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Philip Bechtle (until 5/07) * , Rainer Bartoldus SLAC Colin Jessop, Kyle Knoepfel 

Update on the Inclusive Measurement of the b  s Transition Rate Using a Lepton Tag Using Run I-V Data. Philip Bechtle (until 5/07) * , Rainer Bartoldus SLAC Colin Jessop, Kyle Knoepfel  Notre Dame University Al Eisner, Bruce Schumm, Luke Winstrom  UC Santa Cruz Minghui Lu

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Philip Bechtle (until 5/07) * , Rainer Bartoldus SLAC Colin Jessop, Kyle Knoepfel 

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  1. Update on the Inclusive Measurement of the b  s Transition Rate Using a Lepton Tag Using Run I-V Data Philip Bechtle (until 5/07)*, Rainer Bartoldus SLAC Colin Jessop, Kyle Knoepfel Notre Dame University Al Eisner, Bruce Schumm, Luke Winstrom UC Santa Cruz Minghui Lu University of Oregon John Walsh University of Pisa Students * Now at DESY Bruce Schumm SCIPP 6/07 BaBar Coll. Meeting

  2. Direct searches (LEP) b  s is a leading constraint on new Electroweak scale physics… The SM transition is high order (two weak plus one EM vertex… So new physics can enter at leading order SUSY Extra Dimensions B  s constraints MSSM Constraints

  3. (J. Walsh) b motion 1.9 b  s also provides universal constraints on hadronic effects Photon spectrum can be used to measure universal heavy quark parameters (largest uncertainty in |Vub| from inclusive measurement of b  ul)  In addition to partial BF, we measure 1st and 2nd moments of the photon distribution

  4. Current Status of b  s  BF Measurements BaBar 2006 inclusive result (Run I-II only): B(B  Xs ; 1.9 < EB < 2.7) = 3.67  0.29 0.34 0.29, where errors are statistical, experimental, and model uncertainty, and EB is the photon energy in the B rest frame. Phys.Rev.Lett.97:171803,2006 BaBar Sum of Exclusive Modes Run1-2 Babar Fully Inclusive To interpret the partial BF, one must extrapolate from EB = 1.9 GeV (experimental lower limit) to EB = 1.6 GeV (where theoretical calcul-ations are done). [We are not yet concerning ourselves with that step for Run 1-V analysis.]

  5. qq + ττ BB XSγ Inclusive b s: little effect from long distance physics, but how do you eliminate backgrounds? • Continuum Bkgds: • Shape variables (was Fisher discriminant; now Neural Net) • Lepton tag indicates heavy flavor in “rest-of-the- event” decay • (4S) Bkgds: • Reconstruct (usually asym- metric) 0 and  decays • Calorimeter cluster shapes sup- press merged 0s, hadrons Source: BAD 323, based on the 81 fb-1 Run I-II sample

  6. Sig. Region B/Bbar background control region BB Cont. Signal After Selection Cuts Source: BAD 323, based on the 81 fb-1 Run I-II sample • And then… • Subtract off small remaining continuum using off-resonance (dominant statistical term) • Develop independent estimates B/Bbar backgrounds and subtract them (critical step) • Confirm B/Bbar estimates with control region • Theorists would love us to push below 1.9 GeV, but B/Bbar backgrounds intimidate… What are the sources of B/Bbar background?

  7. B/Bbar background contribution “guess” (selection not yet finalized) 82% of B/Bbar background Nominal B/BBar Background Sources Electron categories x2 larger than that of prior simulation (was 3.7% combined). This raises questions, in-cluding the modeling of bremsstrahlung

  8. Constraining the 0 -  Background with a Measurement of Inclusive Production • Measure p0/h yields in on- and off-peak data and MC • Determine MC correction factors in bins of E(p0): Correction = [(On-peak data) – s*(off-peak data)]/[BB MC] • Use corrected MC to predict background contribution • Also need to know recon. efficiency. of background p0s gg invariant mass MC Correction Factors Fits done to both data and MC

  9. How Do We Reconstruct 0s and ’s? From Run I-II Analysis; subject to further optimization for current Run I-V result • Begin with reconstructed high-energy (HE)  with cms energy E* • Search GoodPhotonsLoose list for potential sibling  with the following minimum lab energy (E2,lab) requirement (from Run 1-2; not yet optimized for current analysis): • Find potential sibling that, in combination with HE , has invariant mass M closest to the 0 () mass. • Reject event if 115 < M < 155 (508 < M < 588) MeV for the best 0 () combination.

