Transcript Document

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Recent D0 results on Quarkonium
HAN, Liang
Univ. of Science & Technology of China
Univ. of Manchester
presenting D0 Collaboration
(commented by Rick Van Kooten D0 B-convener)
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Tevatron & D0 Run2
X(3872)
Bc meson
Upsilon(1S)
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Tevatron & DØ RunII
Chicago

Booster
CDF
DØ
Tevatron
p source
Main Injector
(new)
• com: 1.96 TeV PPbar
• lumi: 2E32 cm-2s-1
• Xing: 396 ns
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Tracking & Vertex:
- Silicon Microvertex Tracker (SMT) + Central Fiber Tracker (CFT) + 2T Solenoid
- good tracking, vertex, impact parameter measuring performance
Pseudo rapidity:
Spatial separation:
h = -ln(tg(q/2))
△R2=△f2+△h2
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Muon system:
- 3 layer, 1 layer (A) in 1.8T Toroid
- Good coverage:
central |h|<1
forward 1<|h|<2
- Muon-Tracking match  muon candidate
- fast and efficient Di-Muon Trigger
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The observation of
X(3872)  J/y(m+m-) p+p-
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First observed
confirmed
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Events Selection:
- Apr 02 – Jan 04, ~230pb-1
- di-muon triggered
- 2 well identified muon tracks, opposite charged
- 2.80 ＜ M(m+m-) ＜ 3.35 GeV/c2
m+m- from J/y
- pT(m+m-) ＞ 5 GeV/c2
- 2 opposite charged tracks, with spatial separation as
△R(J/y p+p-, each p) ＜ 0.4
- pT(p) ＞ 0.7 GeV/c2
- M(p+p-) ＞ 0.52 GeV/c2
- A good (m+m-p+p-) Vertex, c2 <16 for 5 degree of freedom,
i.e. 4 tracks from the same vertex
- ≤100 tracks in the event
add ”p+p-” tracks
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After CUT
- Use mass difference (to J/y) for
better resolution
△M = M(m+m-p+p-) – M(m+m-)
- data fit:
y(2S),
Gaussian (solid)
X(3872),
Gaussian (solid)
background, 3rd order polynomial
(dashed)
Results:
- X(3872) candidates
522 ± 100
- mass difference
774.9 ± 3.1(stat) ± 3.0(syst) MeV/c2
- fitted width
17 ± 3 MeV/c2
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X(3872) production and decay property studies:
split data into two sub-samples with production variables:
a) pT(J/ypp) :
- pT＜15 GeV
- pT＞15 GeV
b) Rapadity:
- |y|＜1 (central)
- 1＜|y|＜2 (forward)
d) xy decay length dl
(“prompt” or from B-decay):
- dl＜100 mm
- dl＞100 mm
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spliting with decay variables:
c) Helicity Cos(qp), i.e.
boost X and one of pions into di-pion rest frame and measuring the open angle:
- Cos(qp)＜0.4
- Cos(qp)＞0.4
e) Isolation, i.e.
the ratio of X momentum to the sum of all tracks’ momentum in Cone 0.5 to X:
- iso ＝1 , “isolated”
- iso ＜1
f) Helicity Cos(qm), i.e.
boost X and one of muons into di-muon rest frame and measuring the open angle:
- Cos(qm)＜0.4
- Cos(qm)＞0.4
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For production/decay variables:
The properties of
production and decay
of X(3872) appears
consistent with y(2S)
within errors
Cos(qm) < 0.4
isolated
dl < 0.01cm
Cos(qp) < 0.4
|y| < 1
pT > 15 GeV
- Calculate the ratio of one sub-sample to the total , eg N|y|＜1:Ntotal
- Then compare X distribution with y(2S) benchmark
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What’s the X(3872)
- Charmonium?
L-excited multiplet splits much
more than expected by assuming
Coulomb-Scalar confinement
-“meson-molecule” ?
M(D-+D*+)=3879.5±0.7MeV
M(D0+D*0)=3871.5±0.5MeV (coincident?)
appears unexpectedly narrow
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Summary of X(3872):
- Confirm the existence of X(3872) with mass difference
△M = M(X) – M(J/y) = 774.9 ± 3.1(stat) ± 3.0(syst) MeV/c2
- (522±100) candidates of signal are established with 230 pb-1 data
- Selected production/decay properties of X(3872) are similar
to those of y(2S) within error
- Next step:
search for charged analog, X+J/yp+p0
 search for radiative decays

