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.