1. Andrei Nomerotski (Oxford/Fermilab) ICHEP 2006, 29 July 2006
B Hadrons at DZero
Outline
B hadrons at Tevatron and DZero
Excited B** mesons
First Evidence of Bs**
First observation of BsDs(2536)mnX
Lifetime of LB Baryons
Andrei Nomerotski (Oxford/Fermilab) ICHEP 2006, 29 July 2006

2. Tevatron
Excellent performance in : 1.2 fb-1 on tape per experiment
Successful shutdown ended in June – detectors upgraded
Expect 4-8 fb-1 by the end of Run2 in 2009
Results presented here use 1 fb-1

3. B Hadrons at Tevatron Produced strongly at Tevatron
crossection x10000 wrt B-factories
…but large background
Tevatron has access to B hadron species inaccessible in other colliders
modulo recent U(5S) dataset at Belle gives access to Bs mesons
Long lifetime and heaviness of b quark  significant theoretically and experimentally

4. DZero Detector
Spectrometer : Fiber and Silicon Trackers in 2 T Solenoid
Energy Flow : Fine segmentation liquid Ar Calorimeter and Preshower
Muons : 3 layer system & absorber in Toroidal field
Hermetic : Excellent coverage of Tracking, Calorimeter and Muon Systems
SMT H-disks
SMT F-disks
SMT barrels

5. DZero Detector in Collision Hall

6. Light – Heavy Quark Mesons
Light – Heavy quark mesons are hydrogenic atoms of QCD
Heavy Quark limit  static colour field & decoupling of light degrees of freedom
Light quarks characterized by their total angular momentum jq = sq + L
jq is combined with SQ to give total angular momentum
SQ and jq are separately conserved
In Heavy Quark Limit, each energy level has pair of degenerate states :
L=1 states, also known as B**
L=0
jq=1/2
J=0,1
B0*, B1*
jq=3/2
J=1,2
B1, B2*
jq=1/2
J=0 B
J=1 B*

7. B** Spectroscopy B1 and B2* decay through D-wave  narrow resonances
B0* and B1* decay through S-wave  wide resonances, difficult to distinguish from phase space

8. Excited B Analysis Search for narrow states decaying to B+(*)p
B1  B*+p-; B*+  B+g
B2*  B*+p-; B*+  B+g
B2*  B+p-
Reconstruct B+  J/y K+ with J/y  mm
For each B hadron look for additional track with
PT> 0.75 GeV
Correct charge correlation (B+p- or B-p+)
Since B** decays immediately after production, track was required to originate from primary vertex.
~16K B+  J/y K+
Primary vertex

9. Excited B Results Form mass difference DM=M(Bp)-M(B)
Three peak structure
Direct decay B2*  B+p
B2*  B+*p with B+*  B+g
Eg = 46 MeV and since g is not reconstructed, expect a peak separated from direct peak by g energy
B1  B+*p with B+*  B+g
B1  Bp is forbidden by angular momentum and parity conservation
Results:
M(B1)= ± 2.5(stat) ± 5.3 (sys) MeV
M(B2*)-M(B1)= 25.2 ± 3.0(stat) ± 1.1 (sys) MeV
G1=G2= 6.6 ± 5.3(stat) ± 4.2 (sys) MeV

10. Excited B Results First measurement of production rate, world’s best
mass measurement
0.513 ± 0.092(stat) ± 0.115(sys)
0.545 ± 0.64(stat) ± (sys)
0.165 ± (stat) ± (sys)

11. Bs2*: Excited Meson
States similar to B1 and B2* should exist in (bs) system, i.e. there should be Bs1 and Bs2* mesons
Almost no information exist on these objects: few claims of indirect observation at LEP by OPAL and DELPHI
Like for normal B**, there should be narrow Bs1 and Bs2* states
Due to the isospin conservation, possible decays are:
Bs1B* K
Bs2*B K, Bs2B* K

12. Search for Bs2* For each B hadron an additional track
Search for excited states decaying to B+K - very similar to B** search
For each B hadron an additional track
PT > 0.6 GeV
Charge opposite to charge of B+
Track was required to originate from primary vertex
Kaon mass assigned to track
Primary vertex

13. Bs2* Results First Direct observation of B*s2
Wrong sign charge correlations shows
no evidence of a peak
Mass difference DM=M(B+K-)-M(B+)-M(K-)
Significance of signal > 5
MC B** decaying to B(*) p but
reconstructed as B+K- show no
evidence of a peak.
First Direct observation of B*s2
M(B*s2) = ± 1.3 MeV

14. M(Bs1)M(Bs2*) – 26 MeV= 5813 MeV < M(B*)+M(K).
Where is Bs1?
Suppose that M(Bs2*) – M(Bs1)  M(B2*) – M(B1),
Take M(B2*) – M(B1) = 26 MeV from our B** results,
We conclude that decay B1sB* K should be prohibited, or at least strongly suppressed, because:
M(Bs1)M(Bs2*) – 26 MeV= 5813 MeV < M(B*)+M(K).
It means that the only possible decay of Bs1 is EM decay:
Bs1Bs(0)

15. Orbitally Excited Ds1(2536) Meson
Look for narrow (L=1,jq=3/2,JP=1+) in
Muon plus 5-Track final state
1 fb-1
82130
D* candidates
In GeV
mass difference window

16. Reconstruction of Ds1(2536) Meson
43.8±8.3 D±s1(2536) candidates
5.3 σ significance
2535.7±0.5(stat)±0.6(sys) MeV
±0.31 PDG

17. Br measurement Measure product Br Assuming
To be compared to theoretical predictions for

18. Lb Lifetime Lightest b baryon (udb) Access to various important topics
Spin role in heavy hyperons (polarization)
CP violation
Exotics : T violation or other new physics in
Lifetime : Tests of HQE Theory in b baryons
Controversy between experimental and theoretical results seems to disappear as more precise measurements and calculations become available
At the same time the CDF most recent measurement is considerably above the world average

19. Measurement of Lb Lifetime in Lb L J/y
174 ± 21 candidates reconstructed in J/ymm decay mode

20. Measurement of Lb Lifetime in Lb L J/y
D0 Run2 preliminary, 1fb-1
this result
t(LB) = ± 0.137(stat) ± 0.050(syst) ps
t(LB)/t(B0) = ± 0.102(stat) ± 0.041(syst)
Main systematics from background modelling and from contamination from B mesons

21. Summary
Good progress in understanding of excited heavy flavour mesons at Tevatron with 1fb-1 dataset
Observation of B1 and B2* as two separate peaks, measurement of masses
First direct observation of Bs2* with > 5 significance, precise mass measurement of Bs2*
First observation of BsDs(2536)mnX decay and measurement of its Br
Updated LB lifetime measurement – agrees with world average
4-8 fold increase of statistics before 2009 with upgraded detectors