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

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 Direct searches (LEP) B  s  constraints MSSM Constraints Extra Dimensions SUSY

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

Run1-2 Babar Fully Inclusive BaBar 2006 inclusive result (Run I-II only): B(B  X s  ; 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. Current Status of b  s  BF Measurements Phys.Rev.Lett.97:171803,2006 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.] BaBar Sum of Exclusive Modes

qq + ττ BB XSγXSγ 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  0 s, hadrons Source: BAD 323, based on the 81 fb -1 Run I-II sample

What are the sources of B/Bbar background? 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… After Selection Cuts B/Bbar background control region BB Cont. Signal Sig. Region Source: BAD 323, based on the 81 fb -1 Run I-II sample

Truth MatchParentage Fraction of Total 1.5 < E  * < 1.9 Fraction of Total 1.9 < E  * < 2.7 Photon 0 Photon  Photon  Photon  PhotonB Photon J/  Photonelectron Photonother0.004 All Photon 00 Any0.000 electronAny neutron/antineutronAny proton/antiprotonAny K0LK0L Any   or K  Any0.002 noneAny otherAny0.000 All non-photon All1.000 Nominal B/BBar Background Sources 82% of B/Bbar background Electron categories x2 larger than that of prior simulation (was 3.7% combined). This raises questions, in-cluding the modeling of bremsstrahlung B/Bbar background contribution “guess” (selection not yet finalized)

Constraining the  0 -  Background with a Measurement of Inclusive Production  invariant mass Fits done to both data and MC MC Correction Factors Measure  0 /  yields in on- and off-peak data and MC Determine MC correction factors in bins of E    : 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   s

How Do We Reconstruct  0 s and  ’s? Begin with reconstructed high-energy (HE)  with cms energy E  * Search GoodPhotonsLoose list for potential sibling  with the following minimum lab energy (E 2,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. Reconstruct  0 E 2,lab > 40 MeV for E  * < 2.3 GeVE 2,lab > 80 MeV for E  * > 2.3 GeV Reconstruct  E 2,lab > 175 MeV for E  * < 2.3 GeVE 2,lab > 275 MeV for E  * > 2.3 GeV From Run I-II Analysis; subject to further optimization for current Run I-V result

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

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?).

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

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

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

Econes I better statistical precision larger model error Event-Shape NN Selection Legendre Moments more stats in  0 /  control sample reduced model error eff. slope = 1.5 eff. slope = 3.2 Eff vs. E  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  *

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) ?] ECAL Lateral Moment Data MC

Other Backgrounds:  and  ’ BAD private updates BAD 163  : nominally 2.1% of B/Bbar background; d  /dp * measured; use to correct rates in MC (correction factor “  ”)  / : nominally 0.8% of B/Bbar background; less well-constrained, but less of a contribution. X  ’ = E  ’ /E beam Range B(B  / ) DataB(B  / ) MC 0.1 = 0.39 (1.54  0.41) x x – 0.52 (1.00  0.33) x x 10 -4

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? Other Backgrounds: B   X

b  s  Outlook I 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  0 s …) 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 An admirable goal would be Lepton/Photon – what kind of shape are we in?

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 1 st and 2 nd moments of photon energy distribution  generic constraint on fermi motion of b quark A CP  Independent probe for new physics (current: .115 .017) We have our work cut out for us… b  s  Outlook II