1 / 10

Overview of the experiment

Overview of the experiment. Produce X - by the (K-,K+) reaction, make it stop in a target, and measure X-ray from X - atom. Physics: X -nucleus interaction, especially at nuclear peripheral Real part – shift of X-ray energy Imaginary part – width, yield

scottwebb
Download Presentation

Overview of the experiment

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. Overview of the experiment • Produce X- by the (K-,K+) reaction, make it stop in a target, and measure X-ray from X- atom. • Physics: • X-nucleus interaction, especially at nuclear peripheral • Real part – shift of X-ray energyImaginary part – width, yield • Candidates for proper targets are given by Batty-Friedmann-Gal [PRC59 (1999) 295]

  2. Setup overview (tentative) • K1.8 beamline. • The target is Pb: • Use other targets in the future • Target size: 20 mm (23 g/cm2) thick (range of 550 MeV/c X- is about 15 mm), 60 mm wide and 15mm high (depends on beam size). • K+ spectrometer: we cannot use SKS+ (~0.03 sr) -- acceptance is too small. We will use KURAMA (~0.2 sr) instead. • X-ray detector: Hyperball-J (~13%@558 keV) • Beam intensity: 2.3x106/spill (1 spill=4 sec) • in 100 shifts, 1.6x1012 K- in total

  3. Yield estimation Y=NK x sXx t x WK x eK x RX x RX x (1-hX) x eX x eo • Beam: NK (total number of K-) = 1.6×1012 • Target: • sX：　(differential) cross section = 300 mb/srTaken from IIjima et al. [NPA 546 (1992) 588-606] • t: target thickness （particles/cm2） = 6.6x1022 • RX: stopping probability of X in the target = 15%(according to a GEANT4 simulation: see later) • RX: branching ratio of X-ray emission = 15%(Taken from Fig. 2 of BFG paper) • hX: probability of self X-ray absorption in the target = 73%(GEANT4 simulation: mean free path for 558 keV X-ray is ~6 mm)

  4. K+ spectrometer • WK: acceptance = 0.2 sr • eK:detection efficiency = 0.51 (taken from the proposal of BNL-AGS E964 ) • X-ray detection • eX: X-ray detection efficiency = 6.5％[13% (from LOI) x 0.5 (in-beam live time)] • Others • eo: overall efficiency (DAQ, trigger, etc.) = 0.8

  5. Yield summary • Yield of X • production:2.6x106 • stopped: 3.9×105 • X-ray yield：　1000 • Comparison with BNL-AGS E964 • NK: x15, t x sX: x0.3, RX: x11, (DAQ: x0.8) Number of stopped X is 40 times larger • X-ray detection efficiency – about the same • Self-absorption becomes very severe. • While detector acceptance is much larger. • In total, we expect x30 more statistics  FEASIBLE

  6. simulation on X stopping • target: Pb 60 (wide) x 15 (high) x 20 (thick) mm3 • X production point (must be within target): • x: Gauss distribution of s=20 mm (beam size) • y: Gaussian, s=3.2 mm • z: uniform in the target • X momentum – assume Px, Py, Pz independent • x: uniform, -0.4~0.4 GeV/c (to match K+ spectrometer acceptance) • y: uniform, -0.22~0.22 GeV/c • z: Gaussian, 0.52 +- 0.2 GeV/c (elementary kinematics + Fermi momentum) • Average momentum: 0.59 GeV/c

  7. Simulation result • X stopping probability is ~100% for PX < 0.2 GeV/c, while it becomes 0 at PX = 0.65 GeV/c. • Total stopping probability ~ 0.2 • However, this dependsvery much on the PXspectrum – when <PX>is as high as 0.65 GeV/c,this reduces to 0.14 • Conservative to use0.15 as stopping probability stopping probability of X

  8. Simulation on X-ray absorbtion • Same target setup as stopping simulation • Emit 558 keV X ray from the X stopping point • Uniformly • limit |cos(q)| < 0.5 to avoid forward/backward where no Ge’s exist. • Result of absorption probability is 71% for case 1 and 73% for case 2 • For 412 keV X ray (N=1110), the result is83% for case 1 and 84% for case 2. • The difference looks quite small. • Only top/bottom detectors can detect X rays.

  9. X-ray background • Estimation based on E419 • E419: For 120k events of (p+,K+) reaction, we got 20 counts/5 keV around 560 keV. Compared to this: • Number of (K-,K+) events: x21 • g-ray detection efficiency: x4 • Other effect:x2 (considering different reaction)  ~3500 counts/ 5keV • Continuous BG is OK • Is there line BG in 558±10 keV? • How can we estimate?

  10. Summary • The experiment looks feasible. • X-ray yield: ~1000 • Background: ~3500 • Statistical precision of X ray energy ~ 50 eV • systematic error will be dominant? • Line BG may be a problem • none found so far, but ... • Another setup possible • Diamond + Pb + Si strip (E964-like) • Yield estimation/simulation will come soon

More Related