Update on ttbar background

Data in CR= 2mu+2j50+T6>0.05modelled in MC by sum of all SM backgrounds + SUSY with CR cuts

Background ETmiss shape in Signal Region b(ETmiss)

modelled in MC by sum of all SM backgrounds

b(ETmiss)

100 GeV

2mu+2j50background only

c(ETmiss)

2mu+2j50+T6>0.05a(ETmiss)=b(ET

miss) +s(ET

miss)

Data in 2mu+2j50 signal + backgroundcontains signal and backgroundmodelled in MC by sum of all SM backgrounds + SUSY

b(ETmiss) is shape for the

backgrounds(ET

miss) is shape for the signalin 2mu+2j50

Same shape of ETmiss b/w bkg CR and SR <=> b(ET

miss)=k c(ETmiss) Need

to find kAll events in mu2+2j50a(ET

miss)=b(ETmiss) + s(ET

miss) and k = b(ETmiss) / c(ET

miss) but we do not have b(ET

miss)

If s(ETmiss)<< b(ET

miss) in a certain region NR (normalisation region) then for ETmiss

in NR a(ET

miss) ≈b(ETmiss) and

k = a(ETmiss) / c(ET

miss) ≈ b(ETmiss) / c(ET

miss) in NR k ≈ ∫ b(ET

miss) dETmiss / ∫ c(ET

miss) dETmiss integration over NR

OBSERVABLE DISTRIBUTIONS a(ETmiss ) and f(ET

miss)

NOT DIRECTLY OBSERVABLE b(ETmiss)

b(ETmiss) / c(ET

miss) = k => verify by plotting total background divided by

ETmiss in CR

s(ETmiss) / b(ET

miss) << 1 in NR => verify by plotting s(ETmiss) / b(ET

miss)

What are the approximations being made?

Exact equations

a(ETmiss)=b(ET

miss) + s(ETmiss)

k (1+ε(ETmiss)) = b(ET

miss) / c(ETmiss)

Formula effectively used: k = ∫ a(ETmiss) dET

miss / ∫ c(ETmiss) dET

miss over NR k = ∫ (b(ET

miss) + s(ETmiss)) dET

miss / ∫ c(ETmiss) dET

miss o=> Presence of signal in the NR leads to overestimate of k

Nbkg,SR = ∫SR

b(ETmiss) dET

miss

= k ∫SR

c(ETmiss) (1+ε(ET

miss) dETmiss

= k ∫SR

c(ETmiss) (1+ε(ET

miss) dETmiss

= k ∫SR

c(ETmiss) dET

miss + k ∫SR

c(ETmiss) ε(ET

miss) dETmiss

≈ k ∫SR

c(ETmiss) dET

miss

Size of the approximation due to shape assumptionNbkg,SR - k ∫

SR c(ET

miss) dETmiss = k ∫

SR c(ET

miss) ε(ETmiss) dET

miss

2mu + 2j50 CR= 2mu + 2j50 + T6 > 0.05

NR = 2mu + 2j50 + 60<ETmiss<80< GeV

SR = 2mu + 2j50 + ETmiss > 100 GeV

10pb-1 7 TeV

b(ETmiss) / c(ET

miss) = k => verify by plotting total background divided

by ETmiss in CR

Control Sample

At least 1 solution

T6> 0.10 T6> 0.05

CR statistics 25.5 29.2 30.1

T6> 0.10

T6> 0.05

Background shape from CR/ True background shape

ETmiss spectrum from CR is harder than for real backgroundif there is indeed SUSY, due to SUSY contamination.

At least 1 solution

At least 1 solutionNO SUSY

if no SUSY b(ETmiss) / c(ET

miss) = k is a very good approximation

In presence of SUSY, ETmiss spectrum from CR is harder than for real backgroundif there is indeed SUSY, due to SUSY contamination.

b(ETmiss) = ET

miss for background only c(ET

miss) = ETmiss in control region

Problem with statistics in CR @ 10pb-1

Control Region: T6> 0.10

Expect less than 1 eventin the useful region with ET

miss>100 GeV Useless=> Either find a different approach or looser cuts.

