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Status of Invisible Higgs Study

Sunil Bansal, Prof. Kajari Mazumdar, Prof. Jasbir Singh. Status of Invisible Higgs Study. Overview: Introduction First look using CMSSW Estimation of ttbar background. HLT Exercise : Signal Efficiency for Jet + MET trigger Background Generation Conclusions and Plans. Introduction.

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Status of Invisible Higgs Study

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  1. Sunil Bansal, Prof. Kajari Mazumdar, Prof. Jasbir Singh Status of Invisible Higgs Study • Overview: • Introduction • First look using CMSSW • Estimation of ttbar background. • HLT Exercise : Signal Efficiency for Jet + MET trigger • Background Generation • Conclusions and Plans. INDIA-CMS meeting, BARC 20-21 July,2007

  2. Introduction • Invisible decays of the Higgs Boson do not play any role in the Standard Model. • Discovering them would be clear indication of physics beyond the Standard Model. • Many models with invisible decays: 4th Generation Neutrino Extra Dimensions SUSY Littlest Higgs Model … . . • Different models give very different branching ratio to invisible decay mode vs. Higgs-mass  not a problem: reconstruction of the Higgs mass as a resonance structure is anyway not possible in this mode. • Only event excess can be seen.  Crucial aspect of analysis is precise estimation of backgrounds. • Hence challenging and interesting ! INDIA-CMS meeting, BARC 20-21 July,2007

  3. Phenomenological Considerations • Invisible decay of Higgs  event should be identified using other particles produced along with Higgs. • Hence ggH production channel is not suitable though rate is highest. In LO there is no other particle in final state. • Best process, Weak Boson Fusion (qq  qqH) has distinctive event topology tagging jets in forward-backward direction. • Associated production processes (W/Z H, ttH ) are more difficult due to many backgrounds and lower rates. INDIA-CMS meeting, BARC 20-21 July,2007

  4. More on Weak/Vector Boson Fusion (VBF) Process • Final state: qq  qqH  Missing energy (MET) + VBF jets • Absence of color connection between incoming partons leads to jets which are mostly in forward-backward direction  large rapidity gap between jets. • Jets carry lot of energy, not much in transverse direction. • Final state jets, satisfying these condition  tagging jet • Due to absence of color exchange among involved particles there is hardly any hadronic activity in the central region of detector. • Jets get balanced by Higgs so azimuthal angle between jets is relatively small. INDIA-CMS meeting, BARC 20-21 July,2007

  5. First Look Using CMSSW • Till one year back all related studies done with CMSJET, OSCAR+ORCA  • CMS note (2002), Internal note (2005) etc. • During CSA06 exercise, analysis tools in CMSSW were handled, but signal • samples were not available. • Data sample available during Spring07 production (May) • (Generation + Simulation CMSSW_1_2_0, Digi + Reco with CMSSW_1_3_1). • 20k event for Higgs mass ( GeV) 100, 120, 140, 160, 200. • Signal selection criteria used has been taken from previous study, to be tuned • with latest reconstruction codes and analysis, after comparing with various • backgrounds. • Presented results of on-going studies regularly in Higgs meeting during May/June. • (quoted by Y. Sirois during his talk in June CMS Week at CERN) • Being considered as a priority analysis topic in CMS . INDIA-CMS meeting, BARC 20-21 July,2007

  6. Event kinematics for Invisible Higgs • Sample : /qqHinv200/CMSSW_1_3_1-Spring07-1130/GEN-SIM-DIGI- RECO • Jet Algorithm  iterativeCone5 • Jet matching (reco. Vs. MC) for jets with pT > 20 GeV • Each reconstructed jet is looped over generated jets, jets with ΔR < 0.1 are accepted ( matching efficiency 97 %). • Most of the events have only one jet above 40 GeV (Forward- backward jets, so pT is not high). • We need 2 jets above 40 GeV  low acceptance of signal events INDIA-CMS meeting, BARC 20-21 July,2007

  7. Signal event properties: ∆η for leading jets ( pT( j1 , j2) > 40 GeV) Reconstructed jet have lower pT compared to generated jet as these are uncalibrated MET after VBF (∆η > 4.4) INDIA-CMS meeting, BARC 20-21 July,2007

