Search for Heavy Neutral the SPS

Transcription

1 arxiv: v1 Search for Heavy Neutral the SPS W. Bonivento 1,2, A. Boyarsky 3, H. Dijkstra 2, U. Egede 4, M. Ferro-Luzzi 2, B. Goddard 2, A. Golutvin 4, D. Gorbunov 5, R. Jacobsson 2, J. Panman 2, M. Patel 4, O. Ruchayskiy 6, T. Ruf 2, N. Serra 7, M. Shaposhnikov 6, D. Treille 2( ) 1 Sezione INFN di Cagliari, Cagliari, Italy 2 European Organization for Nuclear Research (CERN), Geneva, Switzerland 3 Instituut-Lorentz for Theoretical Physics, Universiteit Leiden, Niels Bohrweg 2, Leiden, The Netherlands 4 Imperial College London, London, United Kingdom 5 Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 6 Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland 7 Physik-Institut, Universität Zürich, Zürich, Switzerland ( ) retired How does this proposal fit in the physics landscape? Why HNLs? How to produce/detect HNLs. Backgrounds. The experimental set-up. Symbiosis with active ν physics. Conclusions

2 Triumph of SM: Higgs found! Boson found consistent with SM-Higgs. Atlas: M H = 125.5±0.2 stat syst GeV CMS: M H = 125.7±0.3 stat ±0.3 syst GeV - 2 -

3 What is not found

4 What is not found

5 SM: No tree level decay Helicity suppressed Expected: B(B s µ + µ )= (3.6±0.3) 10 9 (Phys. Rev. Lett. 109 (2012) ) NP: B s µµ found and SM MSSM: B tan 6 β/m 4 A 0 Pre-LHC parameter space example: D.Straub: arxiv: arxiv:

6 NP from quark flavour observables CKM-fitter excluded area has CL > 0.68 excluded area has CL > FS + - Γ s & τ s & τ s (K K ) & τ s (J/ψf ) 0 1 SM point 1 SM point m d & m s m d & m s Im d 0 α exp sin(φ d +2β ) d Im s 0 φ s-2β s -1 A SL & a SL (B ) & a (B ) d SL s -1 A SL and a SL (B ) & a (B ) d SL s -2 CKM f i t t e r New Physics in B - B d mixing d FPCP 13-2 CKM f i t t e r New Physics in B - B s mixing FPCP 13 s Re d Re s Scale of NP in B B-mixing: > TeV depending on assumptions of couplings

7 Higgs and Vacuum Stability Higgs mass is fine tuned? SM located in narrow meta-stability wedge. Most likely multiverse near such a wedge? Vast majority of sand-dunes have a slope angle roughly equal to the so-called angle of repose. Not anthropic, but P(multiverses) peaks near wedge? Vacuum might be stable, or has a τ τ universe SM may work successfully up to Planck scale, i.e. no need for a new mass scale Stability Meta-stability Instability - 7 -

8 SM case closed? NO, SM unable to explain: Matter anti-matter asymmetry in universe Neutrino mixing masses Non-baryonic dark matter Astrophysical Journal, Vol. 295, Aug. 15,

9 First decades of last century: β-decay: Meitner, Hahn, Ellis, Neary History Lesson(s) (after B. Batell) Continous spectrum observed for n p+e? Note: SM (1930): N, e, γ Pauli (1930) proposed: n p+e +ν I admit that my remedy may appear to have a small a priori probability (..). However, only those who wager can win, (...) Nowadays: call this a hidden sector! New particles, neutral, very weakly interacting. Interacts with SM through portal

10 Ptolomy ( AD): It is a good principle to explain phenomena by the simplest hypothesis possible! νmsm: T.Asaka, M.Shaposhnikov PL B620 (2005) 17 Adding three right-handed Majorana Heavy Neutral Leptons (HNL): N 1, N 2 and N 3 : N 1 can provide dark matter candidate N 1,2,3 can provide neutrino masses via Seesaw mechanism N 2,3 can induce leptogenesis baryogenesis

11 νmsm: closer look at N 1 N 1 can provide dark matter candidate: very weak mixing with other leptons hence, stable enough for dark matter Seesaw: one M ν active 10 5 ev Radiative decay: τ > τ universe E γ = M N 1 2 X-ray detection: View dwarf spheroidal galaxies E E Proposed missions: Astro-H, LOFT, Athena+, Origin/Xenia W N 1 ν ν l γ inspirehep.net/record/ ?ln=en

12 2/2014: two papers on ArXiv: 10/2/14: arxiv.org/abs/ : Detection of an Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters E γ 3.56 kev 17/2/14: arxiv.org/abs/ : An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster E γ 3.5 kev Both papers refer to Astro-H (with Soft X-Ray Spectrometer, 2015 launch) to confirm/rule-out the DM origin of this signal. N 1 : stop the press... Andromeda Blank sky arxiv.org/abs/

13 N 2,3 Use N 2,3 to explain: ν masses: Seesaw constrains Yukawa coupling and M N2,3, i.e. M ν U 2 /M N2,3 Baryo(Lepto)genesis: make N 2 nearly degenerate with N 3, and tune CPV-phases to explain baryon asymmetry of universe (BAU). U 2 1/τ N2,3 M 3 N 2,3 τ N2,3 < 0.1 s, otherwise Big Bang Nucleosynthesis (BBN, 75/25 % H-1/He-4) would be affected by N 2,3 decays. τ µ These are the particles SHiP is after!

