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PILE-UP studies for H->bb

PILE-UP studies for H->bb. Marek Taševský (Physics Inst. Prague) FP420 meeting - Manchester 10/12 2006. Irreducible background Pile-up. H->bb and H->WW in SM. Both the signal and bg studied at detector level using FAMOS. The following packages used in the analyses:

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PILE-UP studies for H->bb

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  1. PILE-UP studies for H->bb Marek Taševský (Physics Inst. Prague) FP420 meeting - Manchester 10/12 2006 Irreducible background Pile-up

  2. H->bb and H->WW in SM Both the signal and bg studied at detector level using FAMOS. The following packages used in the analyses: - Fastcalorimetry,FastTsim, FastBtag, FastJets, - FastMuon, FastMuonTrigger, FastTotem (just Roman Pots) Jet algorithm: o) Iterative cone, Cone radius = 0.7 o) Jet energy scale corections applied to detector level jets Signal for H->bb composed of two main categories: 1) b-dijets – 85% of signal, challenging channel – topic of the talk 2) muons from B-decays ….. 15% of signal, clean, no problems

  3. Roman Pot acceptances for Totem and CMS

  4. Irreducible bg to H->bb Sources of bg itself without considering PU Generated and fast simulated: 1. DPEMC - Excl. DPE bb (pt>30 GeV): (σ = 520 fb, 60k) 2. DPEMC - Incl. DPE dijets (pt>30 GeV): (BPR model: σ = 30 nb, 170k, CF model: σ = 13.2 nb, 130k) Reduction factor from double b-tag requirement: 500 3. PYTHIA - Non-diff. dijets (30<pt<50): (σ=156 μb, 1 mil.) Jet selection efficiency: 5.6% Reduction factor from double b-tag requirement: 560 4. PYTHIA – Non-diff. dijets (50<pt<80): (σ = 20 μb, 1 mil.) Jet selection efficiency: 24.6% Reduction factor from double b-tag requirement: 310

  5. P(g/b) and P(anything/b) Red. factors from double b-tag are 500, 560 and 310 for Incl. DPE dijets (pt>30 GeV), non-diffr.dijets (30<pt<50) and non-diffr.dijets (50<pt<80), resp. Why the red.factors from double b-tag requirement aren’t close to 104 (corresponding to P(g/b)~1% as expected)? Because in the inclusive dijet processes, there are - gluons + light quark dijets which may be mis-b-tagged - bbbar pairs + other sources of b-jets which are correctly b-tagged • So P(anything/b)~4-5% looks realistic Some rough numbers: P(g/b)~2.5% for εb~55% (CMS) P(g/b)~1.3% for εb~60% (ATLAS) Pythia 6.4 Physics sources of b-jets in inclusive dijet production

  6. Phojet generation of PU events All processes 118 mb Non-diff.inelastic 68 mb Elastic 34 mb Single Diffr.(1) 5.7 mb Single Diffr.(2) 5.7 mb Double Diffr. 3.9 mb DPE 1.4 mb Number of pile-up events per bunch crossing (BX) Ξ NPU = Lumi x cross section x bunch time width x LHC bunches/filled bunches = 1034cm-2s-1x104cm2/m2 x 10-28m2/b x 110mb x 10-3b/mb x 25*10-9s X 3564/2808 ~ 35 5*1033 ~ 17.6 , 2*1033 ~ 7.0, 1*1033 ~ 3.5, 1*1032 ~ 0

  7. PU mixing to S and B for H->bb Generated and fast simulated: 1. PHOJET MB : σ = 118 mb, 200k Prob. to se a proton in one RP per interaction: 420: 1.0%,220: 3.1% - These numbers are crucial for the PU study! Unfortunately, they are model-dependent. Which data to take to tune our MC models??? ZEUS? CDF? 2. PYTHIA – Non-diff. dijets – properly mixed with PU events: NPU 3.5 | 7.0 | 17.6 | 35.0 ----------------------------------------------------------------------------- pt 30-50 50-80 | 30-50 50-80 | 30-50 50-80 | 30-50 50-80 Stat. 3.1 M 2.5 M | 2.5 M 2.4 M | 420k 440k | 428k 399k 3. DPEMC – Excl. DPE bb (pthat>30 GeV), 30k 4. DPEMC – Incl. DPE bb (pthat>30 GeV), 90k

  8. For too eager and too unpatient CDF points just tentative! Just to have a look at what correction factors we might get…. (before KMR come up with their precise calculations…) The main idea from KMR: concentrate on CDF measurement rather than on ZEUS because of closer type of collision and closer Ecm. The xL spectrum expected to be almost Ecm independent between 1.8 TeV and 14 TeV. Still need to check the CDF data…. What about t-ranges of CDF and ZEUS measurements and of Phojet?

