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DOE Site Visit: Effective Neutral Currents and Radiative Penguins

This document outlines the discussions and findings of the 2009 DOE Site Visit on the topic of effective neutral currents and radiative penguins in physics research, specifically focusing on the b -> sγ and b -> dγ transitions. It explores the motivation, implications, and measurements related to these processes within the Standard Model and supersymmetry parameter space.

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DOE Site Visit: Effective Neutral Currents and Radiative Penguins

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  1. DOE SITE VISIT Thursday, June 18, 2009 BaBar BaBar Radiative Penguin Physics at SCIPP Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz

  2. People • Senior • Al Eisner (b  s) • Bruce Schumm • Post-Doctoral • Juergen Kroseberg (RadPen Convener; to U. Bonn 2/08) • Students • Patrick Spradlin (B   Ph.D. June 2007; Oxford P.D.) • Tim Beck (b  d Ph.D. June 2008; college teaching) • Luke Winstrom (Ph.D. June 2009; many P.D. offers) • Joel Martinez (B   Ph.D. expected June 2010) 2009 DOE Site Visit

  3. Outline • Effective Neutral Currents: General Motivation • b  s Penguins • SUSY parameter space implications • b  s “Inclusive” approach • b  d Penguins and |Vtd/Vts| • Motivation • B →(ρ,ω)g “Exclusive” approach • B→Xd “Semi-Inclusive” approach • CP Violation in B →ρog • Conclusions 2009 DOE Site Visit

  4. Effective Neutral Currents and Radiative Penguins The SM b  s(d)  transition is high order (two weak plus one EM vertex) … Vtb Vt(s,d) so new physics can enter at leading order: + photon off any charged leg (d) (d) (d) Although rare (~ 5x10-4 for s and ~10-5 for d), the isolated high-energy photon is a powerful signature. 2009 DOE Site Visit

  5. Outline • Effective Neutral Currents: General Motivation • b  s • SUSY parameter space implications • Inclusive approach • b  d and |Vtd/Vts| • Motivation • B →(ρ,ω)g (“Standard” Approach) • B→Xd (“Semi-Inclusive” Approach) • Status of |Vtd/Vts| • CP Violation in B00 • Conclusions 2009 DOE Site Visit

  6. B  s and SUSY Parameter Space C.F. Berger, J.S. Gainer, J.L. Hewett, T.G. Rizzo, “Supersymmetry Without Prejudice”, arXiv:0812.0980v1 [hep-ph] Explore 107 points over 19-dimensional parameter space of CP-conserving MSSM b  s most effective constraint (72% of models surviving prior constraints are eliminated; better than direct searches for SUSY partners) 2009 DOE Site Visit

  7. The e+e- Cross Section in the Upsilon Region The (4S) resonance is the lightest resonance that decays into “open Beauty” ( or ) Off-Peak Data (~10% of Sample) On-Peak Data (4S) resonance is ~1 nb at peak, competing with a “continuum” background of ~3 nb 2009 DOE Site Visit

  8. B Factory Data Sets 440 fb-1 700 fb-1 2009 DOE Site Visit

  9. qq + ττ BB XSγ Inclusive Measurement of b  s: Introduction Most exacting approach (“Inclusive”) is aggressive: Use only high-energy  as signature Suppress continuum with event shapes, requirement of a high-energy lepton. Estimate remaining continuum by scaling off-peak data. Challenge: background from 0()   decays (plus some fakes) in B decays 2009 DOE Site Visit

  10. Inclusive Measurement of b  s: Signal/Background Sig. Region B/Bbar background control region BB Cont. Signal • After event selection, S/B is roughly 1:1 • Continuum measured from below-peak running • B/Bbar backgrounds must be identified and constrained 2009 DOE Site Visit

  11. If high-energy  passes selection, then 0,  look for low-energy  and veto event Inclusive Measurement of b  s: 0, Backgrounds Major source of BB background due to high-energy photons from 0()   (67% + 15% = 82% of total BB background according to MC) ~50% of the time the low-energy photon is missing. Modeling of low-energy (30-80 MeV) photon efficiency to ~ 1% critical to lowering systematic error One example of SCIPP group contribution Also: Anti-neutron backgrounds, photon efficiency, … 2009 DOE Site Visit

