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Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP1 Physics Simulation Studies in HIP Outline: –Introduction –Pre-TDR physics studies.

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Presentation on theme: "Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP1 Physics Simulation Studies in HIP Outline: –Introduction –Pre-TDR physics studies."— Presentation transcript:

1 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP1 Physics Simulation Studies in HIP Outline: –Introduction –Pre-TDR physics studies –Full simulation studies for the CMS Physics TDR MSSM H ±   jet+X MSSM H/A    e  +X MSSM H/A    jet+jet+X –Educational activities –Publishing activities –Future plans

2 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP2Introduction Main fields of interest: –Higgs boson production and the experimental methods related to Higgs boson searches at the LHC Principal framework of physics studies studies: –Minimal Supersymmetric Standart Model (MSSM) The group has particular experties in the following experimental methods: –  identification –  tagging with impact parameter and vertex measurement –b tagging

3 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP3 Pre-TDR physics studies during These studies were based on particle level simulation, fast simulation and partially full simulation The work started 1992 with the first Higgs boson simulation work in CMS: –R. Kinnunen, H. Plothow-Besh and J. Tuominiemi, ”Search for H  ZZ*  4 l ± with the CMS detector at the LHC”, CMS TN-1992/008. Followed with studies on –the SM Higgs boson searches, H  ZZ/ZZ*, H  gg, H  WW, H  .. –the searches of the MSSM Higgs bosons with H   and H ±   –experimental methods, b tagging, in-situ calibration, trigger studies The fast simulation era was finished with a summary work on the CMS studies on the Higgs boson searches under the responsability of HIP group, –”Summary of the CMS Discovery Potential for the Higgs Boson”, European Physical Journal C, Particles and Fields, vol. 39, (2005) Specialization to  physics and on the H   and H ±   discovery channels started early in HIP…

4 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP4 H/A   and H ±   channels Due to the tan  enhancement of the Higgs couplings to down type fermions, these channels are the principal discovery channels for the heavy MSSM Higgs bosons at the LHC: –H/A   in the associated production with b quarks, gg  bbH/A –H ±   in the associated production, gg  tbH ± In these searches: –the bbH process can be disentangled from the large Drell-Yan production of  pairs through tagging one b jet –the hadronic jet background can be suppressed with  identification  identification is based on isolation and pT cuts at the High Level Trigger and in offline analysis, and on vertex reconstruction and impact parameter measurement in the offline analysis  identification and b tagging are the basic methods for the four discovery channels studied for the TDR by the HIP group with full simulation and reconstruction : –fully hadronic H ±  , –fully hadronic H/A    2 jets+X, –semileptonic H/A    electron+jet+X and –fully leptonic H/A    ll +X

5 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP5 Hadronic  trigger HIP group has been involved in developing hadronic  trigger algorithms Hadronic  trigger needed for –fully hadronic H ±  , single  + missing E T trigger –fully hadronic H/A    2 jets+X and single  + missing E T trigger, double  + missing E T trigger –semileptonic H/A    electron+jet+X e +  trigger, single e trigger HLT  trigger algorithm: –Start with L1 central calorimeter jets –Then either ECAL isolation + pixel track isolation or –Fast algorithm; gives good performance –Preferred approach in H/A    2 jets+X Tracker isolation (regional track reconstruction) –Slower algorithm, but gives a more accurate track p T estimation –Useful in channels like H ±  

6 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP6 Full simulation study on heavy charged MSSM Higgs bosons with the hadronic H ±   decay R. Kinnunen There are few possiblities to discover the charged Higgs bosons at the LHC: –the dominant H ± -> tb decay channel difficult due to large background systematics –H ± ->  decay promising, The H ± ->  decay channel can be used –for m H± bH ± with leptonic triggers with a discovery up to almost the kinematical limit, m H± < m top - m b –for m H± > m top, in fully hadronic final states from associated production with top Advantages of the fully hadronic channel: –possibility to exploit  helicity correlations, –large missing transverse energy and –possibility to reconstruct a transverse Higgs boson mass Production of t + H ± through gb -> tH ± (LO) and gg(qq) -> tbH ± (NLO) processes Merging the two processes is not possible in the full simulation: gg(qq) -> tbH ± used

7 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP7 Backgrounds and trigger Signal events are characterized with: one energetic  jet, large missing transverse energy, one b jet and 2 hadronic jets Main backgrounds are from genuine  ’s in multi-jet events: –tt, t 1 -> , t 2 ->qqb –Wt W 1 -> , W 2 ->qq –W+3 jets, W->  –and from fake  ’s in QCD multi-jets The H ± ->  decay in fully hadronic final state can be triggered with: –Single  + missing transverse energy trigger CMS trigger for single  : –Narrow calorimeter jet at Level-1 (E T > 93 GeV) –Full regional track reconstruction, isolation and p T cut at the High Level Trigger Efficiencies for the signal 9 – 40%, with  jet purity around 90%

