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Spectrometer overview and requirements

Spectrometer overview 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. SHiP (as of EOI).

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Spectrometer overview and requirements

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  1. Spectrometeroverview and requirements briefreminder of whatSHiPneeds (as of EOI) glimpse at vacuum tank and magnet EOI baseline"design" Whatnext, workahead: requirementsfrom full simulation

  2. SHiP (as of EOI) Scope of spectrometer in twopaddlestrokes (as of EOI): • Detecttwooppositelychargedparticleswith a vertex in the decay volume and measure an invariant mass • Make sure it's not background... HNLproducedfromcharmdecay at dump, before 60m muon shieldN 5m Two setups in series=> 2 decay volumes, Twospectrometers HNL daughters To be revisited for extended physics (other hidden particles or decays)

  3. EOI "SHiPcanbe made withexistingtechnologies" (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 view see Hans Danielson's and SergeijMovchan'stalks

  4. Magnet • Chosensuch as to give MS  Intrinsicresolution Thanks to W. Flegel Multiple Scattering Givensuch a magnet and tracker, we are stilldominated by MS (0.5% total x/x0 for 4 views/station) • Task: revisitmagnetrequirementsfrom detector simulation • Task: produce a conceptual design, with FEA

  5. 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 ?

  6. Vacuum suppose (conservative, no bake-out, startpumping): 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 Neededdistributedpumping speed S > Qoutgassing A / p = 5000 liter/s Thanks to G.Barber 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

  7. Assumptionsfor now ... (as of EOI) * 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 SergeijMovchan's talks

  8. Straw arrangement NA62 or LHCbOuterTracker

  9. 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

  10. Backgrounds • Main identified sources of backgrounds to HNL decays: • -A or -A inelastic interactions in restgas of fiducialvolume • strangeness-producing -A or -A interactions in last (few) interaction lengthsbeforefiducial volume, givingmainlyKLdecays • 2- combinatoricsfromspurious muon flux, givingfakevertices in fiducial volume • SHiPnow in the process of trying to redefine detector requirementsbased on more sophisticated MC simulationof signal and background processes • In parallel, investigatetechnological aspects

  11. Interactions in restgas • inel,Nscaleswith E and rate withnuclearthickness (N/cm2 ) • EOI: expect a few 105 neutrino interactions per 0.1m of W (int) per 21020 protons-on-target • for 40m of 1atm air, thiswouldscale down by a factor 40, thus to about 104neutrino interactions per 21020protons-on-target • Task: simulateactual-Air interactions with detector acceptance and revisitlimit on tank pressure => impact on vacuum system design. • NB: "high energy" neutrino flux isreasonablywellunderstood (depends on dump target, but not on whatcomesafter) • NB: inel,Aismanyorders of magnitude larger. But canbeVETOed... Requirement on VETO efficiency. Here, N = nucleon, not HNL in N/cm3, tungsten:air ratio  16200

  12. KLdecays (EOI) • Task: simulate KLdecayswithrealisticdetector => impact on trackermaterial budget, spatial resolution, magnet design

  13. HNL (signal)  DOCA / 2 plots from Thomas Ruf (work in progress) cm cm cm GeV/c2 GeV/c2

  14. Background from interactions  DOCA / 2 plots from Thomas Ruf (work in progress) cm cm cm GeV/c2 GeV/c2

  15. 2-muon combinatoricsbkg • Was not addressed at time of EOI • Assumedthat muon shieldwouldreduce muon flux to sufficientlylow flux • challenging... • and muon flux is not soeasilypredicted! Now • Task: simulate 2-muon combinatoricsas func of expectedmuon flux => define VETO efficiency, time resolution, spatial coverage and granularity...

  16. 2-muon combinatoricsbkg • Was not quantified in EOI • Assuming 1s spillwith 105comingthrough... • Number of time windowswith >1 muons • Can reduce by veto efficiencysquared… still not negligible? plots from Hans Dijkstra (work in progress)

  17. 2-muon combinatoricsbkg plots from Hans Dijkstra (work in progress)

  18. 2-muon combinatoricsbkg plots from Hans Dijkstra (work in progress)

  19. Still a lot of (fun) work to be done… Join the ship crew !

  20. bACKUP

  21. An alternative design low pressure drift gas p =10...100 mbar thinmylar (C-reinforced ?) window vacuum p<10-2 mbar vacuum p<10-2 mbar wire planes

  22. How much mass is there ? Material: dominated by the gas-confiningwalls • NA62-like: • one straw of 36um, 1cm, 5m contains 7.9g of PET • assume 1000 straws/view, 4 views, the mass in the circularacceptance of 5m is: mPET = 24.8kg • Including the impact angle (~28% more mass traversed) mPET = 31kg equivalent mass for perpendicular impact • Low-pressure window: • Circularwindow of 5m, try to getlessthan 15kg per window • For PET (1.4 g/cm3) thismeans a thickness of at most 0.55mm • For a para-aramid-reinforcedmylarwindow, carbon fibre & resindominate the mass (PET isonly for vacuum sealing), densitycanbe of order ~ 0.3 g/cm3equivalent (full surface) Is thatrealistic ? 2-layer view

  23. Who tried such a window before ?

  24. With 5m diameter… a preliminary FEA Thanks to C. Garion (TE-VSC) • Very preliminary estimate: window strength given by a multi-layered grid of carbon-fibreribbons 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.

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