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EW Physics at a SuperB Flavour Factory with Polarized Beam and status of some Flavour Physics with Taus J. Michael Roney University of Victoria III Prometeo.

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Presentation on theme: "EW Physics at a SuperB Flavour Factory with Polarized Beam and status of some Flavour Physics with Taus J. Michael Roney University of Victoria III Prometeo."— Presentation transcript:

1 EW Physics at a SuperB Flavour Factory with Polarized Beam and status of some Flavour Physics with Taus J. Michael Roney University of Victoria III Prometeo Workshop IFIC 16 November 2010

2 EW physics at LEP & SLC J.Michael Roney 2 SLC machine and SLD

3 EW physics at LEP & SLC J.Michael Roney 3 at LEP: 15M hadronic Z decays, unpolarised at SLC: 0.5M hadronic Z decays, polarised e- at SuperB: Z-term ~30M hadronic Z, polarised

4 EW physics at LEP & SLC J.Michael Roney 4

5 EW physics at LEP & SLC J.Michael Roney 5 correcting back to 100% pol Asymmetries at Z-pole from measured cross-sections:

6 EW physics at LEP & SLC J.Michael Roney 6 A FB for leptons and b l events at LEP

7 EW physics at LEP & SLC J.Michael Roney 7 A FB for b events (decay vertex charge) at SLC A FB for leptons at SLC

8 EW physics at LEP & SLC J.Michael Roney 8 Also Measure Polarisation in the final state at LEP

9 EW physics at LEP & SLC J.Michael Roney 9

10 EW physics at LEP & SLC J.Michael Roney 10 comparing only A LR and A 0,b fb 3.2 σ

11 EW physics at LEP & SLC J.Michael Roney 11 2.8 σ

12 EW physics at LEP & SLC J.Michael Roney 12

13 If A FB b is omitted from the SM fit MHiggs=76± 54 33 i.e a low mass Higgs is strongly preferred EW physics at LEP & SLC

14 J.Michael Roney 14 from M. Chanowitz, arXiv:0806.0890 hep-ph EW physics at LEP & SLC

15 EW physics at SuperB J.Michael Roney 15 at SuperB:  Z interference term dominates over pure Z-exchange

16 A  -pair selection in BaBar Efficiency = 53.4% Purity = 99.6% Projected no. of selected mu-pair events at SuperB for 75/ab is 45.6 billion Z. Yun thesis 2005 expected stat. error on A LR = 4.6x10 -6

17 e + e -     - @ √s=10.58GeV Scales as s DiagramsCross Section (nb) A FB A LR (Pol = 100%) |Z+  | 2 1.010.0028-0.00051 |Z| 2 +|  2 No interference 1.010.0088-0.00002 The interference term is (nearly) everything - A LR interference term ~ g A e g V 

18 Polarised Beams provide an impressive Precision EW Programme at SuperB polarised beam provide measurement of sin 2 Θ w(eff) of using muon pairs of comparable precision to that obtained by SLD, except at 10.58GeV Similar measurement can be made with taus and charm Test neutral current universality at high precision Because it depends on gamma-Z interference it is sensitive to Z’ Measure NC Z-b-bbar vector coupling with higher precision and different systematic errors than determined at LEP with A FB b and at high precision 18 J.Michael Roney

19 e + e -    - @ √s=10.58GeV DiagramsCross Section (nb) A FB A LR (Pol = 100%) |Z+  | 2 1.010.0028-0.00051  A LR =5x10 -6   (sin2  eff) = 0.00018 measured at 10.58GeV, run to M z cf SLC A LR  (sin2  eff) = 0.00026 at M z Would be most precise measurement: precision test of running to low √s relative stat. error of 1.1% (pol=80%) require ~0.5% systematic error on beam polarisation 19 J.Michael Roney expected stat. error on A LR = 4.6x10 -6

20 Comments on Beam Polarization Systematic Errors at SLC (thanks for discussions with Peter Rowson – SLD/SLD SLAC) 1) The left-right luminosity asymmetry must there be controlled to the level of the stat error (10 -6 ). At the SLC, able to monitor this asymmetry (using various beamline instruments) to a precision of ~ 0.5x 10 -4. One needs two orders of magnitude improvement here. 2) SLC needed to experimentally limit the level of accidental positron polarization - which was done at the SLC to the 7 x 10 -4 level. In principle, this too would have to be improved by two orders of magnitude, but in a storage ring perhaps this effect might be expected theoretically to be very much smaller and not an issue. 3) SLC able to completely ignore left-right asymmetric effects in the SLD detector efficiency at the SLC where ALR was ~10% (These effects that cause the response of the detector to a fermion at a given polar angle to differ from the response to an anti-fermion at the same polar angle). When effects at the part per million level are relevant, this issue would have to be re-examined. Perhaps this is still OK. 20 J.Michael Roney

21 The L-R luminosity asymmetry is the most important and has to be controlled. This can likely be achieved with good luminosity monitoring using Bhabhas. Some thought needed to go into this. Comments on Beam Polarization Systematic Errors at SuperB 21 J.Michael Roney