14 N 2,3 production and decay N 2,3 mix with ν Produced in (semi-)leptonic decays, f.i. K µν, D µνx, B µνx, Z ν ν σ D U 2 U 2 2 = U 2 2,ν e +U 2 2,ν µ +U 2 2,ν τ B(N µ/e π): % B(N µ/e ρ): % B(N νµe): 1 10 % τ N2,3 U 2, i.e. cτ O(km)

15 Sensitivity for N 2,3 U 4! SHiP looks for (light) HNL from D-decays, i.e. M < 2 GeV B-decays: smaller σ, and Dµν, i.e. still limited to 3 GeV. arxiv.org/pdf/ v1 Where to produce charm? LHC ( s = 14 TeV): with 1 ab 1 (i.e. 3-4 years): in 4π. SPS (400 GeV p-on-target (pot) s = 27 GeV): with pot (i.e. 3-4 years): Fermilab: 120 GeV pot, 10 smaller σ c c, 10 pot by 2025 for LBNE

16 Experimental status on searches Already searches in K/D/Z-decay performed: PS191( 19.2 GeV, pot, 128 m from target. CHARM( 86)@SPS 400 GeV, pot, 480 m from target. NuTev( 99)@Fermilab 800 GeV, pot, 1.4 km from target. DELPHI( 97)@LEP 91 GeV, 10 6 Z 0 ν ν. BBN, BAU and Seesaw constrain more than experimental searches for M N > 400 MeV

17 Spectrometer for GeV pot HNL search is different from ν µ, ν e physics (but ν τ similar): ν µ, ν e cause background: heavy (W) target to avoid π/k-decay. Example: Cu iso W-target doubles ν-background! Place detector as close as possible to target as background (huge µ-flux!) allows, i.e. 60 m? Decay vessel: vacuum to avoid ν-interactions Magnetic spectrometer to reconstruct HNL mass. < θ HNL >= 50 mrad π N 2,3 µ p-beam Target µ-shield HNL decay vessel spectrometer

18 Where to put this spectrometer? Some words about the target bunker The muon shield Decay vessel, and ν-interaction background The spectrometer: Straw chambers Magnet Calorimeter Expected sensitivity

19 SHIP Taskforce Report v1.0.pdf

20 Accelerator department studies: Beam-line from SPS Civil engineering Target design Radiation environment Target Bunker ship.web.cern.ch/ship/document/ship Taskforce Report v1.0.pdf

21 Without µ-shield: /SPS-spill( pot) Low-p: still from π/k-decay High-p: ω/ρ-decays to µµ Reduce background from µ-interactions to below ν-background (see later) Acceptable µ rate 10 5 /spill. µ Flux and Shield Two alternatives for shield: Passive: i.e. use high Z material to stop muons: Example: need 54 m of W to stop 400 GeV µ. Active (+passive): use magnets to deflect muons: Example: need 40 Tm to deflect 400 GeV µ outside acceptance

22 Active µ-shield 350 GeV: µ ± separated by ±20 cm in z=20 m, close to x=0: no more muons! Put the return field of 2nd magnet in centre, to avoid back-scatter from return field

23 Active µ-shield 2.7 m 3.2 m 48 m What it looks like in 3D (for Geant) ton of Fe. Reduces µ background in spectrometer from to << m 5 m

24 ν-background and Decay-Vessel Pythia/Genie/Geant, compare to CHARM: ν-flux at end of µ-shield (/ pot): CC+NC interactions/λ 1 bar air in decay volume: ν-int/ pot Reduce pressure to 10 µbar! ν-interactions in µ-shield: Use veto-station to suppress short lived. ν µ +p X +K L µπν main background

25 Spectrometer µ-shield and chambers µ π Straw chambers Vacuum vessel Taggers Veto Straw chambers N 2,3 Magnet Calorimeter Spectrometer to reconstruct signal: Ecal and muon filter/chambers at the end. Tracking straw chambers (thin!) and magnet for reconstruction. Background rejection: µ or ν interactions in decay volume: evacuated vacuum vessel: (10 µbar) K/Λ-decays produced in surrounding material in µ, ν-interaction: Taggers: liquid scintillator in double walled vessel to veto candidates with accompanying particles. Veto: veto short lived K S, Λ, or candidate with accompanying particles

26 Tracking Chambers NA62 (K + π + ν ν): 2 m µbar. 10 mm straws made of PET. Demonstrated to work in vacuum. X/X0=0.5 % for 4 view station! 120 µm resolution/straw

27 Magnet With X/X0=0.5 % chambers: modest 0.5 Tm Need 40 m 2 aperture. LHCb magnet: 4 Tm, 16 m 2 exit-aperture LHCb magnet

28 Mass resolution Resolution for 1 GeV N µπ: 15 MeV. K L background suppression: Use pointing of candidates to target area Detect CC via extra µ in coincidence with µπ? Instrument µ-filter to tag CC/NC shower?

