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

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Presentation on theme: "1 Acceptance & Scraping Chris Rogers Analysis PC 04-05-06."— Presentation transcript:

1 1 Acceptance & Scraping Chris Rogers Analysis PC

2 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 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 4 Effect on Emittance Measurement Measured x variance ( meas ) is related to true x variance, ( true ) from rejected signal by: N meas meas = N true true - N rs rs Ref: Analysis PC Aug N is number of muons rs is Rejected signal Assume that the scraping aperture is at > 2  x and 2  px Then after some algebra emittance  is given by  meas >~  true [1 - (2 2 -1) N rs /N true ] 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 More like The emittance measurement is very sensitive to transmission

5 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 6 Scraping in a Neutrino Factory In a Neutrino Factory cooling channel, scraping is a first order effect on transmission into an accelerator acceptance Typical input emittances ~ 12  transverse (FS2A) vs scraping aperture ~ 20  We should be aiming to measure it to the same high precision as we aim to measure emittance FS2 Z (m) nn Emittance  //  trans

7 7 Scraping Aperture 1 TransportAperture 2 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 1TransportAperture 2 x px

8 8 Halo 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 Soft edged Hard edged

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

10 10 Physical Model No absorbers or windows Hard edge - Kill muons that scrape TrackerAFC Tracker RFCC

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

12 12 Max Radius vs z - Lcan spread 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 L can radius z Radius of MICE acceptance vs z

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

14 14 Max Radius vs z - 10  beam Repeat the exercise but now use a full 10  beam Max diffuser = Max window 1 = Max window 2 = Max TOFII = Max. radius z

15 15 W Lau, CM 14

16 16 Gaussian 10 pi beam at Diffuser 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 Diffuser Radius

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

18 18 R at tracker windows 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? Upstream Z~-4.6 m Downstream Z~+4.6m

19 19 R at solenoid end 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 Z=6.111 Z=6.211

20 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 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


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