The Electric Form Factor of the Neutron for SBS

Transcription

1 The Electric Form Factor of the Neutron for SBS Seamus Riordan Stony Brook University July 1, 16 Seamus Riordan SBS 16 G n E 1/1

2 G E /G M at high Q - Spin Observables, Pol. Target Long. polarized beam/polarized target transverse to q in scattering plane polarization axis e e θe ω, q θ φ momentum transfer Helicity-dependent asymmetry roughly proportional to G E /G M σ + σ τ(τ + 1) tan(θ/)g E /G M A = σ + + σ (G E /G M ) + (τ + τ(1 + τ) tan (θ/)) Seamus Riordan SBS 16 G n E /1

3 Neutron Form Factors.8.6 Schlimme, MAMI Riordan, JLab Hall A e'd, JLab Hall A (prelim) E-1 Preliminary n /G M n µ n G E.4.. RCQM - Miller (6) VMD - Lomon (5) Diquark-π - Cloet (1) NJL - Cloet (14) DSE - Cloet (1) F /F 1, Λ = MeV Our Fit Q [GeV ] Seamus Riordan SBS 16 G n E /1

4 Neutron Form Factors 1. Schlimme, MAMI Riordan, JLab Hall A e'd, JLab Hall A (prelim) E-1 Preliminary E1-11-9, Hall C E1-9-16, Hall A SBS n /G M n µ n G E.5 RCQM - Miller (6) VMD - Lomon (5) Diquark-π - Cloet (1) NJL - Cloet (14) DSE - Cloet (1) F /F 1, Λ = MeV Our Fit Q [GeV ] Models for G n E are highly divergent for high Q Seamus Riordan SBS 16 G n E /1

5 High Q G n E Experimental Layout (Not to scale) 48D48 Magnet Veto Polarized He Target n 17m Path HCAL e BigBite w/ upgraded detectors Upgraded Bigbite detector stack for higher rates, better PID Hadron calorimeter at 17 m Place magnet B dl = 1.7 T m at.8 m from target to deflect protons Seamus Riordan SBS 16 G n E 4/1

6 PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT D C B A R.5 DRAWN labuser 1//14 CHECKED QA MFG APPROVED.4 TITLE SIZE SCALE 8.7 DWG NO Target chamber length - 6 cm Pumping chamber diameter cm SHEET 1 OF 1 1 REV D C B A Target cell design for SBS G E n experiment PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT All units are in inches. PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT In the QCD DSE approach, it is the diquark that causes Protovec1 + Metal End Windows C Assembly Gas convection Metal windows 6 cm target-chamber length will deliver desired luminosity with 6 µa electron beam. Convection-based design, now well tested in Protovec-series cells. 1 µa 6 µa Contains 6 STP liters of He in 75 cm volume cell. Will use copper metal end windows with gold electroplating on inner surface. 4 cm 55 cm Wednesday, October 1, 15 Stolen from Gordon Cates Upgrades P = 45% 6% Seamus Riordan SBS 16 G n E 5/1

7 HCAL + 48D48 HCAL uses cm iron/scintillator design for hadron calorimetery 48D48 removes background and deflects protons out of QE acceptance - loss of % statistics at.8 m for extended target Spatial resolution of 1.5 cm 1 mrad ToF resolution critical for QE selection - see later slides Detector plane can provide additional PID Seamus Riordan SBS 16 G n E 6/1

8 HCAL + 48D48 HCAL uses cm iron/scintillator design for hadron calorimetery 48D48 removes background and deflects protons out of QE acceptance - loss of % statistics at.8 m for extended target Spatial resolution of 1.5 cm 1 mrad ToF resolution critical for QE selection - see later slides Detector plane can provide additional PID Seamus Riordan SBS 16 G n E 6/1

