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Acceptance & Scraping

Chris RogersAnalysis PC04-05-06

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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

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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)

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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 > 2x and 2px

Then after some algebra emittance is given by meas >~ true [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

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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

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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

FS2Z (m) Z (m)

n

Em

itta

nce

//

trans

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Scraping

Aperture 1 Transport Aperture

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 1

Transport Aperture 2

x

px

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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 edgedHard edged

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Apertures under investigation

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

TOF IIDiffuser Tracker

Window

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Physical Model842 430 30 40

230

15

150 630

No absorbers or windows

Hard edge -Kill muons that scrape

100014941334

150 200

Tracker AFCAFCAFCTracker RFCC RFCC

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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

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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 Lcan

radiu

s

z

Radius of MICE acceptance vs z

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Max Radius vs z - Pz spread

Repeat the exercise but now use a spread in Pz

Max.

rad

ius

z

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Max Radius vs z - 10 beam

Repeat the exercise but now use a full 10 beam Max r @ diffuser = 0.128 Max r @ window 1 = 0.136 Max r @ window 2 = 0.121 Max r @ TOFII = 0.273

Max.

rad

ius

z

15

W Lau,CM 14

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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

DiffuserRadius

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

15014013012011010090807060504030201000

1

2

3

4

5

6

7

8

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Window Radius (mm)

Win

dow

Th

ick

nes

s (m

m)

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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?

UpstreamZ~-4.6 m

DownstreamZ~+4.6m

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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

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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

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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