Andrei Nomerotski (Oxford/Fermilab) ICHEP 2006, 29 July 2006

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

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

SMT H-disks SMT F-disks SMT barrels 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

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

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 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 Search for Bs2* Primary vertex

Bs2* Results 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

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 0

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 LbLifetime in Lb L J/y • 174 ±21 candidates reconstructed in J/ymmdecay mode

D0 Run2 preliminary, 1fb-1 Measurement of LbLifetime in Lb L J/y 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 this result

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

Andrei Nomerotski (Oxford/Fermilab) ICHEP 2006, 29 July 2006