# Presentation: 877366

## Hot Topics at CDF

- Jennifer Pursley
*The Johns Hopkins University*
- on behalf of the CDF Collaboration

- Weak Interactions and Neutrinos - Kolkata, India
-  January 15-20, 2007

## Heavy Flavor Physics at CDF...

- Mixing:
- Bs0, Bd0, D0

- Lifetimes:
- , b, Bs, Bc,
- B+, Bd,...

- Masses:
- Bc, b, Bs,...

- Rare Decay Searches:
- Bs → +-,
- D0 → ,...

- Surprises!?

- B and D:
- Branching ratios
- and ACP

- Production Properties:
- (*b*), (J/), (D0),...

- New Particles:
- X(3872), b*,...

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## Tevatron performance
CDF detector and heavy flavor triggers
Focus on new results:
First observation of b(*)± baryons
B → h+h’- results
Three new charmless decays
Measurement of branching ratios and Acp
Not covered in this talk:
Many recent results!
Not enough time to mention all 
See A. Rahaman’s talk for Bs0 mixing

- CDF detector and heavy flavor triggers
- Focus on new results:
- First observation of b(*)± baryons
- B → h+h’- results
- Three new charmless decays
- Measurement of branching ratios and Acp
- Not covered in this talk:
- Many recent results!
- Not enough time to mention all
- See A. Rahaman’s talk for Bs0 mixing

- Outline

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## Tevatron Performance

- Collide *p* at √s = 1.96 TeV
- Record peak luminosity 2.52x1032 sec-1 cm-2
- CDF II collected ~ 1.8 fb-1 out of > 2 fb-1 delivered

- Current analyses use about 1 fb-1 of data
- Analyses with more data in the works
- Expect ~8 fb-1 by 2009

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## CDF II Detector

- SVX II – 5 layers of double-sided silicon
- Trigger on displaced tracks
- Particle ID
- dE/dx in COT and Time of Flight detector

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## Heavy Flavor Physics at a p collider

- Advantages:
- Huge *b* cross-section (~100 mb total)
- Produce all *b* species
- B+, B0, Bs, Bc, B**, Bs**, b, b,...
- Disadvantages:
- “messy” environment
- Multiple interactions, *p* debris
- Only 1 *b* per ~1000 soft QCD collisions
- Low acceptance for opposite side *b*-hadron
- → Live and die by the trigger!

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## B Physics Triggers

- Di-muon
- J/→
- B → 
- Two muons with:
- pT() > 1.5 GeV/c

- One displaced track +
- lepton (e, )
- B → lX
- Lepton:
- pT(l) > 4.0 GeV/c
- Track:
- pT > 2.0 GeV/c,
- d0 > 120 m

- Two displaced tracks
- B → hh
- Two tracks with:
- pT > 2.0 GeV/c
- pT > 5.5 GeV/c
- d0 > 100 m

- Used in b and
- B → hh analyses!

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## Observation of b(*) Baryons

## b Motivation

- b Motivation

- b only established *b* baryon
- Enough statistics at Tevatron to probe other heavy baryons
- Next accessible baryons:

- b: *b*{*qq*}, *q* = *u,d*; *J**P* = S*Q* + s*qq*

- = 3/2+(b*)

- = 1/2+ (b)

- HQET extensively tested for *Qq* systems; interesting to check predictions for *Qqq* systems
- Baryon spectroscopy also tests Lattice QCD and potential quark models

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## Reconstructing b

- Reconstructing b

- With 1.1 fb-1, world’s largest sample of  b: ~**3000**
- Use two displaced tracks trigger to reconstruct:

-  b decays at primary vertex
-  Combine b with a prompt track to make a b candidate

- b Mass Plot

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## b Search Methodology

- Separate b- and b+:
-  			       (+ c.c.)
-  			       (+ c.c.)
- Search for resonances in mass difference: 	       Q = m(b) - m(b) – m
- Use reconstructed b mass    → remove b mass  systematic error
- Unbiased optimization
- Optimize b cuts with b signal region blinded:	        30 < Q* *< 100 MeV/c2

- b backgrounds:
- b Hadronization + Underlying Event – Dominant!
- B Meson Hadronization
- Combinatorial Bkg
- Fix background contributions from data or PYTHIA Monte Carlo

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## b Observation

- b Observation

- Signals consistent with lowest lying charged b states at > 5 significance level
- With unbinned likelihood fit, measure events
- And mass difference values:

