Beauty 2005, Assisi (Perugia) Italy [email protected] 1 Λ b and heavy states at Tevatron by Eduard De La Cruz Burelo University of Michigan On behalf of CDF and D0 collaborations
Jan 07, 2016
Beauty 2005, Assisi (Perugia) Italy
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**
[email protected] 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)
[email protected] 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
[email protected] 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
[email protected] 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.
[email protected] 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
[email protected] 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
[email protected] 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)
[email protected] 10Beauty 2005, Assisi (Perugia) Italy
Λb in full reconstructed channels
Invariant Mass, (GeV/c2)
PDG’04 : Seen!
Now:
clear evidence Λb→Λ+
cπ - ~ 11σ
[email protected] 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) ]
[email protected] 12Beauty 2005, Assisi (Perugia) Italy
b b
b
After reconstruction …
Mass measurement Lifetime Branching fractions Etcetera …
[email protected] 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
[email protected] 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)
[email protected] 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
[email protected] 16Beauty 2005, Assisi (Perugia) Italy
[email protected] 17Beauty 2005, Assisi (Perugia) Italy
Branching fractions:
[email protected] 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
[email protected] 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
[email protected] 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
[email protected] 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
[email protected] 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
[email protected] 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.