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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 2 Outline  Properties of  particles  CMS detector   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 3 Characteristics of Tau decays  Lifetime c  87  m (0.29 ps), m   1.78 GeV/c 2  Decays: 65% hadronic, 35% leptonic Hadronic –1 prong 50 % :      n    –3 prong 15 % :    3    n     tau jets at LHC: Very collimated Low multiplicity –One, three prongs Hadronic, EM energy deposition –Charged pions –Photons from  0

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

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 7 ECAL High resolution electromagnetic calorimetry is central to the CMS design  m / m = 0.5 [  E 1 / E 1   E 2 / E 2    / tan(  / 2 ) ] Where:  E / E = a /  E  b  c/ E 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 L c = 155 MeV 770 MeV High L 210 MeV 915 MeV (dq relies on interaction vertex measurement)

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 8 Events used  tau sample –taus only i.e. no pile up, no underlying event –p T jet > 30 GeV, uniform in |   QCD sample –di-jets events in Pythia E T GeV,  R sep > 1.5 –True energy is that found when using cone size 0.5.  Matching:  R(Calorimeter jet 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 9 ECAL isolation  candidates P isol < cut value Efficiency of rejection of QCD jets increases with E T. — Low p T tracks (<2 GeV/c) bent out of cone Achieve 80% efficiency with bkg rejection of factor of 5 for QCD jets with p T > 80 GeV/c (wrt presel. and matching)

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 10 Tracker Isolation axis of calo jet Jets reconstructed with iterative cone algorithm Look for tracks inside jet-track matching cone R m (0.1) with p t > 6 GeV Form signal cone around track with highest p T. Tracks inside R s with z d 0 within  z (2mm) of leading track deemed to be from tau Tracks reconstructed within R i. Require p T > p T i (1 GeV) and within  z (2mm) of leading track. Tracks 8 Si hits with at least 2 pixel hits.    Isolation requires no non-tau tracks within R i.

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 12 Impact parameter tag 1 prong3 prong QCD tail due to fake tracks. Hits on reconstructed track from various true tracks. Majority at large  Extrapolation distances larger Little discrimination in 3-prong events IP for highest p T track

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 13 d 0 performance Efficiency of transverse d 0 significance cut. d 0 < 300  m Mean error ~ 15  m (1-) 16.7  m (3-) : QCD 17.9 (1-) 22.2(3-)  m Tracker isolation requiredSignificance cut

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 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. HCAL cut electron  jet E T GeV  jet E T GeV > 1 GeV > 2 GeV Performance of HCAL cut for leading track p T > 10 GeV All distributions normalised to 1. Tail due to gaps in ECAL

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 15 Decay length tag 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   decays b and c quark jets not a major problem (~12% c 3% b)  -jets QCD jets

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 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   events smear z by 60  m 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 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  R > 0.08 — Use clusters within cone of 0.4 Due to 1-prong decays E T GeV E T GeV

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 19 Mass tag performance — Tracker isolation required — Mass cut < 2.5 GeV/c 2

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 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 of  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 22  ID performance  From R. Kinnunen’s talk on Wednesday For this channel: R m = 0.1, R s = 0.07, R i = 0.4 with veto on tracks with p T > 1 GeV in the isolation cone  ECAL isolation for  jet:  E T cell (0.13<  R<0.4) < 5.6 GeV,  R defined around the jet direction Electron contamination suppressed with a cut on maximal HCAL cell (E T > 2 GeV) inside the jet cone p leading track / E  > 0.8, to exploit the opposite  helicity correlations in in the H ± ->  and W ± ->  decays, leading to harder pions from H ± ->  Efficiency: signal 11-15%, tt->WWbb -> bb   l 5%, W+3jets 1%, tt->WWbb -> bb l’ ’ l 2% Signal process defined as gg -> tt -> W ± H ± bb-> l  bb, l = e or  mH+ = 140 GeV

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 23  ID performance II  From R. Kinunnen’s talk on Wednesday Associated production gg -> tbH ±, H ± ->  Level 1  jet trigger E T > 93 GeV  -selection efficiencies including pre-selection, trigger and off-line m (GeV) m H± (GeV) ttWtW+3jQCD Total efficiency3.8%9.0%5.0x x x x10 -5 Offline  Offline  identification: - jet reconstruction in the direction of the triggered  jet, E T > 100 GeV - leading track within  R < 0.1 around the jet direction - small signal cone around the leading track,  r= one or three tracks in the signal cone - isolation of the signal cone in 0.04<  R<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%) - E T of maximal HCAL cell in the jet > 2 GeV to remove electron contamination - p leading track /E  jet > 0.8, exploits the  helicity correlations

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 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 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 p 0 ) –Corrections parametrized as function of E T and  The jets corrections optimised for true hadronic taus significantly underestimate energy scale for QCD jets

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 29  trigger Level-1 (~µs) 40 MHz High-Level ( ms-sec) 100 kHz Event Size ~ 10 6 Bytes Level-1 (~µs) 40 MHz High-Level ( ms-sec) 100 kHz Event Size ~ 10 6 Bytes 40 MHz Clock driven Custom processors 100 kHz Event driven PC network Totally software 100 Hz To mass storage two trigger levels two trigger levels

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 30 L1 trigger  QCD E T samples in the range GeV were used for the HLT studies. They represent more than the 90% of the total L1 Rate  A factor ~10 3 of QCD background rejection is required at HLT — Reduce rate from ~kHz -> ~Hz Active towers patterns allowed for tau jets candidates

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 33 Calo + Pixel HTL 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 p T > 3 GeV/c. Single tagDouble tag Efficiency calculated w.r.t L1 trigger

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

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

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

Charged Higgs – Uppsala 2006 C.H. Shepherd-Themistocleous- RAL 37 H 0 /A 0   decays Provides best reach large tan  :  +, + had, had + had had+had final state:  Backgrounds: QCD ( muli-jet fake  ) ; Z/  *   tt ; W+jet, W .  Requires hadronic  trigger  Large associated production  allows good rejection with b tag.   “jet” (1-, 3- prong) tagging,  lifetime Potential SUSY background. -        decays. negligible b tagging QCD ~ 10 6 Mass resolution rejection ~ 15% ~ Exploit bbH 0 /A 0 production

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

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