One lepton mode BG estimation (MT and new MT) v12.0.6.5 Full Sim

1. One lepton mode BG estimation (MT and new MT)v12.0.6.5 Full Sim Background meeting CSC1+2 : 01 Oct 2007 Ginga Akimoto , S.Asai, Y.Kataoka, N.Kanaya The University of Tokyo, ICEPP

2. Table of Contents Background Estimation using real data for One Lepton Mode new MT method : SUSY contamination corrected MT method • Data Set • background estimation : MT-method • new MT method • Conclusion & Outlook

3. I. Data Set(12.0.6.5 Full Simulation) We use the CSC full-simulation samples(v12). • SUSY • SU1 : 005401 • SU2 : 005402 • SU3 : 005403 • 1TeV SUSY (Y.Kataoka) • Background • ttlnln : 5535 to 5538 • ttlnqq : 5530 to 5533 • W enu: 6414 to 6417 • Wmunu : 8203 to 8205

4. transverse mass (MT) distribution [1fb-1] Signal Region MT>100GeV Events / 10GeV Control Sample MT<100GeV MT [GeV] 2.Background Estimation : MT-method • One Lepton Mode : Main Background (top / W) • This figure shows MTdistribution of SU3(Bulk) and background. • MT>100GeV : SUSY signal enhanced Region [Signal Region] • MT<100GeV : Background ( top /W) enhanced Region [Control Sample] [MT-Method] Using MT<100GeV region, a background enhanced sample can be obtained. we can estimate the background of MT>100GeV region from real data. (detail has already shown in the previous many meetings.)

5. 2. BG Estimation : MT-method without SUSY • MT-Method works very well if SUSY dose not exist. The shape of missing ET distribution at MT>100GeV region is the same as MT<100GeV region. MT>100GeV missing ET distribution. [1fb-1] Red with error : data driven BG with CS hatched histogram : truth BG (ttlnln dominant) number is also well reproduced. missing ET [GeV] # of mET>300 estimate BG 17.4±4 real BG 15.8±4 10% accuracy

6. 2.Background Estimation : MT method with SUSY • MT method overestimate the background because SUSY-contamination distorts the shape of Control Sample, whose distribution becomes harder due to the pollution. • SUSY excess is still larger than the overestimated BG so we can discover SUSY signal clearly. • post-SUSY discovery  more precise BG estimation (new MT method) [fig.4]Background overestimation [1fb-1] Events / 40GeV Red with error : estimated BG with CS hatched histogram : truth BG (ttlnln dominant) Blue : truth SUSY missing ET [GeV]

7. Effect of SUSY contamination [1fb-1] Similarity of SUSY signal [1fb-1] SUSY contamination MT [GeV] missing ET [GeV] 3.new MT method (I) : Estimation of SUSY contamination • The left figure shows SUSY contamination exists in Control Sample. It should be removed for more accurate estimation of background and SUSY. • We estimated SUSY in control sample as follows. • The left figure shows MT>100GeV region is SUSY enhanced sample. • Various distributions for SUSY signal in MT<100GeV are similar to those in MT>100GeV. The right figure shows the mET distribution at. (solid line is MT>100GeV, dotted line shows (normalized) MT<100GeV). As you can see, the distribution is the same. We checked various SUSY samples (SU1,2,3,4,1TeV sample) and obtained the distribution is similar . • So the Shape of SUSY in Control Sample can be estimated by MT>100GeV sample. • The # of SUSY in Control sample also can be estimated by mET&MT-distribution. (detail abbrev. ) SUSY signal is flat to about 200GeV

8. 3.new MT method (II) : Normalization Study • Not only the Shape but also the normalization factor is also altered by SUSY contamination, which can not be negligible even in low mET region and make BG overestimated as shown in this figure. • Normalization factor is obtained in the region of mET=100-115GeV instead of 100-200GeV (Original MT method). (The Contamination can be reduced, we use lower region of mET=70-115 if trigger effect is taken into account correctly.) normalization [mET =100 - 200] contamination of SUSY mET [GeV]

9. 3.new MT method : Estimated Background MET distribution and new estimated Background [1fb-1] With this correction we can obtain the correct distributions for missing ET. This figure shows estimated background of MT>100 GeV region. red dashed : old est red error bar : new Est hatched : truth mET [GeV]

10. 3.new MT method : the other variables These figure shows the other variables reproduced well. Lepton PT 4th Jet PT [GeV] Leading Jet PT Effective Mass [GeV] [GeV]

11. 3.new MT method : other SUSY model SU1 [1fb-1] • This method can be applied not only SU3 point but also various SUSY points. mET [GeV] SUSY 1TeV ( [1fb-1] SU2 [1fb-1] mET [GeV] mET [GeV]

12. 4.Conclusion & Outlook • Conclusion • We applied new MT method to v12 Full simulation Sample. • With this new MT method, the background distribution of interesting region (MT>100GeV region) is correctly estimated. • Outlook • application to [No-Lepton Mode] and [Di-Lepton Mode] • systematic error study if MC-sample is produced.

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14. SUSY point true ratio estimated SU1 : Coannihilation 0.583 0.614 SU2 : Focus Point 0.556 0.684 SU3 : Bulk 0.591 0.612 SU4 : Low Mass 0.687 0.689 The # of SUSY contamination in Control Sample SUSY amount rate between MT>100GeV and MT<100GeV • truth Scale = [SUSY in MT<100GeV] / [SUSY in MT>100GeV] • data driven estimation Scale = #all[MT<100GeV & mET>100GeV] / (2*#all[MT=100-150GeV & mET>200GeV]) • mET>200GeV  to reduce BG (ttlnln) • 2 * [MT=100GeV-150GeV]  MT distribution of SUSY signal is almost flat (MT<150GeV region) ( within 20%) v12 Full ref : v11 atlfast