1 / 42

Comparisons between Diphox/ResBos/Pythia for gg bkg & signal at LHC/ATLAS

Comparisons between Diphox/ResBos/Pythia for gg bkg & signal at LHC/ATLAS. Signal Background Reducible Irreducible significance. Eurogdr Supersymmetry workshop on SM Backgrounds http://lyoinfo.in2p3.fr/gdrsusy05/. Marc Escalier, LPNHE Paris, 13-14 octobre 2005. ATLAS and CMS at LHC.

bess
Download Presentation

Comparisons between Diphox/ResBos/Pythia for gg bkg & signal at LHC/ATLAS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Comparisons between Diphox/ResBos/Pythiafor gg bkg & signal at LHC/ATLAS • Signal • Background • Reducible • Irreducible • significance Eurogdr Supersymmetry workshop on SM Backgrounds http://lyoinfo.in2p3.fr/gdrsusy05/ Marc Escalier, LPNHE Paris, 13-14 octobre 2005

  2. ATLAS and CMS at LHC • very high energy accelerator : pp √s=14 TeV • interaction rate: 40 MHz • inelastic cross section: σpp=70 mb • luminosity: (2x)1033 cm-2s-1 1034 cm-2s-1 • per year: 10 fb-1 100 fb-1 • 1 year of LHC at 1033 cm-2s-1~10 years at prev. machines • big detectors Detectors optimised for Higgs boson and SUSY searches ATLAS: 25 m x 46 m CMS: 15 m x 21.5 m first collisions in Summer 2007

  3. Constraints on Higgs mass • High constraints • Unitarity (WLWL diffusion) • Triviality • Low constraints • vacuum stability mH<700 GeV mH<750 GeV mH>139 GeV (mt=178,1 GeV) (L=1016 GeV) mH>74 GeV(L=1 TeV) l>0 • Experimental constraints • direct research at LEP: • mH>114.4 GeV (95% CL=2s) • indirect research: • global analysis of electroweak measurements (sensibles to mH) • mH=126+73-48 GeV, MH<280 GeV winter 2005 uncertainty on mH The Hgg channel

  4. Signal To discuss what is background, we have to discuss what is signal significance if S>5 signal >5 x error on background P(bck fluctuates > 5 s)=10-7 discovery

  5. Higgs production at LHC VBF - Opening of Htt MH(GeV) - - W/Z H associated production assoc. prod. ttH, bbH Dominant channel over the whole range of MH :ggH VBF and assoc. prod. : distinct signatures↑S/B, ↓statistics

  6. Higgs decay at LHC • MH<140 GeV: • dominant decay mode bb and tt • overwhelmed by bck (inclusive) • s(ggHbb)~20 pb; s (bb)~500 µb • Accessible channels : • ttH(Hbb), VBF (Htt) • rare decay mode Hgg • cleaner signature, inclusive production - - - LEP • 140<MH<180 GeV • WW* and ZZ* channels have significant BR • HZZ* 4l  good mass reconstruction possible, but low stat. HWW*lnln  either inclusive or VBF production (better S/B) 2mW 2mt • MH>180 GeV • HZZ4l  gold-plated channel « easy »

  7. Signal Direct production dominant Associated production WH, ZH, ttH

  8. Tools available for signal • ggH • LO • Pythia • NLO: K=sNLO/sLO=1.8 • HiGlu (cross section only) • ResBos (MC events) • NNLO (Anastasiou et al.), prog FEHiP • hep-ph/0501130, www.phys.hawaii.edu/~kirill/FEHiP s (mb) production from Pythia Higgs production (eg: 120 GeV) LO NLO NNLO KNLO=1,76 (HiGlu: 1,8) KNNLO=1.16 • VBF • HiGluK=1.04 • +BR corrections HDecay (NLO)

  9. Uncertainty signal ~40 % Need data (bck) To better understand KSV=Kulesza, Sterman, Vogelsang, CTEQ6M RSVN=Ravindran, Smith, Van Neerven, CTEQ6M BCFG=Bozzi, Catani, De Florian, Grazzini, MRST2002

