10/2002
Massimiliano Chiorboli

4. Sbottom and Gluino decay chainp b
Event final state:
 2 high pt isolated leptons OS
 2 high pt b jets
missing Et
10 fb-1 of SUSY events at point B produced with the “ISAPYTHIA” generator
Detector simulation: fast simulation (CMSJET 4.801)
SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW
2 SFOS isolated leptons, pT>15 GeV, |h|<2.4
 2 b-jets, pT>20 GeV, |h|<2.4
B-tagging performed with the FATSIM package of CMSJET: A jet is a b-jet if it contains at least two tracks with a significance sip> sbcut
7/10/2002
Massimiliano Chiorboli

5. Massimiliano Chiorboli
First step: c20  l+l- c10 p b
SUSY only
SUSY + SM
ttll, not only
Z+jet
E(ll) > 100 GeV
ttbar
7/10/2002
Massimiliano Chiorboli

6. Dilepton edge fit Etmiss > 150 GeV
Cut on the EmissT to have a clean SUSY sample
Subtract OFOS lepton pairs to eliminate combinatorial bkg
Fit in good agreement with the MC value
7/10/2002
Massimiliano Chiorboli

7. Sbottom reconstructionp b
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
b-tag: s>3
Etmiss > 150 GeV
Eb-jet 1 > 250 GeV
E(ll) > 100 GeV
10 fb-1 SM
Generated values
Result of the fit
7/10/2002
Massimiliano Chiorboli

8. Gluino reconstructionp b
Next step: reconstruct gluinosbottom
I associate the reconstructed sbottom to the b-jet closest in angle to it
b-tag: s>3
Etmiss > 150 GeV
Eb-jet 1 > 250 GeV
E(ll) > 100 GeV
10 fb-1
Generated values
Result of the fit SM
We achieve a resolution better than 10% (still at CMSJET level!)
7/10/2002
Massimiliano Chiorboli

9. Squark reconstruction
Non-sbottom squarks:
Process
s(pb)
n in 10 fb-1
0.5
5000
1.9
19000
7.0
70000
28.3
283000
1.8
18000
14.1
141000
0.4
4000
0.8
0.7
7000
The right component is almost negligible
(16.4%)
(22.4%)
I have to select non b-jets: more combinatorial
7/10/2002
Massimiliano Chiorboli

10. Squark-gluino event topologies
jet p
jet p
jet
7/10/2002
Massimiliano Chiorboli

11. Massimiliano Chiorboli
Event selection
2 SFOS isolated leptons, pT>15 GeV, |h|<2.4
 2 jets (not b), pT>20 GeV, |h|<2.4
b-jet veto (I reject events having 1 jet with s>3)
Process
n in 10 fb-1
2 lepton
b veto
2 non b-jet
2 SFOS lep
5378
1052
1041 36 27
18999
2278
2178
154 78
4767
865
476
258
130
69943
14533
4528
4185
1325
18880
2683
2422
1084
614
283199
40309
19847
17100
7198
18311
4819
1337
904
215
141609
12034
10513
7917
4355
3616
890
364
262 91
5153
2046
547
409
126
7063
2219
606
516
161
Main squark sources:
7/10/2002
Massimiliano Chiorboli

12. Massimiliano Chiorboli
SM backgrounds
s(pb) N
2 lep
b-veto
2 non b-jets
2 SFOS isolate lep
ttbar
621
6.21*106 (10 fb-1)
886809
336001
170182
14900
Z+jet
(pthat > 60 GeV)
2870
3.9*106
172894
159479
17205
13138
W+jet
7500
2*106
4517
3869
738 2
QCD
50-100
2.86*107
1.9*106
460
270 78
1.64*106
3366
1658
965
6.67*104
11395
5349
4088
8.59*103
19892
9545
7954 1
1.83*103
28149
13961
11832
>500
8.20*102
39902
20343
17581
7/10/2002
Massimiliano Chiorboli

13. Dilepton edge Etmiss > 50 GeV Etmiss > 100 GeV
Reproduce the same procedure as in the sbottom reconstruction method. Start from the dilepton invariant mass edge.
E(ll) > 100 GeV SM
Etmiss > 50 GeV
Etmiss > 100 GeV
Etmiss > 150 GeV
It looks much better than the b-jet case.
Probably a better understanding of the SM bkg’s is needed
Wtb production?
7/10/2002
Massimiliano Chiorboli

14. Squark reconstruction
Etmiss > 50 GeV
Etmiss > 100 GeV
Etmiss > 150 GeV SM
Selecting the most energetic jet to be combined with the leptons
B-quark veto useful but not crucial
Use minimum energy for cut for jet
7/10/2002
Massimiliano Chiorboli

15. Squark mass 10 fb-1 Result of the fit Etmiss > 150 GeV SM
anti b-tag: s<2
Etmiss > 150 GeV
Ejet 1 > 200 GeV
b-veto SM
Generated values
This assumes the mass of the
neutralino-1 to be known
7/10/2002
Massimiliano Chiorboli

16. Gluino reconstruction
Generator level
cos(a)
try to reconstruct the gluino in squark decay chain with the same method.
associate the jet closest in angle to the reconstructed squark
Etmiss > 50 GeV
Etmiss > 100 GeV
Etmiss > 150 GeV
7/10/2002
Massimiliano Chiorboli

