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Spectrometeroverview and requirements

brief reminder of what SHiP needs (as of EOI)

glimpse at vacuum tank and magnet

EOI baseline "design"

What next, work ahead: requirements from full simulation

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SHiP (as of EOI)

Scope of spectrometer in two paddle strokes (as of EOI):

Detect two oppositely charged particles with a vertex in the decay volume and measure an invariant mass

Make sure it's not background...

HNL produced from charm decay at dump, before 60m muon shield N

5m

Two setups in series => 2 decay volumes, Two spectrometersHNL

daughters

To be revisited for extended physics

(other hidden particles or decays)

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EOI

"SHiP can be made with existing technologies"

(but does not have to…)

Magnet:

simple affordable warm dipole, "à-la LHCb"

Tracker:

copy beautiful, super light NA62 tracker

i.e. x/x0=0.11% per viewsee Hans Danielson's and Sergeij Movchan's talks

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Magnet

Given such a magnet and tracker, we are still dominated by MS (0.5% total x/x0 for 4 views/station)

Thanks to W. Flegel

Task: revisit magnet requirements from detector simulation

Task: produce a conceptual design, with FEA

Chosen such as to give MS Intrinsic resolution

Multiple Scattering

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Choice of dimensions (as of EOI)

Yield scales roughly with diameter square

For 5m, a decay volume of about 40 m seems best

Task: Is a 5m diameter still resonable ? In view also of extended physics program, is it optimal ?

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Vacuum

EOI: require p < 1e-2 mbar (NA62 < 1e-5mbar)

Task: define vacuum requirements

Task: investigate possible (cost effective) fabrication techniques, identify possible manufacturers, safety issues

Task: conceptual design of end flanges, FEA

Task: conceptual design of vacuum system

suppose (conservative, no bake-out, start pumping): Qoutgassing = 5∙10-8 mbar liter s-1 cm-2 , surface A = 5000 cm ∙ (250 cm) 2 = 109 cm2 required pressure p < 10-2 mbar Needed distributed pumping speed S > Qoutgassing A / p = 5000 liter/s

Thanks to G.Barber

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Assumptions for now ... (as of EOI)

Item NA62 SHiP

Diameter 2.5 m 5 m

Design rate max 500kHz/straw 2kHz/straw (ø1cm)*

Vacuum requirement p < 1e-5 mbar 1e-2 mbar

Views X, X+45°, X-45°, Y X, X+few°, X-few°, Y

spatial resolution per coord

per space point≤ 130um≤ 80um

similar or better

average track efficiency near 100% similar or better :-)

* assumed ~1e6 muons in whole aceptance per 1s spill

How do these impact the design ?

What needs to be modified from NA62 to SHiP ?

see Hans Danielson's and Sergeij Movchan's talks

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Straw arrangement

NA62 or LHCb Outer Tracker

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Tracker: some work ahead

Task: build a prototype 5m long straw tube

Task: tests on different straw geometries – (larger diameter ? thinner wall ?)

Task: GARFIELD simulations (signal and wire deflection)– check effect of magnetic stray field

Task: define/identify readout front-end electronics

Task: study other tracker designs ?– e.g. low-pressure drift chamber

Task: optimal geometry (layout, straw arrangements, stereo...) to be defined from full simulation

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Backgrounds

Main identified sources of backgrounds to HNL decays:– -A or -A inelastic interactions in rest gas of fiducial volume– strangeness-producing -A or -A interactions in last (few) interaction

lengths before fiducial volume, giving mainly KL decays

– 2- combinatorics from spurious muon flux, giving fake vertices in fiducial volume

SHiP now in the process of trying to redefine detector requirements based on more sophisticated MC simulation of signal and background processes

In parallel, investigate technological aspects

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Interactions in rest gas

inel,N scales with E and rate with nuclear thickness (N/cm2 )

EOI: expect a few 105 neutrino interactions per 0.1m of W (int) per 21020 protons-on-target

for 40m of 1atm air, this would scale down by a factor 40, thus to about 104 neutrino interactions per 21020 protons-on-target

Task: simulate actual -Air interactions with detector acceptance and revisit limit on tank pressure => impact on vacuum system design.

NB: "high energy" neutrino flux is reasonably well understood (depends on dump target, but not on what comes after)

NB: inel,A is many orders of magnitude larger. But can be VETOed... Requirement on VETO efficiency.

in N/cm3, tungsten:air ratio 16200

Here, N = nucleon, not HNL

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KL decays (EOI)

Task: simulate KL decays with realistic detector => impact on tracker material budget, spatial resolution, magnet design

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HNL (signal)

plots from Thomas Ruf(work in progress)

DOCA / 2

cm cm

GeV/c2 GeV/c2

cm

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Background from interactions

plots from Thomas Ruf(work in progress)

DOCA / 2

cm cm

GeV/c2 GeV/c2

cm

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2-muon combinatorics bkg

Was not addressed at time of EOI

Assumed that muon shield would reduce muon flux to sufficiently low flux– challenging...– and muon flux is not so easily predicted!

Now

Task: simulate 2-muon combinatorics as func of expected muon flux => define VETO efficiency, time resolution, spatial coverage and granularity...

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2-muon combinatorics bkg

Was not quantified in EOI

Assuming 1s spill with 105 coming through...

Number of time windows with >1 muons

Can reduce by veto efficiency squared… still not negligible?

plots from Hans Dijkstra(work in progress)

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2-muon combinatorics bkg

plots from Hans Dijkstra(work in progress)

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2-muon combinatorics bkg

plots from Hans Dijkstra(work in progress)

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Still a lot of (fun) work to be done…

Join the ship crew !

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BACKUP

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An alternative design

vacuump<10-2 mbar

vacuump<10-2 mbar

thin mylar (C-reinforced ?) windowlow pressure drift gasp =10...100 mbar

wire planes

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How much mass is there ?

Material: dominated by the gas-confining walls

NA62-like:– one straw of 36um, 1cm, 5m contains 7.9g of PET– assume 1000 straws/view, 4 views, the mass in the circular acceptance

of 5m is: mPET = 24.8kg

– Including the impact angle (~28% more mass traversed) mPET = 31kg equivalent mass for perpendicular impact

Low-pressure window:– Circular window of 5m, try to get less than 15kg per window– For PET (1.4 g/cm3) this means a thickness of at most 0.55mm– For a para-aramid-reinforced mylar window, carbon fibre & resin

dominate the mass (PET is only for vacuum sealing), density can be of order ~ 0.3 g/cm3 equivalent (full surface)

Is that realistic ?

2-layer view

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Who tried such a window before ?

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With 5m diameter… a preliminary FEA

Very preliminary estimate: window strength given by a multi-layered grid of carbon-fibre ribbons with 60% Kevlar, 40% resin, and filling about 20% of the plane. With a thickness of 1 mm one can reach 500 mbar with a displacement at this pressure of about 550 mm. One has about 6 kg of Kevlar+resin and 2.8 kg of Mylar.

My preliminary conclusion: This would easily allow to work e.g. at 100 mbar.

But: Can one make such a window at all ?– Would require building a “small” prototype (1.5 – 2m diameter)

Also to check: drift diffusion ~ 1/sqrt(p), number of primaries, etc.

Thanks to C. Garion (TE-VSC)