slide1 n.
Skip this Video
Loading SlideShow in 5 Seconds..
B Physics at the Tevatron XXVII International Meeting of Fundamental Physics PowerPoint Presentation
Download Presentation
B Physics at the Tevatron XXVII International Meeting of Fundamental Physics

B Physics at the Tevatron XXVII International Meeting of Fundamental Physics

132 Views Download Presentation
Download Presentation

B Physics at the Tevatron XXVII International Meeting of Fundamental Physics

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. B Physics at the Tevatron XXVII International Meeting of Fundamental Physics Benasque, Spain Feb 8-13 2009 Joe Boudreau University of Pittsburgh For the CDF and D0 Collaborations

  2. Origins • B Physics at the Tevatron is about 17 years old—about 14 fully • reconstructed B+ events were found at the Tevatron (CDF) in 1992. • For nostalgics: • B physics at the Tevatron was a spinoff of a high-pT program there. • By Run II, topics in B physics such as CP and B(s) mixing were • among the main physics goals of the upgraded CDF and D0 • experiments, both of which continue to be highly successful. Phys. Rev. Lett.68, 3403 (1992)

  3. What makes B Physics compelling? • The weak decays of the b quark to its isospin partner, the top, is “switched off” due the high top mass. • All b quark decays proceed through off-diagonal elements of the CKM matrix • Many of them involve quantum loop diagrams (penguins, and boxes) involving the top quark (our heaviest fermion) and possibly more. • This gives B decays sensitivity to the magnitudes and phases of many of the CKM matrix elements. • And makes B physics essential for the understanding of CP violation. • The strong interaction is highly calculable in b hadrons • The mass of the b quark enables a theoretical approach to B hadron properties called HQET, allowing for precise calculation of hadron widths & masses and permitting clean extraction of coupling constants.

  4. Why do B physics at the Tevatron? • Proton-antiproton collisions produce all flavors of b mesons and baryons; excited states too: B+, B0, B0s, B+c, L0b, S+b, S-b, X-b, W-b + excited states of many of these have been observed now at the Tevatron U(4S) factories make only B+, B0 U(5S) add B0s, but poor sct resolution precludes time-dependent studies and samples are tiny. • Tevatron production cross sections are very large Triggering strategies now permit the Tevatron experiments to collect hadronic decays, semileptonicdecays, and decays including J/y’s.

  5. In general the most important components of a general purpose • detector system, for B physics, is: • tracking. • muon [+electron] id • triggering: B hadrons comprise O(10-3) of all events. • Charmless decay modes have branching fractions O(10-6)

  6. The D0 Silicon tracker... • surrounded by a fibre tracker at a distance 19.5 cm < r <51.5 cm • now augmented by a high-precision inner layer (“Layer 0”) • 71 (81) mm strip pitch • factor two improvement in impact parameter resolution

  7. CDF Detector showing as seen by the B physics group. Muon chambers for triggering on the J/y→m+m- and m Identification. Strip chambers, calorimeter for electron ID Central outer tracker dE/dX and TOF system for particle ID r < 132 cm B = 1.4 T for momentum resolution.

  8. L00: 1.6 cm from the beam. 50 mm strip pitch Low mass, low M-S. And another thing which is really special about this system is the trigger!

  9. The Silicon Vertex Trigger (SVT) * Provides precision impact parameter information at L2 * Beam crossing: SVX samples & holds on a dual-ported analog pipeline. … when a Level 1 Accept occurs, the readout cell is read without incurring deadtime allows high rate at L1 massive cleanup of B triggers using impact parameter information at L2. Run I: most (almost all) B physics relies on the J/y trigger, yielding now millions of events. other hadronic decays go straight down the beam pipe. Run II: These decays and many more are suddenly visible  Major impact on B physics!

  10. Hadron collider: large cross sections, large data sample, new B triggers: SVT (CDF) collects practically as many reconstructed B decays as the J/y trigger. J/y trigger Hadronic B trigger B+ decays: Lb decays 532 events Lb-> J/y L 2.8 K events Lb→Lcp

  11. Production cross section is large! At sqrt(s)=1960 GeV/c2 : s = 17.6 ± 0.4(stat) + .2.5 -2.3 (syst) mb |y|<0.6 (CDF) [compare 1 nb at Y(4S), 6 nb at the Z0] Total pp inelastic cross section is greater by about three orders of magnitude PRD 71, 032001 (2005) Mesured in inclusive J/y events. PRD 75, 012010 2007 Measured in B+ J/y K+ Phys. Rev. Lett. 85, 5068 - 5073 (2000) Measured using tagged jets. The fragmentation fractions into various b hadron species has been measured in semileptonic decays: Phys. Rev. D77, 072003 (2008).

