p 0

1. p0 Cooler CSB Observation of ddαπ0 Ed Stephenson Indiana University Cyclotron Facility CSB–VII Trento, Italy June 13-17, 2005 Review of the experiment

2. Getting d + d → 4He + π0 right Ed Stephenson Indiana University Cyclotron Facility Bloomington, IN Workshop on Charge Symmetry Breaking Trento June 13-17, 2005 Before you start, remember the history… suggested by Lapidus [JETP 4, 740 (’57)] review by Banaigs [PRL 58, 1922 (’87)] upper limit at 0.8 GeV positive claim by Goldzahl [NP A 533, 675 (’91)] double radiative capture by Dobrokhotov [PRL 83, 5246 (’99)} Be prepared for… very low cross sections ( ~ pb) interference from double radiative capture

3. … thanks to Andy Bacher, Mark Pickar, and Georg Berg PLAN Search just above threshold (225.5 MeV) (No other π channel open for d+d.) Capture forward-going 4He. Pb-glass arrays for π0 γγ. Efficiency on two sides ~ 1/3. Insensitive to other products (γbeam = 0.51) Crucial features: Pb-glass has low backgroud Windowless target Channel with good TOF 6 bend in Cooler straight section Target upstream, surrounded by Pb-glass Magnetic channel to catch 4He (~100 MeV) Reconstruct kinematics from channel time of flight and position. (Pb-glass energy and angle too uncertain for π0 reconstruction. αγγ looks the same.) Target density = 3.1 x 1015 Stored current = 1.4 mA Luminosity = 2.7 x 1031 /cm2/s Expected rate ~ 5 /day

4. 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 228.5 or 231.8 MeV deuteron beam Target D2 jet 20 Septum Magnet Separation Magnet removes 4He at 12.5 from beam at 6 Actual Pb-glass arrangement

5. 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) .

6. 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

7. IDENTIFICATION OF 4He IN THE CHANNEL [online spectra for 5-hour run] DE2 Proton rate from breakup ~ 105 /s. Handle this with: veto longer range protons set timing to miss most protons reduce MWPC voltage to keep Z=1 tracks below threshold divide ΔE-1 into four quadrants Set windows around 4He group. Rate still 103 too high. DE1-C E We absolutely need coincidence with the Pb-glass (decay g) to extract any signal at all. The 4He flux, most likely from (d,α) reactions, is smooth in momentum and angle. It represents the part of phase space sampled by the channel. DE2

8. 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.

9. OTHER ITEMS Stuff you have to get right! Energy of Cooler beam known from ring circumference and RF frequency (~ 16 keV) 3He cone opening angle (deg) Calculation of He momentum depends on good model of energy loss in channel. This is also needed to set channel magnets. RF frequency (MHz) Calculation of time of flight required knowing the time offsets for each scintillator PMT and tracking changes through the experiment. Final adjustments were made in replay. Cooler circumference (m) Run plan: started in June at 228.5 MeV to keep cone in channel during 1-week break decided to raise energy to 231.8 MeV demonstrate that peak stayed at pion mass provide two cross sections to check energy dependence (Limits were luminosity, rate handling, available time.) average circumference = 86.786 ± 0.003 m

10. For good resolution, we need FWHM ~ 0.2 ns. Time Stability Problem PMT signal transit time drifts and occasionally jumps as the tube ages, responding to heat. A narrow peak helps p0 separation statistically. DE2 Timing is affected when people change PMT voltage or swap other equipment. There are 6 PMTs used for TOF. Mean-timing the ones for DE2 leaves 4 free time parameters. A This is also connected to missing mass reconstruction errors arising from 6° magnet dispersion, pulse height, and position effects. B C D DE1

11. To make run-by-run corrections to TOF, we need a marker. We use deuterons that stop and the back of the E scintillator. Choose Energy Choose Trajectory deuteron gate E XY-1 Resulting TOF peaks DE1 scintillator: A d p B DE2 XY-2 C XY-3 D

