Recent results from FNAL E835 on the study of charmonium ... · • Selection of electron / positron candidates: – high energy deposition in calorimeter – signal in the hodoscopes

Matteo Negrini Photon 2003 Frascati, 07-11 April 2003

Recent results from FNAL E835 on the study of charmonium states in

proton-antiproton annihilation

Matteo NegriniUniversità degli Studi di Ferrara - INFN

Photon 2003 – Frascati, 07-11 April 2003


Charmonium spectroscopy in annihilation pp• e+e- annihilation ⇒ only JPC=1–-

states directly formed (J/ψ and ψ’)• γγ fusion ⇒ all C=+ (J≠1) states

directly accessible• B factory• annihilation ⇒ all the states

directly formed through 2 or 3 gluons intermediate states

pp

mbhadpp 70)( ≈→σnbeeJpp 25)/( ≈→→ −+ψσ

•Large hadronic background•Detection of electromagnetic final states


Antiproton beam and targetTARGET:•Hydrogen gas-jet target•Hydrogen clusters density:

1 – 4·1014 atoms/cm3

•The H2 target density can be tuned to obtain constant luminosity:

L INST ~ 2·1031 cm-2s-1

•Target dimension ≈ 7 mm

BEAM:•Antiprotons are accumulated until the desired current is reach. Then they are stochastically cooled and decelerated to the desired energy (continuous beam)•The total CM energy can be determined directly from the antiproton beam parameter

σE≈400keV - σE /E≈10-4

•Beam dimension ≈ 5 mm


Detector

Chargedtracking system(15°<θ<60°)

ThresholdČerenkovcounters(Separation of high energy e± from thehadronicbackground)

Luminositymonitor(Solid state detector.Counter of elastic

interactions at 90°)

Electromagneticcalorimeter (12°<θ<68°)

pp


Experimental technique• The beam energy is moved to scan the

resonance (precision σE≈250 keV)

• The number of events N at energy E is obtained as:

– L = instantaneous luminosity– G(E) = beam energy distribution (gaussian)– ε = detection efficiency

• The resonance cross section is obtained by deconvolution of the measured rate with the beam profile

[ ]∫∫ −+⋅⋅= ')'()'()()( dEEEGEELdtEN BWbkg σσε

( ) ( ) ( )( ) 44

12)(22

2

2RR

RBW ME

fRBppRBk

JEΓ+−

Γ→→+=

πσ


Event selection where final state includes e+e-

• Selection of electron / positron candidates:– high energy deposition in calorimeter– signal in the hodoscopes– signal in Čerenkov

Background

EW1·EW2>1.5• Electron Weight (EW):

– Maximum likelihood method for the single electron selection based oncalorimeter cluster shape and pulse height in Čerenkov and hodoscopes.

• Kinematic fit


χ0 mass and width

γψγχ −+→→ eeJ /0

Luminosity: ~33 pb-1 (~20 pb-1 on resonance) on 17 energy points

Selected channel: radiative decay to J/ψ

N. Selected events: ~400

ElectronWeight

KinematicFit


χ0 mass and width

( ) ( ) ( ) 700

2

10)08.011.061.1(//1.00.18.9

/2.04.04.3415

−−+ ×±±=→×→×→

±±=Γ±±=

eeJBRJBRppBRMeV

cMeVM

ψψγχχ


γγ final state selection

• Exactly 2 “on-time” clusters in the central calorimeter with high energy deposit and invariant mass within20% of ECM

• No “undetermined-time” extra clusters with invariantmass within 35 MeV of the π0 mass

• 4C kinematic fit to γγ

• |cos(θ*)| cut to improve signal to background ratio


γγ background (feeddown)

γππ 400 →→ppγγπ 30 →→pp

•Background mainly from:

where one or more photons aremissing because of acceptance orcalorimeter energy thresholds•Measurement of the cross section for the background processes and Monte Carlo determination of the background contribution