  12. Inclusive Semi-Inclusive Inclusive Inclusive Inclusive Summary of Measurements of the b  s Rate Collaborating with SLAC, Notre Dame; SCIPP playing central role since 2003 (Schmitz thesis, Winstrom candidacy project) A. Limosani, Melbourne BaBar Result on 360 fb-1 expected by end of year 2009 DOE Site Visit

  13. Outline • Effective Neutral Currents: General Motivation • b  s • SUSY parameter space implications • Inclusive approach • b  d and |Vtd/Vts| • Motivation • B →(ρ,ω)g (“Standard” Approach) • B→Xd (“Semi-Inclusive” Approach) • Status of |Vtd/Vts| • CP Violation in B00 • Conclusions 2009 DOE Site Visit

  14. (d) (d) (d) (d) Vt(s,d) (d) (d) Measuring |Vtd/Vts| Two independent diagrams provide sensitivity to CKM parameter Vtd B Mixing Note: In both cases, hadronic uncertainties minimized by comparing to corresponding Vts process (Bs mixing, b  s)  Observable is | Vtd / Vts | Radiative Penguins 2009 DOE Site Visit

  15. SM effects suppressed by 10-5 relative to mixing |Vtd/Vts| from Penguins: Motivation ICHEP ’08 B Mixing Results [Farrington(CDF), Moulik(D0), averaged by Di Lodovico (BaBar)]: How do penguins fit into the picture? Mixing: xd = mB/B ~ 1  mB ~ B Penguins: Br(bd) ~ 10-5 d~ 10-5B With |Vtd/Vts| precisely constrained by mixing, b  d is a compelling testbed for new physics. 2009 DOE Site Visit

  16. (and ) Exclusive Approach: B  ()  Standard (“Exclusive”) Approach: measure exclusive rate Br(B  () ); normalize with Br(B  K* ) Annihilation Diagram Values of 2 and R are available from Ali, Parkhomenko, arXiv:hep-ph/0610149 Ball, Zwicky, J. High. Energy Phys. 0604, 046 (2006); Ball, Jones, Zwicky, Phys. Rev. D 75 054004 (2007) 8% uncertainty on extraction of |Vtd/Vts|. 2009 DOE Site Visit

  17. Measurement of B(B  () ) (continued) Remaining separation achieved by two-dimensional fit to the largely independent kinematic variables “Energy-substituted mass”; since Ebeam ~ MB, largely a measurement of momentum balance EB = Ebeam for properly reconstructed candidate; total energy measurement *In e+e- CMS frame Example: BaBar B0 0  • “self-calibrating” continuum background subtraction • efficiencies (~5-15%) estimated with control samples Continuum Signal bs Feedthrough 2009 DOE Site Visit

  18. Phys.Rev.D78:112001,2008 assuming the world-average |Vtd/Vts| from Exclusive (,) Decays BaBar:  423 fb-1 Phys.Rev.D78:112001,2008 yielding Collaborating with CALTECH; SCIPP contribution data processing, validation, systematics (Spradlin thesis, Martinez candidacy project) 2009 DOE Site Visit

  19. Semi-Inclusive Approach: B  Xd  (Preliminary) “New” Approach (BaBar): Reconstruct seven exclusive final states Xd in range 0.6 GeV/c2 < MXd < 1.8 GeV/c2 |Vtd/Vts|2 related to (bd)/(bs) with ~1% theoretical uncertainty [Ali, Asatrian, Greub, Phys. Lett. B 429, 87 (1998)] Collaborating with Imperial College, London; SCIPP playing central role since inception (Beck thesis) 2009 DOE Site Visit

  20. # bodies # bodies # 0 # 0 Measured Regions for B  Xd(s)  UNMEASURED XS MEASURED K* Region 1.0 < Mhad < 1.8 1.8 < Mhad 0.6 < Mhad < 1.0 UNMEASURED Xd MEASURED Xd analysis only  and Xd analyses Mhad (MXd) 2009 DOE Site Visit

