1. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Bc at the Tevatron William Wester Fermilab for the CDF and DØ collaborations p
e,m, u, …
ne, nm, d, … Bc b c c
J/y
m+ m-
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

2. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Introduction
B Physics at Hadron Colliders
UA1 cross section measurements
CDF fully reconstructed B->J/yK(*)
Study of Bc highlights hadron collider advantages
Large cross section for producing triggerable low background decays not accessible at the B factories.
Since the 1980’s …
Advantages:
Large s(b) x L
All mesons and baryons
Triggerable: l or J/y
Multipurpose detectors
Run 0 (88-89)
No SVX pb-1
Disadvantages: (perceived)
High backgrounds
Limited acceptance
Small Lorentz boost
Unknown initial state
UA1 s(b) in m channel
PLB 213, 415 (1988)
CDF Bu->J/yK
PRL 68, 3403 (1992)
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

3. Tevatron in Run II L = 1 fb-1 CDF DØ beautiful prairie but no hills,
thanks to the organizers DØ
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

4. Innermost silicon layer
CDF
CDF LayerØØ detector (beyond the baseline)
DØ will add inner silicon for Run IIb
s(ip) improves
especially in the
hybrid region
1.35cm
outside hybrid region
Without LØØ
With LØØ
1.61cm
hybrid region
prototype
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

5. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Bc properties
Bc is a heavy-heavy system
Production: Factorization with two scales Mb + Mc and contributions of color singlet / octet
Softer PT distribution?
Decay: both b and c quarks
can participate
Shorter c-like lifetime?
Large number of final state BR’s.
Mass: new system for potential
models and new lattice QCD calculations
All aspects of the theoretical work require experimental measurement => happening now at the Tevatron
Chang et al, PRD, 71 (2005)
curves
represent
different singlet/
octet contributions
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

6. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
CDF: Bc in Run I (‘91-’96)
A few candidate events at LEP and the CDF observation and measurements…
+6.2
signal events
-5.5
CDF
0.11 fb-1
M=6.4±0.39±0.13 GeV
+0.18
ct = ps
- 0.16
PRL 81, 2432 (1998) and PRD 58, (1998)
Production measurement (Pt(B)>6 GeV/c |h|<0.6):
s(Bc) x B (Bc->J/y ln)
= (stat) ± (syst) (ct)
s(Bu) x B (Bu ->J/y K)
Note: assuming harder Pt spectrum in MC
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

7. Run II results: semi-leptonic decays
Bc -> J/y + l with l = e, m
Not fully reconstructed (missing n)
Understanding backgrounds are key
bb events with the J/y from b and l from b
Fake muons or fake electrons
Other backgrounds
Study J/y+track and Bu->J/y K
Look for Bc excess above background and make measurements
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

8. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Bc in DØ
Three muon final state: Bc -> J/y m X
0.21 fb-1 of data
231 J/ymX candidates (signal+background)
Use J/y+track control sample for background
prompt
non-prompt
Combined likelihood fit
Signal + background
mass
pseudo-lifetime mm
Scan Monte Carlo in steps of different mass.
Perform the fit with and without the Bc along with prompt and non-prompt
data bkgd distributions.
Cross-check the results using y(2S) + m/track (background dominated).
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

9. Fit with and w/o Bc Background-only Include Bc contribution
Background-only fit is poor compared with addition of signal:
D2log(likelihood) is 60 for 5 dof
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

10. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
DØ: fits and results
Mass log likelihood
ct log likelihood
NCAND:
95 ±12 ±11
“first 5s Bc result”
Mass:
±0.34 GeV
+0.14
-0.13
ct:
±0.121 ps
+0.123
-0.096
DØ Note: 4539-CONF
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

11. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
CDF: Bc -> J/y m X
Use 2.7M J/y’s in 0.36 fb-1
Combine with third track with & w/o muon ID
PT>3 GeV, ct > 60mm, and Df(J/y-trk) < 90 deg
Use Bu->J/yK from data for normalization
Use Monte Carlo of Bu and Bc for erel
Evaluate backgrounds in the data
Fake muons, bb, fake J/y
Estimate systematic uncertainties
Fit data in 4-6 GeV for signal and backgrounds
Evaluate relative production of Bc to Bu
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

12. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Fake muon background
Fake muons: determine p, K, p composition vs PT (dE/dx and TOF) and then use D*, L decays to find fakes vs PT
How many come from
J/y+track where the
track is a fake muon?
106 evts
4<M<6
Fake muons primarily from
decay in flight: 16.3±2.9
estimated in 4<M<6 GeV.
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

13. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
More backgrounds
bb background from Pythia Monte Carlo normalized to Bu->J/yK data using Df distributions (vary production)
Fake J/y from J/y sidebands
Backgrounds from the
other b: 12.7±1.7 ±5.7
estimated in 4<M<6 GeV.
Backgrounds from fake J/y
(no double counting): 19.0±3.0
estimated in 4<M<6 GeV.
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

14. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Muon channel results
Use MC for relative efficiency for Bc and
Bu along with Bu->J/yK to obtain:
s(Bc) x B (Bc->J/y ln)
PT(B)>4 and
|y| < 1 =
s(Bu) x B (Bu ->J/y K)
5.2s
Other measurements from this sample are
in preparation.
CDF Note: 7649
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

15. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
CDF: Bc -> J/y e X
Fake electron
Use J/y+track data
Estimate fake rate from data (D0Kp,L0pp)
Photon conversion
Use J/y+tagged conversion data
Conversion finding efficiency from MC
bb background
bJ/yX and beX
PYTHIA bb Monte Carlo
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

16. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
Photon conversions
Remove conversions by finding the partner track during the electron selection
Evaluate the conversion finding efficiency from MC
Calculate the residual conversion background as a function of M(J/ye) using J/y+tagged conversions.
Expected background
14.54  4.38(stat)  6.39 (syst)
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

17. electron channel results
Background
63.64.9(stat)13.6(syst)
Observed
178.514.7(stat)
Excess
114.915.5(stat)13.6(syst)
Significance
5.9s
s(Bc) x B (Bc->J/y ln)
PT(B)>4 and
|y| < 1 =
s(Bu) x B (Bu ->J/y K)
0.2820.038(stat.)0.035(yield)0.065(acceptance)
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

18. W. Wester, CDF, Fermilab, Beauty 2005, Assisi
CDF: Bc -> J/y p
Full reconstruction determines precise mass
Estimate events in 0.36fb-1
Perform analysis “blind”
Optimize MC signal using a figure of merit
Collapse background into large discrete bins
Use predetermined threshold
for positive result
Tight requirements
Especially on p coming from
displaced J/y vertex
Perform cross-checks
Bu->J/yK
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

19. Results Mass = 6287.0 ± 4.8(stat.) ± 1.1(syst.) MeV/c2
Small excess at 6.3 GeV above predetermined threshold
18.9 ± 5.7 candidates
10.0 ± 1.4 evts Background
Monte Carlo: prob(bkgd) fluctuates to this signal is 0.3%
Mass = ± 4.8(stat.) ± 1.1(syst.) MeV/c2
hep-ex/
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

20. Cross check: partially reconstructed sample
Look at partially reconstructed decays with M < MBc.
Relax cuts
3rd track of
partially
reconstructed
track should
still point to the
J/y vertex
Upper
sideband should
have no Bc Bc Bu
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

21. Recent lattice QCD calculation
Recent calculation emphasizes new precision from 2+1 flavor lattice QCD with staggered quarks
PLB 453, 289 (1999)
PRL 94, (2005)
hep-ex/
mBc = ± 4.8 ± 1.1 MeV
D(theory-exp)= 17 MeV
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi

22. Summary and conclusions
The study of the Bc is happening in Run II
Semi-leptonic decays observed >5s
D0: J/y m (tri-muon)
CDF: J/y m and J/y e
Small excess in CDF’s J/y p sample
Precision mass compared with theory
Coming soon …
Production spectrum and lifetimes
Stronger fully reconstructed signal
12/4/2018
W. Wester, CDF, Fermilab, Beauty 2005, Assisi