  9. CDF measurement of dσSD/dξ Practically no Ecm Dependence for ξ<0.03 and a weak Dependence around ξ=0.1 CDF data may be used for rough estimates

  10. Mix PU events with signal or bg – using FAMOS Sum RP acceptances over all possible proton pairs in all PU events in one BX and then look at mean over all signal or bg events. NPU properly smeared using Poisson dist. E.g. RRP420 = <ΣiNPU(n)ΣjNPU(n) AL420(i)xAR420(j)>n=90k signal or bg events Rate of PU events with 2 p’s seen in opposite 420 RPs Fake rates of protons in RPs

  11. Fake rates Analytical formula for Rate of p pairs seen in opposite RPs per BX: μ = Acc*NPU, μLR = AccLR*NPU NRP/BX(binomial) = 2*exp(-μ)*[cosh(μ) – 1] + 1 – exp(-μLR) Courtesy NRP/BX(simple) = NPU*(NPU-1)*Acc*Acc Sasha Kupčo (Prague) L3 = (NRP/BX)/Q, Q = red.fact.from quartic det. based on σt=10 ps Q ~ 30 for 220 and 420, for NPU = 3.5 ~ 13 for 220 and 23 for 420, for NPU = 35

  12. Selection cuts for H->bb at mh=120 GeV

  13. Control plots Excl.DPE H->bb Incl.DPE dijets Non-diffr.dijets + PU 35

  14. Effect of PU on DPE processes Event yields for Lumi = 30 fb-1: Excl. DPE H->bb: practically immune to PU Excl. DPE bb NPU 0.0 | 3.5 | 7.0 | 17.6 | 25.0 | 35.0 ---------------------------------------------------------------------------------- conf 420 comb|420 comb|420 comb|420 comb|420 comb|420 comb ---------------------------------------------------------------------------------- 1 8 | 2 8 | 1 6 | 2 6 | 2 6 | --- --- Incl. DPE dijets(BPR model): Red.factor from double btag: 500 NPU 0.0 | 3.5 | 7.0 | 17.6 | 25.0 | 35.0 ---------------------------------------------------------------------------------- 20 100|20 80 | 70 30 | 230 170 | 200 270 |--- --- Incl. DPE dijets (CF model): Red.factor from double btag: 500 6 8 | Large model dependences for Incl.DPE dijets. New H1 data on diffr.pdf may lower the effect even further

  15. Consistency checks Andy’s results from last FP420 meeting at CERN

  16. Consistency checks Nev for Lumi = 30 fb-1 Andy: This analysis Excl.DPE H->bb1.6 0.6 Excl.DPE bb 3.0 1.0 Excl.DPE gg 2.4 -- Incl.DPE bb 2.4 -- Incl.DPE dijets 0.015 6.0

  17. Non-diffr. Dijets + PU NPU 3.5 | 7.0 | 17.6 | 35.0 ------------------------------------------------------------------------------------------------- pt 30-50 50-80 | 30-50 50-80 | 30-50 50-80 | 30-50 50-80 Stat. 3.11 m 2.52 m | 2.46 m 2.39 m| 420k 440k | 428k 399k ------------------------------------------------------------------------------------------------- Scaling 67.2 19.2 | 85.0 20.2 | 497.4 110.0 | 488.2 121.0 ------------------------------------------------------------------------------------------------- All cuts 420|comb|420|comb||420|comb|420|comb But c10 1.0|0.0|0.9|4.3|| 2.0|2.2|1.0|5.4||3.0 | 0.3 | 1.0| 7.5 || 15.0| 9.0| 7.0 | 10.9 ------------------------------------------------------------------------------------------------- Reduction from double b-tag: 560 (30<pt<50) and 310 (50<pt<80) Reduction from quartic:~40 Nr.of surviving events per L=30fb-1: 70| - |20|80||170|190|20|110||1500|130|110|830||7300|4400|850|1300 170 || 490 || 2600 || 13900

  18. Cuts flow - efficiencies Signal | BG Pythia NPU= 0.0 -------------------------------------------------- pt | 30-50 50-80 Stat. 10k | 1.0m 0.96 m --------------------------------------------------- Jetcuts 34.2% | 4.4% 18.3% --------------------------------------------------- 2 btag 36% | 0.18% 0.32% --------------------------------------------------- RP acc 420 | comb | 32%| 25% | 0 0 --------------------------------------------------- All cuts 1% | 1.6% | 0.0 0.0 NPU 3.5 | 7.0 | 17.6 | 35.0 ----------------------------------------------------------------------------------------------------------------------------------------- pt 30-50 50-80 | 30-50 50-80 | 30-50 50-80 | 30-50 50-80 Stat. 3.11 m 2.52 m | 2.46 m 2.39 m | 420k 440k | 428k 399k ----------------------------------------------------------------------------------------------------------------------------------------- Jetcuts 4.8% 18.2% | 5.3% 18.2% | 6.1% 17.7% | 5.6% 15.6% ----------------------------------------------------------------------------------------------------------------------------------------- 2 btag 0.18% 0.32% || 0.18% 0.32% || 0.18% 0.32% || 0.18% 0.32% ----------------------------------------------------------------------------------------------------------------------------------------- RP Acc 0.3%|1.4%|0.3% | 1.4%|| 0.8% |3.7%| 0.8% | 3.7%|| 3.3% | 15.3%| 3.3% | 15.3%|| 10.1% | 38% | 10.1% | 38% ----------------------------------------------------------------------------------------------------------------------------------------- All cuts 1E-2|0.0 |1.5E-3|7E-4 ||4.3E-3|6E-4|4.6E-4|3.1E-4||4.7E-3|7.1E-5|3.3E-4|4.4E-4||5.2E-3|5.1E-4|8.3E-4|2.1E-4 but c10 ------------------------------------------------------------------------------------------------------------------------------------------ Timing 2.5% everywhere

