2003 work in BaBar

1
2003 work in BaBar

• The apparatus
• Physics with BaBar
• Data analysis

2
The accelerator PEP-II _at_ SLAC

• PEP-II is a high luminosity, asymmetric, ee-
  collider
• filled by the 3 km long, linear accelerator
  (Linac)

ECM 10.58 GeV , bg 0.55
Lint160 fb-1
Ldesign 3 x 1033 cm-2s-1 Lpeak 6.93 x 1033
cm-2s-1
3
The BaBar dectector

• 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
• Magnetic Solenoid (1,5T) between EMC and IFR

4
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
5
Physics at a B factory

• CP violation
• Test of standard model
• b quark physics

6
BaBar discovery of DsJ(2317)!
11 Apr 2003
Observation of a Narrow Meson Decaying to Dsp0
at a Mass of 2.32 GeV/c2 Phys.Rev.Lett. 90 (2003)
242001
Ds?KKp
SLAC press-release http//www.slac.stanford.edu/sl
ac/media-info/20030428/index.html INFN
announcement http//www.infn.it/comunicati/detail.
php?id299 Nature http//www.nature.com/nsu/030428
/030428-18.html
Ds?KKpp0
soon after another particle was discovered
DsJ(2460)!
7
cs spectroscopy

• Known particles Ds, Ds, Ds1(2536),
  DsJ(2573)
• New discoveries DsJ(2317), DsJ(2460)
• below the treshold for the DK decay process
• isospin violating decay process Ds() p
• narrow states

S-wave
P-wave
8
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?

9
Study of B?DsJD() decays

• 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

hep-ex/0305100 hep-ex/0307052
hep-ex/0308019
10
DsJ in B decays
Vcs
DsJ
Vcb
B
d, u

• Cabibbo favored
• B, D pseudoscalar
• possibility of quantum number measurement for the
  DsJ from the angular distribution of the decay
  products

11
Analysis Strategy

• look for decays B ? DsJ D()
• consider 24 decays
• D() Ds()
• D() (Ds() p0)
• D() (Ds() g)

Control sample, used to test the analysis chain
DsJ ? Ds() p0 DsJ ? Ds() g

• reconstruct the daughters

D0 ? Kp, Kpp0, K3p D? Kpp DS ? fp, K0K 6 DsD0
or 2 DsD- submodes/B
D0? D0p0, D0g D ? D0p, Dp0 Ds ? Dsg
Studies on simulated data to evaluate
efficiencies and background

• establish signals, measure BRs
• perform angular analysis
• (? DsJ quantum numbers)

12
Analysis strategy (II)

• Resolution studies
• Event Selection Optimization
• Background studies
• Efficiency and significance
• Multiple candidates problem
• Cross-feed between different decay modes

Total 16 D()Ds() p0,g final states
13
DsJ mass resolutions (simulation)
s(m(Dsg)) ?14 MeV/c2
s(m(Dsp0)) ?8 MeV/c2
Signal estimates from a fit to these
distributions on real data
m(Dsg) (GeV/c2)
m(Dsp0) (GeV/c2)
14
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) gt m(Dg)_cut Optimal
selection m(Dg) gt 2.3 GeV/c2 (D) m(Dg) gt 2.4
GeV/c2 (D)
15
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)
16
Candidate multiplicity studies

• Several candidates per event
• Choosing the candidate with the best DE gives
  the largest efficiency on simulated signal (1
  candidate per mode)

DE, mES quantities constructed using kinematic
variables
assuming Br(B? DsJD)xBr(DsJ ? Dp0,g)10-3
17
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
18
Signal example m(Dsg) for B?D()Dsg candidates
(data)
m(D()g)gt2.3(2.4)GeV/c2
1 best B candidate/mode
all B candidates
19
Helicity analysis

• Data is compatible with J1
• Comparison with other hypotheses (J0,J2) still
  to be done

Events
cosqh
20
Conclusions (I)

• The analysis work is going on
• A preliminary BR measurement was shown at the
  BaBar collaboration meeting
• An example
• A preliminary angular analysis was also done

Br(B0?DsJ2460D-) ? Br(DsJ?Dsg)) ( 0.75 0.19)
10-3 Br(B?DsJ2460?D0) ? Br(DsJ?Dsg)) ( 0.65
0.19) 10-3 Br(B0?DsJ2460D-) ? Br(DsJ?Dsg)) (
2.04 0.29) 10-3 Br(B0?DsJ2460 ?D0) ?
Br(DsJ?Dsg)) ( 1.63 0.32) 10-3
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Conclusions (II)

• More work done, not described here
• efficiencies studies
• published paper on B0?DD-
• Plan for this year
• more work to do on cross-feed, estimate
  systematic uncertainties
• Write an internal document and submit a paper

22
Event Selection Optimization

• Tested many combination of different criteria
• 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/?(SB) 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

Ssignal Bbackground
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Expected signal and background with the current
selection
Mode S B B m(Dp0,g) cut S/?(SB) S/?(SB)
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 D0 Ds- p0 4.9 74.0 25.0 0.55
0.90 D0 Ds- p0 1.6 16.5 6.5 0.39
0.58 D Ds- g 15.9 21.0 3.5 2.61
3.60 D Ds- g 14.0 19.5 4.0 2.41
3.30 D0 Ds- g 23.2 119.5 44.0 1.94
2.83 D0 Ds- g 7.2 40.5 16.5 1.04
1.47
assuming Br(B? DsJD)xBr(DsJ ? Dp0,g)10-3
24
MC efficiency

• With the best DE (1 candidate per mode)

The rest of the table here http//www.slac.stanfo
rd.edu/grancagn/internal/DsJD/de-a-2s.txt