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## B → h+h’- Measurement

## Why study charmless B decays?
Study direct CP violation (DCPV) in the B0 system
Large effect (~10%) established; why is it not compatible with the B+ system? [Gronau and Rosner, Phys.Rev. D71 (2005) 074019]
Sensitive to new physics
Comparing rates and asymmetries of B0 → K+- and Bs0 → K-+ uses only SM assumptions [Lipkin, Phys.Lett. B621 (2005) 126]
BR(B0 → -+) and BR(Bs0 → K-K+) may provide info on CKM angle  by comparing to theoretically allowed regions [Fleischer, Matias, PRD66 (2002) 054009]
Comparing rates of Bs0 → K-K+ and B0 → K+- may shed light on the size of SU(3) symm breaking [Descotes-Genon et al, PRL97 (2006) 061801][Khodjamirian et al, PRD68 (2003) 114007]
Primary analysis goals:
Measure ACP(B0 → K+-)
Measure BR(Bs0 → K-+)

- B → h+h’- Motivation

- Why study charmless B decays?
- Study direct CP violation (DCPV) in the B0 system
- Large effect (~10%) established; why is it not compatible with the B+ system? [Gronau and Rosner, Phys.Rev. D71 (2005) 074019]
- Sensitive to new physics
- Comparing rates and asymmetries of B0 → K+- and Bs0 → K-+ uses only SM assumptions [Lipkin, Phys.Lett. B621 (2005) 126]
- BR(B0 → -+) and BR(Bs0 → K-K+) may provide info on CKM angle  by comparing to theoretically allowed regions [Fleischer, Matias, PRD66 (2002) 054009]
- Comparing rates of Bs0 → K-K+ and B0 → K+- may shed light on the size of SU(3) symm breaking [Descotes-Genon et al, PRL97 (2006) 061801][Khodjamirian et al, PRD68 (2003) 114007]
- Primary analysis goals:
- Measure ACP(B0 → K+-)
- Measure BR(Bs0 → K-+)

- J. Pursley, Beauty 06

## B → h+h’- Reconstruction

- B → h+h’- Reconstruction

- Offline trigger confirmation → visible B peak of ~14500 events, S/B ~ 0.2
- Optimize cuts by minimizing statistical error on observable to be measured
- Loose selection to measure ACP(B0 → K+-) and other large yield modes
- Tight selection to measure BR(Bs0 → K-+) and other rare modes

- Combinatorial
- background

- Physical
- bkg

- Loose cuts

- Tight cuts

- Simple 1-dim
- binned mass fit,
- excludes region of
- rare modes

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## Modes will overlap
Despite excellent mass resolution (~22 MeV/c2)
Particle ID (PID) insufficient for event-by-event separation
→ Fit of composition:
Likelihood which combines information from
Kinematics (mass and momenta)
PID (dE/dx)

- Modes will overlap
- Despite excellent mass resolution (~22 MeV/c2)
- Particle ID (PID) insufficient for event-by-event separation
- → Fit of composition:
- Likelihood which combines information from
- Kinematics (mass and momenta)
- PID (dE/dx)

- Signal Extraction

- Monte Carlo simulation
- of reconstructed 
- invariant mass

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## Peak Composition Handles

- Kinematics
- Exploit the small kinematic differences between the modes
-  = (1- p1/p2)·q1 is the signed kinematic imbalance
- p1,2 are the 3D track momenta (p1 < p2)
- q1 is the sign of the charge of track with 3D momentum p1
- Two other kinematic variables are M (invariant  mass) and ptot = p1 + p2
- These 3 variables carry all kinematic information about the 2-body decay
- dE/dx
- 1.4 K/ separation at p > 2.0 GeV/c after calibration on D*

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## “Raw” measurement of ACP(B0 → K+)

- “Raw” measurement of ACP(B0 → K+)

- B0 → h+h’- yield like B factories, and unique large sample of
- Bs0 → h+h’-

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## Direct CP asymmetry of B0 → K+-

- Second best single measurement of ACP(B0 → K+-)

- After correcting for K+/K- interaction rate asymmetry and evaluating
- systematic effects, find:

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## BRs: B0 → +- and Bs0 → K+K-

- BRs: B0 → +- and Bs0 → K+K-

- BR(B0 → +-), BR(Bs0 → K+K-) becoming precision measurements
- Conservative systematics for Bs0, but soon syst. ≈ stat. error
- Not completely in agreement with theoretical predictions:
- [Descotes-Genon et al] BR(Bs0 → K+K-)/BR(B0 → K+-) ≈ 1
- [Khodjamirian et al] predict large SU(3) breaking (≈2)
- CDF measurement disfavors predictions of large breaking

- Using HFAG:

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## Rare modes search (tight cuts)

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## First observation of Bs0 → K-+

- First observation of Bs0 → K-+

- Using HFAG:

- Good agreement with recent theo. predictions.
- From SM, expect large ACP ≈ 0.37 (calculated
- using above BR).  Measure:

- (= 1 SM)

