Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Charmonium Production with Antiproton - Gas Jet Interactions at FNAL Matteo Negrini University of Ferrara - INFN for the E835 collaboration: Fermilab, Ferrara, Genova, Northwestern, Minnesota, Irvine, Torino

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Why ? e + e - annihilation  only J PC =1 – - states directly formed (J/  and  ’)  fusion  all C=+ (J  1) states directly accessible B factory annihilation  all the states directly formed through 2 or 3 gluons intermediate states Large hadronic background Detection of EM final states

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 FNAL Antiproton Accumulator

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 FNAL Antiproton Accumulator Antiprotons are accumulated until the desired current (~50 mA) is reach. Then they are stochastically cooled and decelerated to the desired energy (continuous beam) Energy determined from the orbit length L and the revolution frequency f –L from reference orbit (L REF ) measured at the  ’:  L/L ~ 2  –f measured with precision:  f/f ~ The error on the beam energy measurement is  E  keV Energy spread after stochastic cooling:  E  400 keV. At the charmonium mass scale:

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Hydrogen Gas-Jet Target Jet of clusterized H 2 molecules Density up to 1-4·10 14 atoms/cm 3 Instantaneous luminosity up to 3·10 31 cm -2 s -1 Luminosity is measured from elastic at 90 ° with 3% precision Interaction region: 5  5  7 mm 3

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Experimental technique Charmonium is formed in the complete annihilation of so the E CM is determined from the beam parameters The beam energy is moved to scan the resonance The number of events N of a given final state at energy E is obtained as: –L = instantaneous luminosity –G(E) = beam energy distribution (gaussian) –  = detection efficiency The resonance cross section is obtained by deconvolution of the measured rate with the beam profile

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Charmonium spectrum  c ' observed by Crystal Ball with mass 3594 MeV, later observed by Belle with larger mass (3654 MeV) h c (observed by E760 at M= MeV) needs confirmation

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Historical review - 1 R704 at CERN (1984) –pioneered the technique and proved the feasibility –3 pb -1 collected on J/  and  1,2 E760 at Fermilab ( ) - 30 pb -1 –First observation of 1 P 1 resonance –Precision measurement of  c1 and  c2 masses and widths –First direct observation of  c in annihilations and mass measurement –Search for  c ’ –Coupling to of J/  ’ and  1,2 –Proton form factor in the time like region

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Historical review - 2 E835 at Fermilab ( ) pb -1 –Measurement of  0 mass and width –Measurement of  0,2  –  c1 and  c2 angular distributions measurement –Proton form factor in the time like region –Precise measurement of the  c  parameters –Extensive search of the  ’ c state –Improved  ’ branching ratios measurements –Study of the  final state

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Historical review - 3 E835-II at Fermilab (2000) pb -1 –Extensive study of  0 state –Data taken in the 1 P 1 energy region to confirm resonance –  c1 and  c2 mass and width measurement –Measurement of  ’ branching ratios –Proton form factor in the time like region

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 The E835-II detector Threshold Čerenkov counters (Separation of high energy e ± from the hadronic background) Charged tracking system (15°<  <60°) Luminosity monitor (Solid state detector. Counter of elastic interactions at 90°) Electromagnetic calorimeter (12°<  <68°)

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Detector acceptance and resolution The detector has cylindrical symmetry around the beam axis with 2  azimuthal coverage Central calorimeter: –Acceptance: 11° <  < 70° –Energy resol.: –Angular resol.:    6mrad,    11mrad Forward calorimeter: –Acceptance: 2° <  < 11° –Position resol.:  x  5cm Inner tracking –Acceptance: 15° <  < 55° –Angular resol.:    4mrad,    8mrad

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Selection of J/ ,  '  e + e - final states Selection of high invariant mass e + e - candidates from  '  e + e - or J/  X  e + e - X: –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. Decay products reconstructed in the detector and final state classified with kinematic fit EW 1 ·EW 2 >1.5 Background

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Example of  ’  +  - event Charged tracking  view Charged tracking + Čerenkov + calorimeter  view

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  0 mass and width measurement (E835-II) Luminosity: ~33 pb -1 (~20 pb -1 on resonance) on 17 energy points Selected channel: radiative decay to J/  N. Selected events: ~400 Electron Weight Kinematic Fit

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  0 mass and width measurement (E835-II) S. Bagnasco et al., Phys. Lett. B533 (2002) 237

