E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 1

Update on the ZZllbb search

E. NagyCPPM/Fermilab

for the zh-llbb Team

S.B. Beri, S. Caughron, M.-C. Cousinou, S. Desai, S. Dutt, M. Mulhearn, E. Nagy, H. Nguyen,

L. Welty-Rieger, T. Yasuda

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 2

The principal goal of this analysis is to validate the Higgs search ZHll+bb on an existing signal of the same or similar topology:

ZZll+bb (+qq = uu/dd/ss/cc suppressed by b-tag)ZWll+qq’ (qq’ = ud/cs suppressed by b-tag)

WWlv+qq’+l(fake) considered as background

Therefore:Same analysis as the ZHllbb search until the RF training RF training (only Run2b, since Run2a is not retrained) WZ and ZZ considered as signal instead of background

We use collie to assess the signal (exampleLimitCalculation.cc) to evaluate the xsection (exampleXsecMeasurement.cc) with final variables RF (Run2b) and separately Mbb (Run2a+b)

E.Nagy - Low Mass Higgs 8/9/2011

3

Last time (August 4th) we have shown result only on Mbb (Run2a+b)since RF has shown serious miss-modeling in single b-tag (st)

Having applied cuts:MET > 50 GeVΔΦ(Z,jj) > 1.7

the miss-modeling Is largely improved

Today’s Update:• Results using RF (Run2b)• Comparison w/ Mbb (Run2b) and w/ Mbb (Run2a+2b)• Effect of cuts on ZH searchby applying the cuts

Update on the ZZ-->llbb search

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 4

http://www-d0.fnal.gov/Run2Physics/higgs/zh_llbb/d0_private/plots/latest_summer2011/mva/all/1t/

http://www-d0.fnal.gov/Run2Physics/higgs/zh_llbb/d0_private/plots/archive/analysis_v3.15/mva/all/1t/

All plots w/ MET > 50 GeV and ΔΦ(Z,jj) > 1.7 cuts

All plots without the above cuts

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 5

Xsection calculation and fittest on to_collie RF files with:MET > 50 GeVΔΦ(Z,jj) > 1.7

Only Run2b data Prefit BgOnly: Sg+Bg:Data: 1277 1277 1277Bkg: 1235.8 1269.6 1269.4Sig: 42.8 0. 3.7Χ2: 314.6 314.6SigSc: 0.09+/-0.64(stat)

Observation is more background-like butcompatible w/ both signal (1) and no signal (0)

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 6

The SM xsection value (4.8 pb) cannot exclude the b-only hypothesisw/ the present statistics (Run2b)

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 7

Observation:1-CLb = 4.1x10-1

1-CLsb = 9.1x10-1

1-CLs = 0.84

22/|| LLRsbLLRbsbb RMSRMSLLRLLRS

Separation:

S=1.05

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 8

Bg subtracted data vs RF

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 9

Xsection calculation and fittest on to_collie Mbb files with:MET > 50 GeVΔΦ(Z,jj) > 1.7

Only Run2b data Prefit BgOnly: Sg+Bg:Data: 1213 1213 1213Bkg: 1167.1 1206.7 1206.0Sig: 41.8 0. 33.8Χ2: 338 337 SigSc: 0.78+/-0.79 ( 0.56(stat)+/-0.56(syst))

Observation is compatible w/ both bg-like and sg-like

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 10

The RMS values are ~20% larger than in the RF case

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 11

Observation:1-CLb = 2.1x10-1

1-CLsb = 6.7x10-1

1-CLs = 0.58 S = 0.85 (worse than in the RF case)

22/|| LLRsbLLRbsbb RMSRMSLLRLLRS

Separation:

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 12

Bg subtracted data vs Mbb

E. Nagy - General Higgs 4th of August 2011

Status of the ZZ-->llbb search 13

Comparison w/ Run2a+Run2b Mbb analysis (w/o cut)

Same sensitivity (RMS) for the bg-only hypothesis: 2.20 pbSlightly smaller error (RMS) for the xsection: 3.46 vs 3.52 pb

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 14

Effect of MET > 50 GeV, ΔΦ(Z,jj) > 1.7 cuts for low mass Higgs search

MH = 100 GeV

MH = 105 GeV

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 15

Mass Exp. Lim. Obs. Lim.GeV w/ cut w/o cut w/ cut w/o cut100 3.5 3.4 2.3 2.1105 3.8 3.7 2.4 2.5110 4.4 4.2 3.2 3.0115 5.0 4.8 4.3 4.3120 5.5 5.3 5.9 5.5125 6.8 6.5 8.6 8.4130 8.8 8.4 10 8.9135 12 11 15 14140 15 14 22 22145 23 22 32 34150 36 34 48 38

3-5% deterioration of the sensitivity

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 16

Conclusions

Concerning the ZZ/ZW signal:with the present statistics and selection - we cannot rule out the absence of the ZZ/ZW signal expected p-value: 0.07 expected b-only and s+b separation: ~1 st.dev. - the observed signal is compatible with the SM xsection - the expected xsection error is ~60% - the RF final variable results in ~20% better limit

Concerning the ZH search:The study of the ZZ/ZW signal revealed some miss-modeling in the ST RF distributionThis miss-modeling could be mitigated by a simultaneous MET > 50 GeV and ΔΦ(Z,jj) > 1.7 cutThese cuts didn’t change the preliminary limit values however they deteriorated the previous sensitivity by ~3-5%

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 17

Backup slides

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 18

Collie Xsec measurement:

Minimizing the “profile likelihood”(difference of Χ2 for s+b and b-only hypotheses)

wrt the nuisance parameters θk and the xsection scalefactor, f

Nbins

i

Nparams

kk

bkk

bsk

bi

bsii

bk

bi

bsk

bsibbs RRppdpfp ])()([)]/ln()(),([2 2222

di – datapi – predicted number of events = si + bi (signal + background)f = si/si

SM

siSM – predicted signal of the SM in bin i

Rk – prior of θk

E.Nagy - Low Mass Higgs 8/9/2011

Update on the ZZ-->llbb search 19

RF distributions

Run2b1

Run2b23

ST

ST

DT

DT

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Update on the ZZ-->llbb search 20

Mbb/(200 GeV) distributions

ST

DT

ST

DT

Run2b1

Run2b23

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