b c mass, lifetime and br’s at cdf
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B c mass, lifetime and BR’s at CDF. Masato Aoki University of Tsukuba For the CDF Collaboration International Workshop on Heavy Quarkonium 2006 @ BNL. Outline. Introduction The B c meson Tevatron and CDF s (B c )B(B c J/ y l n )/ s (B u )B(B u g J/ y K) measurement - PowerPoint PPT PresentationTRANSCRIPT
Bc mass, lifetime and BR’s at CDF
Masato AokiUniversity of Tsukuba
For the CDF Collaboration
International Workshop on Heavy Quarkonium 2006 @ BNL
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Outline1. Introduction
a. The Bc meson
b. Tevatron and CDF
2. (Bc)B(BcJ/l)/(Bu)B(BuJ/K) measurement
3. Lifetime measurement4. Mass measurement5. Summary
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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• Ground state of bottom-charm quark bound system Both quarks are heavy
Similar to cc and bb families But the two quarks have different flavor
Only weak decay is possible Bc has measurable lifetime
• Bc provides unique features of heavy quark bound states
• In the future… As a Bs generator CP asymmetry measurement in D0Ds decay mode
The Bc Meson
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Bc in CDF Run I (1991~1996)• Bc signal search using BcJ/l(l=e,) channel• ~20 Bc signal events were observed in 0.11 fb-1 of J/ data
[PRL 81, 2432 (1998) and PRD 58, 112004 (1998)]
M=6.4±0.39±0.13 GeV/c2 =0.46 ±0.03 ps+0.18–0.16
=0.132 ±0.031+0.041–0.037
+0.032–0.020
(Bc)B(BcJ/l)(Bu)B(BuJ/K) * harder pT(Bc)
was assumed
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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The Tevatron Collider• √s=1.98 TeV proton-antiproton collider• Tevatron has already delivered 1.6 fb-1
CDF has ~1 fb-1 available for analysis• We anticipate 4~8 fb-1 by the end of Run II
Record peak luminosity : 1.82 1032
cm-2 s-1
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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B field : 1.4 T
HAD calorimeterHAD calorimeterMuon systemMuon system
Drift chamberDrift chamberSilicon microstrip detectorSilicon microstrip detector
EM calorimeterEM calorimeter
The CDF II detector
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Heavy Flavor Physics at CDF•Huge production cross
sections at Tevatron b~30 b
•Large backgrounds as well
q b
q b
bg
g b
q q
bg
bbg
g g
b
•B triggerslepton trigger displaced track trigger and combined trigger
•Trigger requirementslarge bandwidthbackground suppressiondeadtimeless
primary vertex
secondary vertex
d0
B
J/
Used for current Bc analysis
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Bc Production and Decay• Bc has differently flavored heavy quarks
Much smaller production rate Unique decay (bc,cs,annihilation…)
Rich decay modes
Species Prod. FractionB+ 40%B0 40%Bs 10%
b-baryons 10%Bc ~0.05%Theoretical calculation : 7.4nbPhys. Lett. B605, 311(2005)
Decay BR
bcBcJ/e ~1.9%BcJ/ ~0.13%
csBcBs ~16.4%BcBs
* ~20.2%
ann.Bc ~1.6%Bccs ~4.9%hep-ph/0308214(2003)
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Production Rate Measurement• BcJ/e and J/ semileptonic decays
Use J/ trigger data (0.36 fb-1)Large BR statistical advantageNo narrow mass peak due to missing neutrino (4~6GeV/c2)Need to understand all of backgrounds
fake J/…………………..J/ mass sidebandfake e, and DIF………...J/+track & fake ratebb (bJ/X,blX)….....PYTHIA Monte Carlo photon conversion e……...tagged conv. e & its efficiencyprompt J/……………….require to have a displaced vertex
• Use BuJ/K as a normalization modeTopologically similarMeasure (Bc)B(BcJ/l)/(Bu)B(BuJ/K) Cancel out most of uncertainties
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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(Bc)B(BcJ/l)/(Bu)B(BuJ/K) Measurement : 0.36 fb-1
• electron mode : • 0.282 ± 0.038(stat.) ± 0.035(yield) ± 0.065(acceptance) (pT(B)>4GeV/c) • 0.242 ± 0.036(stat.) ± 0.031(yield) ± 0.051(acceptance) (pT(B)>6GeV/c)
• muon mode : • 0.245 ± 0.045(stat.) ± 0.066(syst.) +0.080/-0.032(life.) (pT(B)>6GeV/c)
J/e J/
5.9 5.2
* softer pT(Bc) was assumed
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Lifetime
• Three major decay diagrams
• Lifetime should be Bc 1/(0.6+1.2+0.1) 0.5 ps if all the three diagrams contribute to the decay
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Lifetime Measurement•BcJ/e semileptonic decay
•Perform a maximum likelihood fit to J/e decay length•Correct neutrino’s momentum using Monte Carlo•Background shapes
•Estimate # of BKGs
fake J/
conversionfake e
bb
Constrained during the fitting
(same way as B ratio measurement)
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Lifetime Measurement
(Bc) = 0.463 +0.073/-0.065(stat.) ± 0.036(syst.) ps
• BcJ/e channel• Data : ~ fb-1
accepted by PRL
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Mass• Theoretical calculations predict M(Bc) 6.3GeV/c2
• Bc full reconstruction is necessary for precise mass measurement
• CDF searches for the BcJ/ decay : (BR~0.1%)
PRL94,172001(2005)
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Observation of the BcJ/ decay and Mass Measurement
• Data : ~1.1 fb-1
• J/ selection is optimized using BuJ/K events
7.5
M(Bc) = 6276.5 ± 4.0(stat.) ± 2.7(syst.) MeV/c2
N(Bc)50
Clo
se u
p
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Summary The Bc signal has been observed in BcJ/e modes
with >5 significance in CDF Run II Measured Bc meson properties
(Bc)B(BcJ/l)/(Bu)B(BuJ/K) e : 0.282 ± 0.038 ± 0.035 ± 0.065 (pT(B)>4GeV/c) : 0.245 ± 0.045 ± 0.066 +0.080/-0.032 (pT(B)>6GeV/c)
Lifetime 0.463 +0.073/-0.065 ± 0.036 ps
Mass 6276.5 ± 4.0 ± 2.7 MeV/c2
Other studies are to follow soon… Lifetime measurements from J/, J/
Masato Aoki International Workshop on Heavy Quarkonium 2006 @ BNL
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Backup slides
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Residual photon conversions
• Electrons coming from photon conversion event are removed from the J/e candidate list
• Find colinear partner track• miss-tracking in low pT region• not 100% finding efficiency residual photon conversion electrons
• Estimate using found conversions and its efficiency