•Comparison with measured γγcross section for off-resonance points


Preliminaryχ0→γγ

2.0cos0 * << ϑ

4.0cos2.0 * << ϑ

800 10)55.018.152.6()()( −×±±=→×→ γγχχ BRppBR

keV9.09.2)( 0 ±=→Γ γγχ)( 0 ppBR →χTaking from the PDG:


Preliminaryηc→γγ• 18.9 pb-1 of data• All the resonance parameters

are measured in the γγchannel:

keVMeV

cMeVM

18.3

0.24.20/0.11.21.2984

9.11.10.10.1

7.77.6

2

++−−

+−

=Γ

±=Γ

±±=

γγ


Interference between →χ0 →π0π0 and the continuum

pp

22

),( BA iiR BeAeixAzx

dzd δδσ

+++

−=

2/0

0

χ

χ

Γ

−=

MEx CM

*cosϑ=z

00ππ→pp

Measurement of the cross section for the processin the χ0 energy region

ResonantInterfering(helicity 0)

Non-Interfering(helicity 1)~500000 π0π0 candidates

Preliminary


χ0 branching ratios700

00 10)25.081.009.5()()( −×±±=→×→ ππχχ BRppBR3

000

0 10)35.050.2(2)()( −−+ ×±=→=→ ππχππχ BRBR4

0 10)10.043.004.2()( −×±±=→ ppBR χ4

0 10)5.02.2()( −×±=→ ppBR χ

Using the PDG value:

( ) ( ) ( )7

00

10)08.011.061.1(

//−

−+

×±±=

=→×→×→ eeJBRJBRppBR ψψγχχ

( )( ) 34.093.034.5/

000

0 ±±=→→

ππχψγχ

BRJBR

( ) 30 10)9.00.33.13(/ −×±±=→ ψγχ JBR

( ) 30 10)7.12.10(/ −×±=→ ψγχ JBR

Preliminary

To be compared with the PDG:

Using the result:

To be compared with the PDG:


Electric dipole trasition (P→S+γ)The value obtained for Γ(χ0→J/ψγ), using the new total

width and the BR measurements, is consistent with the theory of electric dipole transition

232 ||94)( ifQ EkeSP αγ =+→Γ

i

fi

MMM

k2

22 −=

)()(|| 2

0

rRrrRdrE fiif ⋅⋅= ∫∞

389±52290±50130±33

Γ(J/ψγ)exp

(keV)

(4.9±0.7)×10-9430χ2

(4.9±0.8)×10-9390χ1

(4.6±1.2)×10-9304χ0

Γ/k3

(MeV-2)k

(MeV)


e+e- final states selection at the ψ’

• ψ’ and J/ψ detected through their e+e- decay

• All the exclusive channels are selected with kinematic fits

• 14.3 pb-1 of data in the ψ’ energy region collected in year 2000• 12.4 pb-1 on resonance ⇒ 32862 events• 1.9 pb-1 off resonance ⇒ 66 events

−+→ ee'ψ−+−+−+ →→ πππψπψ eeJ /'

γπψπψ 4/' 00 −+→→ eeJγψηψ 2/' −+→→ eeJ

XeeXJ −+→→ ψψ /'

Preliminary


Preliminaryψ’ branching ratios

020.0294.0)/'(

±==→ −+πψπψ JBR

019.0164.0)/'( 00

±==→ πψπψ JBR

004.0028.0)/'(

±==→ ψηψ JBR

0004.00063.0)'(

±==→ −+eeBRψ

J/ψη

J/ψπ0π0

J/ψπ+π-

e+e-


Conclusions• Charmonium states are studied in proton –

antiproton annihilation detecting electromagnetic final states

• Extensive study of the χc0 ...– Mass and total width – γγ width– Interference in π0π0 decay

• ... and of the ηc– Mass and total width – γγ width

• New measurement of BR(ψ’→J/ψ X) and BR(ψ’→e+e-)

Documents

Recent results from FNAL E835 on the study of charmonium ... · • Selection of electron / positron candidates: – high energy deposition in calorimeter – signal in the hodoscopes