  19. S/B for Lumi = 30 fb-1 ||3.5 || 7.0 || 17.6 || 35.0 --------------------------------------------------- Jetcuts ||19.2/33.3E10 || 19.2/35.7E10 || 19.2/39.2E10 || 19.2/35.6E10 ---------------------------------------------------------- Jetcuts || 6.4 / 7.5E8 || 6.4 / 8E8 || 6.4 / 8.5E8 || 6.4 / 7.7E8 +2btag || || || || ---------------------------------------------------------- ||420 |comb || 420 | comb || 420 | comb || 420 | comb --------------------------------------------------- Jetcuts || 2.1 | 1.6 || 2.1 | 1.6 || 2.1 | 1.6 || 2.1 | 1.6 +2btag || / | / || / | / || / | / || / | / +RP ||2.3E6 |10.5E6||5.4E6 | 29.6E6 || 28E6 |130E6 ||77.8E6 | 293E6 ---------------------------------------------------------- All cuts || 0.6 / | 0.9 /|| 0.6 / | 0.9 / || 0.6 / | 0.9 / || 0.6 / | 0.9 / +timing || 85 | 80 || 190 | 300 || 1600 | 970 || 8200 | 5700 ----------------------------------------------------------

  20. Multiplicity cuts at detector level • A very preliminary look at multiplicity cuts at det.level (ATLFAST): • Kt jet alg., ET,jet1,2 > 40 GeV, |ηjet1,2|<2.5, |Δηjet|<1.5, 170°<|ΔΦjet|<190° • - pT,track > 0.5 GeV, |ηtrack|<2.5 • Arbitrary normalization • Nc – Nr. of tracks outside cones of R=0.5, 0.7, 1.0 around axes of two lead. jets • Ncperp – dtto + perp. to jet axes (π/3<|Φjet-Φtrack|<2π/3, 4π/3<|Φjet-Φtrack|<5π/3) • Excl.DPE H->bb Non-diffr.dijets Looks promising By V.Juranek

  21. Summary of PU effect in H->bb channel - PU has no effect on signal. - PU has a little effect on jets. - The main effect comes from fake protons in RPs overlaied with hard jets from dijet events. We need to reduce BG by a factor of 100 to keep S/B~1. BUT! RESULTS ARE NOT FINAL! There are a few big uncertainties in this study! • New H1 Pomeron pdfs: lower pdf at high z -> lowers Incl.DPE contrib. • One-sided RP acceptance for PU events (1.0% for 420, 3.1% for 220) Phojet not tuned for Ecm=14 TeV 3) B-tagging: P(g/b) quite large (in CMS). 4) The same JES factors taken for all lumi. Should be lumi-dependent. 5) Particle multiplicity outside jets – is it as effective as at hadron level?

  22. B A C K U P S L I D E S

  23. SM Excl.DPE H->bb: Mh dependence Masses beyond 120 GeV not interesting in SM but in MSSM (x-sections may be increased by a factor of upto 40 in some mA,tanβ regions for some scenarios). Mass windows (ΔM) used only for S/B studies. Two window widths used: narrower for (420+420) and broader for combined RP configs. Mh=120: σ420=1.6%->ΔM=4GeV and σcomb=5.6%->ΔM=10GeV. S/B(ΔM): S=Excl.DPE H->bb, B= Excl.DPE bb + Incl.DPE bb S=ExHuMe 1.3.1, B=DPEMC 2.4 Effect of PU: Signal immune Excl.DPE bb mutiplies by factor 2 indep.of Lumi Incl. DPE bb increases by 2,4,11,19,21 for NPU=3.5,7.0,17.6,25.0,35.0, respectively

  24. Consistency checks Study of Andy Pilkington: S/B ~1.8 at L=2*10^33 (NPU=7) and 420+420 My study: S/B~1/100 at L=2*10^33 and 420+420 Differences between the analyses: Andy: • looks only at HW generator level (I use Py det.level) • uses the simple quadratic formula for fake rates of protons. at the lumi of interest, this means a factor 2 to the real fake rates 2) uses only bb-dijets for non-diffr.bg and assumes double b-tag eff. = 36%. The latter is OK but one should take inclusive dijets and consider all sources of b-jets there (g->bb…) and consider also misidentification of c-jets as b-jets. 3) applies a multiplicity cut and sees a 99% rejection power to bg and only 10% loss to signal. He claims the multiplicity depends on soft underlying event tuning (it’s different between HW and Py)

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