Sergio Grancagnolo Activity Summary

9 Jan 2003

2003 work in BaBarThe apparatus

Physics with BaBar

Data analysis

2

ECMGeV , = 0.55

PEP-II is a high luminosity, asymmetric, e+e- collider

filled by the 3 km long, linear accelerator (Linac)

The accelerator PEP-II @ SLAC

Ldesign = 3 x 1033 cm-2s-1

Lpeak = 6.93 x 1033 cm-2s-1

Lint=160 fb-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 workDuring 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)!Observation of a Narrow Meson Decaying to Ds

+0 at a Mass of 2.32 GeV/c2

Phys.Rev.Lett. 90 (2003) 242001

SLAC press-releasehttp://www.slac.stanford.edu/slac/media-info/20030428/

index.html

INFN announcementhttp://www.infn.it/comunicati/detail.php?id=299

Naturehttp://www.nature.com/nsu/030428/030428-18.html

11 Apr 2003

DsKK

DsKK

soon after another particle was discovered: DsJ(2460)!

7

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(*)

narrow states

Godfrey-Isgur model

-cs spectroscopy

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 BDsJD(*) 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 BDsJD(*)

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

Cabibbo favored B, D pseudoscalar possibility of quantum number

measurement for the DsJ from the angular distribution of the decay products

DsJ

Bb_

d, uD_

Vcb

Vcs

c

_s

c_

d, u

DsJ in B decays

11

Analysis Strategy look for decays B DsJ

+ D(*) consider 24 decays

D(*) Ds+(*)

D(*) (Ds+(*) 0)

D(*) (Ds+(*) )

D0 KK0, K3D KDS

+ Ds+D0orDs+D-

submodes/B

D*0 D00, D0D*+ D0+, D+0

D*s Ds

establish signals, measure BRs perform angular analysis

( DsJ quantum numbers)

reconstruct the daughters:

Studies on simulated data to

evaluate efficiencies and

background

Control sample, used

to test the analysis chain

DsJ+ Ds

+(*) 0

DsJ+ Ds

+(*)

12

Analysis strategy (II) Resolution studies Event Selection Optimization Background studies Efficiency and significance Multiple candidates problem Cross-feed between different

decay modesTotal: 16

D(*)Ds(*) ,

final states

13

(mDs) 14 MeV/c2

DsJ mass resolutions (simulation)

(mDs) 8 MeV/c2

m(Ds) (GeV/c2)

Signal estimates from a fit to these distributions

on real data

m(Ds) (GeV/c2)

14

Cut optimization: mD

For B DDsJ+ (DsJ

+ Ds

mDis a good discriminating variable

Red is background

Blue is simulated signal

The curve is the fraction of events rejected by

mDmDcut

Optimal selection:

mD2.3 GeV/c2 (D)

mD2.4 GeV/c2 (D*)

15

To compute the background in the DsJ mass region we average the number of events observed in the data into two symmetric (6 wide) sidebands around the DsJ mass region (-4 to -10 and 4 to 10)

Background estimates in the DsJ signal region (from real data)

m(Ds) (GeV/c2)

16

Candidate multiplicity studies

Several candidates per event: Choosing the candidate with the best E

gives the largest efficiency on simulated signal (1 candidate per mode)

criteria mode Signal * E D+ Ds

- 9.2

mES D+ Ds-

6.9

D+ Ds-

6.6

* assuming Br(B DsJD)xBr(DsJ D0,)=10-3

2

2

PDGD

PDGDD

D

i

ii

i

mm

E, mES quantities

constructed using kinematic

variables

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(Ds) for BD(*)Ds candidates (data)

all B candidates 1 best B candidate/mode

m(D(*))>2.3(2.4)GeV/c2

19

Data is compatible with J=1 Comparison with other hypotheses (J=0,J=2) still to be done

Helicity analysis

cosh

Eve

nts

B D(*)DsJ MC

Data

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(B0DsJ+

2460D-) Br(DsJ+Ds)) =( 0.75 ±0.19) 10-3

Br(B+DsJ+

2460D0) Br(DsJ+Ds)) =( 0.65 ±0.19) 10-3

Br(B0DsJ+

2460D*-) Br(DsJ+Ds)) =( 2.04 ±0.29) 10-3

Br(B0DsJ+

2460 D*0) Br(DsJ+Ds)) =( 1.63 ±0.32) 10-3

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Conclusions (II) More work done, not described here

efficiencies studies published paper on B0D*+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

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/(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

S=signal

B=background

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Mode S B B [m(D) cut] S/(S+B) S/(S+B) [m(D)cut]

D+ Ds- 0 9.2 50.0 14.5 1.19 1.88

D+ Ds*- 0 3.5 18.5 6.0 0.75 1.14

D*+ Ds- 0 8.5 43.0 14.5 1.19 1.78

D*+ Ds*- 0 3.4 8.0 2.0 1.00 1.45

D0 Ds- 0 14.6 235.0 71.0 0.92 1.58

D0 Ds*- 0 4.9 83.5 24.0 0.52 0.91

D*0 Ds- 0 4.9 74.0 25.0 0.55 0.90

D*0 Ds*- 0 1.6 16.5 6.5 0.39 0.58

D+ Ds- 15.9 21.0 3.5 2.61 3.60

D*+ Ds- 14.0 19.5 4.0 2.41 3.30

D0 Ds- 23.2 119.5 44.0 1.94 2.83

D*0 Ds- 7.2 40.5 16.5 1.04 1.47

Expected signal and background with the current selection

assuming Br(B DsJD)xBr(DsJ D0,)=10-3

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MC: efficiency With the best E (1 candidate per mode)

B mode Sub decays Eff% evts forBr=10-3

B0 D* Ds1 Ds

K 5.0 3.0B0 D Ds1 Ds

K 6.6 9.3

B0 D* Ds1 Ds*

K 1.3 0.8B0 D Ds1 Ds

* K 1.3 1.9

B0 D Ds0 Ds

K 4.3 6.1B0 D* Ds0 Ds

K 4.0 2.4

B+ D0 Ds0 Ds

K 7.9 4.7B+ D*0 Ds0 Ds

K 2.1 1.2

The rest of the table here:

http://www.slac.stanford.edu/~grancagn/internal/DsJD/de-a-2s.txt