03/09/2008 Md. Naimuddin 1 Masses, Lifetimes and Mixings of B and D hadrons Md. Naimuddin (on behalf...
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Transcript of 03/09/2008 Md. Naimuddin 1 Masses, Lifetimes and Mixings of B and D hadrons Md. Naimuddin (on behalf...
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
03/09/2008 Md. Naimuddin 2
– B physics at the Tevatron
– Fermilab Tevatron
– CDF and D0 Detectors
– Mass measurement
– Lifetimes
– Mixings
– Conclusions
OUTLINE
03/09/2008 Md. Naimuddin 3
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
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Fermilab Tevatron
Highest Luminosity achieved: 2.92x1032 cm/s2
Expected: ~7 fb-1 by end of 2009
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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
03/09/2008 Md. Naimuddin 6
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.
03/09/2008 Md. Naimuddin 7
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 .
03/09/2008 Md. Naimuddin 8
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)
03/09/2008 Md. Naimuddin 9
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
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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
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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
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(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:
03/09/2008 Md. Naimuddin 14
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
03/09/2008 Md. Naimuddin 15
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
03/09/2008 Md. Naimuddin 16
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
03/09/2008 Md. Naimuddin 17
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
03/09/2008 Md. Naimuddin 18
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.
03/09/2008 Md. Naimuddin 19
• Back-up slides
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Data Taking
Excellent performance by the Tevatron and anti-proton stacking rate.
Total data will be doubled in the next couple of years.
03/09/2008 Md. Naimuddin 21
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.)
03/09/2008 Md. Naimuddin 22
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
03/09/2008 Md. Naimuddin 23
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
03/09/2008 Md. Naimuddin 24
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