P.M. King Ohio University for the MOLLER Collaboration

Transcription

1 Parity violating electron scattering at JLab: the MOLLER experiment P.M. King Ohio University for the MOLLER Collaboration SESAPS, 10 November 2016; University of Virginia, Charlottesville, VA

2 The Standard Model Very successful! Described by symmetry groups SU(3) C x SU(2) L x U(1) Y It is incomplete; some open questions are: Why is the observable universe dominated by matter? What sets the scale of neutrino masses and mixing? What about gravity and dark matter? P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 2

3 Testing SM and Physics Beyond SM Standard Model is a Low energy effective theory And there are three approaches to uncover underlying physics Energy frontier: direct searches for new particles High energy Tevatron and LHC Cosmic frontier : Cosmic rays, cosmic wave background, and dark matter Broad range of energies Fermi telescope : dark matter signatures Planck satellite : CMB Precision or intensity frontier: searches for indirect effects Low/modest energy EDM searches, rare decays, double beta decays Parity violation in electron scattering Fundamental Symmetries P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 3

4 Parity-Violating Electron Scattering e e s(+) s(-) p p θ θ Parity violated in the weak interaction: form an asymmetry P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 4

5 Some things we can learn using PVES Parity violation in deep inelastic scattering Some examples: E122 (SLAC), PVDIS-6GeV, PVDIS-12GeV, SOLID (JLab) Quark flavor decomposition of the nucleon form factors Weak & EM exchanges with u, d, s quarks have different weights to their contribution to FFs, allowing separation Some examples: HAPPEX, G0 (JLab), PVA4 (Mainz, Germany), SAMPLE (MIT Bates, MA) Neutron distribution in large nuclei Since the neutron has a larger weak charge than the proton, PVES more directly probes the neutron distribution Some examples: PREX I and PREX II, CREX (JLab) Weak charges of fermions as a standard model test Some examples: QWEAK and MOLLER (JLab) P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 5

6 PV in Møller Scattering AA PPPP = GG FF mm EE 4 sin 2 θθ CCCC 2 ππππ (3 + cos 2 θθ CCCC ) 2 QQ WW ee QQ WW ee = 1 4 sin 2 θθ WW ~ Because the weak vector charge is close to zero, small shifts in the values due to new physics are more noticeable The reach of the MOLLER experiment can be most generally expressed in terms of a new contact interaction; MOLLER would be the best contact interaction search for leptons at low or at high energy Best current limit on contact interaction scales available from LEP2, but it is only sensitive to parity conserving quantities, g 2 RL and g 2 RR +g2 LL, not the parity violating quantity, g 2 RR -g2 LL. g ij =g * ij are contact interaction coupling constants for chirality projections of the electron spinors Mass scale reached for MOLLER for parity violating interactions : P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 6 Λ gg 2 RRRR gg 2 LLLL = 7.5 TeV

7 New Physics beyond SM Possible shifts due to R-Parity Violating SUSY Relative shifts in couplings due to SUSY effects Erler and Su, arxiv: P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 7

8 New Physics beyond SM Dark Z to invisible Particles Davoudiasl et. al. arxiv: v2 and Dark Z boson at low masses Effect will be dependent on the mass of the dark Z MOLLER will offer an excellent opportunity to constrain such dark matter interaction Observe such dark Z boson as a shift in the weak mixing angle value P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 8

9 Challenges in PVES PVES asymmetries are small In the order of 10-6 to 10-9 Need large numbers of electron scattering events Relative error goal is a few % High luminosity is required High electron beam current and long targets High precision needed Custom low-noise detectors and dedicated electronics Must keep beam polarization high, and measured with high precision (~ 1%) Keep many different systematic effects under control Precision vs smaller asymmetry P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 9

10 How to Do A PVES Experiment Zero is few km down! Helicity of electron beam flipped periodically, delayed helicity reporting to prevent direct electrical pick up of reversal signal by detectors Detector signal integrated for each helicity window and asymmetry formed from helicity patterns P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 10

11 Continuous Electron Beam Accelerator at Jefferson Lab Hall D Polarized Injector A B C P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 11

