1. The Univ. of Tokyo Dept. of Physics Back Ground Estimation One Lepton Mode 31 Aug 2007 Ginga Akimoto

2. Dept of Physics Table of Contents  normal BG estimation (case :no SUSY & SUSY)  Causes of BG deviation  corrected BG-estimation method

3. Dept of Physics Back Ground Estimation ( case : no SUSY ) BG[Signal Region (MT>100)] shows close similarity to the shape of BG[Control Sample (MT<100)]. estimated BG,which is scale- converted BG[CS] (normalized by # of (mET=100-200)) is the same by 10% as BG[SR].

4. Dept of Physics Back Ground Estimation (case : existence of SUSY(SU3)) the case SUSY exists -> we can discover surplus events (SUSY signal) by this method.  Control Sample = Background dominant & similar to BG[SR]  Signal Region (low mET) = assume BG-dominant -> decide normalization constant (region:mET=100-200)  red marker: estimated BG, bold black line: Signal(=BG+SUSY) shaded area: Real BG, bold blue line: SUSY events somewhat overestimate BG (differ by about factor 2-3)

5. Dept of Physics Causes of BG deviation Control Sample[CS] includes measurable SUSY events  [CS] #SUSY < 0.1*#BG (mET=overall)  but #SUSY ～ #BG (mET>200)  overestimate : factor 2 to 3 normalization constant (mET=100-200)  [CS] #SUSY <0.1*#BG but [SR]  #SUSY ～ 0.5*#BG  overestimate : +50% >detail next pages

6. Dept of Physics Deviation : CS includes measurable SUSY. We use Sig[Control Sample (MT<100)] as Background dominant sample, but Sig[CS] includes considerable SUSY events.  [CS]: #SUSY < 0.1*#BG (overall)  but (mET>200) #SUSY is comparable to #BG  BG vs Sig : differ by a factor of 2-3 (large mET)

7. Dept of Physics BG Deviation : normalization constant We regard #(Sig[SR])/#(Sig[CS]) at mET=100-200 as the ideal normalization constant : #(BG[SR])/#(BG[CS]),but  Control Sample[CS] : #(SUSY)<<#(BG) so #(Sig)=#(BG)  Signal Region [SR] : #(SUSY) ～ 0.5*#(BG) <- not negligible

8. Dept of Physics Correction of estimated BG correction of normalization constant  close a observable value #(Sig[SR])/#(Sig[CS]) to the ideal normalization constant #(BG[SR])/#(BG[CS])  shift matching region lower: #(mET=100-200) -> #(mET=100-115) (we will #(mET=70-110),but yet)  -> minimize #(SUSY)/#(BG) @ Signal Region [SR] correction of Control Sample[CS] (remove SUSY events) BG[CS] = Sig-SUSY[CS] ～ Sig-α*Sig[SR] SUSY[CS] and SUSY[SR] are similar. SUSY[CS]=α*SUSY[SR] the factor α is # of SUSY ratio :α=#(SUSY[CS])/#(SUSY[SR]) (large mET region) Sig[SR]=SUSY + BG ～ SUSY (small mET region) Sig[SR](includes BG)<<Sig[CS] direct contribution of BG[SR] to BG[CS] : negligible

9. Dept of Physics Estimation of the SUSY ratio α = #(SUSY[CS])/#(SUSY[SR])  #SUSY[CS] = 2*#SUSY[MT=100-150] (more precisely ～ -10% )  #SUSY[CS]/#SUSY[SR] ～ #SUSY[CS*]/#SUSY[SR] ( ※ Control Sample prime [CS*]=2*(1.1)*#(100-150) ) #SUSY[CS*]/#SUSY[SR] ～ #Sig[CS*]/#Sig[SR] <-Observable value  only integrate mET>200 : to reduce effect of BG(tt->bblnln)  α= #(SUSY[CS])/#(SUSY[SR]) ～ #Sig[CS*]/#Sig[SR](mET>200) #(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 Transverse Mass (MT)

10. Dept of Physics ideal α vs estimated α SUSY[CS]=(#SUSY[CS]/#SUSY[SR])*SUSY[SR] ～ α*Sig[SR] ideal α #SUSY[CS]/#SUSY[SR] (mET=overall) estimated α #Sig[CS]/#Sig[SR]@(mET>200) <-Observable mSuGra modelideal αestimated α SU1 : Coannihilation0.5830.614 SU2 : Focus Point0.5560.684 SU3 : Bulk0.5910.612 SU4 : Low Mass0.6870.689

11. Dept of Physics Estimated BG : Corrected Control Sample  red marker : estimated Background  red line : real Background(=BG[CS])  bold black line : Sig(=BG+SUSY)[CS] mET ( Control Sample )

12. Dept of Physics Corrected Control Sample (other physical quantities) use the same α derived from mET & estimate BG=Sig-αSig[SR] Leading Jet PT Lepton PT # of Jet

13. Dept of Physics Corrected BG estimation using estimated new BG[CS] and new normalized constant, we estimate BG of Signal Region[SR]. red marker : new BG estimation, shaded area: real BG, green line : old BG estimation,

14. Dept of Physics SUSY(mSuGra) model dependence (mET) SU3 : Bulk SU1 : CoannihilationSU2 : Focus Point SU4 : Low Mass

15. Dept of Physics Error and applicable range of this method large deviation at SU4(Low Mass) -> mainly normalization constant: even in new normalization region (mET=100-115), Control Sample includes substantial SUSY events.->needs another method. Other Points -> model uncertainty and error of α (at least 10%), similarity between CS and SR(10%), normalization constant (less than 15% and can reduce it) SU4 : Low Mass

16. Dept of Physics Conclusion  Control Sample method : overestimate Background by factor 2 to 3  We can estimate Background of Signal Region (MT>100) (about 20% ～ accuracy) by means of Corrected Control Sample.  uncertainty of this method is normalization the SUSY ratio α estimation.(large Xsec SUSY(cf.SU4) cases -> error of normalization constant )