one lepton mode background mt and new mt method (including systematic errors)

1

The Univ. of TokyoDept. of Physics

One Lepton Mode BackgroundMT and new MT method

(including systematic errors)

SUSY Background meeting (CSC1&2) 27. Nov 2007

Ginga Akimoto , S.Asai, Y.Kataoka, N.KanayaThe University of Tokyo, ICEPP

Dept of Physics

SUSY Background meeting (CSC 1&2) Ginga Akimoto

Table of Contents

1. Update2. Digest of BG estimation 3. Systematic Error Study4. BG estimation with K factor5. Conclusion & Outlook

I have already shown the detail of our method in the previous meeting, so I focus on the systematic errors today.

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I. Update

1. 2nd Lepton (PT>10GeV) veto

2. Effective Mass : add Lepton PT

3. Transverse Mass : add Lepton PT

4. Systematic Error Study of ( lepton efficiency , Enegy Scale, STACO muon selection , MC @ NLO)

5. BG estimation with K factor

Used samples are the CSC full-simulation samples (v12.0.6.5) and systematic error samples (including fast simulation) . [same to previous meeting]In Addition to these , we use ATLFAST alpgen samples to study lepton efficiency.

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II. Bakground Estimation : MT and new MT MethodThis figure shows MT distribution of SUSY(SU3) and background processes, which is calculated with missing ET and Lepton PT. The main background processes are top and W.

1. MT<100GeV : Background ( top &W) enhanced Sample [Control Sample]

2. MT>100GeV : SUSY signal enhanced Sample [Signal Region]

Signal RegionMT>100GeV

ControlSampleMT<100GeV

[MT-Method]

The background distributions of One Lepton Channel are estimated with Control Sample.

(detail has already shown in the previous many meetings.)

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II. Background Estimation (w/o SUSY)

Magenta with error :

estimated BG with C.S.

Black line : (truth) all BG process

(ttbbll dominant)

1. Following figure shows missing ET distribution of background processes (and estimation with original MT method). Magenta line shows estimated background processes with MT method and black line is truth background .

2. # of mET>100GeV and mET>300GeV is also reproduced well.

Truth BG Estimated BG

mET>100GeV 135+/-11 127+/-4 (94+/-7%)

mET>300GeV 9.8+/-3 7.0+/-1 (71+/-24%)

Events number is also well reproduced.

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II Background Estimation ( with SUSY)

Background distributions are overestimated with original MT method as following reasons if SUSY exists. (But SUSY signals are detectable with this method).

1. SUSY contamination in Control Sample distorts the distribution of Control Sample . It makes main discrepancy from truth BG.

2. In addition to the distribution, normalization factors are affected by SUSY contamination, which cannot be negligible even in lower mET region and makes the background overestimated.

To remove these contamination effects.l The distribution of the contamination is estimated with Signal Region.l The amount of the contamination is about 0.7 (times scaled Signal Region).l Normalization factor is obtained in the region of mET=[100-150GeV] in stead o

f mET=[100-200GeV].

1. With these corrections we can estimate the background correctly. (detail has already shown in the previous meetings.)

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III Systematic error study : original CSC sample

This figure shows Missing ET and Effective Mass distribution (truth (black line)& estimated BG with new MT method (red line ) ). With MT and new method we can estimate the background correctly. Statistic Errors and ratio

BG(estimated) over BG( truth ) is following table.

mET Truth BG estimated BG R=Estimated BG /BG

>100GeV 135+/-11 140+/-5 1.04+/-0.08

>300GeV 9.8+/-3 9.91+/-2.34 0.92+/-0.35

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III Systematic Error Study

List of Systematic Error Study1. Energy scale (change mET and Jet PT by +/-5% )

2. Top : LO-> NLO3. STACO muon collection4. Lepton efficiency 2%

We chacked these systematic errors

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III systematic error : Enegy scale x1.05

mET >100GeV mET>300GeV

MT w/o SUSY New MT method MT w/o SUSY New MT method

BG 143+/-12 12.2+/-3.5

BG est. 137+/-3.8 153+/-5 9.4+/-1.1 8.7+/-2.3

R = BG est. / BG 0.96+/-0.08 1.07+/-0.09 0.77+/-0.23 0.71+/-0.27

BG(syst.) / BG (original) 1.06+/-0.13 1.24+/-0.45

R(syst.) / R(original) 1.01+/-0.12 1.13+/-0.14 1.08+/-0.36 1.01+/-0.39

[BG] means real BG.

[BG est] is estimated BG(MT w/o SUSY and new MT with SUSY).

[BG(syst.)/BG(original)] is [BG] difference from original sample.

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III Systematic error : Top (T1) MC @ LO->NLO



BG 277+/-17 26.7+/-5.2

BG est. 238+/-6 244+/-416 10.7+/-1.5 9.15+/-1.9

R = BG est. / BG 0.85+/-0.05 0.88+/-0.05 0.40+/-0.09 0.34+/-0.09


R(syst.) / R(original) 0.90+/-0.08 0.93+/-0.09 0.56+/-0.14 0.48+/-0.14

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III Systematic error: STACO Muon Collection



BG 140+/-11 9.2+/-3.0

BG est. 133+/-4 136+/-5 7.12+/-0.93 6.72+/-1.9

R = BG est. / BG 0.95+/-0.09 1.10+/-0.13 0.76+/-0.26 0.72+/-0.31


R(syst.) / R(original) 1.01+/-0.12 1.10+/-0.13 1.07+/-0.39 1.01+/-0.42

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III Systematic error: Lepton Efficiency (2%)



BG 151+/-12 10.6+/-3.2

BG est. 154+/-3 177+/-4 11.9+/-0.8 13.6+/-1.4

R = BG est. / BG 1.02+/-0.08 1.16+/-0.09 1.12+/-0.35 1.28+/-0.41

These figures show mET and Meff distribution of ATLFAST. We assumed 2% lepton efficiency (Results are next page). Lepton efficiency is negligible (1%).

