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Md. Naimuddin (on behalf of CDF and D0 collaboration) Fermi National Accl . Lab Recontres de Moriond 09 th March, 2008. Masses, Lifetimes and Mixings of B and D hadrons. OUTLINE. B physics at the Tevatron Fermilab Tevatron CDF and D0 Detectors Mass measurement Lifetimes

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Md. Naimuddin

(on behalf of CDF and D0 collaboration)

Fermi National Accl. Lab

Recontres de Moriond

09th March, 2008

Masses, Lifetimes and Mixings of B and D hadrons

Md. Naimuddin



  • B physics at the Tevatron
  • Fermilab Tevatron
  • CDF and D0 Detectors
  • Mass measurement
  • Lifetimes
  • Mixings
  • Conclusions

Md. Naimuddin


B Physics at the Tevatron

  • The “beauty”- b quark: Second heaviest quark amongst the quark family – discovered at Fermilab in 1977, in a fixed target experiment.
  • Produced at the Tevatron in abundance via three main processes:
  • quark-anti quark annihilation

gluon fragmentation

flavor excitation

B hadrons – Produced as a result of hadronization of b quark

B+( ) = 38%

B0( ) = 38%

Bs( ) = 10%

Bc( ) = 0.001%

Rest b baryons

Md. Naimuddin

fermilab tevatron
Fermilab Tevatron

Highest Luminosity achieved:

2.92x1032 cm/s2

Expected: ~7 fb-1 by end of 2009

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cdf detector
CDF Detector
  • Solenoid 1.4T
  • Silicon Tracker SVX
    • up to |h|<2.0
    • SVX fast r- readout for trigger
  • Drift Chamber
    • 96 layers in ||<1
    • particle ID with dE/dx
    • r- readout for trigger
  • Time of Flight
    • →particle ID

Md. Naimuddin

d0 detector
D0 Detector
  • 2T solenoid
  • Fiber Tracker
    • 8 double layers
  • Silicon Detector
    • up to |h|~3
  • forward Muon + Central Muon detectors
    • excellent coverage ||<2
  • Robust Muon triggers.

Md. Naimuddin


Discovery of b-

Theoretical prediction of the masses

Predicted mass hierarchy:

M(Λb)< M(b) < M(b)

E. Jenkins, PRD 55 ,

R10-R12, (1997).

Searching for b in b-→J/+-

Natural constraints in b-→J/+-

Reconstruction strategy for b

- The final state particles

(p, -, ) have significant

Impact parameter with

respect to the interaction


- - has a decay length of few


-  has a decay length of few


- b has a decay length of few

hundred microns, PV


- Reconstruct J/→+-

- Reconstruct →p

- Reconstruct→+

- Combine J/+ 

- Improve mass resolution

by using an event-by

event mass difference

correction .

Md. Naimuddin


Discovery of b-

  • Fit:
  • Unbinned extended
  • log-likelihood fit
  • Gaussian signal,
  • flat background
  • Number of
  • background/signal
  • events are floating
  • parameters

Number of signal events: 15.2 ± 4.4

Mean of the Gaussian: 5.774 ± 0.011(stat) GeV

Width of the Gaussian: 0.037 ± 0.008 GeV

PRL 99, 052001 (2007)


M(Ξb-)  = 5792.9 ± 2.5 (stat.) ± 1.7(syst.) MeV/c2

Significance of the observed signal: >7.0

PRL 99, 052002 (2007)


Significance of the observed signal: 5.5

Md. Naimuddin


Bc Mass

  • Bc system consists of two heavy quarks.
  • Each can decay quickly.
  • Non-perturbative QCD effects are not well understood.
  • Measurement of the production properties are expected to provide test of theoretical calculations.
  • Mass of Bc is not well known theoretically and has been estimated using potential models and QCD sum rules. Varies from 6150 to 6500 MeV/c2.
  • Recent lattice QCD calculations predict:

F. Allison et. al, PRL 94, 172001 (2005)

Mass measurement in Bc → J/

  • CDF and D0 both uses this channel to measure the mass.
  • The CDF result is based on 2.2 fb-1 and D0 on 1.3 fb-1.

Md. Naimuddin


Bc Mass

The distribution was fitted with a Gaussian for signal and fit returns a total of 5412 signal candidates.

A total of 137 events with invariant mass between 6240 and 6300 MeV/c2 observed. 80.4 are attributed to Bc signal and rest to background.


D0: m(Bc) = 630014 (stat)5 (sys) MeV/c2


From the negative log-likelihood of S+B and background only hypothesis, the signal significance was extracted to be 5.2.

CDF: m(Bc) = 6274.13.2 (stat)2.6 (sys) MeV/c2

Using toy MC the signal significance was extracted to be larger than 8.

  • Both the results are in agreement with each other and also in agreement with the most precise lattice QCD predictions.

Md. Naimuddin


Bc lifetime

  • The decay property of Bc mesons are influenced by presence of both b and c quarks.
  • Since either quark may participate in the decay, Bc lifetime is predicted to be shorter than other B hadrons.

Theory: 0.48 0.05 ps (QCD sum rules)


Lifetime measurement in Bc → J/

Most precise measurement to date

Using an unbinned likelihood simultaneous fit to J/ invariant mass and lifetime distributions, a signal of 85680 candidates estimated.


