Md. Naimuddin (on behalf of CDF and D0 collaboration) Fermi National Accl . Lab

03/09/2008 Md. Naimuddin 1

Masses, Lifetimes and Mixings of B and D hadrons

Md. Naimuddin(on behalf of CDF and D0 collaboration)

Fermi National Accl. LabRecontres de Moriond

09th March, 2008


– B physics at the Tevatron

– Fermilab Tevatron

– CDF and D0 Detectors

– Mass measurement

– Lifetimes

– Mixings

– Conclusions

OUTLINE


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 annihilationgluon fragmentationflavor excitation

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

B+( ) = 38%

B0( ) = 38%

Bs( ) = 10%

Bc( ) = 0.001%

Rest b baryons

ub

db

sb

cb


Fermilab Tevatron

Highest Luminosity achieved: 2.92x1032 cm/s2

Expected: ~7 fb-1 by end of 2009


CDF Detector

• Solenoid 1.4T• Silicon Tracker SVX

• up to ||<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


D0 Detector

• 2T solenoid• Fiber Tracker

• 8 double layers• Silicon Detector

• up to ||~3• forward Muon +

Central Muon detectors• excellent coverage

||<2• Robust Muon

triggers.


Theoretical prediction of the masses

E. Jenkins, PRD 55 ,

R10-R12, (1997).

Predicted mass hierarchy:

M(Λb)< M(b) < M(b) MeV 1.117.6068)(

MeV .92.5824)(

MeV 1.87.5805)(

b

b

b

M

M

M

Searching for b in b-→J/+-

Discovery of b-

Natural constraints in b-

→J/+-

- The final state particles (p, -, ) have significant Impact parameter with respect to the interactionpoint.- - has a decay length of few centimeters. - has a decay length of fewcentimeters.

- b has a decay length of fewhundred microns, PVseparation

Reconstruction strategy for b

- Reconstruct J/→+-- Reconstruct →p- Reconstruct →+- Combine J/+ - Improve mass resolution by using an event-by event mass difference correction .


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

Significance of the observed signal: >7.0Significance of the observed signal: >7.0

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

Fit:Fit:

Unbinned extended

log-likelihood fit

Gaussian signal,

flat background

Number of

background/signal

events are floating

parameters

(syst) 0.015(stat) 0.0115.774)(

bM

Significance of the observed signal: 5.5Significance of the observed signal: 5.5

Discovery of b-

D0

CDF

PRL 99, 052001 (2007)

PRL 99, 052002 (2007)


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:

2cMeV180

126304)cm(B

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.

Bc Mass


D0: m(Bc) = 630014 (stat)5 (sys) MeV/c2

CDF: m(Bc) = 6274.13.2 (stat)2.6 (sys) MeV/c2

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.

The distribution was fitted with a Gaussian for signal and fit returns a total of 5412 signal candidates.

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

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.

Bc Mass

hep-ex/0802.4258

Hep-ex/0712.1506


Bc lifetime

Lifetime measurement in Bc → J/

pssyststatB )(039.0034.0

)(039.0036.0

444.0)(

Theory: 0.48 0.05 ps (QCD sum rules)

CDF: pssyststatB )(036.0)(073.0065.0

448.0)(

Most precise

measurement to date

hep-ph/0308214

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.

Using an unbinned likelihood simultaneous fit to J/ invariant mass and lifetime distributions, a signal of 85680 candidates estimated.

12

Bs Lifetime (hadronic)

03/09/2008 Md. Naimuddin

Used two decay hadronic modes of Bs to measure its lifetime:Bs → Ds

- (-) +: Fully reconstructed (FR) – More than 1100 events reconstructedBs → 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 modesFit the proper decay time of Bs candidate. K-factor multiplied to correct for missing tracks or wrong mass assignment for partially reconstructed events

PR

(Bs) = 1.5450.051 ps


(Bs) = 1.4560.067 ps

Com

(Bs) = 1.5180.025 ps

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

c(Bs) = 455.012.2 (stat) 7.4 (syst) m

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

Bs Lifetime (hadronic)

FR:


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) = 1.520.040.02 ps D0: (Bs) = 1.520.060.01 ps hep-ex/0802.2255hep-ex/0712.2348


MixingMixing: 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 Bs

0 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:

12 MMx

2

12y21

21

Mean lifetime


Charm mixing

Measure mixing in D*→D0; D0→K

x’ = x cosK + y sinK

y’ = y cosK - x sinK

222

/4

// tyx

tyRRtR DD

Mixing X y

Bs0- 25 0.10

B0- 0.77 0.01

K0- 0.474 0.997

D0- 0.010 0.008

0sB

0B

0K0D

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 evolutionIdentify charm at productionIdentify charm at decay

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


Result: y’ = 0.0085 and x’2 = 0.00012

Bayesian probability contour excludes no mixing point at 3.8.

Charm mixing

BaBary’ = 0.0097, x’2 = -0.00022

Belley’ = 0.0006, x’2 = 0.00018

Alternate checks of the significance also resulted in 3.8

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

hep-ex/0712.1567


Conclusions

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.


• Back-up slides


Data Taking

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

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


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.)


Mass measurement of orbitally excited B**0

CDF measurements:

D0 measurements:m(B1

0) = 5720.6±2.4(stat.) ±1.4(syst.) MeV/c2

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

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 MeVm(B2

*)-m(B1) 14 MeV

2cMeV (syst)0.50.6

(stat)1.71.8

5739.90*2

Bm

2cMeV (syst)0.81.1

(stat)1.62.1

5725.301

Bm

2cMeV(syst)3.52.6

(stat)3.63.1

22.10*2

BΓ


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

Significant improvement sincethen, 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

ps)()(29.1)( 087.0

091.0

119.0

110.0syststat

b


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.

ps)(042.0)(218.1)( 130.0115.0 syststatb

B ) = 1.251- 0.096 + 0.102 ps

Combined Semileptonic and hadronic

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Md. Naimuddin (on behalf of CDF and D0 collaboration) Fermi National Accl . Lab

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