Λ b and heavy states at Tevatron

Beauty 2005, Assisi (Perugia) Italy

[email protected] 1

Λb and heavy states at Tevatron

byEduard De La Cruz Burelo

University of MichiganOn behalf of

CDF and D0 collaborations

[email protected] 2Beauty 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**


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)


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 ( )

llb llb


Experimental statusPDG’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

1. Some indirect lifetime estimations

2. Some “seen” decay channels


Example …

This was just less of a couple of years ago.

A lot of theoretical

work

Just last month !!!

HFAG

hep-ex/0505100

(*) Includes D0 and CDF Run II measurements

(*)

)(

)(

d

b

B

LO NLO

C. Tarantino, Monday 20

This was just less of a couple of years ago.


First step: “Reconstruction”Quite a challenge

For both detectors:

• Only charge particles reconstructed

• A lot of things going on in the silicon detector


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 fb~ 10% (b→X)

(pp X)

1 1inst

(pp bX) 100 b

~ 100 b s 10 kHz

L


Λb in full reconstructed channels

Both experiments have clear signal of Jb

Invariant Mass, (GeV/c2) Invariant Mass, (GeV/c2)


Λb in full reconstructed channels

Invariant Mass, (GeV/c2)

PDG’04 : Seen!

Now:

clear evidence Λb→Λ+

cπ - ~ 11σ


Λb in semileptonic decays

c pKSc0

Xcb

Toward the direct measurement of τ(Λb)/τ(B0d), similar to τ(B+)/τ(B0

d)

[PRL 94, 182001 (2005) ]


b b

b

After reconstruction …

Mass measurement Lifetime Branching fractions Etcetera …


Λb mass measurement

2/)(2.1)(2.17.5619)( cMeVsyststatm b Most precise b mass measurement in the world !!!

2b 9MeV/c5624)m( Λ:PDG


Lifetime measurement

TT p

MpLc ˆ

λ + mass distribution

(signal + bkg)

Models for λ + mass

distribution

Simultaneous Mass & lifetime

likelihood fit

Signal selection

Fit p

rocedu

re

cmc 3.7cmc 7.2

Models: Signal (λ)

2

Background (λ)Background (λ)


Λb lifetime[1]

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

DØ

pssyststat )(04.0)(22.1 22.012.0

First measurement in a full reconstructed

decay channel !!!

DØ )(9.12)(0.366)( 2.656.53 syststatct b


Branching fractions:


From MC: 1.65±0.03

From PDG: 1.84±0.493

)(22.0)(11.0)(08.082.0)(

)(0

0

0

BRsyststatDBBR

BR cb

B

b

)(1.1)(4.0)(3.03.3)(

)(0

FRBRsyststatDBBR

BR cb

043.0249.0)6(

)6(

0

0

0

0

BTB

T

f

f

GeVp

GeVpbb

Assuming: (PDG ’04)

0

0

0

0

0

0

)(

)(

)(

)(

)6(

)6(

0b

bb B

Bc

cb

TB

T

N

N

pKBR

KDBR

DBBR

BR

GeVp

GeVp

From the fit:

NΛb=214±19(stat)

NB0=790±32(stat)

Branching Fraction: b → c


First measurement of this ratio !!!

semi

had

had

backgroundsemiinclusive

had

semi

N

NN

B

B

)(5.0)()(2.1)(0.30.20)(

)( 7.01.2 UBRBRsyststat

B

B

cb

cb

Branching Fraction: Bsemi/Bhad

%)()(19.041.0)( 06.008.0 spectrumPsyststatB Tcb

%))((3.4)()(2.11.8)( 1.16.1

cbcb BsyststatB


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(B0→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% .).%90(1022)( 6 LChhBR b

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


B** resonances

B1 & B*2 observed by first time as separate states!!!

• B meson spectroscopy only well established for ground states BB meson spectroscopy only well established for ground states B++,B,B00,B,Bss. .

• Few models with precise predictions: mass/widths/BRFew models with precise predictions: mass/widths/BR

1

2

* 22 1

5274 4 7 /

23.6 7.7 3.9

Bm MeV c

m B B MeV c


Semileptonic decays to excited states BD**

0 *01 2

0 *0 *1 2

[ (2420), (2460)]

[ (2420), (2460)]

0.280 0.021 0.088 %

Br B D D X

Br D D D

Excess: 20.6 5.6 3.7

BsDs**Ds**D*KS


Summary A lot of new results from Tevatron on the b baryonBest mass measurementFirst lifetime in full reconstructed channelBranching 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.

Λ b and heavy states at Tevatron

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