Md. Naimuddin


Bs Lifetime (hadronic)

  • Used two decay hadronic modes of Bs to measure its lifetime:
  • Bs → Ds- (-) +: Fully reconstructed (FR) – More than 1100 events reconstructed
  • Bs → Ds-+ (+0): Partially reconstructed (PR)
  • - 0 not reconstructed.
  • These candidates are from actual Bs
  • mesons so they contribute to lifetime
  • measurement and double the available
  • statistics.
  • Lifetime determined in two steps: First fit mass to determine relative fraction in different modes
  • Fit the proper decay time of Bs candidate.
  • K-factor multiplied to correct for missing tracks or wrong mass assignment for partially reconstructed events


(Bs) = 1.5450.051 ps

Md. Naimuddin


Bs Lifetime (hadronic)

  • The fit procedure was tested extensively on three control samples:
  • B0→D-(K+--)+, B0→D*-[D0(K+-)-]+ and B+→D0(K+-)+


(Bs) = 1.5180.025 ps


(Bs) = 1.4560.067 ps

c(Bs) = 455.012.2 (stat)  7.4 (syst) m

  • Toy Monte Carlo studies were used to set the size of the systematic uncertainty.

Md. Naimuddin


Lifetime in Bs→J/ψϕ

  • Average lifetime of Bs, Bs(bar) system can be measured with
  • Bs → J/ decay.
  • Average lifetime s = 1/s, where s = (H+L)/2
  • CDF results are based on 1.7 fb-1 and D0 on 2.8 fb-1 data.

CDF: (Bs) = 1.520.040.02 ps

D0: (Bs) = 1.520.060.01 ps



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  • Mixing: The transition of neutral particle into it’s anti-particle, and vice versa.
  • First observed in the K meson system.
  • In the B meson system, first observed in an admixture of B0 and Bs0 by UA1 and then in B0 mesons by ARGUS in 1987.
  • In the Bs system, first double sided bound measurement was announced right here by D0 and then it was observed and discovered in 2006 at CDF.
  • In the D meson system first observed by Belle and BaBar and was announced here last year.
  • Mixing occurs when mass eigenstates have different masses or decay widths.

Characterized by mixing parameter:

Mean lifetime

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Charm mixing

  • Value of x, y much larger compared to SM will hint a signal of New Physics.
  • To measure charm mixing, we need:
  • Proper decay time for time evolution
  • Identify charm at production
  • Identify charm at decay

Measure mixing in D*→D0; D0→K

  • Identify the right sign (when pions are of same charge) and wrong sign (when pions are of opposite charge).
  • Get the ratio of WS to RS (with x, y << 1, i.e. assuming no cp violation

x’ = x cosK + y sinK

y’ = y cosK - x sinK

Md. Naimuddin


Charm mixing

  • Likelihood ~ exp(-2/2)
  • Solid point = best fit
  • Cross = no-mixing (y’=x’=0)
  • Open diamond = highest probability physically allowed


y’ = 0.0085 and x’2 = 0.00012

Bayesian probability contour excludes no mixing point at 3.8.


y’ = 0.0097, x’2 = -0.00022


y’ = 0.0006, x’2 = 0.00018


Alternate checks of the significance also resulted in 3.8

Md. Naimuddin

  • Tevatron is performing quite well and we are collecting more than 100 pb-1 (equivalent of total run 1 data) of data every month.
  • New particles are discovered and the measurements are becoming more and more precise.
  • Uncertainties are still mostly statistically dominated, will reduce with more data.
  • Unique and strong B physics program as many of the B species are produced only at Teavtron and proves complimentary to B factories.
  • On our way to double our current data set by the end of 2009.

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Back-up slides

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data taking
Data Taking

Excellent performance by the Tevatron and anti-proton stacking rate.

Total data will be doubled in the next couple of years.

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Observation of Orbitally Excited Bs2*

  • An excited state of bs(bar) system.
  • When properties of this system compared with the properties of bu(bar) and bd(bar) provides good test of various models of quark bound states.
  • Decay via D-wave process (L=2).
  • In this analysis, Bs2* is reconstructed as B+K-.

M(Bs2*) = 5839.6±1.1(stat.)±0.7 (syst.)

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Mass measurement of orbitally excited B**0

B1 → B*+-; B*+ → B+

B2* → B*+-; B*+ → B+

B2* → B+-

B0*(J=0), B1*(J=1): Jq = ½, decay via S-wave  too broad (  ~ 100 MeV) to be observable.

B1(J=1), B2*(J=2): Jq =3/2, D-wave decay,  ~ 10 MeV

m(B2*)-m(B1)  14 MeV

CDF measurements:

D0 measurements:

m(B10) = 5720.6±2.4(stat.) ±1.4(syst.) MeV/c2m(B2*0) = 5746.8±2.4 (stat.) ±1.7(syst.) MeV/c2

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  • Before Tevatron run2, theory and experiment did not agree “b lifetime puzzle”.
  • World average was dominated by LEP semileptonic measurements.

Significant improvement since

then, theory has included NLO

calculations, but experiments still have large uncertainties

• important to revisit this with data sets now available at the Tevatron

b →J/ ~ 10-4

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Λb Lifetime (semileptonic)

  • b→cX; c→ Ks0p
  • First Ks0 are reconstructed from two oppositely charged tracks that are assigned pion mass.
  • 4.4K c+ events are reconstructed.
  • Define visible proper decay length M = mc(LT.pT(c+))/ |pT(c+)|2
  • c events are split into 10 visible decay length bins.

Combined Semileptonic and hadronic

(LB ) = 1.251- 0.096 + 0.102 ps

Md. Naimuddin