29 LHCb Shashlik ECAL: m 2 σ(e) E < 10%/ E 1.5% Better than required, roughly same size But for N µρ(ππ 0 (γγ)) need small (10 10 cm 2 ) cells everywhere. Electromagnetic Calo

30 Liquid Scintillator Taggers Taggers: liquid scintillator in double walled vessel to veto candidates with accompanying particles. SHiP aims for a background-less design!

31 Conditions: M N = 1 GeV: N 2-charged. Expected HNL Sensitivity U 2 µ, e > U 2 τ pot of 400 GeV. No (background) events observed. For factor 10 in U 2 need: 10 more pot/z 0, AND 10 larger acceptance! arxiv: v2-31 -

32 Extended Physics Program Experiment designed for HNL studies in νmsm, but.. Ideally suited for studying interactions of ν τ, since they are produced from D s -decay, hence have similar kinematics as HNLs. next slides Can search for any other weakly interacting, yet unstable particles with 100 < M < 2000 MeV. Example of hidden sector models on the market : Light SUSY goldstinos (hep-ph/000735): Production/decay might be like HNL, i.e. D πx, X ππ cτ X O(km)? Light R-parity violating neutralinos in SUSY (hep-ph/ ): D Xχ 0, χ 0 µ + µ ν LSP, with R-parity slightly violated: BBN: τ χ 0 < 0.1 s Dark/massive/para photons (hep-ph/ ): Produced via p-bremstrahlung, γ e + e, µ + µ. BBN limit: τ γ < 0.1 s. Insert your favourite model here... SHiP preparing physics paper evaluating many hidden sector models!

33 ν τ Physics Experimental status: DONUT results (PR D 78, (2008)) 1997: pot, 800 GeV, using 260 kg emulsion ν-target. α kink from τ-decay in CC interactions. Charm/hadronic-interaction background. 9 candidates, including 1.5 background. Opera: 4 candidates (from ν µ ν τ oscillations)

34 ν τ Physics with pot Scaling from DONUT: 20 times more CC with same ν-target mass. But can increase ν-target mass easily, lets say to 5 % of OPERA emulsion surface: Active µ-shield Magnet Emulsion Decay vessel µ-spectrometer Expect 3000 CC ν τ interactions. B-field in emulsion and muon-filters in µ-spectrometer: distinguish ν τ from ν τ. HNL-background: tag ν +p K L +l+x 10 5 ν e interactions, produced predominantly in charm-decay: HNL normalization

35 SPSC status Oct 2013: submitted our EOI: CERN-SPSC ; arxiv: ; SPSC-EOI SPSC assigned 4 referees, who came with a list of questions. 3/1/2014: answers to questions: ship.web.cern.ch/ship/eoi/spsc-eoi-010 ResponseToReferees.pdf 15/1/2014: SPSC discussed our proposal. 17/1/2014: The official feedback from the Committee is as follows : The Committee received with interest the response of the proponents to the questions raised in its review of EOI010. The SPSC recognises the interesting physics potential of searching for heavy neutral leptons and investigating the properties of neutrinos. Considering the large cost and complexity of the required beam infrastructure as well as the significant associated beam intensity, such a project should be designed as a general purpose beam dump facility with the broadest possible physics programme, including maximum reach in the investigation of the hidden sector. To further review the project the Committee would need an extended proposal with further developed physics goals, a more detailed technical design and a stronger collaboration. Cheers, Gavin, Lau, Matthew and Thierry (for the SPS Committee)

36 Following the endorsement of the SPSC: Next Steps The CERN directorate has set-up a task force to assess the implications of the Heavy Neutral Lepton Experiment at the SPS. The CERN-DG received summer 2014 a report including the layout and the resources which are required to set-up the beam-dump and its calendar: ship.web.cern.ch/ship/document/ship Taskforce Report v1.0.pdf SHiP (Search for Hidden Particles) collaboration was officially founded 15/12/2014: already 170 authors from 42 institutes for producing a Technical Proposal (due spring 2015). Institutes are from: Bulgaria, Chile, Denmark, France, Germany, Italy, Japan, Russia, Sweden, Switzerland, Turkey, UK. Switzerland: Geneva, Lausanne, Zurich (and CERN). SHiP is preparing a physics paper and a Technical Proposal for spring

37 Conclusions SHiP complementary to LHC searches Detector is based on existing technologies. CERN task force to study accelerator part. TP expected spring 2015, if approved: TDRs by 2018 civil engineering in LS2 ( ), and start experiment The impact of HNL discovery on particle physics is difficult to overestimate! Discovery would shed light on BSM physics: The origin of the baryon asymmetry of the Universe The origin of neutrino mass The nature of Dark Matter, did we get a hint?