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The observation of
Bc  J/y(m+m-) m+nm
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Bc -- last of ground state of meson
- Theory predictions:
[1] C.Chang et al, PRD49(1994)3399
[2] E.Ebert et al, hep-ph/0401237; PRD68(2003)094020
MBc ~ 6.4 GeV
tBc ~ 0.3-0.5ps
-- ct~100mm, significantly shorter than B
Bc±  J/y(m+m-) m± n
-- Br~2.4% + trilepton final state + easy to trigger
- The only previous evidence by CDF RunI
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Events Selection:
- 210pb-1 data
- di-muon triggered
- M(m+m-)
within
0.25 GeV of J/y
- a third track (pT>1.5) with best common vertex fit to J/y(mm) :
“J/y+1 track” data control sample
- The third “+1” track should be muon, with M(J/ym) ＜8 GeV
after Selection:
 due to missing neutrals, the select samples are polluted by background severely
 use
(ym) invariant mass and pseudo proper time distributions to fit
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Background shape (data):
- use J/y+1 track control data sample
- divided into 2 subsets:
1) “prompt” J/y
2) “heavy flavor” one from B decay
- cross-checked with
y(2S) + 1 track bkg dominated data
Bc mass log likelihood
+0.14
5.95
-0.13
Signal shape (MC):
- MC templates of MBc 5.5 – 6.7 with
0.1GeV interval
- Full detector smearing + Selection
Bc Fit:
extract signal from a combined
unbinned likelihood fit to J/ym
invariant mass and proper time
±0.34 GeV
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“Floating” fit signal + bkg distributions:
Number of events
231
Total
Signal
95.5±11.8
Prompt
66.0
Heavy F
69.5
With significance SB in excess
of
5 standard deviations
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Consistency check:
• Simple counting analysis
- normalize background J/y+1 track
sample to selected sample with T>2
- check excess consistency with data
• Fit w/o signal
D2log(likelihood)=60 for 5
degrees of freedom
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Systematic uncertainties:
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Something else:
b
b
c
c
-The associated c-quark likely results in
a charmed hadron proximity to the Bc
- charmed mesons decay
semileptonically occasionally
Test Probability of extra m within f±90°:
- J/y+1 track background control sample,
- Selected Bc candidates, 5 out of 108,
1%
5±2%
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Summary:
Preliminary results on Bc with significantly more statistics
• Events: 95 ± 12±11
+0.14
• Mass: 5.95 -0.13 ±0.34 GeV/c2
+0.123
• Lifetime: 0.448 -0.096±0.121 ps
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The production of
Upsilon(1S)
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Theory modeling of production:
- factorized QCD calculations to O(a3)
currently employed by Pythia
- color-singlet, color-evaporation, color-octet models
U(1S) Production @ Tevatron:
- 50% produced promptly, i.e. at primary vertex and
relatively isolated
- 50% from excited states radiative decay
Event selection:
- luminosity: 159.1 ± 10.3 pb-1
- di-muon: pT>3, tight Tracking and Calorimeter isolation cut
- invariant mass in 7 – 13 GeV
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U’s |y| 
Data sample partition:
- Dy1: 0 ＜ |yU| ＜ 0.6
- Dy2: 0.6 ＜ |yU| ＜ 1.2
- Dy3: 1.2 ＜ |yU| ＜ 1.8
U‘s PT 
Sample fit:
- Background: 3rd order polynomial
- U(1,2,3S) resonances: double Gaussian
- the mass and width of U(1S) are
free parameters; others are fixed
relative to the mass
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Evaluating the U(1S) Production Xsec:
with eff in different rapidity region:
The measured cross-section×BR(U(1S)mm) is as
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749±20±75
781±21±78
598±19±56
with 6% luminosity uncertainty
- No strong dependence on rapidity observed
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Run2 preliminary results consistent with CDF Run1
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Summary:
measurements of U production at D0 to 1.8 rapidity region
• The pT spectrum does not show significant
difference in various rapidity region
• Results consistent with CDF RunI’s
- CDF √s=1.8TeV, |y|<0.4, ds/dy*Br =680±15±18±26 pb
- D0 √s=1.96TeV, |y|<0.6, ds/dy*Br =749±20±75±49 pb
- PYTHIA predict a factor of 1.11 from 1.8 to 1.96 TeV
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Thank
you!
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Backup slices
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