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SLHC Physics and B tagging

SLHC Physics and B tagging. Joe Incandela University of California, Santa Barbara 10/12/06. Outline. The SLHC Physics Argument (cf. Eur. Phys. J. C39 (2005) 293) The physics case as from the viewpoint of the tracker Tracking and tagging at high luminosity ATLAS B tag study

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SLHC Physics and B tagging

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  1. SLHC Physics and B tagging • Joe Incandela • University of California, Santa Barbara • 10/12/06

  2. Outline • The SLHC Physics Argument (cf. Eur. Phys. J. C39 (2005) 293) • The physics case as from the viewpoint of the tracker • Tracking and tagging at high luminosity • ATLAS B tag study • CMS Heavy Ions: • Lepton track triggers • B tagging in CMS @ LHC. • B tagging in CMS @ SLHC: • Does it become less important? • What would be needed to make it work as well as at LHC? • Some remarks

  3. Disclaimer • This talk was put together on short notice and mostly in an airplane… • Not intended as a final word on anything… • In the spirit of a workshop – it is meant mostly as a point of departure for more work and discussion

  4. SLHC Physics P.Allport @Hiroshima ‘06

  5. As viewed from the tracker If no light higgs seen, this will be a major emphasis of SLHC • Can divide SLHC physics into several relevant categories • Relies on tracking and/or b tagging • Requires absence of a track and/or b tag • Requires both 1 and 2 • E.g. Vector boson resonance Need to identify high energy leptons Veto events with b tags to help eliminate tt background

  6. Leptons are top priority All new ground. up to 6 l final states! • Multi-boson couplings & Higgs pair production • Both rely upon efficient detection of leptons • Leptons should be the 1st priority of SLHC tracking Only sensitive if H above threshold to decay to VB pairs- 170 ≤ MH ≤ 200

  7. The case for track triggers @ L1 • From Gianotti et al. Eur. Phys. J. C 39, 293-333(2005) • Larger event size due to higher occupancy means that 100 kHz L1 rate will probably need to be maintained…”such a strategy… implies raising transverse momentum thresholds on candidate electrons, photons, muons, etc. and using less inclusive triggers…”

  8. Higgs • Discovered Higgs at LHC • At SLHC interested in rare decays, couplings to fermions and bosons. • HZ, H  +- … • H and WH  ln Comparison tells us about Htt coupling since gg  H proceeds via top loop • Or if SUSY seen, we would want to extend our reach for a 2nd and heavier SUSY higgs • Need b/tau tagging.

  9. Degradation of b tagging & Electron id • No studies by CMS yet. • ATLAS has studied current detector w/full simulations • Mistagging rises x3 to x8 for fixed 50% b tag rate • Rate of jets faking electrons at fixed 80% electron efficiency nearly doubles.

  10. B tagging in CMS • Very similar to Tevatron tagging • Track tags • Jet probability • Number of tracks (2 or 3) above some impact parameter significance • Vertex tagging • Effectively similar in many ways to CDF SECVTX algorithm but developed in a much more intelligent way* * ( I can say this since I was one of the original developers of the CDF algorithm)

  11. Inputs to Combined B tag Algorithm • Jet Reconstruction: Iterative Cone Algorithm with cone size = 0.5 • Track Reconstruction: CombinatorialTrackFinder • ≥ 8 hits in total (pixel + strips) and ≥ 2 pixel hits • pt > 1 GeV/c • χ2/dof < 10 • dxy < 2 mm (transverse impact parameter) • Vertex Reconstruction: • Primary Vertex: Global Reconstruction • PVFPrimaryVertexFinder with reduced pt=0.7 GeV/c for tracks • See CMS AN 2005/043 (C.Piasecki, C.Weiser et al.) • Cone based association of tracks to jets: ΔR < 0.3

  12. 1) “Physics” Definition: Match reconstructed jets to “initial” partons from the primary physics process (within ΔR < 0.3 of reconstructed jet cone) e.g. For tt the initial partons are: 2 b jets from top decays 2 non-b jets per hadronic W decay & no initial gluon jets jets from radiation are not matched with full efficiency Gluon jets splitting to c- or b- quarks are labeled “gluon” 2) “Algorithmic” Definition: Try to find the parton that most likely determines the properties of the jet and assign that flavour as true flavour here, the “final state” partons (after showering, radiation) are analysed (also within ΔR < 0.3 of reconstructed jet cone) jets from radiation are matched with full efficiency if there is a b/c within the jet cone: label it as b/c otherwise: assign flavour of the hardest parton Two Definitions

