Zurich contribution to the DØ Experiment

Introduction: DØ experiment Zurich people & involvement Detector contribution Physics contribution Conclusions

Frank Lehner, U ZurichCHIPP workshop on high energy frontier

Zurich, 04.09.06

Reporting on work from others …

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

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

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

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

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

5fb-1 7fb-1

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

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 !

SMT

L0

45 mm

Layer 0 - performance

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

Noise

L0 Impact Parameter

0

10

20

30

40

50

60

0 5 10 15 20

Momentum (GeV)

IP R

eolu

tion

(m

icro

ns)

No Layer 0Layer 0Layer 0 MCNo Layer 0 MC

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->

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 FCNC transitions Bs -> +- Bd -> +- K* B+ -> +- K+

B decays into (2S) charmonium final states, e.g., Bs -> (2S)

Purely leptonic decay Bs->

dimuon triggered data blind analysis to avoid

experimenter’s bias side bands for background

determination use B+ -> J/ K+ as

normalization mode J/ -> cancels

selection efficiencies B meson has long lifetime –

exploit discriminating variables in random grid search for optimization

blinded signal region:DØ: 5.160 < m < 5.520 GeV/c2; ±2 wide, =90 MeV

Purely leptonic decay Bs->

‘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/0507233SO(10) GUT model withsoft SUSY breaking para-meters and dark matterconstraints

Search for Bs -> +-

investigate b -> s l+ l- FCNC transitions in Bs meson

exclusive decay: Bs -> +- SM: short distance BR: ~1.6×10-6

about 30% uncertainty due to B-> form factor

2HDM: enhancement possible, depending on parameters for tan and MH+

use ~450 pb-1 of dimuon triggered data normalize to resonant decay Bs -> J/ cut on mass region to exclude J/& ’

resonance

Dilepton mass spectrum in b -> s l l decay

J/ ’

Limit on Bs -> +-

expected background from sidebands: 1.6 ± 0.4 events observe zero events in signal region

BR(Bs -> )/BR(Bs -> J) < 4.4 × 10-3 @ 95% C.L.

using central value for BR(Bs -> J) = 9.3×10-4 PDG2004:

BR(Bs -> ) < 4.1×10-6 @ 95% C.L. x10 improvement

w.r.t previous limit

Published in PRD74, 031107R (2006)

search for exclusive decay Bs -> +- will be updated and complemented with other exclusive b ->s FCNC transitions: B -> (K, K*)

Bs -> +- using 2fb-1 of DØ data PhD thesis of A. Wenger

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*

master thesis of C. Salzmann

preliminary

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