J. Michael Roney University of Victoria III Prometeo Workshop IFIC 16 November 2010

EW Physics at a SuperB Flavour Factory with Polarized Beam and status of some Flavour Physics with Taus

J. Michael RoneyUniversity of Victoria

III Prometeo Workshop IFIC

16 November 2010

J.Michael Roney2

EW physics at LEP & SLC

SLC machine and SLD

J.Michael Roney3


at LEP: 15M hadronic Z decays, unpolarisedat SLC: 0.5M hadronic Z decays, polarised e-at SuperB: Z-term ~30M hadronic Z, polarised

J.Michael Roney4


J.Michael Roney5


correcting back to 100% pol

Asymmetries at Z-pole from measured cross-sections:

J.Michael Roney6


AFB for leptons and b l events at LEP

J.Michael Roney7


AFB for b events (decay vertex charge) at SLC

AFB for leptons at SLC

J.Michael Roney8

EW physics at LEP & SLCAlso Measure Polarisation in the final state at LEP

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J.Michael Roney10


comparingonly ALR and A0,b

fb

3.2σ

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2.8σ

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If AFBb is omitted

fromthe SM fit MHiggs=76±54

33

i.e a low mass Higgsis strongly preferred


J.Michael Roney14

from M. Chanowitz, arXiv:0806.0890 hep-ph


J.Michael Roney15

EW physics at SuperBat SuperB: -g Z interference term dominates over pure Z-exchange

A m-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 ALR = 4.6x10-6

e+e-m+m- @ √s=10.58GeVScales as s

Diagrams Cross Section

(nb)

AFB ALR(Pol = 100%)

|Z+g|2 1.01 0.0028 -0.00051

|Z|2+| |g 2

No interference

1.01 0.0088 -0.00002

The interference term is (nearly) everything - ALR interference term ~ gA

e gVm

J.Michael Roney18

Polarised Beams provide an impressive Precision EW Programme at SuperB

• polarised beam provide measurement of sin2Θw(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 AFB

b and at high precision

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e+e- m+m- @ √s=10.58GeVDiagrams Cross

Section (nb)

AFB ALR(Pol = 100%)

|Z+g|2 1.01 0.0028 -0.00051

sALR =5x10-6 s(sin2qeff) = 0.00018 measured at

10.58GeV, run to Mz

cf SLC ALR s(sin2qeff) = 0.00026 at Mz•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

expected stat. error on ALR = 4.6x10-6

J.Michael Roney20

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.

J.Michael Roney21

• 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

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Similar approach for taus and electrons

Will give most precise NC universality measurements

All error ellipses would be only slightlylarger than redelectron ellipse

J.Michael Roney

What of Z - b-bar couplings?

• g-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

Z - b-bar couplings

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next two slides courtesy of Oscar Vives

BOTTOM LINE: work concludes that ALR 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

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J.Michael Roney27

slides from Oscar Vives

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SM expectation & LEP Measurement of gV

b

• SM: -0.34372 +0.00049-.00028

• AFBb: -0.3220±0.0077

• with 0.5% polarization

systematic and 0.3% stat

error, SuperB can

have an error of ±0.0021

J.Michael Roney29

SM expectation & LEP Measurement of gV

b

• SM: -0.34372 +0.00049-.00028

• AFBb: -0.3220±0.0077

• with 0.5% polarization

systematic and 0.3% stat

error, SuperB can

have an error of ±0.0021

J.Michael Roney30

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

J.Michael Roney31

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

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What if unpolarized beams?

• Can still access some information for e+e-

m+m- via AFB but very difficult:

• Competition with AFB from QED box diagram

• Need to control real detector FB charge asymmetries: note that at LEP the smallest systematic error achieved on AFB was 0.0005, this would translate into an unacceptably large error on sin2ϑeff

W

• other errors arise, e.g. boost

J.Michael Roney33

What if unpolarized beams?

• Can’t directly access Z-b coupling from AFB : 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 Roney34

Neutral Current Physics Programme

• Measure sin2ϑeffW at 10.58GeV with ALR

• 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 3σ effect from LEP AFB• Start to consider L-R luminosity and other

systematic errors• Z’ limits etc that we can achieve

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The polarization is initially motivated by searches for NP in taus, but precision EW measurements represent a new ‘killer app’

• 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

J.Michael Roney36

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 Roney37

CKM Matrix

€

d' s' b'( ) =

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

d

s

b

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

In SM weak charged transitions mix quarks of different generations Encoded in unitary CKM matrix

Unitarity 4 independent parameters, one of whichis the complex phase and sole source of CP violation in SM

Wolfenstein parameterisation:CKM

V

€

=1− λ2 /2 λ Aλ3(ρ − iη )

−λ 1− λ2 /2 Aλ2

Aλ3(1− ρ − iη ) −Aλ2 1

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟+ O(λ4 )

qi

W -

qjGFVij

quark transition

J.Michael Roney38

CKM Unitarity TrianglePhysics beyond the SM signaled by

breakdown of unitarity of CKM matrix

€

λ2 =Vus

2

Vud

2+ Vus

2 ; A2λ4 =Vcb

2

Vud

2+ Vus

2 ; ρ + iη = −VudVub

*

VcdVcb*

* * * 0ud ub cd cb td tbV V V V V V

*

* *

*

*

* *

*

arg arg

arg arg

tb cd cb

ud tb

ud tb

td

ub td

ub tss

cd cb cs cb

V V VV

V VV V

V V

V V

V

V V

V

Area of Δ~CP violation

Wolfenstein parameterisation defined to hold to all orders in ~0.2 l and rephasing invariant