22 Similar approach for taus and electrons 22 J.Michael Roney Will give most precise NC universality measurements All error ellipses would be only slightly larger than red electron ellipse

23 What of Z - b-bar couplings?  -Z interferometry at the Phi factory (hep-ph/9512424 (Bernabeu, Botella,Vives) Assuming only resonance production Same arguments for ϒ (4S) (ignoring non-4S open beauty) J.Michael Roney

24 Z - b-bar couplings J.Michael Roney

25 next two slides courtesy of Oscar Vives BOTTOM LINE: work concludes that A LR from BBbar events at the 4S giving access to the Z-b-bbar vector coupling is indeed sound and in fact very robust! INDEPENDENT of whether via Continuum or Resonance 25 J.Michael Roney

26 26 J.Michael Roney

27 slides from Oscar Vives 27 J.Michael Roney

28 SM expectation & LEP Measurement of g V b SM: -0.34372 +0.00049-.00028 A FB b : -0.3220±0.0077 with 0.5% polarization systematic and 0.3% stat error, SuperB can have an error of ±0.0021 28 J.Michael Roney

29 SM expectation & LEP Measurement of g V b SM: -0.34372 +0.00049-.00028 A FB b : -0.3220±0.0077 with 0.5% polarization systematic and 0.3% stat error, SuperB can have an error of ±0.0021 29 J.Michael Roney

30 At SuperB no QCD corrections At LEP QCD corrections were required – hadronization effects, hard gluons, etc We think it was done properly with correctly assessed systematic uncertainties, but… Real advantage at SuperB over a high energy machine, e.g. Z-factory, is that these corrections do not exist: we are coupling to pseudoscalars with no hadronization 30 J.Michael Roney

31 Similar approach can be used for Charm Operate at a ccbar vector resonance above open charm threshold psi(3770) If we want to get charm in the same way, need to have polarization at lower energies with sufficient luminosity Alternatively, use 4S data and deal with hadronization 31 J.Michael Roney

32 What if unpolarized beams? Can still access some information for e + e -    - via A FB but very difficult: Competition with A FB from QED box diagram Need to control real detector FB charge asymmetries: note that at LEP the smallest systematic error achieved on A FB was 0.0005, this would translate into an unacceptably large error on sin 2 ϑ eff W other errors arise, e.g. boost J.Michael Roney 32

33 What if unpolarized beams? Can’t directly access Z-b coupling from A FB : Y(4s) decays to pseudoscalars, so no sensitivity Proposal to measure at Y(3S) via tau polarization where tau-pairs are produced in decay of Y(3S) (Bernabeu, Botella, Vives, Eur.Phys.J.C7:205-215,1999. ) In principle, very nice idea. In practice, need: to: Run at Y(3S) Need precise determination of continuum to Y(3S) production rate: so need equal amount of off-resonance data Then, deal with backgrounds &tc…. J.Michael Roney 33

34 Neutral Current Physics Programme Measure sin 2 ϑ eff W at 10.58GeV with A LR Competitive precision EW measurements with muon – probe running, NuTeV result with muons and taus – probe NC universality at low Q2 with charm with b’s: probe residual 3 σ effect from LEP AFB Start to consider L-R luminosity and other systematic errors Z’ limits etc that we can achieve 34 J.Michael Roney

35 The polarization is initially motivated by searches for NP in taus, but precision EW measurements represent a new ‘killer app’ 35 J.Michael Roney e.g. tau EDM with polarization ~7-10x10 -20 e-cm cf 17 – 34x10 -20 e-cm without polarization BACKGROUND SUPPRESSION TOOL Disentangle NP model with LFV discovery

36 Shifting gear: standard model's flavour sector ~two dozen fundamental SM parameters Couplings of EW and strong interactions Weak mixing angle, Z boson mass Masses of quarks and leptons Matrix characterizing the mixing of weak and mass eigenstates of quarks and, recently in extended SM, leptons Higgs mass, strong-CP angle Heavy flavour sector primarily touches on the Cabibbo-Kobayashi-Maskawa (CKM) matrix J.Michael Roney 36

37 CKM Matrix J.Michael Roney 37 In SM weak charged transitions mix quarks of different generations Encoded in unitary CKM matrix Unitarity  4 independent parameters, one of which is the complex phase and sole source of CP violation in SM Wolfenstein parameterisation: qiqi W W  qjqj G F V ij quark transition

38 CKM Unitarity Triangle Physics beyond the SM signaled by breakdown of unitarity of CKM matrix J.Michael Roney 38 Area of Δ~CP violation Wolfenstein parameterisation defined to hold to all orders in  and rephasing invariant

39 CKM experimental programme J.Michael Roney 39 Make as many precision measurements as possible that overconstrain the four CKM parameters (A, λ, ρ, η ) New Physics would be revealed in discrepancies between measurements Generally requires non-perturbative QCD input to convert measurements to a SM CKM interpretation

40 Programme: Over constrain CKM with broad set of measurements J.Michael Roney 40 Quantity Sample Measurement(s) Although we probe the charged weak interaction, we need input from strong interaction calculations, which are difficult and often need data

