heavy flavour physics news from the tevatron

Heavy Flavour PhysicsNews from the Tevatron

Wendy Taylor

for the CDF and DØ Collaborations

APS/AAPT 2010, Washington, DC, February 13-16, 2010

• Where is the antimatter in the Universe?• Why are there 3 generations of matter? (only 3?)• How does the strong force bind quarks into hadrons?• How does the electroweak force cause hadrons to decay?

W. Taylor, APS/AAPT 2010 2

The b Quark as a Physics ProbePrimary vertex

B decay vertexDisplaced track

• Why study B physics at the Tevatron?– Large rate:

– Tevatron energy sufficient to create states not accessible at the e+e- B factories

• However, backgrounds are large:

The Tevatron is a B Factory


bbbpp 30)(

310/ inelasticbb

Run II Tevatron Proton-Antiproton Collider

• s=1.96 TeV• L = 2.51032cm-2 s-

1 • Ldt = 50 pb-1 per

week

Main Injector

Tevatron

DØCDF

Chicago

p source

Booster

Fermi National Accelerator Laboratory


Detectors

· Excellent muon and tracking coverage high yields

Extended muon system ||<2.0 Tracking up to ||<3.0

• Solenoid and muon toroid polarities flipped every two weeks

· Excellent mass resolution· Particle ID: p, K and by dE/dx and

TOF · L1 trigger on displaced two-track

objects



• Flavour-changing neutral current decays are highly suppressed in the SM as they do not occur at tree-level (i.e., lowest order)

• New physics (e.g., SUSY, technicolour, 4th generation*) might occur in internal loops– Could enhance the branching fractions significantly– Could also affect the angular distributions

B(u,d,s)→+-h FCNC Decays

* W.-S. Hou et al., PRD 76 016004 (2007)

B(u,d,s)→+-h Decays• Trigger on two muons in 4.4 fb-1

• Final offline selection uses neural network • Use unbinned maximum log-likelihood fit

to invariant mass• CDFnote 10047


8.5 9.7 6.3

KKB

KKKB

KB

s

,

,0

0*0*0


B(u,d,s)→+-h Decays• SM predicts Br ~ O(10-6)• Use as normalization channel for branching

fraction to avoid many systematic uncertainties

• Precision competitive to world average values:

• First ever measurement:

– The rarest measured Bs0 decay!

– Theoretical prediction of 1.6110-6 (Geng and Liu, J.Phys.G29:1103-1118,2003) agrees well

hJB /

60*0

6

10)](09.0)(14.006.1[)(

10)](03.0)(05.038.0[)(

syststatKB

syststatKB

BB

615.013.0

0*0

608.007.0

10]05.1[)(

10]52.0[)(

KB

KB

BB

60 10)](46.0)(33.044.1[)( syststatBs B


B0→K*0+- Decays• K*0 forward-backward asymmetry AFB

– µ is helicity angle between µ+ direction and the opposite of the B direction in the dimuon rest frame

• K*0 longitudinal polarization FL from angle K between the kaon and the B direction in the K*0 rest frame

• Divide data into 6 bins of q2=m2(µ+µ-)c2

))(θ,Γ(q))(θ,Γ(q))(θ,Γ(q))(θ,Γ(q

)(qAμμ

μμFB 0cos0cos

0cos0cos22

222


B0→K*0+- Decays• Precision is competitive with B

factory measurements• Experimental results are consistent

Belle

SM

Babar

SM

SM lower than data by 2.7

PRD 79, 031102(R) (2009)PRL 103, 171801 (2009)


B(d,s)→+- Rare Decays• SM expected limits:

– Br(Bd→+-)<(1.00±0.14)x10-10 ~|Vtd|2

– Br(Bs→+-)<(3.86±0.57)x10-9 ~|Vts|2

• New physics could introduce tree-level contributions – can enhance the branching fraction by x100 over

the SM prediction

B(d,s)→+- Rare Decays• Utilize muons with ||<2.0,

pT>2.0 GeV/c• Boosted decision tree

– B-candidate decay length significance

– B-candidate pT

– B-candidate track isolation– Impact parameter significance– Vertex 2 probability

• Assume no contribution from Bd→+- (|Vtd/Vts|2~0.04)

• DØnote 5906W. Taylor, APS/AAPT 2010 12

B(d,s)→+- Rare Decays• Utilize muons with ||<1.0,

pT>2.0 GeV/c• Muons form B-candidate

vertex• Neural-net variables

– B-candidate decay length and significance

– B-candidate track isolation– Opening angle between B-

candidate momentum and decay length

– pT(B) and pT(µLow)• CDFnote 9892



B(d,s)→+- Rare Decays

• At 95% CL in 3.7fb-1:

Br(Bd→+-)<7.6x10-9

Br(Bs→+-)<4.3x10-8

• Expected upper limit in 5fb-1 : Br(Bs→+)<5.3x10-8 (95% CL)

B(d,s)→+- Rare Decays• Enhancements over SM

greater than ~10x already excluded

• Combined Tevatron expected limits may reach 4x with 8fb-1

• Stay tuned!


NP?


