1. Λb and heavy states at Tevatronby
Eduard De La Cruz Burelo
University of Michigan
On behalf of
CDF and D0 collaborations
Beauty 2005, Assisi (Perugia) Italy

2. Outline: Tevatron & Detectors Λb quick overview Physics with the Λb
Λb at Tevatron
Reconstruction
Semileptonic decays channels
Full reconstructed decays channels
Mass measurement
Lifetime measurement
Branching Fractions
B**
B decays to narrow D**
Beauty 2005, Assisi (Perugia) Italy

3. Overview on the Λb Lightest b baryon (udb)
First observed by AU1 collaboration in 1991 in the decay channel Λb→J/ψΛ.
First lifetime measurement from LEP experiments using semileptonic decays in 1992.
Currently produced in high statistics only at Tevatron, (non produced in B factories)
Beauty 2005, Assisi (Perugia) Italy

4. Rich physics program in the Λb
Testing HQE theory in b baryons (lifetime)
Spin role in heavy hyperons (polarization)
CP violation
T violation ( )
New physics ( )
Beauty 2005, Assisi (Perugia) Italy

5. Experimental status PDG’04 Lb Other b-baryons Mass (σM~0.16%)
Lifetime (σct~6.5%)
Decay channels:
Λ+c l- ν X (BR, σBR~23%)
J/ψΛ (BR, σBR~60%)
Λ+cπ- (seen)
Λ+ca1(1260)- (seen)
pK- , pπ- , Λγ upper limits
Some indirect lifetime estimations
Some “seen” decay channels
Beauty 2005, Assisi (Perugia) Italy

6. A lot of theoretical work
Example … LO
NLO
C. Tarantino, Monday 20
This was just less of a couple of years ago.
This was just less of a couple of years ago.
A lot of theoretical work
Just last month !!!
HFAG
hep-ex/
(*) Includes D0 and CDF Run II measurements
(*)
Beauty 2005, Assisi (Perugia) Italy

7. First step: “Reconstruction” Quite a challenge
For both detectors:
Only charge particles reconstructed
A lot of things going on in the silicon detector
Beauty 2005, Assisi (Perugia) Italy

8. Reconstruction of the Λb
Tevatron is like a B factory, but a dirty one
Only ~5% reconstructable
Zoo of b hadrons: B0, B+, Bs, Bc, b,  b, B**
But:
O(103) higher
Difficult to find other b
In b events , only fb~ 10% (b→X)
Beauty 2005, Assisi (Perugia) Italy

9. Λb in full reconstructed channels
Both experiments have clear signal of
Invariant Mass, (GeV/c2)
Invariant Mass, (GeV/c2)
Beauty 2005, Assisi (Perugia) Italy

10. Λb in full reconstructed channels
Invariant Mass, (GeV/c2)
PDG’04 : Seen!
Now:
clear evidence Λb→Λ+cπ - ~ 11σ
Beauty 2005, Assisi (Perugia) Italy

11. Λb in semileptonic decays
Toward the direct measurement of τ(Λb)/τ(B0d), similar to τ(B+)/τ(B0d)
[PRL 94, (2005) ]
Beauty 2005, Assisi (Perugia) Italy

12. After reconstruction …
Mass measurement
Lifetime
Branching fractions
Etcetera … Lb
Beauty 2005, Assisi (Perugia) Italy

13. Most precise Lb mass measurement in the world !!!
Beauty 2005, Assisi (Perugia) Italy

14. Simultaneous Mass & lifetime likelihood fit
Lifetime measurement
Signal selection
λ + mass distribution
(signal + bkg)
Fit procedure
Models for
λ + mass distribution
Background (λ)
Signal (λ)
Background (λ)
Models:
Simultaneous Mass & lifetime likelihood fit
Beauty 2005, Assisi (Perugia) Italy

15. First measurement in a full reconstructed decay channel !!!
Λb lifetime[1] DØ DØ
First measurement in a full reconstructed decay channel !!!
[1] V.M Abazov et al, PRL 94, (2005)
Beauty 2005, Assisi (Perugia) Italy

16. Beauty 2005, Assisi (Perugia) Italy

17. Branching fractions: Beauty 2005, Assisi (Perugia) Italy

18. Branching Fraction: Lb → Lc p
From PDG: 1.84±0.493
From MC: 1.65±0.03
From the fit:
NΛb=214±19(stat)
NB0=790±32(stat)
Assuming:
(PDG ’04)
Beauty 2005, Assisi (Perugia) Italy

19. Branching Fraction: Bsemi/Bhad
First measurement of this ratio !!!
Beauty 2005, Assisi (Perugia) Italy

20. Search for Lb→hh decays
Prediction[2]:
Br (Lb→ pK)=( )×10-6
Br (Lb→ pp)=( )×10-6
compare to
Br(B0→Kp)= 18×10-6
Large CP asymmetries O(10%) expected in b-baryons
Previous best limit from ALEPH
BR(b pK) < 90%
BR(b p) < 90%
[2] Mohanta, Phys. Rev. D63:074001,2001
Beauty 2005, Assisi (Perugia) Italy

21. B1 & B*2 observed by first time as separate states!!!
B** resonances
B meson spectroscopy only well established for ground states B+,B0,Bs.
Few models with precise predictions: mass/widths/BR
B1 & B*2 observed by first time as separate states!!!
Beauty 2005, Assisi (Perugia) Italy

22. BD**mn BsDs**mn Semileptonic decays to excited states Ds**D*KS
Beauty 2005, Assisi (Perugia) Italy

23. Summary A lot of new results from Tevatron on the Lb baryon
Best mass measurement
First lifetime in full reconstructed channel
Branching fractions by first time measured
More in preparation:
Direct lifetime ratio measurement τ(Λb)/τ(B0)
Others b baryons and studies…
CDF and D0 are looking forward to contribute to a best knowledge of the b baryons.
Beauty 2005, Assisi (Perugia) Italy