  10. Study mass resolution of Hgg • Parameters for analysis • photons cuts: PT(1)>40 GeV, PT(2)>25 GeV • |h|<2.4, exclude transition region at |h|=1.45 • f corrections • clusters sizes (TDR): EMB:3x7:conv., 3x5 non-conv., EC :5x5 • calibration • constant term 0.6 % • vertex correction: • low lumi: vertex z : inner detector • truth+smearing s=40 µm • high lumi: vertex z : elmg clusters • Resolution : 2 cm

  11. Resolution obtained

  12. Reducible background 20 millions > signal s jets quarks ~10>jets gluons • g+jet Partonshadrons (« jets ») • jet+jet 58 % jet gluon 4.7 % jet quark 37.3 % mixture

  13. g/jet separation f h Full simulation of detector Some examples g jets Hadronic leakages h (3x7/7x7) f (3x3/3x7) elmg calo 2nd layer HCAL f h Width h (3x5) 2ème max. min-2nd max Elmg calo 1er layer +1st layer: (width 40 strips, 3 strips, % E outside hearth shower) Goal: efficiency 80 %, R=5000

  14. Efficiency for photons |h| ET

  15. Jets rejection PT>25GeV ~3 • all jets: • R~6680 • quarks jets • R~2880 • gluons jets • R~20650 p0=70 % remaining events

  16. Irreducible background • Bremsstrahlung (correction to Born) • Born(aQED2) • Box gggg (as2aQED2) NLO computations NLO: cross-sections, scale dependence, final state PT ~10 > signal Diphox *NLO Born+brem w/o resum. *LO Box Eur. Phys. J. C 16,311-330 ResBos *NLO Born+brem w/ resum. *NLO Box w/ resum. Phys. Rev. D 57, 6934-6947,1998 [hep-ph/9712471] Pythia distributions Mgg (GeV)

  17. fragmentation

  18. Resummation Factorisation theorem Partonic cross-section long distance physics (pdf) At NLO, divergent terms as log PT/Q PT<<Q collinear and infrared divergences isolation cone for photon (eg:R=0.4 ET<15 GeV)

  19. Background with ResBos • P « Perturbative » contains all terms (divergent terms also) • A « Asymptotic » contains divergent terms only • W contains resummed « divergent terms » • W+P-A, but resummation not valid at high PtsmoothingfW+P(+F)-fA PTgg Born construction fW+P(+F)-fA Smoothing of background Frag=fragmentation PT(gg) PT(gg) ResBos not easy to use: need 3 distributions to have one physical distribution

  20. ResBos included Feynman diagrams

  21. Born+brem No resummation in Diphox Phase space cut in PT Regularization of divergent terms better fragmentation in Diphox Mgg (GeV) PTgg (GeV)

  22. Box Bern, Dixon, Schmidt NLO ResBos NLO Diphox (LO) Bern, Dixon, Schmidt LO

  23. Events at LHC for 120 GeV and 30 fb-1 Diphox is scaled by 1.6 to take into accound NLO of box Gives an uncertainty of 5 %

  24. Parton shower problem of Pythia News from Pythia 6.3 « contains a completely new multiple interactions model, with new transverse-momentum-ordered showers for initial- and final-state radiation » To have backward compatibility: PYEVNT (old) and PYEVNW (new) http://www.thep.lu.se/~torbjorn/Pythia.html Hep-ph/0408302: transverse-momentum-ordered showers and interleaved multiple interactions

  25. Comparison data/simulations Diphox suffers infrared divergence in the « qT » (PTgg) distribution ResBos resums effects of soft and/or collinear gluon emissions to all orders, predicts a smooth qT distribution.

  26. Invariant mass Mgg at CDF, run II w/ gg contribution wo/ gg contribution 207 pb-1 NLO Diphox Pythia contrib x 2 R. Blair, R. Culbertson, J. Huston, S. Kuhlmann, Y. Liu, X. Wu http://yliu.home.cern.ch/yliu/diphotonReBlessed_30Jan_2004/diphoton_reblessed.html

  27. Transverse momentum of pair qT=PTgg ≠scales may give 10% effect • ResBos < Diphox • BUT • Old version of ResBos • (since NLO box included) Pythia contrib x 2 • What about high PT ? • need more statistics R. Blair, R. Culbertson, J. Huston, S. Kuhlmann, Y. Liu, X. Wu