Upsilon Polarization• Non-Relativistic Quantum Chromodynamics (NRQCD)

– QQ production is perturbative short-distance process– Hadronization into is long-distance process, which is

expanded in powers of heavy quark velocities• Past CDF measurements of J/ and (2s) polarization

do not agree with NRQCD• Reconstruct (1s)→+- decays

• In the rest frame, + makes an angle * with respect to the direction in the lab frame

• = 1 for fully longitudinal polarization• = +1 for fully transverse polarization

*2* cos1

cos

d

d 11


Upsilon Polarization

• Apply simulated trigger conditions and offline cuts

• Get templates reflecting how fully polarized events would appear in the detector

• Dimuon trigger: pT(1)>4GeV/c, pT(2) >3GeV/c, <0.6; Offline: require good dimuon vertex, with mass consistent with (1s)

• Generate MC samples with fully transverse and fully longitudinal polarizations


Upsilon Polarization• Determine

polarization parameter by matching a polarization-weighted combination of templates to the *(+) distributions in the data in each of eight pT () bins

• Apparent disagreement with NRQCD and DØ result

• Look forward to new DØ J/ and polarization results


CP Violation• Violation of the Charge-Parity Symmetry• Charge symmetry: matter antimatter• Parity symmetry: like a mirror symmetry but in 3D


CP Violation• Violation of the Charge-Parity Symmetry• Charge symmetry: matter antimatter• Parity symmetry: like a mirror symmetry but in 3D

• Large sources of CP violation would explain the observed matter-antimatter asymmetry of the universe


• Bs0 mixing:

• If , an excess of Bs0

would “build up” CP violation• Search for a charge asymmetry in decays

versus decays

CP Violation in Bs0 Mixing

Antimatter Matter

)(Prob)(Prob 0000ssss BBBB

XDB ss 0

XDB ss 0

)(

)(2)(

)(0

0

0

0

tB

tBiM

tB

tBdtdi

s

s

s

s

5102: sSLASM

ftBftB

ftBftBAss

sssSL

)()()()(

00

00

W. Taylor, APS/AAPT 2010

CP Asymmetry in Bs0 Semileptonic Decays

• Need to correct for detector asymmetries– Muon toroid polarity flip

• Use decay time information

• Tagging mixed versus unmixed decays helps

22

)()(0091.00017.0 0012.00023.0 syststatAs

SL

arXiv:0904.3907

CP Phase s in Bs0J/ Decays

• Get two mass eigenstates:

• SM predicts• New physics (e.g., 4th generation) could contribute a

large phase sNP

• Use Bs0J/ decays: golden mode

– yield both CP-even and CP-odd final states, which have different angular distributions

• Can separate the CP components via a time-dependent angular analysis of decay products

23

0 0

0 0

even

odd

sL s s

sH s s

B p B q B CP

B p B q B CP

31212 10)4.12.4()/arg( ΓMs


122 MMM=Δm LHs sHLs ΓΓΓ=ΔΓ cos2 12


CP Phase s in Bs0J/ Decays

24

DØnote 5928

CDFnote 9787

2.12

NPsss 2For large s

NP:

CP Phase s with ASL Constraint

25W. Taylor, APS/AAPT 2010

Assl=ΔΓs/Δms tan(s)


• B spectroscopy measurements provide sensitive tests of potential models, heavy quark effective theory (HQET), and lattice gauge theory

b Baryons

b-

b-

• Reconstruct 84893 b0c

+-+- events where c+pK-

+ in 2.4 fb-1

• Observe resonant structures: – b

0c(2595)+- c+-+-

– b0c(2625)+- c

+-+-

– b0c(2455)++-- c

+-+- – b

0c(2455)0+- c+-+-

• Measure branching fractions relative to b0c

+-+-

• Compare theoretical predictions to measured branching fractions to test heavy quark effective theory (HQET)

• Important for measurement of Br(b0c

+-)

Resonant Structure in b0c

+-+-



+-+-

• Sample collected by the impact-parameter trigger

• Look for resonances with respect to M(c

+)• Veto c* resonances for c*

search




+-+-

b- (ssb) Baryon Observation

• Use J/µ+µ- sample• Need to reconstruct three

decay vertices

• DØ uses BDT selection, unbinned likelihood mass fit and b

-J/ - decays for many cross-checks

• CDF uses a cut-based selection with B0J/K*0

and B0J/Ks0 decays for

cross-checks




M=|MD0-MCDF|~6

4.2fb-1

M(b-)=6054.46.8(stat)0.9(syst) MeV/c2

PRD 80, 072003 (2009)

M(b-)=616510(stat)13(syst) MeV/c2

PRL 101, 232002 (2008)

S. Godfrey, DPF 2009 Proceedings

• CDF and DØ measurements of the b- mass agree

– DØ: M(b- )=577411(stat)15(syst) MeV/c2 (PRL 99,

052001 (2007))– CDF: M(b

- )=5790.92.6(stat)0.9(syst) MeV/c2

• DØ is performing new analysis with 5 x data– Half the new sample includes the new Layer 0 silicon

detector • CDF could at best double its dataset, but could also

include additional channels• Stay tuned!




Conclusions• The Tevatron experiments are very active in B

physics and things are getting interesting! – CDF/DØ polarization– CDF/DØ b

- mass– CP violation in Bs

0J/– Bs

0→+-

• Tevatron is funded to run through 2011 10fb-1 – Need to improve analysis techniques too

• Can expect many improved results and maybe new discoveries in the next two years!

heavy flavour physics news from the tevatron

Documents

heavy flavour physics

strong force bind quarks

b quark

generations of matter