BPhysics at D coming attractions

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B-Physics at DØ (coming attractions)

• Hal Evans Columbia U.
• Outline
• Why B-Physics?
• Why DØ?
• Wild Predictions Comparisons!

2
Philosophy 101(B)

• Why should we study the b-Quark?
• Probes an area of the SM that is poorly
  understood
• CKM Matrix CP-Violation
• Sensitive to Physics beyond the Standard Model
• b-quark is the most massive fundamental particle
  that is easily accessible
• Important input to QCD models used in other
  measurements
• B-Hadron properties lend themselves to modelling
• crucial in studying Higgs, t-quark

LEP EW-WG Summer 00
3
Stalking the Wild b-Quark

• Mass (3rd Family) mb 4.5 GeV
• couples to t-quark
• couples to New Physics
• perturbative QCD regime
• Lifetime ? 1.6 ps
• a useful ID tool
• Spectroscopy
• light-q mesons
• heavy-q mesons
• baryons
• Decays 25 modes meas (B0)
• 165 modes listed by PDG
• light quark spectator
• Mixing
• ?md0.47ps-1 ?msgt15ps-1
• CP Violation
• large effects (gt10) in some modes

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Their Natural Habitats

• Acceptance at DØ

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Glorious Tevatron History
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ch- ch- ch- ch- Changes!

• Major upgrade to the Tevatron nearing completion
• main injector
• antiproton recycler
• First collisions in 36x36 mode last week !

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DØ Run II Upgrade
Forward Scint
Central Scintillator
Forward Mini-drift chambs
Central PDTs
Shielding
Calorimeter
Tracking Solenoid,Silicon,Fiber
Tracker,Preshowers
New Electronics,Trigger,DAQ
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Detector Performance
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Triggering on Bs
?
? -
?
b
? -
? -
b

• Handles
• Tracks
• rates too high for DØ
• Leptons BR(B?l?X)11
• only DØ tool at L1
• Displaced Vs ltLgt2.3 mm
• Si info used at L2
• Mass, Isolation, etc
• L2, L3

?
multi-level trigger required
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Triggering at DØ

• Single Sub-Dets
• Towers, Tracks, ET-miss
• Some correls
• Not deadtimeless

• Correlations
• Calibrated Data
• Physics Objects e,?,j,?,ET-miss

• Simple Reco
• Physics Algos

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L1 L2 Systems
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The DØ Silicon Track Trigger

• Trigger Benefits
• Improved Momentum Res
• factor 2-3
• Sharper Thresholds
• Impact Param at Trigger
• Resolutions
• 30?m at PT2GeV
• 15?m at PT15GeV
• Physics Benefits
• New Phenomena
• incr Higgs sens 20 ZH???bb
• double sens hA?bbbb
• Top
• Trigger on Z?bb (increase yield x6)
• Cut Mt Syst in half
• B-Physics
• Increase B??KS yield by 50
• General
• Reduce e Rate by a factor of 2

50 ms Time Budget
Online summer 2002
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DØ Now !
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DØ Ambitions in Run II

• QCD Tests
• X-Sections Correlations
• Excl. Decays, lJet Incl., ll
• Onium Physics
• J/?, ? X-Sects and Pol.
• Fragmentation
• B-Hadrons (B?,B0,Bs,Bc,?b)
• Spectroscopy
• Lifetimes
• Pol. Helicity Analyses
• Rare Decays
• B ? ll-, ll- K
• Bs ? ?K

• B Mixing
• Bs ? ?lX, Ds?, J/?K
• Bd (t-dep) Tagging Studies
• CP Violation CKM
• J/?Ks0 sin 2?
• ??, KK (limits) ??
• Bs ? J/?? non-SM

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B Production

• Theory says Yes!
• mbgtgt?QCD NLO should work
• but scale uncertainties large
• Experiment says Kinda!
• normalization x2.5-4 high
• shape OK (but high vs low PT)
• correlations as expected from Higher Order
• nagging uncertainty
• PDFs (note personal bias!)
• New for Run II (DØ)
• exclusive final states
• vertex tagging
• electrons
• more correlation studies

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CP Violation and the CKM Matrix

• CP Violating Asymmetry
• SM expl for CP Asym in K B
• Complex Phase in CKM
• Wolfenstein param O(?4)

• Unitarity of VCKM ? 12 eqns
• the Unitarity Triangle is one

(?,?)
?
?
?
(0,0)
(0,1)
(? sin?c)
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but does it All Fit?