  10. Require 2nd photon to be above minimum energy cut Require 2nd photon to be in fiducial volume -.74 < coslab < .94 1 2 3 E* coslab Of remaining bkgd events, almost all make a good 0 candidate with the HE  Require 2nd photon to have a truth match E* E* And with What Efficiency? If high-energy (HE)  truth-matches to a 0 daughter, make succession of requirements on MC truth properties of other (low-energy) daughter • Observations: • Typically reconstruct only about ½ (depends on E*) of background 0s • 20% truth-matching inefficiency; only about 6% due to merged 0s. Could the rest be conversions? • must understand conversion effects to subtract background correctly (not appreciated before)

  11. Material and the Inclusive Measurement of b  s • Material enters into the measurement of b  s in three substantial ways: • Conversions  HE  efficiency, • Conversions  0 reconstruction efficiency • Bremsstrahlung  electron fake rate • There are complications associated with esti- • mating these effects. For example, a photon • converting in the DIRC may or may not be • reconstructed as the original photon, depending • on its energy, the depth in the DIRC, etc. • This must be understood, in addition to the distribution of material in the detector and the brem/conversion cross-sections. Additional control samples may need to be developed and applied (“radiative bhabha” to understand bremsstrahlung?).

  12. E2,lab M E* More clever rejection of 0 backgrounds? ( analysis used likelihood based on  mass and E2,lab)  try NN rejection Run I-II analysis performance Signal Efficiency Using E* information Variables considered: M E* E2,lab coslab HE  2nd moment HE  isolation HE  Lat. Moment LE  2nd moment LE  isolation LE  Lat. Moment Signal Efficiency Ignoring E* information Most power in M, E2,lab (already in use) and E* (dangerous). Will not pursue. Background Efficiency

  13. Continuum Suppression for Run I-V Analysis • Develop Neural Net to make most efficient use of shape variable information. Inputs include Fox-Wolfram moments, lepton tagging variables, energy-flow variables: • Two classes of NNs, separated by energy-flow approach: • Energy cones (three variants) • Two different cuts on NN output (standard and relaxed) • One without lepton momentum • Legendre moments plus momentum-tensor quantities (similar to sphericitiy tensor) • Prior (Run I-II) analysis used Fisher Discriminant composed only of shape variables • Note: At the end of the day, the continuum subtraction will be determined from the off-resonance data, not from a-priori understanding of the NN efficiency

  14. % of total Error Statistitical Model Systematic Neural Net Selection: A Word About Run I-II Syst. Errors Run I-II Result (Phys.Rev.Lett.97:171803,2006 ) Br (BXsg) = (3.67  0.29  0.34  0.29) x 10-4 Different b  s models (b mass, Fermi motion) E* [GeV] Selection efficiency vs. E* for Run I-II selection Important: Run I-V optimi-zation must consider both statistical and systematic (especially model) error! E* [GeV]

  15. Event-Shape NN Selection • Consider both partial BF as well as moment calculations. All in all… • None of the candidate NNs is clearly preferable • Choose Legendre-moment-based NN in view of its modest dependence of signal efficiency on E* Eff vs. Eg* Econes I • better statistical precision • larger model error eff. slope = 3.2 Legendre Moments • more stats in p0/h control sample • reduced model error eff. slope = 1.5

  16. Other Backgrounds: Antineutrons Was 7.7% of the B/Bbar background for RUN I-II Contribution can be constrained by looking at antiprotons. Must understand: Production Rate Two components: fragmentation and  decay; have different isospin relations (p/n fraction) and different momentum spectra Working with hadronics group (D. Muller) to sort out. Signature in EMC Use -bar sample (high momentum) [Develop dE/dX-identified sample (low momentum) ?] Data MC ECAL Lateral Moment

  17. Other Backgrounds:  and ’ BAD 163 : nominally 2.1% of B/Bbar background; d/dp* measured; use to correct rates in MC (correction factor “”) BAD 179 + private updates /: nominally 0.8% of B/Bbar background; less well-constrained, but less of a contribution.

  18. Other Backgrounds: B   X Simulation estimates that HE backgrounds photons with B meson parents are twice as common than that of Run I-II simulation (1.4% vs. 0.7% of B/Bbar background) . These gammas seem to be coming predominantly from SL decay; how well do we understand this number? Why did it change in the MC simulation?

  19. b  s Outlook I An admirable goal would be Lepton/Photon – what kind of shape are we in? • The lepton-tagged inclusive analysis is gelling… • CM2 migration complete • Low-energy  truth-matching work-around • Shape-variable selection (NN) finalized • 0 and production rates measured • 0 background rejection revisited • Several other selection cuts established (merged 0s …) • A number of “standard” things remain (treatment developed for Run 1-2) • Anti-neutron rejection criteria • Final optimization • “Control region” test of B/Bbar background contribution • Estimation of most sources of systematic errors

  20. b  s Outlook II • However, some new considerations have arisen • Brehmsstrahlung and conversions (material effects) • Non-DST level study of conversion, brehm properties • New control samples (radiative Bhabha?) • Understanding of direct B   backgrounds. • Also, the loss of Philip Bechtle (to DESY) was a set-back, but students (Kyle, Luke) now coming up to speed on production code. • Initial preliminary results will include measurements of: • Partial branching fraction (1.9 < E* < 2.7)  further tighten constraint on new physics • 1st and 2nd moments of photon energy distribution  generic constraint on fermi motion of b quark • ACP  Independent probe for new physics (current: -.110.115.017) • We have our work cut out for us…

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