12. Results for June run: 1 ns

13. Calibrating the luminosity of the IUCF Cooler PLAN: Monitor with d+d elastic. Measure ratio of d+d cross section to d+p (known) with molecular HD target. 44° 25° beam deuteron telescope (present only for calibration) tapered/displaced scintillator pair for added position info. Reference d+p cross sections: thesis of Karsten Ermisch, KVI, Groningen (‘03). dσ/dΩ (mb/sr) NOTE: Target distribution monitored using position sensitive silicon detector looking at recoil deuterons from small-angle scattering. Detector acceptance determined using Monte-Carlo simulations. dot = 108 MeV circle = 120 MeV X = 135 MeV line = adopted cross section at 116 MeV θc.m.

14. Recent measurements by the Japanese confirm their old cross section values at 135 MeV and disagree with the data from the KVI. Japanese data original d-beam data from RIKEN remeasurements from RIKEN and RCNP KVI data . An independent measurement is needed !

15. Forward scintillator – silicon system position-sensitive silicon detector distinguish H from D by pulse height in silicon beam target ½-inch copper absorbers delta- E E H silicon position D E energy Position becomes template for target distribution. Issues include reaction losses and multiple scattering.

16. Detail on second luminosity monitoring system oppositely tapered scintillators for X-position beam two halves displaced vertically to check vertical centering results not satisfactory, relied on transit alignment

17. Scintillator spectra: (44° – 44° coincidence) right F – B F + B x = xL by xR gated on deuterons 44° scintillator, back vs. front pulse height (zero suppressed to remove no-hits) beam z-position angle left position span angle beam z-position deuterons cut protons

18. 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 Spectra are essentially free of random background. η = pπ/mπ 0 0.1 0 0.2 missing mass (MeV)

19. EXISTENCE? For the candidate events, check to see whether there is any cone. XY-1 position T = 228.5 MeV, qmax = 1.20° T = 231.8 MeV, qmax = 1.75°

20. EXISTENCE? For the candidate events, check to see whether there is any cone. XY-1 position T = 228.5 MeV, qmax = 1.20° T = 231.8 MeV, qmax = 1.75° Circles with these centers also minimize the missing mass width.

21. missing mass (MeV  100) T = 228.5 MeV T = 231.8 MeV 135 MeV raw TOF IS IT CORRECT? The missing mass should be independent of the TOF. A B In fact, the time adjustments are made separately for each segment of DE1. C D

22. Experimental (active): Theoretical: C. Allgower, A.D. Bacher, C. Lavelle,H. Nann, J. Olmsted, T. Rinckel, and E.J. Stephenson,Indiana University Cyclotron Facility, Bloomington, IN 47408 M.A. Pickar, Minnesota State University at Mankato, Mankato, MN 56002 P.V. Pancella, Western Michigan University, Kalamazoo, MI 49001 A. Smith, Hillsdale College, Hillsdale, MI 49242 H.M. Spinka, Argonne National Laboratory, Argonne, IL 60439 J. Rapaport, Ohio University, Athens, OH 45701 Antonio Fonseca, Lisbon Anders Gardestig, Indiana Christoph Hanhart, Juelich Chuck Horowitz, Indiana Jerry Miller, Washington Fred Myhrer, South Carolina Jouni Niskanen, Helsinki Andreas Nogga, Arizona Bira van Kolck, Arizona Technical support: J. Doskow, G. East, W. Fox, D. Friesel, R.E. Pollock, T. Sloan, and K. Solberg, Indiana University Cyclotron Facility, Bloomington, IN 47408 Experiment (historical): V. Anferov, G.P.A. Berg, and C.C. Foster, Indiana University Cyclotron Facility, Bloomington, IN 47408 B. Chujko, A. Kuznetsov, V. Medvedev, D. Patalahka, A. Prudkoglyad, and P.A. Semenov, Institute for High Energy Physics, Protvino, Moscow Region, Russia 142284 S. Shastry, State University of New York, Plattsburgh, NY 12901 spokesperson for CE-82 and letter of intent post-doc technical manager student Underline did June/July shift work