  21. Continuum background Xs, MisID background Errors: Stat.  Experimental Syst. arXiv:0807.4975 [hep-ex]; to appear in PRL Primary experimental result B  X(s,d)  Decay Width Ratio Results Fit in high-mass Xd region 1.0 < Mhad < 1.8 GeV/c2 BABAR BABAR E MES 2009 DOE Site Visit

  22. Expt. Theory Calculation of |Vtd/Vts| arXiv:0807.4975 [hep-ex]; to appear in PRL Ali Asatrian Greub Ratio of partial widths related to |Vtd/Vts| with very small uncertaintys 2009 DOE Site Visit

  23. Global Status of |Vtd/Vts| No evidence for non-Standard-Model contribution to the b  d decay width. Is the implication of this constraint fully understood? 2009 DOE Site Visit

  24. CP Violation in B00 Separate out B0 (“+”) and anti-B0 (“-”) decays; look at asymmetry in time-evolution: 2009 DOE Site Visit

  25. 0 CP Violation Sensitivity Study Toy Monte Carlo study based on Br(B) selection S SENSITIVITY SIGNAL SIGNIFICANCE vs. Event Selection Parameter (“Decision Tree” Output) Full re-optimization nearing completion; next step will be to confirm fitting strategy and identify leading systematics Collaborating with SLAC; SCIPP playing central role since inception (Martinez thesis topic) 2009 DOE Site Visit

  26. Concluding Remarks • SCIPP playing central role in key, high-impact radiative penguin measurements • Inclusive b  s measurement very challenging; expect to have result to better than 10% in ~6 months • Intensive focus on b  d transition * Rates  One PRL, one PRD in last year * CP Violation  Expect result in ~1 year • Ground-breaking semi-inclusive b  d measurement promising for higher-statistics running • Impact of b  d signature may not yet be fully appreciated • 4 PhD theses; 5th on the way; recent talks at CKM’08, Miami’08, FNAL Wine & Cheese, DESY Exptl Seminar 2009 DOE Site Visit

  27. Backup Slides 2009 DOE Site Visit

  28. Inclusive Measurement of b  s: B/Bbar Backgrounds Sources of B/Bbar Background (after full selection) 2009 DOE Site Visit

  29. Inclusive Measurement of b  s: 0, Backgrounds Define cosh  (E,high - E,low)/ (E,high + E,low) = energy asymmetry Signal selection requirement of E* > 1.8 GeV pushes asymmetry up, and energy of 2nd photon down.  Sensitive to reconstruction efficiency for 30-80 MeV photons. Measurement of 0 reconstruction efficiency from ()/() Expected/Measured cosh cosh But: can bootstrap to lower E with dedicated 0 sample 2009 DOE Site Visit

  30. BX(d,s): Correction for Missing Modes • MC Simulation • Two-body Xs(d)  decay; mass spectrum of Xs(d) system given by Kagan-Neubert model • A.L. Kagan, M. Neubert, Phys. Rev. D 58, 094012 (1998) • Fragment Xs system via prior experimental constraint • Fragment Xd system via phase space • Missing modes with 0.6 < MX < 1.0 • MC suggests this region is dominated by resonances ( and ); confirmed by K*dominance of B Xs • Correction for missing modes well understood 2009 DOE Site Visit

  31. BX(d,s): Correction for Missing Modes • Missing Modes with 1.0 < MX < 1.8 • Force 50% of decays to un-weighted mix of higher-mass resonances • Force Xd decay to be identical to Xs decay up to substitution s  d • B  Xd  Resonances • h10 (1170) • b10 (1235) • b1+ (1235) • a10 (1260) • a1+ (1260) • f20 (1270) • f10 (1285) • a20 (1320) • a2+ (1320) • B  XS  Resonances • K1 (1270) • K1 (1400) • K* (1410) • K2*(1430) • K* (1680) 2009 DOE Site Visit

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