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LHCb sensitivity to  with B  h + h - and U-spin Symmetry

LHCb sensitivity to  with B  h + h - and U-spin Symmetry. Laura Fabbri on behalf of the LHCb collaboration. Physics at LHC Vienna, 13 -17 July 2004. Outline. Physics motivation Extraction of the weak phase  from the B d   +  - and B s  K + K - decays

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LHCb sensitivity to  with B  h + h - and U-spin Symmetry

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  1. LHCb sensitivity to with Bh+h- and U-spin Symmetry Laura Fabbri on behalf of the LHCb collaboration Physics at LHC Vienna, 13 -17 July 2004

  2. Outline • Physics motivation • Extraction of the weak phase  from the Bd+-and BsK+K- decays • Bd(s)h+h-event selection • Strategy, event yields and background-to-signal ratios • CP sensitivity • Bayesian determination of  • Conclusions Physics at LHC

  3. CKM (new?) physics Indirect CKM fitsexpect 65o • When LHCb starts taking data in 2007, sin2 will be already known with very good accuracy • To isolate signals of new physics, it is crucial to measure the other two angles of the Unitarity Triangle, as  ( -arg Vub) • In case of new physics, more complementary measurements of  will help to understand where the new contributions come from • Bh+ h- have sizeable contribution from penguin graphs which may evidence new physics in loops  from LHCb? Tree Diagram Penguin Diagram Physics at LHC

  4. d =2Bd-Bd mixing phase(measured with BdJ/Ks) s =-22Bs-Bs mixing phase(can be probed with BsJ/) Extracting  from Bd+-andBsK+K-  4 equations and 5 unknowns: d, ,d’,’ (hadronic parameters) and One needs other inputs to solve for  [R.Fleischer, Phys. Lett. B459 (1999)] Physics at LHC

  5. Unique solution for  Using U-spin Symmetry Bd+-  U-spin (d,s quark exchange)  BsK+K- 6 eqs. and 5 unknowns the system can be solved unambiguously U-spin symmetry In this example Physics at LHC

  6. Bd(s)h+h-event selection • Selection cuts are simultaneously optimized in order to maximize • Two major sources of backgrounds taken into account • Combinatorial background from bb inclusive events • Due to the huge minimum bias MC statistics required for a detailed study of combinatorial background, we make the plausible assumption that most of the combinatorial background will come from beauty events (presence of high pT and large IP tracks from B) • Specific background from B decayswith same two-track topology • e.g. BdK+-, BsK+K-, Bs+K- as backgrounds for Bd+- • After event selection, tagging and trigger algorithms are tuned on selected events LHCb Public Note 2003-123 Physics at LHC

  7. , K B0(s) , K IP Beam axis (z) IPB L IP Selection cuts • Reconstruction and Particle ID • Each charged track identified asa Pion or Kaon using the Particle ID detectors (RICHs in particular) • Selection cuts on identified tracks • p • Max[pT(h+), pT(h-)] • Min[pT(h+), pT(h-)] • Max[IP/IP(h+), IP/IP(h-)] • Min[IP/IP(h+), IP/IP(h-)] • 2 of common vertex • Selection cuts on the candidate B • pT • IP/IP • L/L • Invariant mass Physics at LHC

  8. Mass spectrasignals + specific backgrounds only Bd+- BdK+- Two-body background only if not using RICH… 17 MeV/c2 BsK+K- Bs+K- Mostly BdK+-(same signature) Physics at LHC

  9. Proper time acceptance and resolution Acceptance suppression at low proper time due to cuts on IPs and distance of flight 1=341 fs 2=673 fs (15%) Resolution on proper time fitted with double Gaussian(single Gaussian 40 fs) Physics at LHC

  10. Signal yields andbackground-to-signal ratios • Annual yields after L0+L1 triggers and offline selection (assumed bb = 0.5 mb and L =2fb-1/yr) Physics at LHC

  11. CP sensitivity studiesFast Monte Carlo Simulation • In order to study the sensitivity on the  angle we generated many data samples, each corresponding to different settings of the relevant unknown parameters: • Ms,, s, d, , etc. • The Fast Monte Carlo produces proper time and invariant mass distributions {(t, m)k; k=1, N}of tagged B decays (combinatorial background included). • The {(t, m)k; k=1, N} distributions are parameterized according to the proper time acceptance, resolution and invariant mass distributions obtained from the full GEANT simulation, which takes into account realistic pattern recognition, trigger and offline selection. Physics at LHC

