Zurich contribution to the DØ Experiment

1. Zurich contribution to the DØ Experiment • Introduction: DØ experiment • Zurich people & involvement • Detector contribution • Physics contribution • Conclusions Reporting on work from others … Frank Lehner, U Zurich CHIPP workshop on high energy frontier Zurich, 04.09.06

2. The DØ Detector • Run IIa DØ detector (2001): • beamline shielding • new fwd. & central muon scintillator w/ excellent coverage ||<2 • preshowers • fiber tracker • silicon detector SMT • 2T Solenoid • upgrade for Run IIb (2006): • silicon detector layer 0 inserted into existing SMT • L1 Trigger upgrade for Calo and fiber tracker

3. DØ tracking region • Silicon detector SMT • 6 barrels w/ 4 layers silicon- mostly double-sided silicon, axial and stereo • interspersed double-sided disks • large external area disks at end • tracking/vertexing up to ||<3 • New: layer 0 inserted into existing SMT • Fiber Tracker • scintillating fibers Ø 0.82 mm • 8 layers - each axial/stereo • R/O through VLPC in LHe

4. Luminosity, data, etc. • Run IIa ended March 2006 • DØ recorded 1.2 fb-1 • high data taking efficiency of 85% • typical peak luminosity ~1.5×1032 cm-2s-1 • physics analysis w/ 1fb-1 presented at ICHEP ’06 • Run IIb started June 2006 • machine + detector is doing very well since shutdown • typical peak luminosity started at ~2×1032 cm-2s-1 aiming to 3×1032 cm-2s-1 by Feb ‘07 • expect to nearly double statistics every year Run IIb Run IIa

5. Zurich People • members from U Zurich affiliated with DØ since 2001 – first as visitors, since Oct 2005 as institute • seniors/postdocs: FL, Ralf Bernhard • PhD student: Andreas Wenger • master student: Christophe Salzmann • funding partially through various research grants from U Zurich • contributions to • hardware: silicon detector, layer 0 • software: silicon alignment • physics: B physics • output: 1 PhD thesis (R. Bernhard 2005), 2 publications, many DØ notes … • future: will retire from DØ by end of this year Flag parade in DØ pit

6. Layer 0 • radiation damage on SMT ladders studied since 2001 • at 5-7 fb-1 innermost SMT layer will significantly degrade • after cancellation of silicon replacement upgrade project in fall 2003: design a new layer that fits into existing silicon • 48 modules, w/ up to 12 cm long silicon, arranged in 6 ‘facets’, distance to beam 16 mm • signal transferred to R/O chip using low-mass analog cables • carbon fiber support, slides over beampipe, mounted on existing SMT bulkheads 7fb-1 5fb-1

7. Layer 0 – design goals • additional Layer 0 - improves primary & secondary vertex resolution for enhanced b-tagging by • decreasing distance of first hit to beam line from 2.7 to 1.6 cm • reducing material associated with first hit • mitigating radiation induced performance loss of SMT Bs Mixing Sensitivity

8. SMT L0 Layer 0 - design • minimize material, locate hybrids outside active area • long, fine-pitch kapton cables as interconnection between silicon sensors and R/O chip • cables designed at U Zurich, prototyped & procured through swiss-based company Dyconex • Layer 0 installed April 2006 into existing ~46 mm diameter aperture – leaving 0.9 mm clearance ! 45 mm

9. Layer 0 - performance Noise • coherent noise can be nasty in this design where cables acts as antenna • substantial efforts made to eliminate these effects by design and tests: stable and nearly noise-free detector • first pass alignment done – looks very encouraging • at low momentum improvement of impact parameter by factor 2 • alternative alignment approach based on Millepede (V. Blobel) program underway by A. Wenger Hit Residuals

