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The Univ. of TokyoDept. of Physics

New MT method to remove SUSY contaminations

CSC Note 1&2 : 27 Aug 2007Ginga Akimoto, Y. Kataoka , S. Asai

The University of Tokyo ,JPN

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Dept of Physics

Table of Contents

1. Original MT methods (no SUSY)

2. SUSY contamination to control sample

3. new method to remove SUSY contamination

4. conclusion and outlook

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Dept of Physics1. Background Estimation ( the case : no SUSY ) These figures show the mET distribution for MT>100GeV and MT<100GeV.

The shape of distribution of MT>100 is the same as Control Sample (MT<100).

11 detail one already show in the previous speakers. MT method works well if SUSY dose not exist.

mET ( Control Sample : MT<100GeV ) mET ( Signal Region : MT>100GeV )

mET (MT>100) and scaled Control Sample

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2. Background Estimation ( with SUSY )

If SUSY exists, SUSY contamination contributes to control sample. [fig.1] shows mET distribution (SU3) of Control Sample. Hatched area shows t

he background, bold blue line is SUSY, bold black line is Observed Signal (SUSY+BG). The shape become harder due to SUSY contamination.

[fig.2] shows mET distribution (SU3) of Signal Region (MT>100). Red points with error bar are estimated background. The background is overestimated.

[fig.1] mET ( Control Sample : MT<100 )

[fig.2] mET ( Signal Region : MT>100 )

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2. Background Estimation II (with SUSY)

Not only the Shape but also normalization factor is also altered by SUSY contamination.

This figure shows mET distribution of Signal Region (MT>100) . Hatched histogram shows BG , blue shows SUSY and black line shows the sum of BG and SUSY. SUSY contamination can not be negligible even in low mET and make overestimate of BG.

contribution of SUSY

background

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3. Correction of Background Estimation correction of normalization 1. Normalization factor is obtained in the region of mET=100-115GeV in stead of 100-20

0GeV2. SUSY effect can be reduced, we use lower region if trigger effect is taken into account.

correction of Control Sample 1. SUSY contamination is removed from Control Sample as follows.2. This figure show mET distribution of SUSY signal. Line shows MT>100GeV point and p

oints with error bar show (normalized) MT<100GeV . Distribution is similar for the various SUSY point.So we can expect the distribution in CS can be estimated from MT>100GeV region.

[figure] Similarity : normalized Control Sample (points with error bar ) and Signal Region [MT>100GeV] (Bold Line)

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Dept of Physics3. normalization factor of the SUSY component Shape of SUSY signal in Control Sample can be estimated in MT>100GeV

region,but we need a new normalization factor. The MT distributions of SUSY are similar to each points [fig.1], so the events ratio

(Control Sample:MT<100) over (Signal Region : MT>100) is almost constant for varies SUSY point. [table]

the event ratio (normalization factor) [# of MT<100]/[# of MT>100]～ 0.6

SUSY point Events RatioSU1 : Coannihilation 0.583SU2 : Focus Point 0.556SU3 : Bulk 0.591SU4 : Low Mass 0.687

SUSY component of (Control Sample) is similar to about 0.6 times scaled (Signal Region)

Control

Sample

Signal

Region

[fig.1] MT distribution

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Dept of Physics3. an experimental way to estimate the SUSY ratio 0.61. If we believe MC we can use the ratio 0.6 . This normalization factor can be estimated

with out of MC information as follows.2. [fig.1] and [table.1] show that the lowest Signal Region (MT=100-150GeV) still has t

he same amount of SUSY events per MT as Control Sample (MT<100GeV) , because SUSY is not sensitive to the mass scale of W(~90GeV).

3. With information of the region [MT=100-150] , we can estimate the amount of SUSY in Control Sample and the event ratio to Signal Region (cut off mET<200 region : to reduce BG contamination ). The estimated value in each Model is in [table.2].

#(0-100)CS

2 *#(100-150)

#(100-200)

SU1 173.916 164.732 136.585

SU2 21.4488 19.5048 16.2

SU3 323.865 283.926 240.641

SU4 3530.3 2986.78 2240.8

tt-bblnln 169.22 165.021 121.858

[ っふぃｒｇふぃ fig.1]Transverse Mass (MT)

SUSY pointtrue ratio

estimated

SU1 : Coannihilation 0.583 0.614

SU2 : Focus Point 0.556 0.684SU3 : Bulk 0.591 0.612SU4 : Low Mass 0.687 0.689[ っふぃｒｇふぃ table.1] # of SUSY events in each MT bin

[ っふぃｒｇふぃ table.2] estimated normalization factor

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Leading Jet PT

3. New Background Estimation (SU3)

With this new method we can obtain the correct distributions for various variables. These figures show new estimated background of MT>100 region.

Red points with error bar shows estimated background , hatched area is real background and green line is old background estimation.

mET @ Signal Region (MT>100)

Lepton PT

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3.SUSY points dependence ( mET )

SU3 : Bulk

SU1 : Coannihilation SU2 : Focus Point

SU4 : Low Mass

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Dept of Physics3.Error and applicable range of this method large deviation at SU4(Low Mass) mainly normalization factor : eve

n in the new region (mET=100-115GeV), Control Sample includes substantial SUSY events. needs another method.

Other Points model uncertainty and error of the SUSY events ratio estimation ( ～ 10%) , similarity between Control Sample and Signal region (10%), normalization constant (less than 15% and can reduce it).

SU4 : Low Mass

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4.Conclusion & Outlook

Conclusion1. Original methods overestimate the background by a factor two to thr

ee.2. With this new MT method, the background of Signal Region (MT>10

0) is correctly estimated ( XX% accuracy).

Outlook1. application to [No Lepton Mode] and [Di-Lepton Mode] 2. estimate the effect of lepton efficiency 3. proceed to var.124. estimation : the systematic error