DAMTP, University of Cambridge HPQCD

Transcription

1

2 Outline of Talk Phenomenological Motivation Overview of lattice methodology Results Future work

3 -Motivation The CKM Matrix After EW symmetry breaking the standard model in the mass basis contains the flavour changing current Exclusive results use lattice QCD. Here we focus on the decay to D*.

4 -Motivation The CKM Matrix The determination using exclusive decays uses fits to experimental data for the differential decay rate One output of such fits is the factor The electroweak factor, accounting for box diagrams, can be calculated perturbatively with good precision. The remaining parameter is the zero recoil form factor.

5 -Motivation The CKM Matrix The axial and vector matrix elements we are interested in can be parametrised in terms of the four form factors In the zero recoil limit only the term remains. It is only non-zero for spatial currents.

6 -Methodology Lattice Actions Bottom quark - NRQCD Non-relativistic effective theory

7 -Methodology Lattice Actions Bottom quark - NRQCD Non-relativistic effective theory Improved through

8 -Methodology Lattice Actions Bottom quark - NRQCD Non-relativistic effective theory Improved through Simple time evolution equation fast and simple to compute propagators

9 -Methodology Lattice Actions Bottom quark - NRQCD Non-relativistic effective theory Improved through Charm, up and down quarks - HISQ flavours in the sea Simple time evolution equation fast and simple to compute propagators

10 -Methodology Lattice Actions Bottom quark - NRQCD Charm, up and down quarks - HISQ Non-relativistic effective theory flavours in the sea Improved through Physical, relativistic charm Simple time evolution equation fast and simple to compute propagators Light quarks going down to physical masses

11 -Methodology Lattice Actions Bottom quark - NRQCD Charm, up and down quarks - HISQ Non-relativistic effective theory flavours in the sea Improved through Physical, relativistic charm Simple time evolution equation fast and simple to compute propagators Light quarks going down to physical masses Improved through order at leading order and

12 -Methodology Perturbative Matching Use of NRQCD means we must use several currents to match to the continuum to given order in : Here we use currents matched through the currents which requires - Christopher Monahan, Junko Shigemitsu, Ron Horgan, However, at zero recoil Luke's theorem states that the corrections vanish. Hence we only need the leading order current and its matching coefficient though we compute higher order currents as well.

13 -Methodology Fits We compute the correlation functions where each operator is projected onto zero spatial momentum, and i and j label different smearings.

14 -Methodology Fits T=24

15 -Methodology Fits Use Bayesian fitting, minimise modified χ2 including priors for parameters - Constrained Curve Fitting, G.P. Lepage et al Allows for a very general fit function. Parameters which are not strongly determined by the data default to their prior value.

16 -Results Results

17 -Results Chiral Continuum Limit Preliminary! Once we have determined the currents on each lattice, must extrapolate to the continuum. Simultaneously fit pion mass dependence using chiral P.T. result.

18 -Results Vcb and ha1(1) Preliminary!

19 -Future work Future work Recent confirmation of R(D*) deviation of ~2σ by LHCb run 1 from standard model prediction

20 -Future work Future work Recent confirmation of R(D*) deviation of ~2σ by LHCb run 1 from standard model prediction Work currently being done to constrain leading extrapolation. error using heavy-hisq

21 -Future work Future work Recent confirmation of R(D*) deviation of ~2σ by LHCb run 1 from standard model prediction Work currently being done to constrain leading extrapolation. error using heavy-hisq Increase precision of Vcb result

22 -Future work Future work Recent confirmation of R(D*) deviation of ~2σ by LHCb run 1 from standard model prediction Work currently being done to constrain leading extrapolation. error using heavy-hisq Increase precision of Vcb result

23 Thank you for listening

24 Backup slides

25 -Backup slides Fits Including oscillations in fits, the full form of the fit functions are