10. Physics accomplishments • Physics activities of U Zurich focus on rare B decays • Flavor-changing neutral current processes forbidden at tree level, proceed at small rate at higher order • sensitive to new particles in loop – indirect probe of new physics (high scale) at low momentum • excellent preparation ground for forthcoming LHCb activities • B-physics program of U Zurich: • purely leptonic B decay Bs->m+m- • helicity suppressed, small BR in SM • high sensitivity to new physics at large tan • search belongs to the core physics program of Tevatron • exclusive b -> s m+m- FCNC transitions • Bs -> m+m-  • Bd -> m+m- K* • B+ -> m+m- K+ • B decays into (2S) charmonium final states, e.g., Bs -> (2S) 

11. Purely leptonic decay Bs->m+m- • dimuon triggered data • blind analysis to avoid experimenter’s bias • side bands for background determination • use B+ -> J/ K+ as normalization mode • J/ -> m+m- cancels m+m- selection efficiencies • B meson has long lifetime – exploit discriminating variables in random grid search for optimization blinded signal region: DØ: 5.160 < mmm < 5.520 GeV/c2; ±2 wide, =90 MeV

12. Purely leptonic decay Bs->m+m- • ‘panta rhei’: search is an ongoing process as data come in • published limit with 240 pb-1 in PRL94, 071802 (2005): 5.1×10-7 • sensitivity for 700 pb-1: <2.3×10-7> • plan for Run IIa limit using ~1.2 fb-1 • in addition: Tevatron combination, (hep-ex/0508058) e.g. Dermisek et al., hep-ph/0507233 SO(10) GUT model with soft SUSY breaking para- meters and dark matter constraints

13. Search for Bs -> m+m- • investigate b -> s l+ l- FCNC transitions in Bs meson • exclusive decay: Bs -> m+m- • SM: short distance BR: ~1.6×10-6 • about 30% uncertainty due to B-> form factor • 2HDM: enhancement possible, depending on parameters for tanb and MH+ • use ~450 pb-1 of dimuon triggered data • normalize to resonant decay Bs -> J/y f • cut on mass region to exclude J/y & y’ resonance Dilepton mass spectrum in b -> s l l decay y’ J/y

14. Limit on Bs -> m+m- • expected background from sidebands: 1.6 ± 0.4 events • observe zero events in signal region Published in PRD74, 031107R (2006) BR(Bs -> f m+m-)/BR(Bs -> J/y f) < 4.4 × 10-3 @ 95% C.L. using central value for BR(Bs -> J/y f) = 9.3×10-4 PDG2004: BR(Bs -> f m+m-) < 4.1×10-6 @ 95% C.L. x10 improvement w.r.t previous limit • search for exclusive decay Bs -> m+m- will be updated and complemented with other exclusive b ->s m+m- FCNC transitions: • B-> (K, K*)m+m- • Bs -> m+m- • using 2fb-1 of DØ data • PhD thesis of A. Wenger

15. B decays into charmonium (2S) • investigate B decays into charmonium state (2S) relative to decays into J/ • observation of Bs -> (2S)  and measurement of BR(Bs -> (2S) )/ BR(Bs -> J/ ) • compare BR ratio with heavy quark decay models • sample of Bs -> (2S)  events useful to add statistics for / determination in Bs system • cross check analysis with B± -> (2S)K± and Bd -> (2S)K* preliminary master thesis of C. Salzmann

16. Conclusions • over last years we accomplished to maintain a fruitful participation at DØ without compromising in the slightest, the LHCb TT detector project @ U Zurich • achieved physics output: two publications, one more in preparation, several conference proceedings … • DØ activities are/were necessarily limited to a few people, committed to both experiments: DØ and LHCb • cross links (LHCb-DØ) for synergetic effects were • silicon detector – impact on cable design, sensor test procedures for LHCb • one common physics topic: heavy flavor physics at hadron colliders • good preparation ground for LHC physics • educate/train master/PhD students in data analysis • future: • two of us will leave Zurich soon • will retire from DØ by end of this year