  12. Orbitally excited (L=1) mesons in the B0 system. S-wave D-wave

  13. Observation based on a fully reconstructed • B+ plus a “soft” pion. • CDF: more than half of the data comes from SVT. B2* B1 B1* B0* p B* B g PRL99 172001 (2007) CDF Internal note 8945

  14. Bs** : same transitions as for B0** except substitute p→K. Expected: Bs2* Bs1 Bs1* Bs0* Bs0* Bs1 Bs1* Bs2* K B* B g B* B PRL 100 082002 (2008) arXiv:0710.4199

  15. The Sb Baryons: 4 new particles Sb+ (buu) → Lbp+ Sb- (bdd) → Lbp- I-spin partners, not antiparticles! Lb (from SVT) + “soft” pion The splitting of J=1/2 Sb and J=3/2 Sb* states is a hyperfine splitting. PRL 99, 202001 (2007)

  16. The X-b and W-b are similar particles with similar decay topologies. ct~ 5 cm ct~ 2.4 cm Xb- = (bsd) Wb- = (bss) The charged daughter hyperons can be followed in the silicon! D0: Dedicated tracking to recover efficiency for tracks with high impact parameter. CDF: Dedicated tracking to follow the charged hyperon, reconstructed through its daughters, through the silicon. D0 has been the first to observe both particles.

  17. The X-b Baryon PRL 99 052001 (2007) PRL. 99, 052002 (2007)

  18. The WB Baryon, so faronly D0. Significance: 5.4s M(Wb-) = 616510 (stat)  13(syst) Phys. Rev. Lett. 101 , 232002 (2008 ) Prediction 6052  2.4 MeV/c2 Karliner, Keren-Zur, Lipkin, Rosner hep-ph/0804.1575

  19. u d A small sample of Bc+ events has been collected in Bc+J/yp+ p- D0: 54 ± 12 signal events (1.3 fb-1) CDF: 108 ± 15 signal events (2.4 fb-1) b c c c Bc J/y optimize on B+… Observe Cabbibo- suppressed B+J/yp+ and the Bc+ arXiv:0802.4258v1 M(Bc)CDF = 6275.6 ± 2.9 ± 2.5 MeV/c2 Phys. Rev. Lett. 100, 182002 (2008). M(Bc)D0 = 6300 ±14 (stat) ± 5 (sys) MeV/c2 Phys. Rev. Lett. 101, 012001 (2008) arXiv:0712.1506v1 M(Bc)LAT = 6304 ± 12 +18 -0 MeV/c2 Phys. Rev. Lett. 94, 172001 (2005)

  20. Lifetime measurements are based on semileptonic decay modes, trilepton events with a J/y and a third lepton. No mass peak, no sidebands, so data, MC is needed to estimate physics background (gbb) and fake leptons. hep-ex/0805.2614 J/y e J/y m CDF Public Note 9294

  21. PHYSICS OF B HADRON LIFETIMES: Pauli interference prolongs lifetimes: +5% for B+, +3% for Lb Spectator model: all b hadron lifetimes are equal. HQET: Weak annihilation or scattering reduces lifetimes -7% Lb

  22. For the B0s, lifetimes: the decay B0s J/y f is a combination of • two states (B0s ,H and B0s,L) in unequal proportions. Further analysis • of this system described later. • Alternative: measure the lifetime in a flavor-specific decay mode BsDspX • Measure the lifetime from the SVT Trigger, which makes a very jagged cut • on the lifetime.ct(Bs) = 455.0 ± 12.2 (stat.) ± 7.4 (syst.) μm Analysis uses fully reconstructed and partially reconstructed decays. PRL 97 241901 (semileptonic) cdf 9293 HQET: ct(B0s)= (1.00±0.01) ct(B0) PDG: ct(B0) = 459 ±0.027 mm