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CKM experimental programme

•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

J.Michael Roney40

Programme: Over constrain CKM with broad set of measurements

€

Vud superallowed β decays

Vus K l 3 → πl ν ;K l 2 → l ν /

εK CPV in K0

Vub b → ul ν ; B → (π /ρ)l ν ;B → τν

Vcb B → D(*)l ν

Δmd Bd0 - Bd

0 mixing

Δms Bs0 - Bs

0 mixing

β B0 → J /ψ K(*)

α B0 → ππ/πρ/ρρ

γ B0 → D(*)K(*) Vtd /Vts b → dγ /b → sγ;Bd

0 & Bs0mixing

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

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Graphically present results as overconstrained Unitarity Triangle

CKM Fitter group uses frequentist framework UTFit uses Bayesian framework

€

ρ =0.139−0.023+0.027 η = 0.342−0.015

+0.016

€

ρ =0.130 ± 0.020 η = 0.355 ± 0.013

levels@95%Prob

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Select Two interesting non-CP violating measurements

• B leptonic decays

• |Vus| measurements

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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 (fB|Vub|)2

• Ds→τν or Ds→μν rate α (fDs|Vcs|)2

• K→μν rate α (fK|Vus|)2

J.Michael Roney44

Leptonic decaysParticularly 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 ml dependence from Yukawa coupling

• Branching fraction theoretical expression depends on the NP model

+ W+b

u

l+

nℓ

B+

H+b

u

l+

nℓ

B+

W. S. Hou, Phys. Rev. D 48 (1993) 2342.

A.G. Akeroyd and S.Recksiegel J.Phys.G29:2311-2317,2003

J.Michael Roney45

B+→τ+ντ 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 Btag reco)

2. Reconstruct Btag in exclusive modes and check if remaining particles consistent with Bsignal

Fully reconstructthis side: ‘tag’

Then look for signal this side: ‘signal’

ντ

τ+

ντ

νμ, νe

e+,μ+

X-

D(*)0

ϒ(4S)

B+B-

In reality at the ϒ(4S) the B+ and B- decay products all overlap

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Reconstruct event to select B-

events from background…

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....and look for excess of missing energy associated with the neutrino

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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+ντ Results

B+→τ+ντ Results

New BaBar preliminary result: see ICHEP 2010 deNardo talk

J.Michael Roney50

B+→τ+ντ Results world average pre-ICHEP 2010:B(B+→τ+ν)=(1.73±0.35)x10-4

~2.5σ higher than expected from CKM fit excluding B+→τ+ν

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B+→τ+ντ Resultssame conclusion from UTfit analysis Phys.Lett.B 687, 61 (2010)

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B+→τ+ντ Resultsthis is not easily attributed to problem with fB

because a 2.6σdifference persists when considering:

BBd is the ‘bag parameter’ and is calculatedon the lattice.

J.Michael Roney53

Most precise CKM test is from the unitarity condition:

From the 1st row of the CKM matrix

• |Vub| is negligible in comparison to |Vud| ~1 and |Vus| ~0.2

• |Vud|=0.97425(22) is most precisely obtained from super-allowed nuclear beta decay

• |Vus| is most precisely obtained from Kaon decays

€

Vud

2+ Vus

2+ Vub

2=1

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|Vus| from kaons

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|Vus| from kaons

€

Vus = 0.2254(13), Vus /Vud = 0.2312(13), Vud = 0.97425(22)

€

Fit with no CKM unitarity constraint:

€

Vus = 0.2253(9), Vud = 0.97425(22)

χ 2 /dof = 0.014 /1 (91%)

Fit with CKM unitarity constraint:

€

Vus = 0.2254(6)

χ 2 /dof = 0.024 /2 (99%)

€

Vus

2+ Vus

2+ Vus

2−1 = −0.0001(6)

this analysis fromAntonelli et al arXiv:1005.2323(hep-ph 2010)(uses fK/fπ= 1.193(6) )

KLOE, BNL-E865, KTeV, ISTRA+ and NA48

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|Vus| from inclusive tau decays to kaons:τ+→Xsντ

€

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Belle and BABAR

measured many modeswith significantly higherprecision than previousworld averagesfrom LEP and CLEO.Measurements areconsistent with previousmeasurements, butslightly lower.

€

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€

€

Use δR00 = 0.240 ± 0.032 (Gamiz et al., 2007)

€

Vus = 0.2166 ± 0.0023


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|Vus| fromBABAR (Phys.Rev.Lett. 105 051602 (2010))

€

τ−→ K -ν τ

€

K -ν τ

€

π -ν τ

€

e-ν τν e

€

μ-ν τν μ

Branching Ratios

€

Vus = 0.2193 ± 0.0032

€

fK =157 ± 2 MeV

E. Follana, et al, PRL 100, 062002 (2008).

lattice and experimental: similar contribution to errorValue within 1σ of exclusive |Vus| and within 2σ of unitarity

€

← 1.8σ lower than

π → μν prediction

← 1.8σ lower than

K → μν prediction

http://dx.doi.org/10.1103/PhysRevLett.105.051602



J.Michael Roney60

|Vus| from

€

B(τ − → K -ν τ ) /B(τ − → π -ν τ )

BABAR (Phys.Rev.Lett. 105 051602 (2010))

Improve lattice error by taking ratio:

€

Vus = 0.2255 ± 0.0024€

Using : fK / fπ =1.189 ± 0.007 MeV

E. Follana, et al, PRL 100, 062002 (2008)

Vud = 0.97425 (22)

Consistent with unitarity



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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 University of Victoria III Prometeo Workshop IFIC 16 November 2010

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