17. Gluino combinatorial suppression
Generator level
Un upper cut on the energy of the second jet can suppress jets coming from squarks
Associate the jet closest in angle to the reconstructed quark
E parton (GeV)
1 jet
2 jet
CMSJET
E jet (GeV)
E jet (GeV)
E jet (GeV)
7/10/2002
Massimiliano Chiorboli

18. Massimiliano Chiorboli
Gluino mass peak
10 fb-1
Ejet 2 < 80 GeV
anti b-tag: s<2
Etmiss > 150 GeV
Ejet 1 > 200 GeV
b-veto
Result of the fit SM
Generated value
Worse resolution but better statistics than the gluino from the sbottom chain
7/10/2002
Massimiliano Chiorboli

19. M(gluino)-M(squark)
The difference of masses is independent from the neutralino 1 mass
10 fb-1
Ejet 2 < 80 GeV
anti b-tag: s<2
Etmiss > 150 GeV
Ejet 1 > 200 GeV
b-veto
Result of the fit
Generated value SM
7/10/2002
Massimiliano Chiorboli

20. Point B: Sbottom and Gluino 300 fb-1
Result of the fit
300 fb-1
Generated values
300 fb-1
b-tag: s>3
Etmiss > 200 GeV
Eb-jet 1 > 150 GeV
cos f(b1-gluino) > 0.4
cos f(b1-sbottom) > 0.2
E(ll) > 100 GeV
Result of the fit
Generated value
7/10/2002
Massimiliano Chiorboli

21. Squark and Gluino at 300 fb-1
Result of the fit
300 fb-1
Generated values
300 fb-1
Result of the fit
Generated value
7/10/2002
Massimiliano Chiorboli

22. Questions of the last meeting
Influence of pile-up at 300 fb-1?
Can bL and bR be distinguished?
Effect of the neutralino 1 mass
Effect of the calo energy scale (syst.)
Precision on •BR
(stat: sbottom ~ 5%, squarks ~ 2%)
7/10/2002
Massimiliano Chiorboli

23. Effect of the pile-up on the sbottom and gluino reconstruction
No pile-up
100 fb-1
Pile-up
The background increases and the peaks are shifted on the left
7/10/2002
Massimiliano Chiorboli

24. Separation of the two sbottoms
Even at high integrated luminosities, it doesn’t seem possible to separate the two sbottoms
I try to perform a double gaussian fit on the peak
300 fb-1
Both the mass values and the coefficient seem to be in agreement with the MC
7/10/2002
Massimiliano Chiorboli

25. Sparticle reconstructionb
Problem c10 measurement!
Mass to ~15-25%from
study of various decays
Gluino
7/10/2002
Massimiliano Chiorboli

26. Massimiliano Chiorboli
Sensitivity to M(c1)
At 300 fb-1 we can perhaps have the M(c1) as input from a LC.
To evaluate the effect the error on M(c1) on the sbottom and gluino mass measurements, I reconstruct the peaks changing the M(c1)
Since we have a statistical error of 3 GeV at 300 fb-1, to have an uncertainty on the gluino and sbottom mass given by the M(c1) uncertainty smaller than this statistical error, we should know M(c1) with an error less than 3/1.6 = 1.9 GeV
7/10/2002
Massimiliano Chiorboli

27. Point G: dilepton edge E(ll) > 100 GeV
ran point G using ISAJET BR’s:
(2.5%)
(64%)
E(ll) > 100 GeV
300 fb-1
ttll, not only
7/10/2002
Massimiliano Chiorboli

28. Massimiliano Chiorboli
Point G: dilepton edge
300 fb-1 SM
Etmiss >1 50 GeV
Etmiss > 200 GeV
Etmiss > 250 GeV
7/10/2002
Massimiliano Chiorboli

29. Point G: squark and gluino reconstruction
The squark channel seems more efficient than the sbottom one
300 fb-1
Etmiss > 250 GeV
Eb-jet 1 > 250 GeV
Etmiss > 250 GeV
Eb-jet 1 > 250 GeV
Eb-jet 2 < 100 GeV
7/10/2002
Massimiliano Chiorboli

30. Point I: dilepton chain
(0.25%)
(98%)
300 fb-1
In this point it’s impossible to reconstruct the decay chain
7/10/2002
Massimiliano Chiorboli

31. Results: Direct reconstruction
@ POINT B
Squark, sbottom and gluino reconstruction possible even at low integrated luminosity (10 fb-1) with
Resolution <10%
Errors  5-6% if approximate M(c10)  M(llmax)
(this approximation is valid only in a mSUGRA scenario for which M(c20)  2M(c10))
Precision on mass 1-2% if M(c10) would be known
Sbottom (L,R) separation possible?
At 300 fb-1 and assuming M(c10) measured from a LC, we can have errors of  0.5% (if not limited to a few %). Systematics?
@ POINT G
Sbottom and gluino reconstruction possible only at high luminosity
At 300 fb-1 we can reconstruct sbottoms and gluino with resolution
7%, errors 1-2%, assuming M(c1) known from a LC
7/10/2002
Massimiliano Chiorboli