Reminder : scenarios of light new physics

Transcription

1 Reminder : scenarios of light new physics No new particle EW scale postulated Heavy neutral lepton AND well motivated! Neutrino masses Matter-antimatter asymmetry Dark matter Dark photon Muon g-2 anomaly Parity Dark matter Axion Strong CP Dark matter CUSO 3ème cycle, Spring 2016 Philippe.mermod@cern.ch 1

2 Experimental strategies to search for light new physics Fixed-target facilities Electron beam This Proton beam chapter High-intensity colliders B factories LHC FCC (discussed in previous chapter (3.1)) 2

3 3.2 Light LLPs at non-collider facilities Dark photon Electron beam on target, Apex and HPS experiments Heavy neutral lepton (HNL) Proton beam on target, SHiP experiment Axion Electromagnetic resonators External magnetic field 3

4 Quiz Can one use proton beams to search for dark-photon displaced decays? A) Yes B) No, dark photons couple only to leptons C)No, there is too much background from metastable hadrons 4

5 Quiz (answer) Can one use proton beams to search for dark-photon displaced decays? A) Yes B) No, dark photons couple only to leptons C)No, there is too much background from metastable hadrons Dark photons could be produced whenever photons are produced. With a proton beam on a target, one needs a hadron absorber and a muon shield to reduce backgrounds. One must then place the decay volume at some distance from the target and thus one can only probe long lifetimes, corresponding to very tiny couplings a complementary range of the parameter space. 5

6 Dark photon hidden sector charged under U(1)' A' Dark photon (γd) Hidden / heavy photon Mirror photon Dark Z (ZD) U-boson, etc. g-2, dark matter, positron excess, parity (mirror world),... Production via kinetic mixing with the photon ( vector portal ) Coupling to charged particles suppressed by ε Decay to fermion pairs Search for resonances 6

7 Electron-beam fixed-target experiments Advantage of electrons: electromagnetic interactions only Low radiation levels Low backgrounds Not so much shielding needed detector close to target (~1 m) Some high-intensity electron beams in the world Jefferson Lab (USA, 6-12 GeV), MESA (Germany, 150 MeV) 7

8 The APEX experiment (Jefferson Lab 2 12 GeV electron beam) Forward-going e+e- produced in a thin tantalum target at a very high rate Septum dipole magnet for detection of e+e- produced at small angles probe dark photon mass around 200 MeV Search for resonance no possibility to look for displaced vertex Test run results at 2.3 GeV (Phys. Rev. Lett. 107, (2011)) New run at 12 GeV this year 8

9 The Heavy Photon Search (HPS) experiment (Jefferson Lab 6 12 GeV electron beam) Tungsten target Fast silicon tracker/vertexer in dipole magnet Two signatures resonance in e+e- invariant mass spectrum Displaced decay vertex (~20 mm from target) Physics runs planned this year 9

10 Quiz What is needed to probe a very small mixing ϵ? A) Very high-energy beam and resonance search B) Very high-energy beam and displaced vertex search C)Very high-intensity beam and resonance search D)Very high-intensity beam and displaced vertex search 10

11 Quiz (answer) What is needed to probe a very small mixing ϵ? A) Very high-energy beam and resonance search B) Very high-energy beam and displaced-vertex search C)Very high-intensity beam and resonance search D)Very high-intensity beam and displaced-vertex search High energy is needed to probe high particle masses. High intensity is needed to probe small mixing. Small mixing also means long lifetime, and thus one needs to look for a displaced-vertex signature. 11

12 Dark photons expected future reach prompt decay (resonance) displaced decay 12

13 Heavy neutral lepton (HNL) right-handed neutrino N Heavy neutral lepton (HNL) Right-handed neutrino Heavy neutrino Majorana neutrino Sterile neutrino, etc. Neutrino masses, dark matter, X-ray astronomy, matter-antimatter asymmetry Production via mixing to neutrinos ( neutrino portal ) No interaction except through coupling to the Higgs field Decay to llν or l+hadron(s) N1 stable dark matter N2,3 long-lived, mass in GeV range 13

14 Proton-beam fixed-target experiments Advantages / disadvantages of protons High beam energies High beam intensities High cross sections High radiation levels Need hadron absorber Need muon shield detector quite far from target ( m) Some high-energy, high-intensity proton beams in the world CERN SPS (Switzerland, up to 450 GeV), Fermilab (USA, up to 120 GeV), J-PARC (Japan, up to 50 GeV) 14