  8. Cont…. Mjj after MET (> 100 GeV) ∆φjj after Mjj (1.2 TeV) Selection efficiency is 2.48 in CMS IN 2004/028 ( K. Mazumdar & A. Nikitenko INDIA-CMS meeting, BARC 20-21 July,2007

  9. Estimation of ttbar background ttbar background not checked so far, so given priority. ttbar sample: 2.5M events at CERN /ttbar_inclusive_TopRex/CMSSW_1_3_1-Spring07-1122/GEN-SIM-DIGI-RECO Additional Conditions: i) Only hadronics events  Lepton veto: no electron with pT > 10 GeV, |η| < 2.5 and no muon with pT > 5 GeV, |η| < 2.5 ii) Central jet veto : For Signal there is low jet activity in central region. If 3rd jet exist it is due to ISR or FSR. No track information is involved. Zeppenfeld variable Z i = ηi - (η1 + η2) / 2 For signal this variable is large. INDIA-CMS meeting, BARC 20-21 July,2007

  10. Comparsion of ttbar events with Signal Δη between leading jets after lepton veto. Missing transverse energy after cut | ∆η |>4.4 INDIA-CMS meeting, BARC 20-21 July,2007

  11. Comparison cont… Higgs120 Mjj after lepton veto, VBF and MET > 100 GeV ttbar ΔΦjj between leading jets after Lepton veto, VBF, MET > 100 GeV and Mjj > 1.2 TeV INDIA-CMS meeting, BARC 20-21 July,2007

  12. Comparison cont… Zeppenfeld variable Zi = ηi –(η1 + η2)/2 | Zi | > 2 for signal events. Jet veto  no jet with pT > 20 GeV and | Zi | < 2 ΔΦjj after jet veto INDIA-CMS meeting, BARC 20-21 July,2007

  13. Selection efficiency for Signal and ttbar background INDIA-CMS meeting, BARC 20-21 July,2007

  14. HLT Exercise • All triggers ( L1 and High Level ) thresholds being optimized for LHC startup Luminosity 10 32 cm -2 s -1. • pp interaction event rate is ~ 105 Hz • L1-trigger accept rate is 17 kHz and that for HLT is 150 Hz. Sequence in CMSSW: MC-generated events are simulated, digitised. L1 Emulator duplicate the behavior of the L1-trigger hardware at bit lavel Subsequently L1 seeds are used for HLT information. A trigger table (variables with optimised kinematic thresholds) is used for trigger studies to check event rates. eg., di electron, isolated: Pt >10 GeV  event rate = 0.2 Hz di electron, non isolated: Pt >12 GeV  event rate = 0.8 Hz A report is submitted to LHCC in June by CMS collaboration. CMS Note  80 authors (including S. Bansal, K.Mazumdar) INDIA-CMS meeting, BARC 20-21 July,2007

  15. Trigger Study for Invisible Higgs Signal • Final state is forward-backward jets satisfying VBF conditions and large MET. • L1-trigger : L1 MET is calculated using x and y components of energy deposited in each trigger region. • HLT : Jets are reconstructed using IC5 algorithm, inputs are calorimeter towers ( pT > 0.5 GeV) . A correction for the calorimeter response is applied for jets ( Full simulated QCD dijet sample used for correction). • MET is also calculated with same algorithm as used in offline. MET is not corrected. INDIA-CMS meeting, BARC 20-21 July,2007

  16. L1 Trigger used MET > 30 GeV VBF filter is used which select events with η1 * η2 < 0 ,Δη > 4.2 and Jet pT > 40 GeV. HLT condition is MET > 60 GeV + VBF Total rate (due to QCD) for these thresholds is 0.2 Hz Higgs Signal samples are stored only at Wisconsin, to be accessed via CRAB. But required software (CMSSW 1_3_1_HLTX) was not installed there, so Grid job submission was not possible. Samples for Mh = 200 and 160 GeV copied to cern castor, but failed for other samples. L1 : MET > 30 GeV eff. = 79.07% for mH = 200 GeV eff. = 77.80% for mH = 160 GeV HLT: MET > 60 GeV + VBF eff. = 8.53% for mH = 200 GeV eff. = 7.02% for mH = 160 GeV Trigger Details INDIA-CMS meeting, BARC 20-21 July,2007