• Many measurements constrain CKM params
• but no real test of whether CP-violation is
  described by SM or not
• Two Possibilities
• all angle/sides consistent w/ a triangle
• Hooray for the SM !
• no triangle fits all meass
• New Physics !
• Why expect New Phys here?
• many beyond SM models have additional
  CP-violation
• matter antimatter asym not consistent w/ SM CP

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What can We Do About It?

• Easiest angle to measure is ?
• use time dependent CP asymmetry in Bd?J/?Ko
• Theoretical uncertainties small !
• Need to tag Flavor of B at production
• remember it can mix before decaying

Bd Mixing
K Mixing
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B ? J/? Ks Experimentally

• Experimental Technique
• measure Lxy ? t
• tag initial flavor
• worry about asymmetric systematics
• Experimental Advantages
• Leptons for triggering
• simple, excl final state
• J/? Ks mass constrs

?

• (some) Tagging Possibilities
• Opposite Side Lepton
• Opposite Side Jet Charge
• Same Side Fragmentation ?

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Flavor Tagging

• Opposite side tags
• identify the flavor of the other B in the event
• soft lepton tags b l - X
• jet charge tags Qjet lt 0 for b
• Same side tags
• correlation of flavor and charge of closest
  particle produced in fragmentation or decay

Efficiency (e ) and dilution factor (D) D 2
P - 1 P is the correct tag probability e D2 is
the tags effectiveness
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B? J/? KS Reconstruction

• J/? ? ? ? -
• two muon tracks
• pT gt 1.5 GeV/c
• h lt 2

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B? J/? KS Reconstruction

• KS ? ? ? -
• pT (p) gt 0.45 GeV/c
• pT (KS) gt 0.75 GeV/c
• hp lt 1.8
• Lxy/? gt 5

• Combined mm- ??- invariant mass
• (before fit)

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B? J/? Ks decay length reconstruction

• Two secondary two-track vertices
• Average B decay length 2.3 mm
• Measured decay length resolution 100 mm
  
  

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B?J/?Ks Reconstruction

• J/????-
• 2 Muons ?lt2.0, PTgt1.5GeV
• Ks???-
• Long lifetime rejects bgrd
• Lxy/? gt 5
• 4-Track Constrained Fit
• mass J/?, Ks
• vertex Ks?B, B ?primary
• Decay Length Resolution
• 100 ?m

• unconstr
• ? 41 MeV

• constr
• ? 10 MeV

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Effectiveness

• Measure of tagging weight
• Quality ? D2

• ? efficiency of tag
• D (2P 1) P correct tag prob

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sin(2?) Expectations (2 fb-1)

• DØ Assumptions
• S/B 0.75
• ?D2 9.8
• Time res ?t 100 fs
• 2.0 fb-1 of data

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sin2? Past, Present Future
() Preliminary
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Rare Decays and FCNCs

• Theoretically
• FCNC B0 decays forbidden at tree level in SM
• Beyond SM effects could be large !

• Experimentally
• Triggering
• Leptonic Modes easy
• Event Reconstruction
• ??- easy but low BR
• B mass
• secondary vertex
• isolation
• ??-K promising
• all of above
• K ID
• cut out ? resonances
• ??-Xs difficult
• small M(??) window
• large backgrounds

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Beyond the SM w/ Rare Decays

• ??-
• in 2 Higgs-Doublet Model

• ??-K

Ali,Ball,Handoko,Hiller hep-ph/9910221
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Bd???-K Asymmetry
Reconstructed no bgrd (a,b)
Generated distribs

• Expect 700 events in 2 fb-1
• Asymmetry results (plot d)
• A 0.11 0.11 m?? lt 2 GeV
• A -0.33 0.06 m?? gt 2 GeV
• To do
• Bd?ee-
• B?ll-K

Reconstructed SB11 (c,d)
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Big List o Predictions
all predictions for 2 fb-1 of data
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Conclusions

• How can you have a conclusion when you havent
  started yet ?