B physics and X(3872)

production at DØ

Introduction DØ-Detector Results on B physics Results on X(3872) Summary

Frank LehnerU Zurich

DIS 2004, Strbske Pleso 15-18 April, 2004

All results are preliminary

Accelerator Status

excellent performance of Tevatron in 2004

DØ recorded 70 pb-1 in 2004 important milestone:

reprocessed full dataset in fall 2003 greatly improved

tracking performance good fraction processed

off-site current datasets

~300 pb-1 on tape ~200-250 pb-1

analyzed ~100 pb-1 Run I

B production at Tevatron

Pro’s: large cross section ~105 x larger

than at present B-factories (4S)

all kinds of b hadrons produced: Bd, Bs, Bc, b,..

Con’s: QCD background overwhelming efficient trigger and reliable

tracking necessary soft pt spectrum, smaller boost

than LEP

Key for B physics program at DØ: Muon system Muon trigger (single and

dimuon triggers) Silicon Vertex + Tracker

TeV2s @

μb150)bbpp(

DØ detector

upgraded Run II DØ detector: beamline shielding

reduce background

new Forward Muon + Central Muon Scintillators excellent

coverage ||<2 Preshowers

helping for e-ID Fiber Tracker Silicon Detector 2T Solenoid

DØ tracking region

Silicon detector 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

Fiber Tracker scintillating fibers Ø

0.82 mm 8 layers - each

axial/stereo R/O through VLPC in LHe

Tracking performance

|| for kaons from D*D0 pT spectrum of soft pion from D*D0

efficient muon and tracking system give us a large

sample of semileptonic B decays

Tracks are reconstructed• over a wide range• starting from pT = 180 MeV

Data from semileptonic decays (B D X)

Benchmark: exclusive B decays & yields

accumulated large exclusive samples of B+ and B0

find in ~225 pb-1

B0 J/K* 1900 events B+ J/K+ 4300 events B0 J/Ks

375 events good S/B Lifetime cuts applied

Benchmark: exclusive B decays & yields

b-> J/ 52 events

Bs -> J/ 400 events We have good potential in all B J/

exclusive modes, work in progress on Lifetime measurement of

different B species Studies of CP effects in Bs & Bd

mesons

250 pb-1

Lifetime ratio (B+)/(B0) from

semileptonic decays

measure from semileptonic B decays directly lifetime ratio instead of absolute lifetimes

select following samples: B D0 X B D* X

sample compositions: “D0 sample”: + K+ - + anything

B+ 82%, B0 16%, Bs 2% “D* sample”: + D0 - + anything

B+ 12%, B0 86%, Bs 2% estimates based on measured BR

and isospin relations group events in 8 bins of visible

proper decay length (VPDL)

VPDL = LT / pT( D0) MB

LT = transverse decay length

Lifetime ratio (B+)/(B0) from semileptonic decays

Measure ratio r= N(+ D*-)/N(+ D0) in each bin iCombinatorial background with true D0 in D*

sample issubtracted using wrong-sign distribution no need for parameterisation of background VPDL distribution

Additional inputs to the fit:

- sample compositions (previous slide)

- K-factors (from simulation) K = pT(D0) / pT(B) (separately for different

decay modes)

- relative reconstruction efficiencies for different B decay modes (from simulation)

- slow pion reconstruction efficiency [flat for pT(D0) > 5 GeV (one of our cuts)]

- decay length resolution (from simulation)

- (B+) = 1.674 0.018 ps [PDG]

one example VPDL bin

Lifetime ratio (B+)/(B0) from semileptonic decays

systematics currently dominated by time dependence of slow

pion reconstruction efficiency

relative reconstruction efficiencies CY

Br(B+ + D*- + X) K-factors decay length resolution

differences D0 D*

use binned 2 fit of event ratios to determine (B+)/(B0)

Preliminary result:

(B+)/(B0) = 1.093 0.021 (stat) 0.022 (syst)

Lifetime ratio (B+)/(B0) from semileptonic decays

New DØ result(average not updated, plot not official or approved by HFAG)

This is one of the most precise measurements to date:

B0/B0 mixing

in SM Bd mixing is explained by box diagrams

constrains Vtd CKM matrix element

mixing frequency md has been measured with high

precision at B factories (0.502 0.007 ps-1) use our large sample of semileptonic Bd decays to measure md

benchmark the initial state flavor tagging for later use in Bs and ms measurements

B0/B0 mixing

initial flavor tagging opposite side tight muon tag muon pT > 2.5 GeV/c cos < 0.5

asymmetry of ‘oscillated’ and ‘non-oscillated’ B mesons as function of VPDL

use binned 2 fit for asymmetry this is already one of the best

measurements in hadron colliders work in progress to reduce

systematics use other tagging methods add more D0 decay channels

Preliminary results:

md=0.5060.055(stat)0.049(syst) ps-1

%19.076.4notagWR

WR

NNN

NN

%1.20.73WR

R

NN

N

Tagging efficiency:

Tagging purity:

Towards Bs mixing

semileptonic decays (Bs-> Ds) very good statistics excellent yield: 9500 candidates in

~250 pb-1

if ms 15 ps-1 a first indication of Bs mixing might be possible with 500 pb-1

fully reconstructed hadronic decays: poor statistics excellent proper time resolution need a few fb-1 of data to reach ms 18 ps-1

Observation of B D** X

D** are orbitally excited D meson states, see diagram

in heavy quark limit w/ L=1 expect two sets of doublet states two broad (decay through S-

wave) two narrow (decay through D-

wave) narrow D**

D01(2420) -> D*+

-

D2*0(2460) -> D*+ -

D10, D2*0 have been observed and

studied in several experiments, most recently by BaBar and Belle in B- D**0 -

we study D10, D2*0 produced in

semileptonic B decays.

Figure from Belle, hep-ex/0307021

Observation of B D** X

• start from B D*X sample, add another +

• look at invariant mass of D*- + system

• observed merged D10(2420)

and D2*0(2460) • excess in right-sign

combinations can be interpreted as interfering D1

0 and D2*0

• DØ’s preliminary result constrains the resonant contribution

Work in progress: extract separate amplitude, relative phase

Br(B {D10,D2*0} X) Br({D1

0,D2*0} D*+ -)

= 0.280 0.021 (stat) 0.088 (syst) %

Bs + - sensitivity study

purely leptonic B decay is a flavor changing neutral current (FCNC)

forbidden at tree level highly suppressed in SM BR(Bs->)~ 3·10-9

BR grows with tan6 in MSSM

very attractive probe for any new physics with extended Higgs sector (Two-Higgs Doublet models)

SM:

Two-Higgs Doublet models:

Bs + - sensitivity study

blind analysis: optimization cuts using Random Grid Search based on mass sideband

discriminating variables isolation of pair decay length opening angle between

pair and decay length direction

expected signal is normalized to B+-> J/ K+

expect 7.3 1.8 background events in signal region

Current expected limit (Feldman/Cousins):Br(Bs + -) < 1.0 10-6 @ 95 % CL (stat + syst)

The box has NOT been opened yet -Reoptimisation still in progress - further improvements expected

X(3872) J/ + -

last summer on LP ‘03, Belle announced new particle at ~3872 MeV/c2

observed in B+ decays: B+ K+ X(3872) X(3872) J/ + -

Belle’s discovery has been confirmed by CDF and DØ

DØ preliminary: 300 61 events 4.4 effect M = 0.768 0.004

(stat) 0.004 (syst) GeV/c2

X(3872) J/ + -

nature of X(3872) is not known mass surprisingly

close to D*D threshold

could be charmonium, hybrid or meson molecule

compare sample of X particles to sample of (2S) using ||<1 and 1<||<2

(plot) decay length dl<0.2

mm and dl>0.2 mm helicity of isolation of X

X(3872) J/ + -

no significant differences between (2S) and X have been observed

surviving fraction of X behaves similar to (2S)

more useful once we have models of the production and decay of, e.g., meson molecules that predict the observables used in the comparison

Note that observation of the

charged analog X+ J/ + 0 would rule out cc hypothesis

observation of radiative decays X c would favour cc hypothesis (Belle set limit). Use DØ’s calorimeter to identify

low energy 0 and : work in progress

Summary

Preliminary results from DØ: precise measurement of (B+)/(B0) measurement of md, benchmark flavour tagging

Observation of B D** X at DØ DØ’s sensitivity to Bs Observation of the X(3872) at DØ and study of its

production properties

The exciting times have started; stay tuned for more

Spare slides

DØ tracking performance

(DCA) 53 m @ PT = 1 GeVand 15 m @ higher PT

Can provide

K/ separation for Ptot< 400 MeV

p/ separation for Ptot<700 MeV

NOT yet used for PID

Triggers

Robust and quiet single- and di-muon triggers Large coverage |<2 Variety of triggers based on

L1 Muon & L1 CTT (Fiber Tracker) L2 & L3 filters

Typical total rates at medium luminosity (40 1030 s-1cm-2) Di-muons : 50 Hz / 15 Hz / 4 Hz @ L1/L2/L3 Single muons : 120 Hz / 100 Hz / 50 Hz @ L1/L2/L3

Rates before prescaling: typically single muon triggers are prescaled or/and used with raised pT threshold at L1

Muon purity 90% - all physics! Current total trigger bandwidth 1600 Hz / 800 Hz / 60 Hz @ L1/L2/L3

B-physics semi-muonic yields are limited by L3 filters and L3 bandwidth

Calibrations using J/sample

Large J/ sample – currently1.2 M events in 250 pb-1

• J/mass is shifted by 22 MeV• Observe dependence on Pt and on material crossed by tracks• Developed correction procedure based on field & material model • Finalizing calibration of momentum scale using J/Ks, D0

NOT yet used

Mass resolution 60 MeV/c2

in agreement with expectations

After magnetic field and material corrections

Before corrections