Transcript B D(*)DsJ - Universita' del Salento

2003 work in BaBar
The apparatus
Physics with BaBar
Data analysis
Sergio Grancagnolo
Activity Summary
9 Jan 2003
The accelerator
PEP-II @ SLAC
PEP-II is a high luminosity,
asymmetric, e+e- collider
filled by the 3 km long,
linear accelerator (Linac)
Lint=160 fb-1 ECM = 10.58 GeV , bg = 0.55
Ldesign = 3 x 1033 cm-2s-1
2 = 6.93 x 1033 cm-2s-1
Lpeak
The BaBar dectector
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BaBar is mounted on the
interaction point of PEP-II
Layers of subdetectors:
 Silicon
Vertex Tracker
 Drift CHamber
 Detector of Internal Reflected
Cherenkov light
 Electro Magnetic Calorimeter
 Instrumented Flux Return
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Magnetic Solenoid (1,5T)
between EMC and IFR
SVT commissioner work
During the Apr-Jul 2003 period of data taking at SLAC, I was
responsible for the correct working status of the innermost part
of the BaBar detector: the Silicon Vertex Tracker
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Physics at a
B factory
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CP violation
Test of standard model
b quark physics
…
11 Apr
2003
DsKKp
BaBar discovery of
DsJ(2317)!
Observation of a Narrow Meson
Decaying to Ds+p0 at a Mass of
2.32 GeV/c2
Phys.Rev.Lett. 90 (2003) 242001
SLAC press-release
DsKKpp0
http://www.slac.stanford.edu/slac/mediainfo/20030428/index.html
INFN announcement
http://www.infn.it/comunicati/detail.php?id=299
Nature
http://www.nature.com/nsu/030428/030428-18.html
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soon after another particle was
discovered: DsJ(2460)!
-cs spectroscopy
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Known particles: Ds+,
Ds*+, Ds1+(2536),
DsJ+(2573)
New discoveries:
DsJ+(2317), DsJ+(2460)
 below
Godfrey-Isgur model
S-wave
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P-wave
the treshold for
the DK decay process
 isospin violating
decay process Ds(*) p
 narrow states
Interpretation of these
narrow states?
 38 theoretical preprints
between 1st May to 30th Sep
Among others also exotic
explanations like:
4-quark states?
DK molecule?
…
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Study of BDsJD(*)
decays
hep-ex/0305100
hep-ex/0307052
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hep-ex/0308019
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The other B-factory experiments, Cleo
and Belle, confirmed the discovery and
started to study the new particles
Belle announced the observation of the
decays BDsJD(*)
on 1st Sept I started to work with the
French group of Annecy on this topic
I will spend ~10 months in Annecy
 The results will be an important part of
my thesis
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DsJ in B decays
Vcs
c
_
DsJ
s
B
_
b
d, u
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Vcb
_
c
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D
d, u
Cabibbo favored
B, D pseudoscalar
possibility of quantum number
measurement for the DsJ from the angular
distribution of the decay products
Analysis Strategy
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Control
sample, used
to test the
analysis chain
Studies on
simulated data to
evaluate
efficiencies and
background
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look for decays B  DsJ+ D(*)
consider 24 decays
 D(*)
Ds+(*)
 D(*) (Ds+(*) p0)
 D(*) (Ds+(*) g)
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reconstruct the daughters:
D*0 D0p0, D0g
D*+  D0p+, D+p0
D*s  Dsg
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DsJ+  Ds+(*) p0
DsJ+  Ds+(*) g
D0  Kp, Kpp0, K3p
D+ Kpp
DS+  fp, K*0K
6 Ds+D0 or 2 Ds+D- submodes/B
establish signals, measure BRs
perform angular analysis
( DsJ quantum numbers)
Analysis strategy (II)
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Total: 16
D(*)Ds(*) p0,g
final states
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Resolution studies
Event Selection Optimization
Background studies
Efficiency and significance
Multiple candidates problem
Cross-feed between different
decay modes
DsJ mass resolutions
(simulation)
s(m(Dsp0)) 8 MeV/c2
s(m(Dsg)) 14 MeV/c2
Signal estimates from a
fit to these distributions
on real data
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m(Dsp0) (GeV/c2)
m(Dsg) (GeV/c2)
Cut optimization: m(Dg)
For B  DDsJ+ (DsJ+ Dsg)
m(Dg) is a good
discriminating variable
Red is background
Blue is simulated signal