8 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP8 Event selection A quasi two-body situation between the  jet and the missing transverse energy, for a good transverse mass reconstruction, can be obtained only if E T miss originates from H ± ->  Other sources of missing transverse energy: W-> l and semileptonic b decays Start offline selection with a veto on isolated leptons, exploiting tracker isolation and electron identification in the calorimetry Results: –Measured ”BR(W->  )” = 8.9%, purity 84% –Measured ”BR(W->e )” = 7.9%, purity 93%

9 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP9 Fraction of  momentum carried by the leading   Signal tt background Event selection 2  identification for H ± : Two scopes in this channel: –suppress efficiently hadronic jets and –the genuine  ’s from W ->  Identification based on calorimeter jet, motivated with a large fraction of  ->  ± + n  0 + decays in the signal (~ 52%) Reconstruction of the  jet around the HLT  direction in a cone of 0.4 Select  identification cuts to exploit helicity correlations in H ± ->  Decay angular distributions in the CMS frame: –H ± -> ,  ->  ± + :  N/  cos  ~(1+cos  ) –W ± -> ,  ->  ± + :  N/  cos  ~(1-cos  ) Harder charged pion from H ± ->  than from W->  –For decays through vector mesons more –complicated but still harder pions from H ±

10 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP10 Event selection 3   identification cuts: –leading track within  R < 0.1 the jet direction –small signal cone around the leading track,  R = 0.04 –isolation in the cone 0.04 <  R < 0.4 –p leading track /E T jet > 0.8 to exploit the helicity correlations Further event selections: Top mass reconstruction with minimization of  2 = ((m jj –m W )/  W ) 2 + ((m jjj –m top )/  top ) 2 from all hadronic non-  jets, E T > 20 GeV, with  W = 10 GeV,  top = 17 GeV B tagging with a probabilistic secondary vertex algorithm with discriminator cut

11 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP11 Transverse mass reconstruction m T = (2 E T  jet E T miss (1 -  jet, E T miss )) 1/2 Discovery potential Transverse mass and discovery reach An almost background-free signal can be reached in the signal area defined by  (  jet, E T miss ) > 60 o or by m T (  jet, E T miss ) > 100 GeV Sources of systematic uncertainty in the background determination: E T miss and jet scale,  identification, b tagging, cross section uncertainties

12 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP12 Study of MSSM H/A    jet+jet+X L. Wendland Channel studied in collaboration with S. Gennai and A. Nikitenko Final state search strategy: –two isolated  jets, –one b jet, –veto for other jets and –missing energy Trigger with –single  trigger (E T > 92 GeV) –double  trigger (E T > 76 GeV) Main backgrounds: –QCD di-jets, Z/  *, tt MC event visualization for bbH(500)->  ->2jet  jet 2 b jet 1 b jet 2  jet 1

13 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP13  identification in jet + jet final state  identification algorithm: –leading track within  R < 0.1 the jet direction –small signal cone around the leading track,  R = 0.07 –isolation in the cone 0.07 <  R < 0.4 –number of reconstructed tracks: one or three –pT cut for leading track, p T > 35 GeV –quality cuts for the leading track at least 8 hits,  2 at most 10 –upper limit on impact parameter IP T < 0.3 mm, IP < 1.0 mm

14 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP14 Impact parameter reconstruction The principle: –Taus have IP > 0 because they fly several mm before decaying; QCD jets come from interaction point New result: –A significant number of QCD jets with only one reconstructed track have a large IP value; explanation: track contains hits from different tracks –Effect is increased with jet E T and sensor displacement Significance of full IP is used Background rejection –One track final state: ~ at greater than 92 % signal level –Three track final state: ~2.2 at greater than 85 % signal level Transverse IP, mmFull (3D) IP significance Efficiency curves based on cut on the significance

15 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP15 Vertex reconstruction in 3-prong  jets The principle: –Taus have an average flight path of several mm before decay; QCD di-jets are produced at the interaction point Challenges: –kinematically very difficult final state; the first few hits can be merged as one because of high track collimation –background with long lived particles (B or D mesons) could be enhanced Significance of full flight path is used Sign of flight path is used Systematics from simulated sensor misalignment very small Background rejection ~4 at 80 % signal level Masters thesis in 2005 Signed full reco fl.path in mmSigned tr. reco fl.path in mm Efficiency curves based on cut on the significance Hit merging on first pixel layer  from H(500) QCD jet, E T GeV c jet, E T GeV