  12. Likelihood Fit • In order to extract CP asymmetries and mistag fraction simultaneously from data we perform a combined extended unbinned maximum likelihood fit of Bd+ - and BdK+ - (BsK+K- and Bs+K-) event samples (plus background) • BdK+ - (Bs+ K-) is a flavour specific decay and is used as control channel • Bd+ - (BsK+ K- ) and BdK+ - (Bs+ K-) have the same two-track topology (same tagging power) • extract the wrong tag probability from data itself • The fit is performed against 17 parameters describing the shape of the decay rate and invariant mass distributions • In particular we obtain the joint p.d.f. for the CP asymmetry coefficients Adir and Amix • Bivariate gaussians G(Adir, Amix) for the Bd+ - andGKK(Adir, Amix) for the BsK+ K- LHCb Public Note 2003-124 Physics at LHC

  13. Bayesian approach to determine the  p.d.f. • To propagate the experimental joint p.d.f. for Adir, Amix, the weak mixing phases dand s to a joint p.d.f. for d,  and  the Bayesian approach is used: Exp. joint p.d.f. (bivariate gaussian) for Gaussian priors for the weak mixing phases(from LHCb BdJ/KS and BsJ/) Physics at LHC

  14. Perfect U-spin O(20%) U-spin breaking would induce only a few degreesshift on  Sensitivity on  from Bd+-andBsK+K- (1 year) Correct Solution   65o Fake solution(disappears with more statistics) d- plane 95% confidence region from Bd+- only 95% confidence region from BsK+K- only Yellow and White contours: 68% and 95% confidence regions using all the information Physics at LHC

  15. Sensitivity scan () vs  d=0.3, = 160°, =65°, s=-0.04°, s/s=0.1 () vs ms d=0.3, = 160°, s=-0.04°, s/s=0.1, ms=20 ps-1 Physics at LHC

  16. Conclusions • The LHCb experiment will select and tag very large samples of Bd (Bs) charmless two-body decays • By combining the measurements of the Bd+-andBsK+K- asymmetry coefficients LHCb can measure  with a 5° statistical uncertainty, in one year, assuming U-spin symmetry and Standard Model • This strategy could disclose new physics effects in penguin diagrams providing a different measurement of  with respect to e.g. and • see LHCb talks by Eduardo Rodrigues and Sandra Amato Physics at LHC

  17. Backup slides Physics at LHC

  18. PAPenguin Annihilation Ccolour-suppressed Tree Pgluonic Penguin TTree PEWelectroweak Penguin PCEWcolour-suppressed electroweak Penguin EExchange AAnnihilation Charmless two-body decays of B mesons: diagrams Gronau, Hernandez, London and Rosner, Phys. Rev. D50 (1994) 4529 Physics at LHC

  19. Bd+-andBsK+K- decay amplitudes Bd+- BsK+K- Physics at LHC

  20. Distributions of selection variables for BsK+K- and combinatorial bb background Bs Mass  bb background ——— signal cut value and accepted region Max[IP/IP(K+), IP/IP(K-)] Min[IP/IP(K+), IP/IP(K-)] 2 of common vertex Bs pT Bs IP/IP Max[pT(K+), pT(K-)] Bs L/L Min[pT(K+), pT(K-)] Physics at LHC

  21. Selection cuts Identifiedtracks candidate B Physics at LHC

  22. Fast MC input values Nominal parameters: Bd +-, Bd K+- Bs K+K-, Bs +K- tagging efficiency 42% 50% wrong tagging fraction 35% 33% M 0.5 ps-1 20 ps-1  1/1.54 ps-1 1/1.46 ps-1 / 0 0.1 d 0.3 0.3  160o 160o  65o 65o weak mixing phase 0.82 -0.04 Sensitivity scan: parameters are varied one at a time d: 0.1 0.2 (0.3) 0.4 : 120o 140o(160o) 180o 200o : 55o(65o) 75o 85o 95o 105o s: 0 (-0.04) -0.1 -0.2 Ms (ps-1)15 (20) 25 30 s/ s: 0 (0.1) 0.2 Physics at LHC

  23. Sensitivity on  Resolution computed as half the 68% confidence interval Physics at LHC

  24. U-spin Symmetry How much rely on it? • U-spin symmetry in the relations d=d’ and =’ is not broken within naïve factorization approximation (Fleischer, Phys. Lett. B459, 1999) • Fleischer and Matias (hep-ph/0204101) allow for a SU(3) violation of 20%: d’/d  0.8÷1.2 • Matias (hep-ph/0311042) claims that a SU(3) breaking of 20% would induce only a5o shifton ; a phase difference =’- as large as 40o induces only a shift on  of1o • Beneke (hep-ph/0308040) estimates through QCD factorization a possible SU(3) violation at 30% level:d’/d  0.85÷1.3,   ±15o • A better understanding of SU(3) breaking would be desirable, but a O(20%) breaking does not spoil the measurement Physics at LHC

  25. Mass spectrasignals + combinatorial beauty background only BdK+- Bd+- BsK+K- BsK+K- Bs+K- Physics at LHC

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