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C. H. Shepherd-Themistocleous Rutherford Appleton Laboratory, UK

Rutherford Appleton Laboratory. Identification of tau particles in the CMS detector. C. H. Shepherd-Themistocleous Rutherford Appleton Laboratory, UK. cH ± arged 2006, Uppsala University, Sweden, 13-16 September 2006. Outline. Properties of t particles CMS detector

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C. H. Shepherd-Themistocleous Rutherford Appleton Laboratory, UK

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  1. Rutherford Appleton Laboratory Identification of tau particles in the CMS detector C. H. Shepherd-Themistocleous Rutherford Appleton Laboratory, UK cH±arged 2006, Uppsala University, Sweden, 13-16 September 2006 Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 1

  2. Outline • Properties of t particles • CMS detector • t identification techniques in hadronic decays at CMS • Isolation • Decay length • Impact parameter • Invariant mass • N.B. HLT performance later this afternoon Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 2

  3. Characteristics of Tau decays • Lifetime ct 87 mm (0.29 ps) , mt=1.78 GeV/c2 • Decays: 65% hadronic , 35% leptonic • Hadronic • 1 prong 50 % : t -> nt + p+/- + n(po) • 3 prong 15 % : t -> nt + 3p+/- + n(po) • tau jets at LHC: • Very collimated • Low multiplicity • One, three prongs • Hadronic, EM energy deposition • Charged pions • Photons from p0 Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 3

  4. tau tagging • Properties used for tagging at CMS • Narrow jets • ECAL isolation • Tracker isolation • Significant lifetime • Impact parameter • Decay length • Invariant Mass • Backgrounds • QCD jets • Electrons Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 4

  5. 4T solenoid HCAL Total weight: 12,500 t Overall diameter: 15 m Overall length: 21.6 m Magnetic field: 4 T Plastic scintilator/ brass sandwich Muon chambers Barrel Drift tubes (DT) Resistive plate chambers (RPC) Endcaps Cathode Strip Chambers (CSC) Resistive plate chambers (RPC) Tracker ECAL Si microstrips Pixels Scintillating PbWO4 crystals Iron yoke Compact Muon Solenoid Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 5

  6. The CMS Tracker Outer Barrel Strips TOB The World’s largest Silicon Tracker = 250 m2 ! Pixels Inner Barrel Strips TID Endcap Strips TEC 10 layers of Silicon Strip Sensors surrounding 2-3 layers of Silicon Pixel Sensors. 2.4 m 5.4 m 15000 silicon modulescontaining 76000000 pixels + strips ! Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 6

  7. ECAL Aim: Barrel End cap Stochastic term: a = 2.7% 5.7% (p.e. stat, shower fluct, photo-detector, lateral leakage) Constant term: b = 0.55% 0.55% (non-uniformities, inter-calibration, longitudinal leakage) Noise: Low Lc = 155 MeV 770 MeV High L210 MeV 915 MeV (dq relies on interaction vertex measurement) High resolution electromagneticcalorimetry is central to the CMS design m /m = 0.5[E1/E1  E2/E2   / tan(/2)] Where:E/E = a/E  b  c/E Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 7

  8. Events used • tau sample • taus only i.e. no pile up, no underlying event • pT jet > 30 GeV, uniform in |h| < 2.2 , f • QCD sample • di-jets events in Pythia ET 30-150 GeV,DRsep > 1.5 • True energy is that found when using cone size 0.5. • Matching:DR(Calorimeterjet axis – MC jet axis) < 0.2 • Efficiency for QCD events to pass preselection and matching ~12% Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 8

  9. ECAL isolation t candidates Pisol < cut value Efficiency of rejection of QCD jets increases with ET. — Low pT tracks (<2 GeV/c) bent out of cone Achieve 80% efficiency with bkg rejection of factor of 5 for QCD jets with pT > 80 GeV/c (wrt presel. and matching) Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 9

  10. Tracker Isolation • Jets reconstructed with iterative cone algorithm • Look for tracks inside jet-track matching cone • Rm (0.1) with pt > 6 GeV • Form signal cone around track with highest pT. • Tracks inside Rs with z d0 within Dz (2mm) • of leading track deemed to be from tau • Tracks reconstructed within Ri. • Require pT > pTi (1 GeV) and within • Dz (2mm) of leading track. • Tracks 8 Si hits with at least 2 pixel hits. c2 < 10 • Isolation requires no non-tau tracks within Ri. axis of calo jet Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 10