  13. The Algorithm • Inclusive vertex reconstruction in jets using the “Trimmed Kalman Vertex Finder”; • select secondary vertex candidates: • 100 μm < Lxy > < 2.5 cm • Significance (Lxy/σ) > 3 • Invariant Mass of tracks in vertex candidate < 6.5 GeV • Reject if vertex has two oppositely charged particles with invariant mass within 50 MeV of K0 mass • 3 Categories: depend on result of inclusive vertex reconstruction: • “RecoVertex”: at least one accepted SV candidate found • “PseudoVertex” : built from tracks incompatible with the primary vertex (d/s > 2), if at least two such tracks are present • “NoVertex”: the rest

  14. b c uds Vertex Categories QCD 50-80 |η| < 2.4

  15. b c uds Input Variables I Lifetime signed 2D Track Impact Parameter Significances “PseudoVertex” “RecoVertex” “NoVertex” Enter for all categories into the final discriminator Furthermore: -sort tracks in decreasing order of IP significance -compute mass for tracks -look at IP significance of track pushing the mass above threshold related to charm hadron mass (here: 1.5 GeV) QCD 50-80 |η| < 2.4

  16. b c uds PV-SV σPV-SV Input Variables II Additional secondary vertex related variables for category 1 (“RecoVertex”) multiplicity of charged particles at SV inv. mass of charged particles at SV QCD 50-80 |η| < 2.4

  17. b c uds Input Variables III Additional secondary vertex related variables for category 1 (“RecoVertex”) IP sign. of first track above charm mass fractional charged energy at SV Enters for n tracks rapidities of charged particles at SV QCD 50-80 |η| < 2.4

  18. b c uds Input Variables IV Additional secondary vertex related variables for category 2 (“PseudoVertex”) multiplicity of charged particles at SV fractional charged energy at SV inv. mass of charged particles at SV rapidities of charged particles at SV IP sign. of first track above charm mass QCD 50-80 |η| < 2.4

  19. b c udsg b c udsg Final Discriminator II QCD 50-80 |η| < 2.4 Plots have been obtained by scanning the cut on the discriminator

  20. QCD 50-80 GeV

  21. Dependence On PT and η Misidentification efficiencies for fixed b-tagging efficiency of 50% |η| < 2.4 QCD 50-80 non b-jet efficiency ● uds * g ▲ c pt η loss of tracks in this bin!

  22. Heavy Ions as a proxy for pp@SLHC

  23. HI Algorithm Default pp algorithm with following modifications: • Trajectory Seed Generation • Three pixel hit combinations (Pixel triplets) • Primary vertex constraint • Trajectory Building • Includes all material effects • multiple scattering • energy loss • Special error assignment to merged hits • Trajectory cleaning • Allow only one track per trajectory seed: best 2 • Trajectory Smoothing • Final fit with split stereo layers

  24. Acceptance Require 8 strip layers (~12 hits) and 3 pixel layers. • Geometrical acceptance ~80%

  25. Track quality Cuts • More than 12 hits on track (stereo layer => 2 hits) • Require fit probability > 0.01 • (Cut on compatibility with primary vertex) Good reconstruction

  26. Fakes • Efficiency • Fake Rate • Efficiency • Fake Rate nhit > 12 nhit > 12 pchi2 > 0.01 • Fakes substantially higher than at LHC, as seen by ATLAS. looser

  27. Trajectory Building • Number of candidates drops fast as you move to larger radius even though the occupancy does not fall as quickly. • Track gets more refined and so road narrows…

  28. Algorithmic Efficiency and Fake Rate vs h Algorithmic Efficiency and Fake Rate vs h High efficiency setting

  29. Low Fake Rate Setting Algorithmic Efficiency and Fake Rate vs h

  30. CMS Subtraction Would all strips continue to need to be read out?

  31. Go back to that occupancy plot… • Mismatch at system boundaries • Layer 4 appears pretty useless here. • 3 cm strip would cut occupancy to under 10% • Pixel layer would likely ice the cake • Layers 5-13 • Shorter strips but fewer layers to compensate for material? A factor of 3 reduction in strip length would do a lot for this plot.