  17. Backgrounds Generation • Z/W + Jets are potential background for Invisible Higgs: • Z  νν and jets satisfying VBF and • W  l ν where lepton pass undetected . • Z (νν ) /W ( l ν ) + Jets ( EWK & QCD) being generated using Alpgen and Madgraph. • Generating events for few fb -1 Luminosity. • Alpgen Generation : • To achieve good event statistics “soft VBF” preselections have been used at generator level • Soft VBF  | Δη | > 2 && Mjj > 300 GeV in usercut.f • Alpgen Generation is almost done and will be sent for production • MadGraph Generation : • Using Same “soft VBF” condition for generation and generation has to done INDIA-CMS meeting, BARC 20-21 July,2007

  18. To stabilize the post-warm up technique is used. • Grid is created using small run and run the iteration over the previous grid till it become stable ( in term of cross-section fluctutation) • This grid is used for final events generation. • To submit parallel batch jobs, a pearl script is used. This script submit the desired number of parallel jobs by changing the input seed for each job and also unweight the events. • These events hadronised using Alpgen Interface provided in CMSSW • input file to this interface are .unw and .par. INDIA-CMS meeting, BARC 20-21 July,2007

  19. Conclusion and Plans • The signal selection efficiency in CMSSW, in good agreement with previous study using OSCAR+ORCA. • ttbar background has been studied for the first time for this analysis  found to be reducible to very good extent. • L1 + HLT efficiency is calculated for Signal.  contribution to HLT note. • Estimation for QCD background is going on. • Background Generation using Alpgen and Madgraph ( Z/W + NJets) is going on, file be will be sent for Summer production. • W/Z + Jets backgrounds to be studied during CSA07. • Double parton-parton and proton- proton scattering contributation has to estimated. INDIA-CMS meeting, BARC 20-21 July,2007

  20. Back - up INDIA-CMS meeting, BARC 20-21 July,2007

  21. Back-up • Starting from the same grid produces identical events • Change seed1 and seed2 in the input to create parallel jobs from a single grid2 • Alpgen Interface Provided in CMSSW_1_4_X used for hadronisation • In 1_4_0 there were two problems • i) Input file needed to be in same directory • ii) When changed the increased input events there was core dump. • In 1_4_5 these problems has been fixed • Files to be provided as input : file.unw & file_unw.par • Alpgen.cfg : source = Alpgensource { • untracked vstring fileNames = “ file: /tmp/sunil/alpgen” • untracked int32 maxEvents = 1000 • Pset PythiaParameters = { • vstring parameterSets = { "pythia" } • vstring pythia = { "MSEL=0 !(D=1) ", • "MSTJ(11)=3 !Choice of the fragmentation function", • "MSTP(143)=1 !Call the matching routine in ALPGEN" } • } INDIA-CMS meeting, BARC 20-21 July,2007

  22. PSet GeneratorParameters = { vstring parameterSets = { "generator" } vstring generator = { "IXpar(2) = 1 ! inclus./exclus. sample: 0/1", #Inputs for clustering: minET(CLUS), deltaR(CLUS) "RXpar(1) = 20. ! ETCLUS : minET(CLUS)", "RXpar(2) = 0.7 ! RCLUS : deltaR(CLUS)" } } 100 parallel batch submitted for Z ( νν) + 2Jets using soft VBF conditions and post warup technique. Rest are in progress. INDIA-CMS meeting, BARC 20-21 July,2007

  23. Search Strategy Simulation studies needed to optimise potential of the experiment • So generation is always done in Pythia using SM process H  ZZ 4 nu. • No dedicated generator for invisible decay of Higgs available. • Production cross-section ( qq  qqH) and decay branching for • (H  invisible) are both model dependent. • In experimental searches, model independent limits are given, since • the product of two determines the number of events. INDIA-CMS meeting, BARC 20-21 July,2007

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