  23. The Lb lifetime is now precisely measured in CDF using 3K events LbLc+p-from the SVT CDF public note 9408

  24. Beyond b hadrons: A few topics in B0s-physics with big impact.

  25. b m+ m- b B Physics as a probe of SUSY + dark matter? t Z A Highly suppressed FCNC process Very clean signal! SM Expectation: BR( B0sm+m-) = (3.42±0.54) x 10-9 BR( B0dm+m-) = (1.00±0.14) x 10-10 G. Buchalla and A. J. Buras, Nucl. Phys. B400, 225 (1993) A.J. Buras, Phys. Lett. B 566 115 (2003) t n W B0d,sm+m- t m+ s m- s W W In a SUSY context one has other contributions. e.g: ..and these processes go as tan6b (MSSM). They can enhance the S.M. decay rate by 1-3 orders of magnitude.

  26. The D0 Analysis: Use a likelihood ratio product as a discriminant: Based on isolation,Lxy/sxy, P(c2), min(d0/s), m(m+m-). In red, those that improve with the innermost silicon layer: expect 0.80.3 events expect 1.50.3 events B0dm+m- SM: BR( B0m+m-) = (1.00±0.14) x 10-10 CDF Limit: BR( B0m+m-) > 1.8 x 10-8(95% CL) 2fb-1 SM Expectation: BR( B0sm+m-) = (3.42±0.54) x 10-9 CDF Limit: BR( B0sm+m-) > 5.8 x 10-8 (95% CL) 2fb-1 D0 Limit: BR( B0sm+m-) > 9.3 x 10-8 (95% CL) 2fb-1 HFAG: BR( B0sm+m-) > 4.7 x 10-8 (95% CL) B0sm+m- PRL 100,101802 (2008) D0 Conf Note 5344

  27. B0s –B0s Flavor Oscillations There are two states in the B0s system, the so-called “Flavor eigenstates” They evolve according to the Schrödinger eqn and M, G Hermitian Matrices u, c u, c G: Absorptive diagrams M: Dispersive diagrams

  28. Mass eigenstates are superpositions of flavor eigenstates governed by constants p, q: And an initially pure |B0s> evolves (oscillates) mixing probability: The magnitude of the box diagram gives the oscillation frequency Dm. The phase of the diagram determines the complex number q/p, with magnitude of very nearly 1 (in the standard model).

  29. Vub*Vud Vtb*Vtd c c t t u u c u t W+ W+ W+ W+ W+ W+ W+ W+ W+ b s d s b d b s d b Vcb*Vcd The chief prediction of the CKM model is that the CKM matrix is unitary, and that implies a number of constraints, including the “Unitarity Triangle” Vub*Vud + Vtb*Vtd + Vcb*Vcd=0

  30. Mixing is an important constraint on the Unitarity Triangle: Mixing probability Mixing occurs when a B0s decays as a B0s. Decay to a flavor specific eigenstate tags the flavor at decay. One of three tagging algorithms tags the flavor at production. Good triggering, full reconstruction of hadronic decays, excellent vertex resolution, and high dilution tagging are all essential for this measurement, which made news in 2006.

  31. Δms = 18.56 ± 0.87(stat) ps-1 (D0 CONF Note 5474) (PRL 97, 242003 2006)

  32. There are now various formulations summarizing the conclusions of a decade • of running the B factories and the Tevatron, but • ..the CKM mechanism seems to have survived a very stringent round of tests; • & the heros of this got their NOBEL PRIZE in 2007, • The only source of CP violation in the standard model emerges as the • dominant source in all processes covered in this summary plot.

  33. The DA “anomaly” may also have to do with bs • Direct CP in B+K+p0 and B0 K+p- are generated by the • b s transition. These should have the same magnitude. • But Belle measures (4.4 s) • Including BaBar measurements: > 5s Lin, S.-W. et al. (The Belle collaboration) Nature 452,332–335 (2008). • The electroweak penguin can break the isospin symmetry • But then extra sources of CP violating phase would be required in the penguin

  34. Example of new physics: a fourth generation quark that contributes to the Electroweak Penguin Wei-Shu Hou, arXiv:hep-ph/0803.1234 Would have other measureable consequences: e.g. an impact on mixing induced CP violation in B0s mesons.

