1 / 15

p 0

Cooler CSB. Direct or Extra Photons in d+d  ap 0. p 0. Andrew Bacher for the CSB Cooler Collaboration ECT Trento, June 2005. Outline of Talk. Motivation and Overview Near Threshold Considerations Models of Continuum Processes Results of Simulations

dolph
Télécharger la présentation

p 0

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cooler CSB Direct or Extra Photons in d+dap0 p0 Andrew Bacher for the CSB Cooler Collaboration ECT Trento, June 2005

  2. Outline of Talk • Motivation and Overview • Near Threshold Considerations • Models of Continuum Processes • Results of Simulations • What Happens at Higher Energies? • Conclusion

  3. Motivation and Overview To investigate the nature of the underlying continuum in our near-threshold measurements of dd First, I will review why we think the events arise from d + d physical processes. (instead of from accidental background processes) Next, I will describe several models for these physical processes that might contribute to a continuum of events in the vicinity of the  peak in the missing-mass distribution.

  4. Near Threshold Considerations How our apparatus is optimized for near-threshold measurements. • Magnetic channel and 4He parameters • Pb Glass Arrays and  parameters • Results at 228.5 MeV and 231.8 MeV

  5. COOLER-CSB MAGNETIC CHANNEL • and Pb-GLASS ARRAYS • separate all 4He for total cross section measurement • determine 4He 4-momentum (using TOF and position) • detect one or both decay g’s from p0 in Pb-glass array Scintillators DE-2 E Veto-1 Veto-2 Pb-glass array 256 detectors from IUCF and ANL (Spinka) + scintillators for cosmic trigger Scintillator DE-1 Focussing Quads MWPC MWPCs Target D2 jet 228.5 or 231.8 MeV deuteron beam 20 Septum Magnet Separation Magnet removes 4He at 12.5 from beam at 6

  6. SINGLE AND DOUBLE GAMMA SIGNALS data for all of July run Beam left-side array A single g may be difficult to extract. But select on the similar locus on the other side of the beam, and the signal becomes clean. corrected g time keep above here g cluster energy We will require two g’s. List of requirements: > correct PID position in channel scintillator energy > correct range of TOF values > correct Pb-glass cluster energies and corrected times Many g’s come from beam halo hitting downstream septum.

  7. RESULTS Events in these spectra must satisfy: correct pulse height in channel scintillators usable wire chamber signals good Pb-glass pulse height and timing 228.5 MeV 66 events σTOT = 12.7 ± 2.2 pb Background shape based on calculated double radiative capture, corrected by empirical channel acceptance using 4He. Cross sections are consistent with S-wave pion production. σTOT/η 231.8 MeV 50 events Systematic errors are 6.6% in normalization. 100 σTOT = 15.1 ± 3.1 pb average Peaks give the correct π0 mass with 60 keV error. 50 η = pπ/mπ 0 0.1 0 0.2 missing mass (MeV)

  8. Models for Continuum Processes •  via double radiative capture (“Gardestig model” where each n-p pair in the beam and target initiates an npd reaction and the two ds coalesce.) •  via s-wave phase space (“Phase space model” where the matrix element is independent of energy and the directions of final state particles are uncorrelated.) •   via a CS allowed process (We need to discuss the nature of this CS-allowed process and the effort required to estimate its magnitude.) We have used Monte Carlo simulations based on the same GEANT model employed in the analysis of d + d  4He + 

  9. Simulations for the Double Radiative Capture Model Missing Mass Distributions of Events Ed = 231.8 MeV Calculated Efficiencies Starting Distribution Channel Efficiency Events at End of Channel Efficiency (%) Counts/(0.1 MeV) Gamma Efficiency Events with a two gamma condition missing mass (MeV) missing mass (MeV)

  10. Simulations for the  Phase Space Model Missing Mass Distributions of Events Ed = 231.8 MeV Calculated Efficiencies Starting Distribution Channel Efficiency Events at End of Channel Efficiency (%) Counts/(0.1 MeV) Gamma Efficiency Events with a two gamma condition missing mass (MeV) missing mass (MeV)

  11. Comparison of Radiative Capture and Phase Space Ed = 231.8 MeV Starting Distributions Events thru Channel with 2 gammas Phase Space Phase Space Counts/(0.1 MeV) Gardestig Counts/(0.1 MeV) Gardestig missing mass (MeV) missing mass (MeV) Result of Comparison:In our near-threshold measurements of d+d  4He + , our efficiency for the extraction of events in the underlying continuum is independent of the starting distribution.

  12. What Happens at Higher Energies? Motivations for work at higher energies include: (1) measuring the strength of p-wave CSB cross sections, and (2) determining how CSB amplitudes depend on energy. • To determine how the cross-section ratio CSB/continuum varies with energy, we need to consider how the cross section for each process scales with energy. In going from an energy near threshold, 230 MeV,up to an energy of 265 MeV, the s-wave cross section is predicted to increase by a factor of 3. • Other experimental considerations at higher energies include: Recoil alpha particles fill a larger cone and are harder to analyze with a magnetic channel. Gamma measurements with improved angle and energy resolution may allow reconstruction of the ° mass as a way of separating CSB from the continuum.

  13. Conclusion • In addition to the observation of the CSB reaction, d + d  4He + , the near-threshold measurements at IUCF have identified a continuum process that is probably due to the double radiative capture mechanism, d + d  4He +  +  suggested by Gardestig. • Using Monte Carlo simulations similar to those developed to model the CSB reaction, we are able to reproduce the shape of the observed continuum, but we are not able to distinguish the double radiative capture process from a pure s-wave phase space distribution. • Features of d + d measurements at higher energies (e.g., using the WASA detector at COSY) are discussed. Since both the CSB s-wave cross section and the double radiative capture process are expected to scale as the linear power of pp, we expect the ratio of CSB/continuum processes to be about the same.

  14. SEPARATION OF ap0 AND agg EVENTS Calculate missing mass from the four- momentum measured in the magnetic channel alone, using TOF for z-axis momentum and MWPC X and Y for transverse momentum. Major physics background is from double radiative capture. MWPC spacing = 2 mm Y-position (cm) [Monte Carlo simulation for illustration. Experimental errors included.] ap0 peak sTOT = 10 pb MWPC1 X-position (cm) agg prediction from Gårdestig agg background (16 pb) needed TOF resolution sGAUSS = 100 ps missing mass (MeV) Difference is due to acceptance of channel. Acceptance widths are: angle = 70 mr (H and V) momentum = 10% Cutoff controlled by available energy above threshold. Time of Flight (ΔE1 - ΔE2) (ns) .

  15. COMMISSIONING THE SYSTEM using p+d  3He+π0 at 199.4 MeV 3He events readily identified by channel scintillators. Pb-glass energy sums nearest neighbors. It is important to identify loss mechanisms. Recoil cone on first MWPC Construction of missing mass from TOF and position on MWPC. data FWHM = 240 keV Monte- Carlo 130 134 138 NOTE: Main losses in channel from random veto, multiple scattering, and MWPC multiple hits. Response matched to GEANT model. Efficiency (~ 1/3) known to 3%. Channel time of flight

More Related