1. Prospects for sparticle reconstruction at new SUSY benchmark points
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 I 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
Massimiliano Chiorboli

3. Results with 10 fb-1

4. Massimiliano Chiorboli
Point B
I 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%)
Massimiliano Chiorboli

5. 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
Massimiliano Chiorboli

6. 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
Massimiliano Chiorboli

7. 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
Massimiliano Chiorboli

8. 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
Massimiliano Chiorboli

9. 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 peak resolution better than 10% (still at CMSJET level!)
Massimiliano Chiorboli

10. btag parameter optimization
The b-tagging is a very important feature:
With low purity the mass peaks are shifted to fake values
With too high purity (few statistics) we cannot reconstruct the peaks at all
This is a very simple algorithm. We would need a full simulation to properly evaluate this effect b c
uds - g
Massimiliano Chiorboli

11. Massimiliano Chiorboli
Eb1 cut
We can strongly suppress the combinatorial background in the sbottom reconstruction cutting on the energy of the most energetic jet
This cut suppresses b-jets coming from other sparticles
Eb-jet 1 > 250 GeV
Generator level
CMSJET
1 jet
2 jet
Massimiliano Chiorboli

12. Eb1 cut optimization
Also this cut has to be optimized not to deform peaks
At point B, a cut of GeV improves the signal to (combinatorial) bkg ratio without changing the mass values
Massimiliano Chiorboli

13. Mll window optimization
A too broad window improves the statistics but gives untrue mass values (we go far from the ideal kinematic condition)
A narrower mass window improves the width.
Stable masses from Mll>70 GeV (we need more statistics)
Massimiliano Chiorboli

14. 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
0.7
7000
The right component is almost negligible
(16.4%)
(22.4%)
I have to select non b-jets: more combinatorial
Massimiliano Chiorboli

15. Squark-gluino event topologies
jet p
jet p
jet
Massimiliano Chiorboli

16. 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:
Massimiliano Chiorboli

17. 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
Massimiliano Chiorboli

18. Dilepton edge Etmiss > 50 GeV Etmiss > 100 GeV
I reproduce the same procedure as in the sbottom reconstruction method. I 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
Massimiliano Chiorboli

19. Squark reconstruction: selection of the first jet
The jets coming from the squarks are harder than the others
No angular correlation between this jet and ll
Generator level
Generator level
E parton (GeV)
cos(a)
CMSJET
I select the most energetic jet and I associate it to the reconstructed chi2
E jet (GeV)
Massimiliano Chiorboli

20. Sbottom reconstruction
Etmiss > 50 GeV
Etmiss > 100 GeV
Etmiss > 150 GeV SM
Massimiliano Chiorboli

21. Massimiliano Chiorboli
Anti b-tagging
Effect of the anti b-tagging parameter cut on the reconstructed sbottom peak
s < 3
s < 2
s < 1
Effect of b-veto
No b-veto
b-veto
Massimiliano Chiorboli

22. Sources of combinatorial background
Irreducible source: jets coming from other squarks
Reducible source: jets coming from gluinos
Massimiliano Chiorboli

23. Combinatorial suppression
A cut on the energy of the selected jet can suppress the combinatorial
Ejet>100
No Ejet cut
Ejet>200
Ejet>300
Massimiliano Chiorboli

24. Massimiliano Chiorboli
Squark mass
10 fb-1
Result of the fit
anti b-tag: s<2
Etmiss > 150 GeV
Ejet 1 > 20 GeV
b-veto SM
Generated values
Massimiliano Chiorboli

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

26. Combinatorial in gluino reconstruction
The squark-squark events produce fake gluinos.
Jets coming from squarks shift the peak to higher values and produce the tail on the right
Massimiliano Chiorboli

27. Gluino combinatorial suppression
Generator level
Un upper cut on the energy of the second jet can suppress jets coming from squarks
E parton (GeV)
1 jet
2 jet
CMSJET
E jet (GeV)
E jet (GeV)
E jet (GeV)
Massimiliano Chiorboli

28. Gluino combinatorial suppression
Ejet 2 < 80 GeV
Ejet2<150
No Ejet2 cut
Ejet2<120
Ejet2<100
Ejet2<80
all
Massimiliano Chiorboli

29. Massimiliano Chiorboli
Gluino mass peak
10 fb-1
Ejet 2 < 80 GeV
anti b-tag: s<2
Etmiss > 150 GeV
Ejet 1 > 20 GeV
b-veto
Result of the fit SM
Generated value
Worse resolution but better statistics than the gluino from the sbottom chain
Massimiliano Chiorboli

30. 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 > 20 GeV
b-veto
Result of the fit
Generated value SM
Massimiliano Chiorboli

31. Results with 300 fb-1

32. Point B: Sbottom and Gluino
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
Massimiliano Chiorboli

33. 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
Massimiliano Chiorboli

34. 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
Massimiliano Chiorboli

35. 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
Massimiliano Chiorboli

36. 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
Massimiliano Chiorboli

37. Point G

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

39. Massimiliano Chiorboli
Point G: dilepton edge
300 fb-1 SM
Etmiss >1 50 GeV
Etmiss > 200 GeV
Etmiss > 250 GeV
Massimiliano Chiorboli

40. Point G: sbottom and gluino reconstruction
SUSY only
300 fb-1
Eb-jet 1 > 150 GeV
Massimiliano Chiorboli

41. Effect of the SM background
Etmiss > 150 GeV
Etmiss > 200 GeV
Massimiliano Chiorboli

42. Point G: Sbottom and Gluino mass peaks
Etmiss > 250 GeV
300 fb-1
Generated values
Generated value
Massimiliano Chiorboli

43. Point B: 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
Massimiliano Chiorboli

44. Point I

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

46. Massimiliano Chiorboli
Conclusions
At 10 fb-1:
Point B:
we can start the reconstruction of sbottom and gluino
Squark reconstruction seems possible, better than the sbottom chain, with resolution of 12%
At 300 fb-1:
Point B
Very good reconstruction of sbottom, squark and gluino
Possible double gaussian fit on the sbottom peak to evaluate the two sbottom masses
Point G:
Difficult reconstruction of sbottom and gluino
The squark reconstruction seems better
Point I
Any reconstruction is impossible
Massimiliano Chiorboli