Transcript Recent results from FNAL E835 on the study of charmonium states in proton-antiproton annihilation Matteo Negrini Università degli Studi di Ferrara - INFN Photon 2003

Recent results from FNAL E835 on
the study of charmonium states in
proton-antiproton annihilation
Matteo Negrini
Università degli Studi di Ferrara - INFN
Photon 2003 – Frascati, 07-11 April 2003
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
Charmonium spectroscopy in ppannihilation
•
•
•
•
e+e- annihilation  only JPC=1–states directly formed (J/y and y’)
gg fusion  all C=+ (J1) states
directly accessible
B factory
pp annihilation  all the states
directly formed through 2 or 3 gluons
intermediate states
 ( pp  had)  70mb
 ( pp  J /y  ee )  25nb
Matteo Negrini
Photon 2003
•Large hadronic background
•Detection of electromagnetic final states
Frascati, 07-11 April 2003
Antiproton beam and target
TARGET:
•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
E400keV - E /E10-4
•Beam dimension  5 mm
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
Threshold
Čerenkov
counters
(Separation
of high energy
e± from the
hadronic
background)
Detector
Electromagnetic
calorimeter
(12°<q<68°)
Luminosity
monitor
(Solid state detector.
Counter of elastic
ppinteractions at 90°)
Charged
tracking
system
(15°<q<60°)
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
Experimental technique
•
The beam energy is moved to scan the
 BW ( E ) 
resonance (precision E250 keV)
•
The number of events N at energy E is
obtained as:

2 J  1  BR  pp BR  f R2
4 k 2 E  M R 2  R2 4

N ( E )   Ldt  e   bkg ( E )    BW ( E ' )G( E ' E )dE '
– L = instantaneous luminosity
– G(E) = beam energy distribution (gaussian)
– e = detection efficiency
•
The resonance cross section is obtained by
deconvolution of the measured rate with
the beam profile
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
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
•
Electron Weight (EW):
– Maximum likelihood method for the
single electron selection based on
calorimeter cluster shape and pulse
height in Čerenkov and hodoscopes.
EW1·EW2>1.5
Background
• Kinematic fit
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
c0 mass and width
Luminosity: ~33 pb-1 (~20 pb-1 on resonance)
on 17 energy points
Selected channel: radiative decay to J/y
N. Selected events: ~400
c 0  J /yg  e  e g
Electron
Weight
Kinematic
Fit
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
c0 mass and width
M  3415.4  0.4  0.2 MeV / c 2
  9.8  1.0  0.1MeV


BRc 0  pp  BRc 0  J / yg  BR J / y  e  e   (1.61 0.11 0.08) 107
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
gg final state selection
• Exactly 2 “on-time” clusters in the central calorimeter
with high energy deposit and invariant mass within
20% of ECM
• No “undetermined-time” extra clusters with invariant
mass within 35 MeV of the 0 mass
• 4C kinematic fit to gg
• |cos(q*)| cut to improve signal to background ratio
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
gg background (feeddown)
•Background mainly from:
pp   0g  3g
pp   0 0  4g
where one or more photons are
missing because of acceptance or
calorimeter energy thresholds
•Measurement of the cross section
for the background processes and
Monte Carlo determination of the
background contribution
•Comparison with measured gg
cross section for off-resonance
points
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
c0gg
0  cos *  0.2
0.2  cos *  0.4
BR ( c 0  pp)  BR ( c 0  gg )  (6.52  1.18  0.55) 108
Taking BR ( c 0  pp) from the PDG: ( c 0  gg )  2.9  0.9keV
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
•
•
hcgg
18.9 pb-1 of data
All the resonance parameters
are measured in the gg
channel:
M  2984.1  2.1  1.0MeV / c 2
  20.4 67..77  2.0MeV
gg  3.811..0111..901keV
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
Interference between ppc0 00 and
the continuum
Measurement of the
cross section for the
process pp   0 0
in the c0 energy region
~500000 00 candidates
Matteo Negrini
d
 AR
( x, z ) 
 Aei A  Be i B
dz
xi
2
2
x
ECM  M c 0
c 0 / 2
Interfering Non-Interfering z  cos *
Resonant (helicity 0) (helicity 1)
Photon 2003
Frascati, 07-11 April 2003
c0 branching ratios
BR ( c 0  pp)  BR ( c 0   0 0 )  (5.09  0.81  0.25) 107
Using the PDG value: BR(c0   0 0 )  BR(c0     ) 2  (2.50  0.35) 103
BR ( c 0  pp)  (2.04  0.43  0.10) 104
To be compared with the PDG:
BR(c0  pp)  (2.2  0.5) 104


Using the result: BRc 0  pp  BRc 0  J /yg  BR J /y  e  e  
 (1.61 0.11 0.08) 107
BRc 0  J /yg 
 5.34  0.93  0.34
0 0
BR c 0   


3
BR c 0  J /yg   (13.3  3.0  0.9) 10
To be compared with the PDG: BRc0  J /yg   (10.2  1.7) 10
Matteo Negrini
Photon 2003
3
Frascati, 07-11 April 2003
Electric dipole trasition (PS+g)
The value obtained for (c0J/yg), using the new total
width and the BR measurements, is consistent with
the theory of electric dipole transition
2
2
M

M
i
f
4 2 3
2
k
( P  S  g )  eQk | Eif |
2M i

9
2
| Eif |  drRi (r )  r  R f (r )
0
(J/yg)exp
(keV)
k
(MeV)
/k3
(MeV-2)
c0
130±33
304
(4.6±1.2)10-9
c1
290±50
390
(4.9±0.8)10-9
c2
389±52
430
(4.9±0.7)10-9
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
e+e- final states selection at the y’
•
y’ and J/y detected through their
e+e- decay
y '  ee
y '  J /y 0 0  e e  
y '  J /yX  e e X
y '  J /y  
e e 4g
y '  J /yh  e e  2g
• All the exclusive channels are
selected with kinematic fits
• 14.3 pb-1 of data in the y’ energy
region collected in year 2000
• 12.4 pb-1 on resonance  32862 events
• 1.9 pb-1 off resonance  66 events
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
y’ branching ratios
BR (y '  J /yh) 
J/yh
BR (y '  J /y  ) 


 0.028  0.004
J/y00
 0.294  0.020
J/y+e+e-
BR (y '  e  e  ) 
 0.0063  0.0004
BR (y '  J /y 0 0 ) 
 0.164  0.019
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003
Conclusions
• Charmonium states are studied in proton –
antiproton annihilation detecting electromagnetic
final states
• Extensive study of the cc0 ...
– Mass and total width
– gg width
– Interference in 00 decay
• ... and of the hc
– Mass and total width
– gg width
• New measurement of BR(y’J/y X) and
BR(y’e+e-)
Matteo Negrini
Photon 2003
Frascati, 07-11 April 2003