00 Cooler CSB Direct or Extra Photons in d+d  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 What Happens at Higher Energies? Conclusion

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.

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

Target D 2 jet Pb-glass array 256 detectors from IUCF and ANL (Spinka) + scintillators for cosmic trigger or MeV deuteron beam Separation Magnet removes 4 He at 12.5  from beam at 6  20  Septum Magnet Focussing Quads MWPCs Scintillator  E-1 Scintillators  E-2 E Veto-1 Veto-2 MWPC COOLER-CSB MAGNETIC CHANNEL and Pb-GLASS ARRAYS separate all 4 He for total cross section measurement determine 4 He 4-momentum (using TOF and position) detect one or both decay  ’s from  0 in Pb-glass array

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

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

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  4 He + 

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

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

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

What Happens at Higher Energies? 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. 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.

Conclusion In addition to the observation of the CSB reaction, d + d  4 He + , the near-threshold measurements at IUCF have identified a continuum process that is probably due to the double radiative capture mechanism, d + d  4 He +  +  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 p p, we expect the ratio of CSB/continuum processes to be about the same.

SEPARATION OF  0 AND  EVENTS MWPC 1 X-position (cm) Y-position (cm) Time of Flight (ΔE 1 - ΔE 2 ) (ns) needed TOF resolution  GAUSS = 100 ps MWPC spacing = 2 mm 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. [Monte Carlo simulation for illustration. Experimental errors included.]  0 peak  TOT = 10 pb  background (16 pb)  prediction from Gårdestig Difference is due to acceptance of channel. Acceptance widths are: angle = 70 mr (H and V) momentum = 10% missing mass (MeV) Cutoff controlled by available energy above threshold.. Major physics background is from double radiative capture.

COMMISSIONING THE SYSTEM using p+d  3 He+π 0 at MeV 3 He events readily identified by channel scintillators. Recoil cone on first MWPC Channel time of flight Construction of missing mass from TOF and position on MWPC. FWHM = 240 keV Pb-glass energy sums nearest neighbors. Response matched to GEANT model. Efficiency (~ 1/3) known to 3%. data Monte- Carlo NOTE: Main losses in channel from random veto, multiple scattering, and MWPC multiple hits. It is important to identify loss mechanisms.