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III Systematic error :Lepton Efficiency 2% (atlfast)



BG 150+/-12 10.8+/-3.2

BG est. 153+/-3 175+/-4 11.9+/-0.7 13.4+/-1.4

R = BG est. / BG 1.01+/-0.08 1.16+/-0.09 1.09+/-0.34 1.23+/-0.39


R(syst.) / R(original) 1.00+/-0.10 1.00+/-0.12 0.97+/-0.39 0.96+/-0.41

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IV. BG estimation with K factor



BG 261+/-16 17.0+/-4.1

BG est. 246+/-5 256+/-6 11.8+/-0.9 10.6+/-2.3

R = BG est. / BG 0.94+/-0.06 0.98+/-0.06 0.69+/-0.28 0.69+/-0.20


R(syst.) / R(original) 0.99+/-0.10 1.04+/-0.10 0.97+/-0.29 0.87+/-0.30

These K factors are applied .

1. SUSY 1.52. Top 2.023. W/Z 1.244. QCD 2.6

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V. Conclusion

Conclusion & Outlook1. We applied MT / new MT methods to various systematic e

rror sample and study other systematic errors.2. BG estimation with K factor3. In any case SUSY is detectable and estimated background

s are comparatively consistent with statistic errors. These methods are stable against systematic errors.

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Backup

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III Systematic : MT cut 100GeV-->110GeV

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III Systematic : Top ME/PS PT 40GeV->15GeV



BG 196+/-14 10.4+/-3.2BG est. 200+/-4 230+/-6 11.4+/-1.0 12.9+/-2.4

R = BG est. / BG 1.02+/-0.07 1.17+/-0.09 1.11+/-0.36 1.25+/-0.45

BG(syst.) over BG (original) 1.03+/-0.11 0.96+/-0.39

R(syst.) / R(original) 1.02+/-0.10 1.08+/-0.13 1.27+/-0.57 1.35+/-0.73

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III Systematic : Top renormalization scale (x0.5)



BG 316+/-18 16.7+/-4.1

BG est. 322+/-4 368+/-6 15.7+/-1.2 17.8+/-2.0

R = BG est. / BG 1.02+/-0.06 1.16+/-0.07 0.94+/-0.24 1.06+/-0.29


R(syst.) / R(original) 1.02+/-0.09 1.07+/-0.13 1.08+/-0.40 1.15+/-0.48

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III Systematic : W renormalization scale (x0.5)



BG 194+/-14 9.9+/-3.1

BG est. 201+/-4 221+/-6 13.1+/-1.0 14.4+/-2.1

R = BG est. / BG 1.04+/-0.08 1.14+/-0.08 1.32+/-0.43 1.46+/-0.51


R(syst.) / R(original) 1.04+/-0.11 1.05+/-0.12 1.51+/-0.78 1.58+/-0.93

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III Systematic : W ME/PS PT40 - >15GeV



BG 180+/-13 9.7+/-3.1

BG est. 182+/-4 183+/-5 10.4+/-1.0 10.3+/-2.0

R = BG est. / BG 1.01+/-0.07 1.01+/-0.08 1.07+/-0.36 1.07+/-0.40


R(syst.) / R(original) 1.02+/-0.10 0.93+/-0.10 1.23+/-0.56 1.15+/-0.58

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III Systematic : W pythia sample



BG 171+/-13 6.6+/-2.6BG est. 173+/-4 191+/-6 10.6+/-0.9 11.7+/-2.4

R = BG est. / BG 1.01+/-0.08 1.11+/-0.09 1.59+/-0.63 1.77+/-0.78


R(syst.) / R(original) 1.02+/-0.10 1.03+/-0.12 1.81+/-1.25 1.91+/-1.59

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The level of contamination (# of SUSY ratio : [Control Sample] over [Signal Region] ) is assumed to be 0.7 (by MC average from SU1 to SU3 CSC Full). These factors are deferent with each SUSY models by 0.1. So we changed it to 0.6 and 0.8 and applied new MT method.

III Systematic : contamination factor

mET BG truth Estimated BG (default) Estimated BG ( 0.6) Estimated BG (0.8)

>100 189+/-13.7 206+/-6

(1.08+/-0.08)

211+/-6

(1.11+/-0.08)

200+/-6 (1.06 +/- 0.08)

>300 10.7+/-3.2 9.9+/-2.3

(0.92+/-0.35)

12.4+/-2.3

(1.15+/-0.41 )

7.33+/-2.3 (0.68+/-0. 32)

0.6 : we underestimate contamination0.8 :we overestimate contamination

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III Systematic error : summary table of new MT method

Difference between Truth and Est. (mET>300GeV)

Original 19%Energy Scale +5% 26%Contamination amount factor (0.7->) 15%(0.6) 32%(0.8) MT cut 100 -> 110 13%Top W

scale 0.5 original 2%PT 15 original 25%LO -> NLO original 51%original scale 0.5 46%orginal PT 15 7%original pythia 91%

one lepton mode background mt and new mt method (including systematic errors)

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