41 Graphically present results as overconstrained Unitarity Triangle J.Michael Roney 41 CKM Fitter group uses frequentist framework UTFit uses Bayesian framework levels@ 95%Prob

42 Select Two interesting non-CP violating measurements J.Michael Roney 42 B leptonic decays |Vus| measurements

43 Leptonic Decays Remarkably simple pseudo-scalar (spin = 0, Parity is negative) decays carry information about CKM elements, but come with a 'decay constant' factor which accounts for the strong interaction component B →τν rate of decay α (f B |V ub |) 2 Ds →τν or Ds →μν rate α (f Ds |V cs |) 2 K →μν rate α (f K |V us |) 2 J.Michael Roney 43

44 Leptonic decays Particularly interesting because some New Physics theories have charged Higgs which contributed to the observed decay rate, e.g. Additional tree level contribution from a charged Higgs It does not suffer from helicity suppression, but gets the same m l dependence from Yukawa coupling Branching fraction theoretical expression depends on the NP model J.Michael Roney 44 + W + b u l+l+ ℓ B+ B+ H + b u l+l+ ℓ B+ B+ W. S. Hou, Phys. Rev. D 48 (1993) 2342. A.G. Akeroyd and S.Recksiegel J.Phys.G29:2311-2317,2003

45 B + →τ + ν τ Experimental method Two approaches to reconstruct the ‘tag’, which are classified as hadronic or semileptonic 1.select signal candidate and check that remaining particles consistent with B decay (inclusive B tag reco) 2.Reconstruct B tag in exclusive modes and check if remaining particles consistent with B signal J.Michael Roney 45 Fully reconstruct this side: ‘tag’ Then look for signal this side: ‘signal’ ντντ τ+τ+ ντντ ν μ, ν e e +,μ + X-X- D (*)0 ϒ (4S) B+B+ B-B- In reality at the ϒ (4S) the B + and B - decay products all overlap

46 Reconstruct event to select B - events from background… J.Michael Roney 46

47 ....and look for excess of missing energy associated with the neutrino J.Michael Roney 47

48 J.Michael Roney 48 Phys. Rev. D 77, 011107(R) (2008) Phys. Rev. D 81,051101(R) (2010) Phys. Rev. Lett. 97, 261802 (2006) arXiv:1006.4201[hep-ex] BABAR Hadronic BABAR Semi-leptonic BELLE Semi-leptonic BELLE Hadronic B + →τ + ν τ Results

49 New BaBar preliminary result: see ICHEP 2010 deNardo talk

50 J.Michael Roney 50 B + →τ + ν τ Results world average pre-ICHEP 2010: B(B + →τ + ν ) =(1.73±0.35)x10 -4 ~2.5 σ higher than expected from CKM fit excluding B + →τ + ν

51 J.Michael Roney 51 B + →τ + ν τ Results same conclusion from UTfit analysis Phys.Lett.B 687, 61 (2010)

52 J.Michael Roney 52 B + →τ + ν τ Results this is not easily attributed to problem with f B because a 2.6 σ difference persists when considering: B Bd is the ‘bag parameter’ and is calculated on the lattice.

53 Most precise CKM test is from the unitarity condition: From the 1 st row of the CKM matrix |V ub | is negligible in comparison to |Vud| ~1 and |V us | ~0.2 |V ud |=0.97425(22) is most precisely obtained from super-allowed nuclear beta decay |V us | is most precisely obtained from Kaon decays J.Michael Roney 53

54 |V us | from kaons J.Michael Roney 54

55 |V us | from kaons J.Michael Roney 55 Fit with no CKM unitarity constraint: Fit with CKM unitarity constraint: this analysis from Antonelli et al arXiv:1005.2323 (hep-ph 2010) (uses f K /f π = 1.193(6) ) KLOE, BNL-E865, KTeV, ISTRA+ and NA48

56 |V us | from inclusive tau decays to kaons: τ + → X s ν τ J.Michael Roney 56

57 J.Michael Roney 57 |V us | from inclusive tau decays to kaons: τ + → X s ν τ Belle and B A B AR measured many modes with significantly higher precision than previous world averages from LEP and CLEO. Measurements are consistent with previous measurements, but slightly lower.

58 J.Michael Roney 58 |V us | from inclusive tau decays to kaons: τ + → X s ν τ

59 J.Michael Roney 59 |V us | from B A B AR (Phys.Rev.Lett. 105 051602 (2010)) (Phys.Rev.Lett. 105 051602 (2010) Branching Ratios lattice and experimental: similar contribution to error Value within 1 σ of exclusive |Vus| and within 2 σ of unitarity

60 |V us | from J.Michael Roney 60 B A B AR (Phys.Rev.Lett. 105 051602 (2010))Phys.Rev.Lett. 105 051602 (2010) Improve lattice error by taking ratio: Consistent with unitarity

61 Summary and Prospects Flavour sector provides a means of probing physics beyond the SM at the precision frontier Polarised beams provide unique ability to determine both Z-lepton and Z-b couplings to highest precision The SM describes the flavour data, but there are seen a few ‘tensions’ in the flavour sector requiring attention Looking forward to new data from LHCb and in the future SuperB and SuperKEKB J.Michael Roney 61


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