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

Tevatron Excellent performance in 2005-2006 : 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

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

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

DZero Detector in Collision Hall

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*

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

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

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)=5720.8 ± 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

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) ± 0.071 (sys) 0.165 ± 0.024 (stat) ± 0.028 (sys)

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

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

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) = 5839.1 ± 1.3 MeV

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)

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 0.142-0.149GeV mass difference window

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 2535.34±0.31 PDG

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

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

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

Measurement of Lb Lifetime in Lb L J/y D0 Run2 preliminary, 1fb-1 this result t(LB) = 1.298 ± 0.137(stat) ± 0.050(syst) ps t(LB)/t(B0) = 0.870 ± 0.102(stat) ± 0.041(syst) Main systematics from background modelling and from contamination from B mesons

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