# Presentation: 835266

## Λb and heavy states at Tevatron

*by*
***Eduard De La Cruz Burelo***
*University of Michigan*
*On behalf of *
*CDF and D0 collaborations*

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## 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**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## 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)

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## 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 (                       )

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Experimental status

| PDG’04 |  |
| --- | --- |
| b | 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 |

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Example ...

- This was just less of a couple of years ago.

- A lot of theoretical work

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## First step: “Reconstruction”Quite a challenge

**For both detectors:**
** ****Only charge particles reconstructed**
** ****A lot of things going on in the silicon detector**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## 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)

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Λb in full reconstructed channels

- Both experiments have clear signal of

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Λb in full reconstructed channels

**PDG’04 : Seen!**
**Now: **
_**clear evidence**_** ****Λ****b****→****Λ****+****c****π**** ****- ****~ 11****σ**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Λb in semileptonic decays

**Toward the direct  measurement of ****τ****(****Λ****b****)/****τ****(B****0****d****), ****similar to ****τ****(B****+****)/****τ****(B****0****d****)**
- 						 [_[PRL 94, 182001 (2005)](http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PRLTAO000094000018182001000001&idtype=cvips)_ ]

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## After reconstruction ...

- Mass measurement
- Lifetime
- Branching fractions
- Etcetera ...

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Λb mass measurement

**Most precise ********b**** mass measurement in the world !!!**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Lifetime measurement

-  λ + mass distribution
- (signal + bkg)

- Models for
-  λ + mass distribution

- Simultaneous Mass & lifetime likelihood fit

- Signal selection

**Fit procedure**

- Models:

**Signal (****λ****)**

- Background (λ)

**Background (****λ****)**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Λb lifetime[1]

- [1] ***V.M Abazov et al, PRL 94, 100201 (2005)***

- First measurement in a full reconstructed decay channel !!!

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Slide 16

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Branching fractions:

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Branching Fraction: b → c 

- Assuming:

- (PDG ’04)

- _From the fit:_
- NΛb=214±19(stat)
- NB0=790±32(stat)

- Branching Fraction: ******b**** ****→**** ********c**** ******

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Branching Fraction: Bsemi/Bhad

- Branching Fraction: Bsemi/Bhad

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Search for b→hh decays

- Search for b→*hh* decays

- Prediction[2]:
- Br (b→ pK)=(1.4-1.9)×10-6
- Br (b→ pp)=(0.8-1.2)×10-6
*compare to *
*	**	**Br(B**0**→Kp)= 18×10**-6*
- Large CP asymmetries O(10%) expected in b-baryons
- Previous best limit from ALEPH
- BR(b pK) < 50x10-6 @ 90%
- BR(b p) < 50x10-6 @ 90%

- [2] Mohanta, Phys. Rev. D63:074001,2001

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## B** resonances

**B****1**** & B*****2**** observed by first time as separate states!!!**

-  **B meson spectroscopy only well established for ground states B****+****,B****0****,B****s****. **
** ****Few models with precise predictions:  mass/widths/BR**

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## BD**

- BD**

- BsDs**
- Ds**D*KS

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy

## Summary

- A lot of new results from Tevatron on the b 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.

- Eduard.Burelo@cern.ch

- Beauty 2005, Assisi (Perugia) Italy