12 MOLLER Kinematics and Acceptance In Møller scattering backward and forward scattered electrons can be detected Identical Particles With odd number of sectors in an unique design, MOLLER experiment accepts full azimuthal range Electrons of θ CM [90,120] that get blocked at this sector... are collected as θ CM [60,90] at this sector P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 12

13 MOLLER Apparatus APV = 35.6 parts per billion (ppb) δ(apv) = 0.73 ppb δ(q e W) = ± 2.1 % (stat.) ± 1.0 % (syst.) Ebeam = 11 GeV Beam Intensity 85 μa, 80% polarized Luminosity: 3x10 39 cm 2 /s! Scattering angle 5 mrad! P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 13

14 Liquid Hydrogen Target Need as much thickness as technically possible with least radiative losses; trade-off between counting statistics and systematic effects Base design will be from the previous generation MOLLER experiment (E158), with developments based on the experiences with the QWEAK target, and CFD modeling P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 14

15 Toroidal Spectrometer Provides full azimuthal acceptance Have water-cooled warm copper coils The collimators define the acceptance of the experiment Strategic placement of collimators will minimize soft photon backgrounds by achieving a two-bounce system P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 15

16 Toroidal Spectrometer and Detectors Møller and ep scattering signals are separated at the detector plane Optics are still being fine tuned, Reduce backgrounds Optimize the asymmetry Improve symmetric forward/backward 2 ndt hybrid toroid 1 st toroid Tracks are colored by scattering angle from purple to red (low to high) P.M.King; The MOLLER Experiment; SESAPS,

17 Integrating Detectors Overview Detectors are radially and azimuthally segmented For detecting Møller and e-p electrons, Quartz with air light guide and PMTs For Pions and Muons A calorimeter style detector behind a shielding wall Beam and target fluctuations Luminosity monitors P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 17

18 MOLLER Backgrounds The primary irreducible backgrounds : ep elastic and inelastic scattering Other background sources Photons and neutrons from 2 bounce collimation system Pions and muons : photo-production and DIS P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 18

19 Statistics and Systematics Errors P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 19

20 Summary and Outlook Best contact interaction reach for leptons at any energy Similar to LHC reach with semi-leptonic amplitudes To do better for a 4-lepton contact interaction would require: Giga-Z factory, linear collider, neutrino factory or muon collider The unique discovery capability in MOLLER will be very important If LHC sees any anomaly in runs 2 and 3 (~ 2022) MOLLER also provides discovery scenarios beyond LHC signatures Hidden weak scales Lepton number violating interactions Light dark-matter mediators Modular experiment design enable multiple runs Allows other experiments to come to the floor between MOLLER runs Design will allow modest time for deinstallation/installation Commissioning and first physics run would yield major results P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 20

21 SUPPLEMENTAL SLIDES P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 21

22 PV in Møller Scattering Measure weak charge of electron precisely Unprecedented sensitivity Λ gg 2 RRRR gg 2 LLLL = 7.5 TeV Provide best projected uncertainty weak mixing angle at any energy scale use standard model electroweak radiative corrections to evolve best measurements of sin 2 θ W to Q ~ MZ Higgs measured Erler and Su, arxiv: The most precise low energy determination to date Based on LHC Higgs mass and few other parameters P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 22

23 MOLLER Apparatus Technical Challenges High (150 GHz) scattered electron rate High luminosity 85 ua on 1.5 m long LH2 target: 5 KW cooling needed Complete azimuthal acceptance at θ lab of 5 mrad Pair of toroidal spectrometer magnets Highly segmented integrating detectors High beam polarization (~89%) with redundant 0.4 % level beam polarimetry P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 23

24 Polarized Electron Source Electron Gun Requirements Ultrahigh vacuum No field emission Maintenance free Beam helicity is reversed at a pseudo-random pattern Sequences of helicity window multiplets will be used to compute the asymmetry MOLLER will use 2 khz reversal rate Record performance of 180 ua at 89% pol. (2012) P.M.King; The MOLLER Experiment; SESAPS, 2016 Nov 10 24