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  1 and  2 scan (E835-II) New measurement of mass and width of the  1 and  2 Luminosity: ~6 pb -1 (  1 ) - ~1 pb -1 (  2 ) - ~11 pb -1 (bkg) Preliminar y

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Results for   cJ  J/  e + e -   c0 E835-IIE835-I M (MeV/c 2 )  TOT (MeV) BR( )BR(J/  )× ±0.4± ±1.0± ±1.9± ± ± ±1.5  c1 E835-II (prelim.)E760 M (MeV/c 2 )  TOT (MeV) BR( )  (J/  ) (eV) ±0.10± ± ±0.7± ±0.10± ± ±2.7±1.2  c2 E835-II (prelim.)E760 M (MeV/c 2 )  TOT (MeV) BR( )  (J/  ) (eV) ±0.15± ± ±1.9± ±0.11± ± ±2.9±1.5 M. Ambrogiani et al., Phys. Rev. Lett. 83 (1999) 2902 T. A. Armstrong et al., Nucl. Phys. B 373 (1992) 35

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Electric dipole trasition (P  S+  ) The value obtained for  (  0  J/  ), anomalously large in the past, is now consistent with the theory of electric dipole transitions  (J/  ) exp (keV) k (MeV)  /k 3 (MeV -2 ) 00 130±33304 (4.6±1.2)  11 290±50390 (4.9±0.8)  22 389±52430 (4.9±0.7)  10 -9

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Angular distribution   '  e + e - Preliminar y Measurement of the helicity 0 and 1 amplitudes for the interaction Combining the two data set: E835-II (4822 events) E835-I (2579 events)

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  ' branching ratios  ’ and J/  detected through their e + e - decay. The observed channels are: All the exclusive channels are fully reconstructed and selected with kinematic fits 14.3 pb -1 of data in the  ’ energy region collected in year 2000 –12.4 pb -1 on resonance  ~32000 events –1.9 pb -1 off resonance  ~60 events Preliminar y

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  ' branching ratios E760E835-IE835-II (prelim.) Events~2400~13800~ ± ± ± ± ± ± ± ± ± ±0.007 M. Ambrogiani et al., Phys. Rev. D 62 (2000) T. A. Armstrong et al., Phys. Rev. D 55 (1997) 1153 Preliminar y

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  ' branching ratios J/  J/  0  0 J/  +  - e+e-e+e- Preliminar y

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Proton form factor in the time-like region Measurement of non resonant cross section for the process First order QED prediction: –At threshold: |G E |=|G M | (uniform angular distribution) –At high s: |G E | contribution negligible QCD asymptotic behavior: C and  free parameters Upper limits at 90% C.L. M. Andreotti et al., Phys. Lett. B 559 (2003) 20

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  final state selection Exactly 2 “on-time” clusters in the central calorimeter with high energy deposit and invariant mass within 20% of E CM No “undetermined-time” extra clusters with invariant mass within 35 MeV of the  0 mass 4C kinematic fit to  |cos(  * )| cut to improve signal to background ratio

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  background (feeddown) Background mainly from: 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 ISMD-2003, Krakow, September 5-11, 2003  c  18.9 pb -1 of data All the resonance parameters are measured in the  channel: M. Ambrogiani et al., Phys. Lett. B 566 (2003) 45

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  c ’  search E760:  c ’ search in the CBAL energy region (3594 MeV) E835-I: scan on a wider energy range T. A. Armstrong et al., Phys. Rev. D 52 (1995) 4839 22 M. Ambrogiani et al., Phys. Rev. D 64 (2001)

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  0  (E835-II) Preliminar y Taking from the PDG: Interference No Interference

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003  0  0 and  event selection  0 and  detected through their  decay 4  neutral events Search for  0 and  candidates cutting on invariant mass and opening angle of the photon pairs 4-C kinematic fit to

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Study of  0  0 in the  0 region Interference between resonant and non resonant process enhancing the resonance signal Resonant Interfering (helicity 0) Non-Interfering (helicity 1) M. Andreotti et al., hep-ex/ , to be published on PRL

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Study of   in the  0 region Preliminar y

Matteo Negrini ISMD-2003, Krakow, September 5-11, 2003 Conclusions Charmonium states have been investigated at FNAL in proton antiproton annihilation obtaining... Precision measurement of mass and width of the charmonium states Measurement of branching ratios Study of radiative decays: Search for states that need confirmation Interference between resonant and non-resonant multihadron production Proton form factor in the time-like region at s=10-15GeV 2