  35. CP Violation in B0s mesons Results from flavor tagged analyses of B0s J/y f ≠

  36. CDF and D0 use B0s J/y f to measure CKM phases. We determine from this decay the quantity bs. This is in exact analogy to B factory measurement of the b, an angle of the unitarity triangle. The standard model makes very precise predictions for both angles. But other new particles & processes, lurking potentially in quantum mechanical loops such as box diagrams can change the prediction.  Need to measure all possible unitarity triangles to search for NP 38

  37. B0s→J/yf • B0s→J/yf is two particles decaying to three final states.. • Two particles: • Three final states:J/yf in an S wave CP Even • J/yf in a D wave CP Even • J/yf in a P wave CP Odd Light, CP-even, shortlived in SM Heavy, CP-odd, longlived in SM A supposedly CP even initial state decays to a supposedly CP odd final state…. like the neutral kaons Measurement needs DG≠0 but not flavor tagging. The polarization of the two vector mesons in the decay evolves with a frequency of Dms Measurement needs flavor tagging, resolution, and knowledge of Dms

  38. Time dependence of the angular distributions: use a basis of linear polarization states of the two vector mesons { S, P, D}  { P, P||, P0 } CP odd states decay to P CP even states decay to P|| ,P0 • The polarization correlation • depends on decay time. • Angular distribution of decay • products of the J/y and the f analyze the rapidly oscillating • correlation. If [H,CP] ≠ 0 Then Dms~ 17.77 ps-1. • S. Dighe, I. Dunietz, H. J. Lipkin, and J. L. Rosner, Phys. Lett. B 369, 144 (1996), • 184 hep-ph/9511363.

  39. The measurement is a flavor-tagged analysis of time-dependent angular distributions An analysis of an oscillating polarization. This innocent expression hides a lot of richness: * CP Asymmetries through flavor tagging. * sensitivity to CP without flavor tagging. * sensitivity to both sin(2bs) and cos(2bs) simultaneously. * Width difference * Mixing Asymmetries

  40. Very famous measurement of CP Asymmetries in B0J/y K0s |B0> | J/y K0s > |B0> Vub*Vud Vtb*Vtd b Vcb*Vcd BABAR, BELLE have used this decay to measure precisely the value of sin(2b) an angle of the bd unitarity triangle. There was a fourfold ambiguity

  41. Babar, Belle resolve an ambiguity in b by analyzing the decay B0J/y K0* which is BV V and measures sin(2b) and cos(2b) This involves angular analysis as described previously Phys.Rev. D71 (2005) 032005 J/y K0* Phys.Rev.Lett. 95 (2005) 091601 | P|| > |B0> | P0 > |m+m-K0sp0> |B0> |B0> | P >

  42. |Bs0>  J/y fis an almost exact analogy, except this system also contains a difference in lifetime/width) J/y f | P|| > |Bs0> | P0 > |m+m-K+K-> |Bs0> |Bs0> | P >

  43. The decay B0sJ/yf obtains from the decay B0J/y K0* by the replacement of a d antiquark by an s antiquark b d s W W B0→J/y K0* c W d c b s s W W Bs0→J/yf c W s c We are measuring not the (bd) unitarity triangle but the (bs) unitarity triangle:

  44. The analysis of B0s→J/y f can extract these physics parameters: The measurement of bs and DG are correlated; from theory one has the relation DG = 2|G12|cos(2bs) with |G12| = 0.048 ± 0.018 and A. Lenz and U. Nierste, J. High Energy Phys. 0706, 072 (2007). The exact symmetry.. … is an experimental headache.

  45. 2019 ± 73 events 1967 ± 65 events

  46. SST +OST: eD2 = 4.68 ± 0.54% SST: eD2 3.6% OST: eD2 1.2% Flavor Tagging Performance and Validation Each tag decision comes with an error estimate validated: 2. In the B0s mixing (SST) 1. Using B± (OST)

  47. CDF Untagged Analysis (1.7 fb-1) Phys. Rev. Lett. 100, 121803 (2008) Feldman-Cousins confidence region in the space of the parameters 2bs and DG HQET: ct(B0s)= (1.00±0.01) ct(B0) PDG: ct(B0) = 459 ±0.027 mm

  48. Tagged analysis: likelihood contour in the space of the parameters bs and DG Phys. Rev. Lett. 100, 161802 (2008) One ambiguity is gone, now this one remains