The hadronic beamline of the ENUBET neutrino beam
ENUBET collaboration, C. Delogu, F. Acerbi, A. Berra, M. Bonesini, A. Branca, C. Brizzolari, G. Brunetti, M. Calviani, S. Capelli, S. Carturan, M.G. Catanesi, S. Cecchini, N. Charitonidis, F. Cindolo, G. Collazuol, E. Conti, F. Dal Corso, G. De Rosa, A. Falcone, A. Gola, C. Jollet, V. Kain, B. Klicek, Y. Kudenko, M. Laveder, A. Longhin, L. Ludovici, E. Lutsenko, L. Magaletti, G. Mandrioli, A. Margotti, V. Mascagna, N. Mauri, L. Meazza, A. Meregaglia, M. Mezzetto, M. Nessi, A. Paoloni, M. Pari, E. Parozzi, L. Pasqualini, G. Paternoster, L. Patrizii, M. Pozzato, M. Prest, F. Pupilli, E. Radicioni, C. Riccio, A.C. Ruggeri, C. Scian, G. Sirri, M. Stipcevic, M. Tenti, F. Terranova, M. Torti, E. Vallazza, F. Velotti, M. Vesco, L. Votano
TThe hadronic beamline of the
ENUBET neutrino beam
C. Delogu, on behalf of the ENUBET collaboration ∗ INFN Sezione di Padova, via Marzolo 8, Padova, ItalyDepartment of Physics, Universit`a di Padova, via Marzolo 8, Padova, Italy
Abstract
The knowledge of initial flux, energy and flavour of current neutrino beams is cur-rently the main limitation for a precise measurement of neutrino cross sections. TheENUBET ERC project, part of the CERN Neutrino Platform as NP06/ENUBET, isstudying a facility based on a narrow band beam capable of constraining the neutrinofluxes normalization through the monitoring of the associated charged leptons in aninstrumented decay tunnel (tagger). Furthermore, in narrow-band beams, the trans-verse position of the neutrino interaction at the detector can be exploited to determinea priori with significant precision the neutrino energy spectrum without relying on thefinal state reconstruction.A key element of the project is the design and optimization of the hadronic beamline.It requires an efficient focusing and collimation over short distances in order to minimizethe fraction of secondary mesons decaying before the tunnel entrance and to reduce thebackground on the tunnel walls coming from particles different from the large angledecay products.This poster will present progress on the studies of the proton extraction schemes.It will also show a realistic implementation and simulation of the beamline, both ina configuration with a single dipole magnet for charge and momentum selection andin a recently studied one with a double dipole providing a larger bendind angle, withbenecial effects on the beam halo background and on the untagged neutrino componentat the far detector.
Presented at
NuPhys2019: Prospects in Neutrino PhysicsCavendish Conference Centre, London, 16–18 December 2019 ∗ F. Acerbi, A. Berra, M. Bonesini, A. Branca, C. Brizzolari, G. Brunetti, M. Calviani, S. Capelli,S. Carturan, M.G. Catanesi, S. Cecchini, N. Charitonidis, F. Cindolo, G. Collazuol, E. Conti, F. Dal Corso,G. De Rosa, A. Falcone, A. Gola, C. Jollet, V. Kain, B. Klicek, Y. Kudenko, M. Laveder, A. Longhin,L. Ludovici, E. Lutsenko, L. Magaletti, G. Mandrioli, A. Margotti, V. Mascagna, N. Mauri, L. Meazza,A. Meregaglia, M. Mezzetto, M. Nessi, A. Paoloni, M. Pari, E. Parozzi, L. Pasqualini, G. Paternoster,L. Patrizii, M. Pozzato, M. Prest, F. Pupilli, E. Radicioni, C. Riccio, A.C. Ruggieri, C. Scian, G. Sirri,M. Stipcevic, M. Tenti, F. Terranova, M. Torti, E. Vallazza, F. Velotti, M. Vesco, L. Votano a r X i v : . [ phy s i c s . acc - ph ] A p r ENUBET - Enhanced NeUtrino BEams from kaon Tagging
In the near future neutrino physics will require measurements of absolute neutrino crosssections at the GeV scale with 1% precision. Modern cross section experiments are reachingthe intrinsic limitations of conventional neutrino beams: ν e and ν µ fluxes are inferred by afull simulation of meson production and transport from the target down to the beam dumpand are validated by external data and, hence, neutrino fluxes are affected by significantuncertainties, of the order of 5-10%.The goal of the ENUBET project ∗ is to study a facility where the production of electronneutrinos from K e decays can be monitored on a single particle level by instrumenting thedecay region in a narrow band neutrino beam. Positrons produced in association with elec-tron neutrinos in K e ( K + → e + π ν e ) decay are tagged and monitored in an instrumenteddecay tunnel [1]. The beamline is designed to enhance the ν e components from K e andto suppress the ν e contaminations from muon decay. This would allow to measure ν e crosssections with a precision improved by about one order of magnitude, compared to presentresults.Two main pillars are required for the success of the project: • the design and construction of a detector capable of performing positron identificationin a ν beam decay tunnel at single particle level [2]; • the layout of the π/K focusing and transport system with suitable proton extractionschemes to keep the rate of particles in the tunnel at a level sustainable for the tunnelinstrumentation.Secondary particles produced by proton interactions in the target are focused and trans-ported to the decay pipe. Non-interacting protons are stopped in a beam dump. Off-momentum particles reaching the decay tunnel are mostly low energy particles coming frominteractions in other beamline components and muons that cross absorbers and collimators.The optimization of the ENUBET beamline is performed taking into account differentrequirements [3, 4]: • Maximize the number of K + in the momentum range of interest at tunnel entrance. • Minimize the total length of the transferline ( ∼