16 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP16 Event selections SIGNAL m A = 200 GeV/c 2 tan  =20 m A = 500 GeV/c 2 tan  =30 m A = 800 GeV/c 2 tan  =40  × BR (fb)  after selections (fb) N ev. at 30 fb BACKGROUND QCD di-jet >170 GeV/c QCD di-jet GeV/c QCD di-jet GeV/c QCD di-jet GeV/c ttZ/  * m  GeV/c 2  (fb)1.33 × × × ×10 10  after selections (fb) N ev. at 30 fb Most dangerous background

17 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP17 Higgs mass reconstruction Signal Background Signal + background

18 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP18 Discovery reach

19 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP19 Full simulation study on MSSM Higgs bosons with H/A    e +  jet + X R. Kinnunen and S. Lehti Final state searched for: isolated electron,  jet and a b jet These events are triggered with –a single e trigger (E T > 26 GeV) and with a combined electron +  trigger –Double and combined  trigger in CMS: narrow jet at Level-1, regional track reconstruction in the Pixel detector, isolation and soft p T cut for the leading track –Efficiencies for the signal: 8 – 30% for mA = 130 – 500 GeV Background from –genuine  ’s: Z,  *, bbZ,  *, tt, Wt –fake  ’s: W+jet, tt, Wt –electrons: Z,  *  e + e -, bbZ,  *  e + e - –fake electrons and fake  ’s: QCD multi-jet Special feature of this channel: good separation electron versus hadronic jet,  versus hadronic jet and electron versus  mandatory

20 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP20 E T of the most energetic HCAl cell in the  jet Variables for electron /  jet separation pion momentun over HCAL energy  identification To exploit the    + n  0 + decay modes (~52% of hadronic decays) jet reconstruction is used at the offline also  identification algorithm: –leading track within  R < 0.1 the jet direction –small signal cone around the leading track,  R=0.04 –isolation in the cone 0.04<  R<0.4 –p T cut for leading track, p T > 20 GeV –quality cuts for the leading track, transverse impact parameter < 0.3 mm, at least 8 hits –veto on electrons: E T (max HCAL cell) > 2 GeV, 0.35 < p  /E HCAL < 1.5

21 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP21 Several electron candidates from offline reconstruction: ~ 1.3 electron candidates/event Identification starts with Tracker isolation  no track with p T > 1 GeV within  R < 0.4 around the electron candidate Calorimeter identification needed in particular at low part of the p t spectrum and is done with - track-ECAL(super cluster) matching: |  track -  SC |, |  track -  SC |, E SC /p track, |1/E SC - 1/ p track | - HCAL/ECAL energy ratio - ECAL profile cuts : E 3x3 /E 5x5,   Cut optimization for good efficiency and maximal purity with electrons from  ->e agaist hadrons from  ->hadrons+ An identified electron (p T >20 GeV) found in 81.2% of signal events, purity for genuine electrons 97.5% electron from  ->e electron from  ->e hadron from  ->hadrons+ hadron from  ->hadrons+ Electron identification Example of electron identificaton variables: ECAL energy over track momentum

22 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP22 Further background suppression with tagging one b jet –with secondary vertex method and discriminator cut veto on addional central jets, tt suppression ~ 10 upper bound on the transverse mass from the electron and missing transverse energy further suppression of tt and W+jet backgrounds Higgs boson mass reconstruction with collinear neutrino approximation: – ’s emitted along the directions of electron and  jet, excluding back-to-back configurations with  (electron,  jet) < 175 o Efficiency for rejection of negative neutrino solutions: 60% for signal, ~ 40% for tt background, mass resolution ~ 22%

23 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP23 Signal and total background for m A = 200 GeV/c 2, tan  = 20 CMS discovery potential for  H/A    electron+jet+X Higgs boson mass and discovery reach Background under signal mainly from Z,  * -> ee and bbZ,  * -> ee Estimate of the QCD multi-jet background: ~ 10% of the total background Sources of systematic uncertainties on background determination: –the jet scale (4%), E T miss scale (10%), b tagging and mistagging (5%), cross section measurements

24 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP24 Study of MSSM H/A    e  +X S.Lehti Final state search for: –isolated electron, isolated muon and a b jet Events are triggered in CMS with –a single electron trigger (Et > 26 GeV) –a single muon trigger (Et > 19 GeV) –Efficiency for signal 75-85% for mA = GeV Background from –Z/  *, tt, tW, bb, WW/WZ/ZZ

25 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP25 Lepton identification Muon reconstruction and identification from muon chambers and tracker Electron reconstruction from calorimeters and tracker, identification is based on –Track-ECAL matching –HCAL/ECAL energy ratio –ECAL profile cuts Identification optimized against W+jet with jet faking an electron used Lepton isolation : no other tracks p T >1GeV within  R<0.4 around the lepton. Lepton isolation and p T cuts against backgrounds with soft leptons (bb,cc,...).