- Compare rates and asymmetries of B0 → K+- and Bs0 → K-+ to probe NP with only SM assumptions [Lipkin, Phys.Lett. B621 (2005) 126]:

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## First observation: b0 → p-, b0 → pK-

- First observation: b0 → p-, b0 → pK-

- b0 mass
- region

- Use PID variable to
- distinguish the modes in
- the b signal region.
- Measure BR in agreement
- with theory predictions:

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## Upper limits: B0 → K+K-, Bs0 → +-

- Both modes are annihilation-dominated decays
- Hard to predict BR
- Not yet observed anywhere

- World’s best upper limit on Bs0 → -
- Same resolution as B-factories for B0 → K+K-

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##  First observation of lowest lying charged b states!
With m(b) = 5619.7 ± 1.2 (stat) ± 1.2 (syst) MeV/c2,

New B → h+ h’- results
First observation of Bs0 → K-+, b0 → p-, b0 → pK-
First measurement of ACP and BR(Bs0 → K-+)
Precision ACP(B0 → K+-) measurement
Updated BR(Bs0 → K+K-) and BR(B0 → +-) measurements
With more data on the way, more precision measurements and new discovery potential!

- With m(b) = 5619.7 ± 1.2 (stat) ± 1.2 (syst) MeV/c2,
- New B → h+ h’- results
- First observation of Bs0 → K-+, b0 → p-, b0 → pK-
- First measurement of ACP and BR(Bs0 → K-+)
- Precision ACP(B0 → K+-) measurement
- Updated BR(Bs0 → K+K-) and BR(B0 → +-) measurements
- With more data on the way, more precision measurements and new discovery potential!

- Summary

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## Backup Slides

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## b Fit Likelihood Ratios

| Hypothesis | (ln £) | LR |
| --- | --- | --- |
| “NULL” vs. “4 Peak” | 44.7 | 2.6e19 |
| “2 Peak” vs. “4 Peak” | 14.3 | 1.6e6 |
| No b- Peak | 10.4 | 3.3e4 |
| No b+ Peak | 1.1 | 3 |
| No b*- Peak | 10.1 | 2.4e4 |
| No b*+ Peak | 9.8 | 1.8e4 |

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## b Two Peak Fit

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## Offline trigger confirmation
Two opposite charge tracks (i.e. B candidate) from long-lived decay:
Track impact parameter > 100 μm
B transverse decay length > 200 μm
B candidate points back to the primary vertex
B impact parameter < 140 μm
Reject light quark background from jets:
Transverse opening angle [20°, 135°]
pT1 and pT2 > 2.0 GeV/c
pT1 + pT2 > 5.5 GeV/c
Visible B peak of ~14500 events with S/B ~ 0.2

- Two opposite charge tracks (i.e. B candidate) from long-lived decay:
- Track impact parameter > 100 μm
- B transverse decay length > 200 μm
- B candidate points back to the primary vertex
- B impact parameter < 140 μm
- Reject light quark background from jets:
- Transverse opening angle [20°, 135°]
- pT1 and pT2 > 2.0 GeV/c
- pT1 + pT2 > 5.5 GeV/c
- Visible B peak of ~14500 events with S/B ~ 0.2

- B → h+h’- Reconstruction

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## Peak Composition Handle 1: Mass

- Peak Composition Handle 1: Mass

- BR measurements sensitive to detailed shape of mass resolution function
- e.g. radiative tails, non-Gaussian tails
- Need careful parameterization of all resolution effects!
- Used QED calculation from  [Baracchini and Isidori, Phys.Lett. B633 (2006) 309] for B(D) → , K, KK mass resolution templates
- Use huge D0 → K sample for an accurate test of resolution model
- 1 dim binned fit, signal mass line shape fixed from model
- Check model fits data!

- FSR tail left
- of each peak
- affects BR

- FSR

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## Peak Composition Handle 2: Momenta

- Peak Composition Handle 2: Momenta

- Exploit the (small) kinematic difference between the modes:
-  = (1- pmin/pmax) · qmin is the signed kinematic imbalance
- pmin (pmax) are 3D track momenta, with pmin < pmax
- qmin is the sign of the charge of track with pmin
- Two other kinematic variables of interest:
- M, the invariant  mass
- ptot = pmin + pmax, the scalar sum of the 3D track momenta

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## Peak Composition Handle 3: dE/dx

- Strong D*+ decay tags D0 flavor
- ~95% pure K and  samples from ~1.5 million D*+ decays
- dE/dx accurately calibrated over tracking volume and time

- D*+ → D0 +
-          D0 → K- +

- 1.4 K/ separation at p > 2.0 GeV/c
- Statistical uncertainty only 60% worse than achievable with PERFECT separation

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