Signal Region

Normalisation Region

SU4 fraction in NR

SU4

NR=60 < ETmiss < 80 GeV

Normalisation Region

Number of events 10pb-1

SU4 fraction

Comment

60 < ETmiss < 80

GeV2.0 32%

40 < ETmiss < 60

GeV2.7 22.5%

20 < ETmiss < 40

GeV8.3 4% Using Z->mumu number of events to

normalise ttbar ETmiss spectrum-> overestimate. M(mu,mu) mass cut?

Results Based on previous slides chooseNR=40 < ET

miss < 60 GeVCR= 2mu + 2j50 + T6 > 0.05

Results 10pb-1 Based on previous slides chooseNR=40 < ET

miss < 60 GeVCR= 2mu + 2j50 + T6 > 0.05

If SUSY contaminationof NR and CR lead to overestimateof background, poorer exclusion limit

If no SUSY => excellent bkg prediction

SU4

A quick look at supersoft cuts @ 7 TeV 10pb-1

Cut Signal Bkg EFF S/√(B) med[ZW] Nmax σ95(pb) FOM Opal

----------------------------------------------------------------------------------------------------------------------------------

mu2_2j50_met100 2.8094 1.5435 0.0059 2.2613 1.8459 3.9485 67.2 676.2

mu2_mz_1j30_1j20_met30 5.3055 12.8320 0.0111 1.4811 1.3934 8.2491 74.3 729.5

mu2_1j100_1j50_met100 2.5451 1.0672 0.0053 2.4637 1.9284 4.0681 76.4 695.1

mu2_mz_2j20_met30 5.3545 13.0703 0.0112 1.4811 1.3941 8.8498 79.0 728.6

mu2_2j20_met30 5.7167 18.8571 0.0120 1.3165 1.2572 9.7251 81.3 802.5

mu2_1j30_1j20_met30 5.6677 18.3854 0.0119 1.3218 1.2614 9.8994 83.5 800.3

mu2_3j50_met100 1.5858 0.5554 0.0033 2.1279 1.6147 3.0093 90.7 1019.6

mu2_1j100_2j50_met100 1.4781 0.4610 0.0031 2.1770 1.6171 3.0062 97.2 1073.8

med[ZW] : Discovery significance G.Cowan, E. Gross, Stat. Forum December 2nd 2009 Eq.23

better approximation than S/√(B)

Nmax : median 95% CL upper limit on the number of signal events in SR

σ95 : 95% CL upper limit on signal cross section given "Asimov dataset"

FOM Opal : approximate FOM related to maximum possible number of signal events in SR

follows Nmax

Still no systematics included

mu2_1j30_1j20_met30

At least 1 ttbar solution

Normalisation region 2mu 1j30 1j20 20<MET<40 - should be 20-30 GeV ...

Composition of normalisation region

------------------------------------------------------------------Nevents in background region (MC) = 2.76907Nevents in background region (from CR prediction) = 3.2448Nevents in control region = 129.301Nevents in normalisation region = 26.496------------------------------------------------------------------

------------------------------------------------------------------Nevents in background region (MC) = 1.54353Nevents in background region (from CR prediction) = 0.519253Nevents in control region = 25.6899Nevents in normalisation region = 2.69708------------------------------------------------------------------

Soft Cuts (mu2_1j30_1j20_met30) mu2_2j50_met100

Outlook

Complete ttbar bkg with supersoft cuts and mZ cuts

Include systematics for ttbar background in FOM

Include other ballpark systematics in FOM Conclude on ttbar background at 10pb-1

Conclude on cuts for 10pb-1 analysis

Discussion ongoing concerning a softer SUSY model