1. The Univ. of Tokyo Dept. of Physics 1 New MT method to remove SUSY contaminations CSC Note 1&2 : 27 Aug 2007 Ginga Akimoto, Y. Kataoka, S. Asai The University of Tokyo,JPN

2. Dept of Physics 2 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

3. Dept of Physics 3 1. 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). 1.  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

4. Dept of Physics 4 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 the 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 )

5. Dept of Physics 5 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

6. Dept of Physics 6 3. Correction of Background Estimation correction of normalization 1. Normalization factor is obtained in the region of mET=100-115GeV in stead of 100-200GeV 2. 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 points with error bar show (normalized) MT 100GeV region. [figure] Similarity : normalized Control Sample (points with error bar ) and Signal Region [MT>100GeV] (Bold Line)

7. Dept of Physics 7 3. 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) is almost constant for varies SUSY point. [table] the event ratio (normalization factor) [# of MT 100] ～ 0.6 SUSY component of (Control Sample) is similar to about 0.6 times scaled (Signal Region) Control Sample Signal Region [fig.1] MT distribution

8. Dept of Physics 8 3. an experimental way to estimate the SUSY ratio 0.6 1. 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 the 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) SU1173.916164.732136.585 SU221.448819.504816.2 SU3323.865283.926240.641 SU43530.32986.782240.8 tt-bblnln169.22165.021121.858 tt-bblnqq1465.5255.321828.6766 W668.4125.171515.2572 [ っふぃｒｇふぃ fig.1]Transverse Mass (MT) SUSY pointtrue ratioestimated SU1 : Coannihilation0.5830.614 SU2 : Focus Point0.5560.684 SU3 : Bulk0.5910.612 SU4 : Low Mass0.6870.689 [ 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

9. Dept of Physics 9 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

10. Dept of Physics 10 3.SUSY points dependence ( mET ) SU3 : Bulk SU1 : CoannihilationSU2 : Focus Point SU4 : Low Mass

11. Dept of Physics 11 3.Error and applicable range of this method large deviation at SU4(Low Mass)  mainly normalization factor : even 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

12. Dept of Physics 12 4.Conclusion & Outlook Conclusion 1. Original methods overestimate the background by a factor two to three. 2. With this new MT method, the background of Signal Region (MT>100) is correctly estimated ( XX% accuracy). Outlook 1. application to [No Lepton Mode] and [Di-Lepton Mode] 2. estimate the effect of lepton efficiency 3. proceed to var.12 4. estimation : the systematic error