15 HNLs at proton fixed-target experiments Neutrinos from charm decays HNL masses < 2 GeV CHARM experiment at CERN SPS (PLB 166, 473) NuTeV experiment at Fermilab (PRL 83, 4943) Constraints from seesaw and cosmology in neutrino minimum standard model (Ann. Rev. Nucl. Part. Sci. 59, 191) Normal hierarchy Inverted hierarchy 15

16 The SHiP experiment (CERN SPS 400 GeV proton beam) 2020 protons on target 1016 neutrinos from charm decays Probe tiny HNL couplings (mass below 2 GeV) Detector ~100 m length, ~5 m diameter Technical proposal arxiv: (2015) SHiP theory paper arxiv: (2015) Full TDR in

17 SHiP expected sensitivity to HNLs Vast improvement on existing constraints Digs deeply into cosmologically favourable region (explain BAU and dark matter in addition to neutrino masses) 17

18 Quiz Theoretically, what is the highest HNL mass SHiP can probe? A) 0.5 GeV (K meson mass) B) 2 GeV (D meson mass) C)5 GeV (B meson mass) D)28 GeV (beam-target CM energy) E) 91 GeV (Z mass) 18

19 Quiz (answer) Theoretically, what is the highest HNL mass SHiP can probe? A) 0.5 GeV (K meson mass) B) 2 GeV (D meson mass) C)5 GeV (B meson mass) D)28 GeV (beam-target CM energy) E) 91 GeV (Z mass) A 400 GeV proton beam corresponds to 28 GeV CM energy if one considers a proton target. This means that the heaviest particles which can be produced to decay to neutrinos are B mesons. To extend the search to higher masses, one needs higher CM energies to produce Ws and Zs colliders (LHC, FCC). 19

20 HNLs the (approximate) big picture assumes specifications from SHiP technical proposal assumes 50 fb 14 TeV in both ATLAS and CMS assumes 10¹³ Zs for FCC-ee with LHC-sized detector 20

21 Dark-sector search at SLAC E137 electron beam dump experiment (Phys. Rev. Lett. 113, (2014)) Signature: electron shower pointing to dump after large distance through rock Background-free Relies on additional assumption of hidden particle χ charged under U(1)' DM candidate 21

22 Dark photons with SHiP Only assumption: dark photon with coupling strength ε Production dominated by p pγ, π0 γγ, and η γγ Dark photon decays to e+e- and μ+μ Large expected improvement at high mass and low coupling 22

23 Axion Pseudo Nambu-Goldstone boson of new broken U(1) symmetry Strong CP problem, dark matter Main production and decay mode via coupling to two photons gaγγ Electromagnetic cavity with static magnetic field tuned so that the two-photon invariant mass corresponds to the axion mass Axion decay greatly enhanced (inverse Primakoff effect) Cosmological and astronomical constraints on axion mass Ma < 10-3 ev (supernova and white dwarf cooling rates) Ma > 10-6 ev (overproduction in early universe) 23

24 Axion direct search strategies Axions from the Sun photons converted into axions in the Sun Dark-matter axions from local galactic halo Main technique : electromagnetic resonator Strong external magnetic field Cavity with resonant frequency corresponding to that of resultant photon greatly enhanced axion conversion rate Various frequencies correspond to different axion masses to probe 24

25 CERN Axion Solar Telescope (CAST) LHC magnet pointed at the Sun Look for X-ray Running since 2003 Various gas mixtures give sensitivity to different masses (different resonance frequency) Note : probed range excluded by astronomical observations (supernova + white dwarf) 25

26 Axion Dark Matter Experiment (ADMX) 1 x 0.3 m microwave cavity 8 T superconducting magnet All cooled down to reduce noise backgrounds Photon picked up by small antenna at the top and carried to amplifiers Simply expose the apparatus to axion DM underground Probed mass range ev, coupling in unconstrained region expected for axion DM 26

27 Axion Constraints Column 1 Column 2 Column Row 1 Row 2 Row 3 Row 4 27

28 Light new physics summary Given lack of evidence for massive new physics, light new physics is a hot topic Hidden sectors, dark photon LLP Direct search for right-handed neutrino LLP Axion LLP Complementary searches can be made at colliders and dedicated experiments New ambitious projects are being proposed to probe most of the allowed parameter space Axion dark matter detection experiments HPS experiment Displaced-vertex SHiP experiment signatures LHC experiments Future Circular Colliders 28