  11. QCD jets 50<ET<170 GeV Single Tau (30<ET<150 GeV) Ri Ri Tracker Isolation Performance Bins 130-150, 80-110, 50-70, 30-50 GeV ET inc Single tau simulated events QCD events generated in bins of pT. Efficiency wrt preselected and matched events Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 11

  12. Impact parameter tag 1 prong 3 prong IP for highest pT track QCD tail due to fake tracks. Hits on reconstructed track from various true tracks. Majority at large h. Extrapolation distances larger Little discrimination in 3-prong events Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 12

  13. d0 performance Tracker isolation required Significance cut • Efficiency of transverse d0 significance cut. d0 < 300 mm • Mean error ~ 15 mm (1-) 16.7 mm (3-) : QCD 17.9 (1-) 22.2(3-) mm Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 13

  14. Electron Rejection Electrons can fake 1-prong taus. Events selected requiring ECAL and Tracker isolation Background suppressed using HCAL information  Minimum requirement on energy of most energetic HCAL tower in the jet. All distributions normalised to 1. Performance of HCAL cut for leading track pT > 10 GeV Tail due to gaps in ECAL Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 14

  15. Decay length tag b and c quark jets not a major problem (~12% c 3% b) t-jets QCD jets Very collimated jets lead to shared hits in pixel layers. Decay length < 35 mm required. Events required to pass tracker isolation and have 3 tracks in the signal cone. Probability ~ 63% for 3-prong tdecays Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 15

  16. SV - decay length Resolution transverse to jet axis Resolution parallel to jet axis Secondary vertex resolution in t jet events • Analysis used the Kalman vertex fitter (KVF) Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 16

  17. Decay length performance • Performance as a function of • signed transverse decay length • significance • Error in decay length dominated • by secondary vertex. - Primary vertex: • QCD events use pixel vertex finder • t events smear z by 60mm • Rejection factor of 5 possible • for a signal efficiency of 70-80% • (efficiency calculated wrt MC preselection • and matching and tracker isolation) Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 17

  18. Mass tag • Mass reconstruction uses track momenta and energy of ECAL clusters. • Clusters matched to tracks are removed to avoid double counting. • Clusters only used if track - cluster DR > 0.08 • Use clusters within cone of 0.4 ET 30-50 GeV ET 130-150 GeV Due to 1-prong decays Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 18

  19. Mass tag performance • Tracker isolation required • Mass cut < 2.5 GeV/c2 Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 19

  20. t tag efficiency determination • Method: Use in single muon triggers Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 20

  21. efficiency II • Principal backgrounds: t t , W + jet, QCD • Error on tag tag efficiency using 30fb-1 of data. • This method allows verification of MC at Z energies. The efficiency is a function oft jet energy. • Greater collimation • lower probability of signal tracks outside signal cone • greater probability of tracks sharing hits Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 21

  22. t ID performance • From R. Kinnunen’s talk on Wednesday Signal process defined as gg -> tt -> W±H±bb->lntnbb, l = e or m mH+ = 140 GeV For this channel: lRm = 0.1, Rs = 0.07, Ri = 0.4 with veto on tracks with pT > 1 GeV in the isolation cone lECAL isolation for t jet: SETcell (0.13<DR<0.4) < 5.6 GeV, DR defined around the jet direction lElectron contamination suppressed with a cut on maximal HCAL cell (ET > 2 GeV) inside the jet cone l pleading track / Et > 0.8, to exploit the opposite t helicity correlations in in the H± -> tn and W± -> tn decays, leading to harder pions from H± -> tn Efficiency: signal 11-15%, tt->WWbb -> bbt+nln 5%, W+3jets 1%, tt->WWbb -> bbl’n’ln 2% Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 22

  23. t ID performance II • From R. Kinunnen’s talk on Wednesday Associated production gg -> tbH± , H± -> tn Level 1 t jet trigger ET > 93 GeV Offline tidentification: - jet reconstruction in the direction of the triggeredjet, ET > 100 GeV • leading track within DR < 0.1 around the jet direction • small signal cone around the leading track, Dr=0.04 • one or three tracks in the signal cone • isolation of the signal cone in 0.04<DR<0.4 • addional quality cuts for the leading track: transverse impact parameter < 0.3 mm • and at least 10 hits in the tracker (signal efficiencies ~95%) • - ET of maximal HCAL cell in the jet > 2 GeV to remove electron contamination • pleadingtrack/Etjet > 0.8, exploits the t helicity correlations t-selection efficiencies including pre-selection, trigger and off-line Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 23

