Post on 01-Jan-2016
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Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Chargino/ Neutralino Update
Yiming LiUniversity of Oxford
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Outline
SM suppression cut optimization Chargino / Neutralino separation optimization Summary & plan
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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SM bkg suppression cut
Signature of gaugino pair production: two acollinear boson.
Previous cut: acollinearity > 10 Not very effective, > 90% SM bkg survive
Try acoplanarity :
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Acoplanarity of two reco’d bosons
Left: chargino selection; Right: neutralino selection
Red: chargino /neutralino signal; Black: SM bkg.
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Boson energy – acoplanarity > 10
Left: chargino selection; Right: neutralino selection
Red: chargino /neutralino signal; Blue: SUSY bkg; Black: SM bkg.
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Chargino/Neutralino Separation
So far box cut on 2d-mass plane. Low purity-efficiency for neutralino
Try ‘chi square’ cut?
M1 + M2 > 172 GeV (M1-MZ)^2+(M2-MZ)^2 < …
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Chargino/Neutralino Separation
Neutralino on SUSY bkg
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
160 165 170 175 180 185
2d mass cut / GeV
purity
eff iciency
pur*eff
Neutralino on SUSY bkg
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
0 0.01 0.02 0.03 0.04 0.05
2d mass chi2 cut
purity
eff iciency
pur*eff
M1 + M2 > 2d mass cut(M1-MZ)^2+(M2-MZ)^2 <
2d mass chi2 cut * Mz ^2
Chi square cuts allow higher purity.
But this result is a bit too optimistic since Acoplanarity cut is not implemented here…
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Neutralino on SUSY bkg
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
0 0.01 0.02 0.03 0.04 0.05
2d mass chi2 cut
purity
eff iciency
pur*eff
Neutralino on SUSY bkg
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
0 0.01 0.02 0.03 0.04 0.05
2d mass chi2 cut
purity
eff iciency
pur*eff
No cut on acoplanarity
The same as previous page (right)
Acoplanarity > 10
Yiming Li, Oxford Univ. 10 March 2009 SiD Benchmark Meeting
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Summary & plan
SM background is further suppressed by cutting on acoplanarity of two reconstructed gauge bosons.
Chargino /neutralino separation can be improved by optimizing the correlated di-jet masses cut.
Will try template fitting using all four samples to fit three SUSY particles masses.