The curve is the fraction of
events rejected by
m(Dg) > m(Dg)_cut
Optimal selection:
m(Dg) > 2.3 GeV/c2 (D)
m(Dg) > 2.4 GeV/c2 (D*)
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Background estimates in the DsJ
signal region (from real data)
To compute the background in
the DsJ mass region we average
the number of events observed
in the data into two symmetric
(6s wide) sidebands around the
DsJ mass region (-4 to -10 s and
4 to 10s)
m(Dsg) (GeV/c2)
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Candidate multiplicity
studies
DE, mES
quantities
constructed
using
kinematic
variables
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Di
 mDi  m
=
 s

PDG
Di
PDG
Di
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2
Several candidates per event:
Choosing the candidate with the best DE
gives the largest efficiency on simulated
signal (1 candidate per mode)
criteria
DE
mES
2
mode
D+ Ds-p0
D+ Ds-p0
D+ Ds-p0
Signal *
9.2
6.9
6.6
* assuming Br(B DsJD)xBr(DsJ  Dp0,g)=103
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2 body decays used as a
calibration sample (data)
compute the branching
fractions of all decays
B  Ds(*)D(*)
to test if we understand well
our selection efficiencies
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Signal example: m(Dsg) for
BD(*)Dsg candidates (data)
m(D(*)g)>2.3(2.4)GeV/c2
all B candidates
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1 best B
candidate/mode
Helicity analysis
 Data is compatible
with J=1
 Comparison with
other hypotheses
(J=0,J=2) still to be
done
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Events
B D(*)DsJ MC
 Data
cosqh
Conclusions (I)
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The analysis work is going on
A preliminary BR measurement was shown
at the BaBar collaboration meeting
 An example:
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Br(B0DsJ+2460D-)  Br(DsJ+Dsg)) =( 0.75 ±0.19) 10-3
Br(B+DsJ+2460D0)  Br(DsJ+Dsg)) =( 0.65 ±0.19) 10-3
Br(B0DsJ+2460D*-)  Br(DsJ+Dsg)) =( 2.04 ±0.29) 10-3
Br(B0DsJ+2460 D*0)  Br(DsJ+Dsg)) =( 1.63 ±0.32) 10-3
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A preliminary angular analysis was also
done
Conclusions (II)
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More work done, not described here
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efficiencies studies
published paper on B0D*+D*-
Plan for this year:
 more
work to do on cross-feed,
estimate systematic uncertainties
 Write an internal document and
submit a paper
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Event Selection
Optimization
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Tested many combination of different criteria
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S=signal
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B=background
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Used standard discriminating variables to
separate quark b production from other
quarks
Select a window in the invariant mass
around the mass of the particles from the B
and the DsJ
Vertexing, particle identification, etc
computed the significance S/(S+B) for
each set, with S from simulated signal and
B from the real data
choose the criteria that results in higher
significance
a different set of criteria for each submode
will be considered
Expected signal and background
with the current selection
Mode
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B [m(Dp0,g) cut] S/(S+B)
S
B
S/(S+B)
[m(Dp0,g) cut]
D+ Ds- p0
9.2
50.0
14.5
1.19
1.88
D+ Ds*- p0
3.5
18.5
6.0
0.75
1.14
D*+ Ds- p0
8.5
43.0
14.5
1.19
1.78
D*+ Ds*- p0
3.4
8.0
2.0
1.00
1.45
D0 Ds- p0
14.6
235.0
71.0
0.92
1.58
D0 Ds*- p0
4.9
83.5
24.0
0.52
0.91
D*0 Ds- p0
4.9
74.0
25.0
0.55
0.90
D*0 Ds*- p0
1.6
16.5
6.5
0.39
0.58
D+ Ds- g
D*+ Ds- g
D0 Ds- g
15.9
14.0
23.2
21.0
19.5
119.5
3.5
4.0
44.0
2.61
2.41
1.94
3.60
3.30
2.83
D*0 Ds- g
7.2
40.5
16.5
1.04
1.47
assuming Br(B DsJD)xBr(DsJ  Dp0,g)=10-3
MC: efficiency
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With the best DE (1 candidate per mode)
B mode
Sub decays
B0D* Ds1
B0D Ds1
B0D* Ds1
B0D Ds1
B0D Ds0
B0D* Ds0
B+D0 Ds0
B+D*0 Ds0
Dsg Kp fp
Dsg Kpp fp
Ds*p0 Kp fp
Ds*p0 Kpp fp
Dsp0 Kpp fp
Dsp0 Kp fp
Dsp0 Kp fp
Dsp0 Kp fp
Eff% evts for
Br=10-3
5.0
3.0
6.6
9.3
1.3
0.8
1.3
1.9
4.3
6.1
4.0
2.4
7.9
4.7
2.1
1.2
The rest of the table here:
http://www.slac.stanford.edu/~grancagn/internal/DsJD/de-a-2s.txt
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