  24. Summary • Reconstruction utilizes characteristics of tau jets • Principal methods are: • Isolation in ECAL & tracker • Decay length • Impact parameter • Invariant mass • A method for determining efficiency from data has been studied. Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 24

  25. Backup slides Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 25

  26. Choice of jet cone size Cone size of 0.4 chosen. Contains 98% of jet energy and good energy resolution Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 26

  27. Energy scale corrections • Tau jets need softer corrections to their energy, wrt QCD jets. • For the same transverse energy, pions in Tau jets have harder transverse momentum than pions in QCD jets • In Tau jets there is a larger amount of electromagnetic energy (due to the presence of p0) • Corrections parametrized as function of ET andh The jets corrections optimised for true hadronic taus significantly underestimate energy scale for QCD jets Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 27

  28. Performance Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 28

  29. t trigger 40 MHz Clock driven Custom processors 100 kHz Event driven PC network Totally software 100 Hz To mass storage two trigger levels Level-1 (~µs) 40 MHz High-Level ( ms-sec) 100 kHz Event Size ~ 106 Bytes Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 29

  30. L1 trigger Active towers patterns allowed for tau jets candidates • QCD ET samples in the range50-170 GeV were used for the HLT studies. They represent more than the90%of the total L1 Rate • A factor ~103 of QCD background rejection is required at HLT • Reduce rate from ~kHz -> ~Hz Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 30

  31. HLT • Two trigger algorithms “Calo+Pxl trigger ” and “Trk trigger” • “Calo+Pxl trigger”: only pixel hits and calorimeter isolation used • Fast – limited track reconstruction • Good performance for isolation • preferred for decays with two taus in the final state (like A/H->tautau) • “Trk trigger”: (some) hits of the microstrip inner tracker used, no calorimeter isolation • slower than “Calo+Pxl” • much better resolution for track momenta • useful in channels like charged Higgs boson decay ( plus missing energy selection) • tight cut on the pT of the leading track Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 31

  32. ECAL isolation Isolation is applied to the most energetic) HLT calorimeter jet. • Efficiency evaluated for bbH bb+tt sample • w.r.t. L1 trigger. • QCD di-jet events in range pThat:50-170 GeV used to evaluate background suppression. • Rejection factor 3 is given by Pisol < 5.0 GeV • Used with Pixel isolation to form trigger Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 32

  33. Calo + Pixel HTL Single tag Double tag Efficiency calculated w.r.t L1 trigger Track isolation alg. similar to offline. Tracks constructed from 3 pixel hits only. Isolation cone varied from 0.2 to 0.6 (step 0.05). Signal cone 0.07, matching cone 0.1, leading track pT > 3 GeV/c. Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 33

  34. Charged Higgs Trigger • Channel considered • gg->tbH+, gb->tH , H+ ->tn (tau hadronic decay) • L1 output rate: ~ 3kHz • HLT selection • ETmiss>65 GeV: output rate ~30 Hz • After applying Tracker isolation + momentum cut (PTLT>20GeV): • output rate: ~ 1Hz Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 34

  35. performance in example channel Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 35

  36. HCAL Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 36

  37. H0/A0 tt decays • Provides best reach large tan b:tt + ,+ had,had + had • had+had final state: • Backgrounds: QCD ( muli-jet fake t) ; Z/g* tt ; tt ; W+jet, W tn. • Requires hadronic t trigger • Large associated production s allows good rejection with b tag. • t “jet” (1-, 3- prong) tagging, t lifetime • Potential SUSY background. - t ,c20,c1decays. negligible ~ b tagging Exploit bbH0/A0 production QCD ~ 106 Mass resolution rejection ~ 15% Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 37

  38. H±tn decays Provides clear signature for BSM physics. • Production: • mH± < mt: tt , t H± b • mH± > mt: gb  t H± ,gg tbH ±, qq’  H± • Backgrounds: tt ; Wtb, W tn • Signal : Look for lepton from top + t had • Spin correlations p+ from H t harder than • p from W t. Require 80% jet energy • carried by p+ • Plot transverse mass. (missing >1 n) • Signal endpoint ~ mH • Background endpoint mw Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 38

  39. add properties of sub detectors • resolutions Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 39

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