20 m) to reduce kaon decay lossesbefore the entrance of the decay tunnel. • Produce a small beam size: non decaying particles should exit the decay pipe withouthitting the tagger inner surface. • Keep under control the level of background transported to the tunnel, which affectsthe signal-to-noise ratio of the positron selection. • Use of conventional magnet field and apertures (normal-conducting devices, with anaperture below 40 cm).The optics is currently optimized for a reference hadron beam with a momentum of 8.5 GeV/cand a momentum bite of 10%.The secondary particles production from the interaction of primary protons with thetarget are simulated with FLUKA. The optimization of the components of the beamline(dipoles and quadrupoles) is performed with TRANSPORT. A full simulation of particletransport and interaction is performed with G4beamline. Assessment of the doses is ad-dressed using FLUKA. ∗ This project has received funding from the European Research Council (ERC) under the EuropeanUnions Horizon 2020 research and innovation programme (Grant Agreement 681647). “Static” focusing beamline The first proposed focusing system, the static one, consists of a quadrupole triplet placedbefore the bending magnet, downstream the target. This configuration allows to performthe focusing using DC operated devices, instead of pulsed magnetic horns, offering severaladvantages in terms of costs and technical implementation.The reference option consists in a quadrupole triplet followed by a dipole, that provides a7.4 ◦ bending angle, and by another quadrupole triplet (Fig.1a). One advantage with respectto an horn-based line is that there are no intrinsic time limits for proton extractions, upto several seconds. The single resonant slow extraction (2 s) is less challenging than ahorn-based beamline. Moreover, the particle rate at the tunnel instrumentation could bereduced, reducing pile-up effects. Fig.1b shows the expected beam composition at thedetector entrance. (a) Single dipole beamline (b) Particle budget at taggerentrance Figure 1: Static focusing system.A new design is the double dipole configuration (Fig.2). The bending angle is larger,15.2 ◦ , and the length of this transferline is greater than the single dipole option. Significantadvantages of this design are a reduction of the beam halo background (in particular frommuons) and of the untagged neutrino component at the far detector (neutrinos producedin the straight section of the transfer line have a lower probability to reach the detector).Figure 2: Schematics of the ENUBET double dipole beamline.Moreover, since the instantaneous rate of particles hitting the decay tunnel walls isreduced, compared with the horn option, a neutrino interaction in the detector could belinked with the observation of its associated lepton in the decay tunnel. This could leadto a facility where the neutrino is uniquely associated with the other decay particle, a socalled “tagged neutrino beam”. 3 Horn-based beamline - “burst slow extraction”
This option features a magnetic horn, placed between the target and the quadrupoles. Ithas to be pulsed with large currents (180 kA) for 2-10 ms and cycled at 10 Hz duringthe accelerator flat-top. Studies concerning the proton extraction scheme (“burst slowextraction”) to synchronise a few ms proton extraction with current pulsing are on-goingat the CERN-SPS (Fig.3). It is more challenging than the single resonant slow extractionover O(s) times (as in the static option), but higher yields can be achieved at the tunnelentrance using a magnetic horn instead of the quadrupole triplet (Tab.1).Figure 3: Burst slow extraction over a SPS spill [5].Focusing system π + /P OT (10 − ) K + /P OT (10 − ) Extraction lengthHorn-based 77 7.9 2-10 msStatic 19 1.4 2 sTable 1: Expected rates of π + and K + in 6.5 ÷ References [1] A. Longhin, L. Ludovici and F. Terranova, “A novel technique for the measure-ment of the electron neutrino cross section”, Eur. Phys. J. C (2015) no.4, 155doi:10.1140/epjc/s10052-015-3378-9 [arXiv:1412.5987 [hep-ex]].[2] A. Branca, “The instrumented decay tunnel of the ENUBET neutrino beam”. Posterpresented at: NuPhys2019 ( https://indi.to/y4t7M ).[3] F. Acerbi et al. , “The ENUBET project”, CERN-SPSC-2018-034. SPSC-I-248.[4] F. Acerbi et al.et al.