  32. ATLAS Granularity Guide Using mainly strips, they’d get substantially better granularity than CMS has now

  33. But granularity can be wasted… • Fine Granularity is necessary but not sufficient… • It is wasted if there is substantial multiple scattering, radiation, and secondary particles generated in material interactions. • Material can set an effective granularity if one is not careful • Material reduction throughout the tracker would enhance our effective granularity now, without changing anything else.

  34. Multiple Scattering Now Cucciarelli et al. CMS Note 2006/026

  35. Well this is a workshop… • I don’t have answers… want to 1st frame the questions correctly • Main points: • Leptons 1st displaced tracks 2nd on priority list (just in case push comes to shove…) • Granularity can be improved substantially without necessarily using pixels - but it will be meaningless if the material budget is not reduced. • Some thoughts • Some technologies could run warm (e.g. n-in-p discussed in Mara Bruzzi’s talk tuesday) … This might allow us to eliminate much of the cooling related mass in the tracking volume. • Super thin is in. We need to think more like e+e- people regarding our material budgets • Recognizing that material can alter the effective granularity of a tracker, we should carefully consider the possible benefits of a reduction in the number of layers ! • We need to do some serious studies of these issues • Triggering was not covered in this talk, but is important, particularly for leptons

  36. Tangent-Point Reconstruction α 37 J.Jones Imperial College London (Perugia Workshop)

  37. More stuff

  38. construction costs • Upgrade cost ~ 200MCHF • Broad brush estimate reported to CMS MB/CB & DG • ~60-70% tracker related • plus staff costs (significant) G. Hall, Imperial College CMS Tracker Meetings, CERN - August 2006

  39. Roadmap from previous workshop • Installation of modest system at t = to + 5y may be possible • Lower cost and risk • Allows trial of components or devices, which may still evolve • May be possible to react to LHC conditions • machine, experiment or even discoveries • An evolutionary approach to replacing full tracker? • Ideas are still to gel but must do so soon • CMS proposes common EoI (2006), and LoI (mid-2007) • R&D proposals to be evaluated by CMS, and approved/encouraged G. Hall, Imperial College

  40. You can’t always get what you want… • But how much increase in granularity is actually needed? • Present microstrip occupancies are 0.5% - 2.8% in barrel CMS NOTE 2002/047 G. Hall, Imperial College

  41. Potential synergy with ATLAS • ATLAS & CMS have exchanged speakers at several workshops • Initial phases of LHC R&D were common • Although many similarities, also important points of divergence • eg sensor design, electrical & optical interfaces, analogue/digital, DAQ design,.. • Possible common efforts • Sharing ASIC processing runs (in CMS & CERN done well for 0.25µm CMOS) • Advantageous to share circuits, evaluate technology and adopt common standards • Share development of common SLHC systems • Optical links and Timing-Trigger-Control system are prominent items • Common effort on power provision - eg DC-DC conversion? • Dialogue with machine • Agree clock speed, verify current systems, information about machine operation • Special tooling • removal and installation of irradiated systems in irradiated environment • Information exchange via regular meetings • Annual LECC workshops are one common forum for electronic R&D • Comparison of cooling system performance might be profitable G. Hall, Imperial College

  42. Cooling costs • Using power has heavy material cost • For present pixel system • Power in ~4% • Power out ~29% • For microstrips • Cables ≈ Cooling • Cables + Cooling + Support ≈ 2x (Sensors+ Electronics)

  43. Noise & granularity • Leakage current shot noise also determines element size • Noise scales ~ (area, time, fluence, shaping time,...)1/2 • How much can be gained by cooling? (ATLAS discuss -35°C) • Ileak will be more significant power burden so must be contained • thermal runaway is increased danger • Is required lifetime again 10 years?

  44. Seeds

  45. Match Reconstructed tracks to MC input on a hit by hit basis. (Event sample: dn/dy ~3000 + one 100GeV Jet/Event) Performance of the Track Reconstruction Transverse Impact Parameter Resolution Longitudinal Impact Parameter Resolution Momentum Resolution

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