Acceptance & Scraping

1. Acceptance & Scraping Chris Rogers Analysis PC 04-05-06

2. Overview • Why it isn’t easy to place a constraint on detector apertures • General view on the acceptance of the cooling channel • A better - but still not perfect - requirement on the measurement of high emittance particles • Implications

3. Effect of Losing Muons • What is the effect of losing muons? • How does it effect emittance measurement • Is the standard criterion (0.999 efficiency) sufficient? • Quantify the argument that “losing signal muons (because the TOF is too small) at larger amplitude will bias the measurement more” • How does a mis-measurement effect the measurement of cooling channel efficiency? • “Surely muons on the edge of the beam will never make it into an accelerating structure anyway” • Consider the “acceptance measurement” (number of muons within a certain acceptance)

4. Effect on Emittance Measurement • Measured x variance (<x2>meas) is related to true x variance, (<x2>true ) from rejected signal by: • Nmeas<x2>meas = Ntrue<x2>true - Nrs<x2>rs • Ref: Analysis PC Aug 19 2005 • N is number of muons • rs is Rejected signal • Assume that the scraping aperture is at > 2sxand 2spx • Then after some algebra emittance e is given by • emeas >~ etrue [1 - (22-1) Nrs/Ntrue] • Losing signal at high emittance will bias the measurement more • This means that for a 1e-3 emittance requirement the efficiency requirement is much tougher than 0.999 • More like 0.9995-0.9998 • The emittance measurement is very sensitive to transmission

5. Beam Dependence • But the number of muons at high amplitude is very beam dependent • Different beams will have very different tails • It is not satisfactory to place a requirement on detector size based on such a quantity • The beam I use today will give a completely different requirement than the beam I use tomorrow • Really, we want to use these muons to demonstrate that we understand the acceptance of MICE • Scraping is an important effect in a Neutrino Factory cooling channel

6. Scraping in a Neutrino Factory FS2 etrans Emittance nm e// • In a Neutrino Factory cooling channel, scraping is a first order effect on transmission into an accelerator acceptance • Typical input emittances ~ 12 p transverse (FS2A) vs scraping aperture ~ 20 p • We should be aiming to measure it to the same high precision as we aim to measure emittance FS2 Z (m) Z (m)

7. Scraping Aperture 1 Transport Aperture 2 px • There is a closed region in phase space that is not scraped • I want to measure the size of this region • It is independent of the particular beam going through MICE Aperture 1 Transport Aperture 2 x

8. Halo Hard edged Soft edged • Consider hard edge accelerator • Kill muons that touch the walls • No RF or liquid Hydrogen • In a realistic accelerator, there will be some region beyond the scraping region • A reasonable constraint is that we should be able to measure all muons that make it through the hard-edged cooling channel • To get a more serious constraint, need to understand the reduction in cooling channel transmission quantitatively

9. Apertures under investigation TOF II Diffuser Tracker Window • Three “apertures” in MICE that are under investigation • TOF II • Diffuser • Tracker helium window

10. Physical Model 1334 1000 1494 430 30 40 15 842 150 200 150 630 230 No absorbers or windows Tracker AFC AFC AFC Tracker RFCC RFCC Hard edge - Kill muons that scrape

11. Beams • Consider two sets of particles • “Phase space filling” beam • 10 pi beam • Phase space filling • Place muons on a grid in x, px • Muons at x = 0, 10, 20… and px = 0, 10, 20, … • Add spread in either Lcan or pz • 10 pi gaussian beam, 25 MeV rms energy spread • Cuts at 190<E<260 MeV

12. Max Radius vs z - Lcan spread Radius of MICE acceptance vs z radius • This is a scatter plot of muons travelling down the cooling channel • Vertical lines come because I am only sampling the beam occasionally • Drawn a line for the maximum radius of the beam • This is using the beam with a spread in Lcan z

13. Max Radius vs z - Pz spread Max. radius • Repeat the exercise but now use a spread in Pz z

14. Max Radius vs z - 10 p beam Max. radius • Repeat the exercise but now use a full 10 p beam • Max r @ diffuser = 0.128 • Max r @ window 1 = 0.136 • Max r @ window 2 = 0.121 • Max r @ TOFII = 0.273 z

15. W Lau, CM 14

16. Gaussian 10 pi beam at Diffuser Diffuser Radius • A significant number of tracks outside of 10 cm radius • Note some of these tracks also pass through the diffuser mechanism itself • It may be possible to arrange the beamline to run in a less focussed mode with higher energy • Try to punch muons through the diffuser mechanism to populate these tails

17. Absorber window Thickness as a function of R (M Green)

18. R at tracker windows Upstream Z~-4.6 m Downstream Z~+4.6m • No tracks pass through the edge of the windows • But the window gets increasingly thick towards the edges • What effect does this have on emittance?

19. R at solenoid end Z=6.211 Z=6.111 • The downstream solenoid ends at z=6.011 • This is the downstream end of the last coil • But the high amplitude tracks are cut in the tracker • Don’t strike the tracker end r r

20. x at TOF • The edge of the beam lies beyond the tof half width • While this doesn’t look so bad, if I choose to use a different beam it may well get worse • Without materials so this is really a minimum • It may be possible to make the TOF larger than the Ckov and sacrifice some PID in these regions • To avoid a very large Ckov

21. Summary • I would be happier if the TOF could be bigger • It may be possible to compromise by leaving the calorimeter smaller and losing PID on the fringe • While tracks miss the tracker window, I am slightly nervous about the thickness towards the edge • I would be happier if the diffuser could be bigger