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Spectrometer overview and requirements

This document provides a comprehensive overview of the SHiP spectrometer's design requirements as of the Expression of Interest (EOI), detailing essential aspects such as the detector setup, magnet specifications, vacuum requirements, and background noise considerations. It outlines critical tasks for simulator development, including the detection of oppositely charged particles in decay volumes, assessment of background noise from neutrino interactions, and the conceptual design of the spectrometer system. Upcoming tasks emphasize the optimization of detector components and the investigation of cost-effective fabrication techniques.

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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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