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
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