26 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP26 Tau impact parameter Tau’s from Higgs travel couple of mm before they decay Impact parameter, the minimum distance between the track trajectory and the primary interaction point Transverse ip used Significance of the two impact parameter combined into one variable The combined variable is found to suppress efficiently tt events with no genuine tau The fraction of tt events with two intermediate tau’s irreducible

27 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP27 B tagging Two associated b quarks in bbH Against Z,  * for which the associated jets are mostly light quark and gluon jets Signal: soft jets. Tagging efficiency not very high Here a b tagging algorithm based on track ip and secondry vertices used. Jets in tt more energetic, more central, easier to reconstruct and b tag Only 1 jet b tagged, jet veto to suppress tt

28 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP28 Central jet veto tt events have more jet activity than bbH Veto on additional jets in the tracker acceptance region coming from the primary vertex

29 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP29 Mass reconstruction Mass reconstruction using collinear approximation: neutrinos assumed to be emitted along the leptons Events not back-to-back selected Events with neutrinos in opposite direction to leptons rejected: tt suppressed by a factor of 6, signal eff 40% Mass resolution can be improved by higher jet Et cut and stronger  (e,  ) cut, but statistics is decreased significantly

30 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP30 Discovery reach including systematics

31 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP31 bbZ as a benchmark for MSSM bbH search S.Lehti Scope of this study –bbZ cross-section measurement –measurement of b jet and Z spectra –Z mass reconstruction with collinear approximation Z boson production in association with b quarks topologically similar to bbH If the theoretical predictions are verified for bbZ, the predictions for bbH should apply, too

32 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP32 Verification of Monte Carlo Verification of Z p T, associated b jet E T and  distributions and cross section measurement

33 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP33 Mass reconstruction Z boson mass known: collinear approximation tested with Z/  * events Electron+muon final states chosen to select Z/  *  Purity is not important, Z /  *+jet events accepted in addition to bbZ/  * events Can be used to verify the detector calibration

34 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP34 Measurement of the H/A  cross section and possible constrants on tan  R.Kinnunen, S.Lehti, F.Moortgat, A.Nikitenko, M.Spira One of the most important parameters to be determined in MSSM is tan  The dominant part of the gg  bbH,H  proportional to tan 2  tanb measured from event rates Uncertainty of tan  half of the uncertainty of the event rate Results from different H/A  final sates combined

35 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP35 Uncertainty of the cross section (times BR) measurement  =sqrt(N s +N b )/N s  L/L  sel /  sel  N b syst /N s Uncertainty of the tan  measurement  tan  /tan  = ½   ½  theor /  theor Measurement uncertainty on tan 

36 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP36 Educational work of the HIP physics group Academic degrees: –Sami Lehti, Prospects for the detection of neutral MSSM Higgs bosons decaying into tau leptons in the CMS detector, PhD Thesis 2001 –Lauri Wendland, Discovery potential for H,A →  with 3-prong  vertex reconstruction in the CMS detector, Masters Thesis, 2005 –Lauri Wendland, PhD Thesis under preparation (H,A →  → 2jet+X) Student program: –One summer student / year, working on subjects closely connected on the group studies and with proper documentation at the end of the work (CMS note or internal CMS note) Other educational activities: –Help and guidance on groups of young physicists from other countries (Turkey, India, Egypt, Pakistan, Estonia) according to the human resources available –Introductory lectures at different high schools

37 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP37 Publications and conference talks during last 10 years Publications in –International journals: 18 –CMS public notes and preprint series: 53 –Conference proceedings: 3 –CMS internal notes: 5 Plenary talks in international conferences: 5 Invited talks in international conferences: 10 Contributions to CMS TDRs Referee activities: –R. Kinnunen, PhD Thesis opponent, University of Stockholm, December, 2005 –for articles in International journals: one article in EPJCdirect –for CMS public notes: 5

38 Ritva Kinnunen, Sami Lehti, Lauri Wendland: CMS physics simulation at HIP38 Future plans 2006 Introduction and testing of the new CMS software CMSSW Contribution to the ”1 fb Physics” simulation Preparation of calibration, alignment and physics studies with real data 2007 Start up of measurements for calibration constants and background processes: W and Z production, tt, bb, hadronic jets 2008 Expect an integrated luminosity of few fb -1. Intensive measurement of our background processes and search for the MSSM Higgs bosons in the  channels at large tan  (~50) may start Expect to reach 30 fb -1. The physics program presented here can be fulfilled. Exploration of tan  down to ~ 10 around m A = 200 GeV/c 2 Measurement of tan  with a precision of < 20% The strong contribution of the HIP group to tau physics and Higgs boson is important to CMS and will continue


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