Λ b and heavy states at tevatron
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Beauty 2005, Assisi (Perugia) Italy
Eduard.Burelo@cern.ch 1
Λb and heavy states at Tevatron
byEduard De La Cruz Burelo
University of MichiganOn behalf of
CDF and D0 collaborations
Eduard.Burelo@cern.ch 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**
Eduard.Burelo@cern.ch 3Beauty 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 4Beauty 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 ( )
llb llb
Eduard.Burelo@cern.ch 5Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 6Beauty 2005, Assisi (Perugia) Italy
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.
Eduard.Burelo@cern.ch 7Beauty 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 8Beauty 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 fb~ 10% (b→X)
(pp X)
1 1inst
(pp bX) 100 b
~ 100 b s 10 kHz
L
Eduard.Burelo@cern.ch 9Beauty 2005, Assisi (Perugia) Italy
Λb in full reconstructed channels
Both experiments have clear signal of Jb
Invariant Mass, (GeV/c2) Invariant Mass, (GeV/c2)
Eduard.Burelo@cern.ch 10Beauty 2005, Assisi (Perugia) Italy
Λb in full reconstructed channels
Invariant Mass, (GeV/c2)
PDG’04 : Seen!
Now:
clear evidence Λb→Λ+
cπ - ~ 11σ
Eduard.Burelo@cern.ch 11Beauty 2005, Assisi (Perugia) Italy
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) ]
Eduard.Burelo@cern.ch 12Beauty 2005, Assisi (Perugia) Italy
b b
b
After reconstruction …
Mass measurement Lifetime Branching fractions Etcetera …
Eduard.Burelo@cern.ch 13Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 14Beauty 2005, Assisi (Perugia) Italy
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)
Eduard.Burelo@cern.ch 15Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 16Beauty 2005, Assisi (Perugia) Italy
Eduard.Burelo@cern.ch 17Beauty 2005, Assisi (Perugia) Italy
Branching fractions:
Eduard.Burelo@cern.ch 18Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 19Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 20Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 21Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 22Beauty 2005, Assisi (Perugia) Italy
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
Eduard.Burelo@cern.ch 23Beauty 2005, Assisi (Perugia) Italy
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.
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