1 / 11

HAPPEX-III and PVDIS targets

HAPPEX-III and PVDIS targets. D.S. Armstrong July 22 ‘08. Pointing angle measurements – water cell target some old-style nuclear physics… 2) Cryotargets 20 vs. 25 cm racetrack cells – issues. Pointing Angle Measurement. Important for Q 2 measurement

ttemple
Download Presentation

HAPPEX-III and PVDIS targets

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. HAPPEX-III and PVDIS targets D.S. Armstrong July 22 ‘08 • Pointing angle measurements – water cell target • some old-style nuclear physics… • 2) Cryotargets • 20 vs. 25 cm racetrack cells – issues.

  2. Pointing Angle Measurement • Important for Q2 measurement • Use nuclear recoil technique as was done for HAPPEX-II/HAPPEX-He: • Need targets with different recoil (i.e. different mass) to maximize precision • Can use elastic scattering (M*=M) or inelastic to nuclear excited states (M*M) • At 1.18 GeV, 13.8°: • E – E’ • ¹H 41.3 MeV • 9Be 4.4 MeV • 16O 2.5 MeV • 181Ta 0.2 MeV Thus H2O target gives close to optimal performance; BeO possible, much less lever arm in E – E’, TiH has engineering problems. Dave Meekins designed water cell: 5 mm H2O, 2 1-mil thick steel windows. Note: cannot run with cryotargets; need to de-install water cell to install cryotargets (roughly 2-3 day turnaround)

  3. Water cell results from HAPPEX-II Determined  to 0.01° in 2005 Note: Compared to 6°, Q2/ is 42% as large at 13° and 24% as large at 20° scattering angles

  4. Water cell for HAPPEX-III Will H2O target work at HAPPEX-III, PVDIS kinematics? H-II: E = 2.76 GeV =6.1° Q2 =0.085 GeV2 q=1.47 fm-1 H-III: E =3.46 GeV =13.8° Q2 =0.625 GeV2 q=4.0 fm-1 H-III (2-pass) E =2.32 GeV =13.8° Q2 =0.290 GeV2 q=2.7 fm-1 (not feasible) H-III (1-pass) E =1.18 GeV =13.8° Q2 =0.077 GeV2 q=1.41 fm-1  go to 1-pass beam for HAPPEX-III pointing measurement (cross sections about 30% of HAPPEX-II values) 1-pass 2-pass McCarthy and Sick, Nucl. Phys. A 150(1970)63

  5. Water cell – excited 16O states test 1-pass 2-pass T.N. Buti, PhD thesis (MIT, 1984); T.N. Buti et al. Phys. Rev. C 33(1986)755

  6. Water cell for PVDIS PVDIS (1-pass) E =1.2 GeV =12.9° q=1.36 fm-1 (no problem) “ =20° q=2.11 fm-1 (more of a challenge) at 20°: hydrogen elastic cross section down by factor 30 vs. H-II : ratio of elastic 16O/hydrogen similar to H-II : 16O excited states down relative to hydrogen elastic by factors of: 5 (31-), 8 (11-) and 20 (21+) Conclusion: Doable, but fits will have to rely on 16O elastic and the 31- (6.13 MeV) state entirely (I have not looked into 56Fe peaks, don’t expect to see them)

  7. Summary: pointing angle measurement • Water cell is best choice, if one can tolerate the changeover time (scheduling) • Could use BeO, Ta, as less-invasive alternates to water cell… • Need to go to 1-pass beam for both HAPPEX-III and PVDIS  measurements. • PVDIS  measurement at 20° with water cell more challenging, but precision demands reduced…. However PVDIS proposal goal is a Q2 contribution to error budget of 0.12% at =20° which means 0.2 mrad (0.01°), which matches HAPPEX-II precision…

  8. Cryotargets for HAPPEX-III/PVDIS • HAPPEX-II used 20 cm “racetrack” cell (design: Dimitri Margaziotis, Cal State LA) • Excellent boiling performance • Geometry – no problem using • at HAPPEX-III/PVDIS angles with • up to 4 mm raster • (vertical acceptance is issue) • - PVDIS asks for 25 cm version

  9. Cryotargets – issues • Xiaochao and I met with Dave Meekins (July 3): • Need to build to ASME code (CFR 851: DOE Worker Safety and Health Programs, new as/or Feb 9 2006) • Code for pressure vessels: 1/16” walls (62.5 mils!! – reminder, HAPPEX-II windows 3-7 mils) • need exemption: paperwork, reviews…. Dave needs choice on cell geometry by Labour day to meet schedule. • Could have identical cells (if we want) for PVDIS, HAPPEX-III: • act as mutual spares in case of leaks; changeover of lH2 to lD2 on a loop is a couple of shifts; much better than replacing entire cell block on target ladder…..

  10. Cell length for HAPPEX-III • Should we go to 25 cm cell also? • Advantages: • Swap-compatible with PVDIS cell (spares) • Targets group only has to make/certify one design • Ratio of Al (windows) to lH2 smaller by 0.8 • - reduced QE background • - perhaps reduced boiling (if film boiling at window dominates) • (Maybe) reduced acceptance at detector for Al windows • Disadvantages: • Increase radiative tail losses: 20% increase in radiative effects, taking into account Al windows; and, they are the “worst” kind (before scattering vertex, reduces asymmetry) • Perhaps a bit harder to manufacture; can same window thicknesses be maintained as for 20 cm cell? • Maybe boiling performance worse, if bulk-dominated… • Dave Meekins: cryogen load scales as dE/dx times target length; 2nd-order effects not well known. Will do some fluid flow optimization after we settle on geometry.

  11. Aluminum window thickness • HAPPEX-1 15 cm “beer can” cell: • HAPPEX-II 20 cm “racetrack” cell: Al background: (1.4  0.1) % Al background: (0.91  0.12) % (2004) (0.76  0.25) % (2005) Propose asking for 5 mil entrance/exit/side walls Machining and measurement tolerances … Need integrating mode data with variable density gas (target warming) to scale “xt” factor

More Related