  28. DFgg Pythia contrib x 2 R. Blair, R. Culbertson, J. Huston, S. Kuhlmann, Y. Liu, X. Wu

  29. Details of values Mgg qT=PTgg DFgg http://yliu.home.cern.ch/yliu/diphotonReBlessed_30Jan_2004/April25_2004/numbers.ps

  30. background is not so well constrainted: • -resummation important to have a well description of high PT • -difficult to have same parameters for the comparisons • -need update comparisons background/data at Tevatron with • *new version of ResBos, *more statistics (used 200 pb-1 so far…) • *new version of Pythia (new parton shower) • *take same theoretical assumptions (scales, pdfs, order of the pert. devel.) • need manpower

  31. Significance ↑50 % (NLO) 100 fb-1

  32. Likelihood ratio method - qq et qg have fermions exchange in t channelg angles lower than those of Higgs boson (isotropic in q) Significance: 120 GeV, 30 fb-1: 6.24likelihood:9.24

  33. Conclusion • First years of LHC are near : summer 2007 ? • SM Higgs may be discovered in first years of operation with Hgg • Need understanding of systematics • Use data for • detector performance understanding • validation of pdf for cross-sections • validation of MC tools • More information • M. Escalier, F. Derue, L. Fayard, M. Kado, B. Laforge, C. Reifen, G. Unal • Search for a Standard Model Higgs boson in the ATLAS experiment on the H  gamma gamma channel, ATL-COM-PHYS-2005-054 • M. Escalier, F. Derue, L. Fayard, M. Kado, B. Laforge, C. Reifen, G. Unal, Photon/jet separation with DC1 data, ATL-COM-PHYS-2005-048 • M. Escalier, B. Laforge (dir.), Recherche expérimentale de la brisure spontanée de symétrie électrofaible dans le canal H \to \gamma \gamma et d'une solution au problème de hiérarchie dans ATLAS. Participation à la préparation de l'électronique du calorimètre électromagnétique, 2005 Paris : Paris 11, CERN-THESIS-2005-023

  34. Appendix

  35. Rumour on Diphox

  36. Correlations entre variables

  37. g/jet separation (II) Inner detector p0 g • track veto • Non converted g • request : no tracks with PT>5 GeV in DR=0.2 • Isolation • request: SPT tracks in [0.1<DR<0.3] <4 GeV low lumi. • <10 GeV high lumi. • goal • efficiency 80 % • R=5000

  38. The Higgs mechanism solution : new field fPredict existence of a scalar boson V(|f|) f=v+c (µ2<0) non sym. v≠0 v |f| • bosons get a dynamical mass : sym +interaction H-(W; Z) r=MW/MZcos qW=1 • fother mechanism for fermions

  39. Constraints on Higgs mass • High constraints • Unitarity (WLWL diffusion) • Triviality • Low constraints • void stability mH<700 GeV mH<750 GeV mH>139 GeV (mt=178.1 GeV) (L=1016 GeV) mH>74 GeV (L=1 TeV) l>0 • Experimental constraints • direct search at LEP: • mH>114.4 GeV (95% CL=2s) • indirect search : • Global analysis of electroweak measurements • mH=126+73-48 GeV, MH<280 GeV hiver 2005

  40. SM Discovery potential Almost all allowed mass range explored in 1st year (10 fb-1) for ATLAS-CMS With 30 fb-1, more than 7 s for the whole range (provided systematics on the background are under control)

  41. Higgs search in the Hgg channel low masses (80-150 GeV) g p p H g Very rare decay (BR~10-3), σ(ppH115)xBr(H→)=76 fb (NLO), S/B~0.05 bck:irreduciblegg continuum, reducible: g-jet and jet-jet Keys: excellent energy and angular resolutions excellent g efficiency, jet rejection high granularity and response uniformity LAr (ATLAS), PbWO4 (CMS) GH width negligible, resolution dominated by detector σ(m)/m≈1% NLO tools available for signal and bck. PT improve these results CERN/LHCC 96-40 ATLAS TDR 1 CERN/LHCC 96-41 ATLAS TDR 2 CERN/LHCC 97-33 CMS TDR 4 bck from sidebands

  42. Reducible background after rejection

More Related