9 Quasielastic Selection and Backgrounds Cuts on missing momenta (θ pq and ToF), invariant mass allow for suppression of inelastic events Inelastics can be corrected using Monte Carlo with MAID or sideband subtraction/deconvolution.1 E beam =8.8 GeV. E beam = 8.8 GeV He(e,e n(p)π) n σ/ W 1-8 cm /GeV BigBite & BigHAND p <.15 GeV/c per one inelastic event..1 γ cuts: W 1.5 GeV TOF = ± 1 ns q.1 GeV/c p π + π W GeV particle ID Background mostly neutrons, photons probably removable with energy resolution, some inelastic protons Seamus Riordan SBS 16 G n E 7/1

10 MAID vs. DIS - p m, δt =.5 ns p, Q = 1.5 GeV, He QE Cuts, DIS inelastic miss,#papallel 1 4 p, Q =.7 GeV, He QE Cuts, DIS inelastic miss,#papallel p [GeV] miss, p [GeV] miss, p, Q = 1.5 GeV, He QE Cuts, MAID inelastic miss,#papallel p, Q =.7 GeV, He QE Cuts, MAID inelastic miss,#papallel p [GeV] miss, p [GeV] miss, Black - all, blue - QE, red - Inelastic Seamus Riordan SBS 16 G n E 8/1

11 Counts vs. Time of Flight Resolution Total n QE Counts Statistics vs Resolution, Q = 1 GeV, 5% eff DIS 15% cont DIS 5 15% cont DIS 1 % cont DIS 1 15% cont Proposed Stat δ t TOF [ns] Scaling DIS 5, 15% contamination needs about.5 ns resolution Could probably do OK with 1 ns resolution, loss of % statistics Seamus Riordan SBS 16 G n E 9/1

12 Nuclear Corrections Nuclear effects evaluated by M. Sargsian in Generalized Eikonal Approximation Determine effective neutron/proton polarization Evaluate rescattering effects on asymmetry Considers four main diagrams PWIA, MEC, FSI, IC Needs to be redone for new kinematics Seamus Riordan SBS 16 G n E 1/1

13 Two Photon Effects Two photon effects for polarized target related to effects in polarization transfer Only considered proton ground state for box diagrams Asumming similar size correction as proton: P T 1γ+γ / PT 1γ Q = 6 GeV (b) E Q = 1 GeV? E 1 Q =.4 GeV ε ε Blunden, Melnitchouk, Tjon, Phys. Rev. C 7, 461 (5) P L 1γ+γ / PL 1γ (a) Q = 6 GeV 1 Seamus Riordan SBS 16 G n E 11/1

14 Requirements for Instrumentation in G n E /G n M Measurement To achieve 1% at Q = 1 GeV given luminosity Hz/cm (6 cm target, 6 µa), 6% polarization: BigBite Requirements 15 4 cm chambers 5 cm chambers e acceptance 4 msr p e 1. GeV δp e 1% Angular Range 5 4 e detector rates 1 khz/cm e ToF.5 ns δe 1% π rejection 1-:1 δθ e 1 mrad δv z.5 cm Nucleon Arm Requirements N acceptance msr p n 1 1 GeV Angular Range 17 4 δθ pn 1 mrad δt ToF.5 ns B dl 1.7T m Total rate khz Seamus Riordan SBS 16 G n E 1/1

15 Summary G n E can be measured to Q = 1 GeV with SBS to 1 % accuracy HCAL needs ToF resolution on order of.5 1 ns Upgraded target that can handle 6 µa with 6% polarization required Other requirements fall within SBS defintions Seamus Riordan SBS 16 G n E 1/1

16 BACKUP SLIDES Seamus Riordan SBS 16 G n E 1/1

17 Polarized Target Measurements - Nulling asymmetry Long. polarized beam/polarized transverse to q in scattering plane σ + σ σ + + σ = A sin θ cos φ + A cos θ = τ(τ + 1) tan(θ/)g E /G M sin θ cos φ (G E /G M ) + (τ + τ(1 + τ) tan (θ/)) τ 1 + τ + (1 + τ) tan (θ/) tan(θ/) cos θ (G E /G M ) + (τ + τ(1 + τ) tan (θ/)) A provides reference asymmetry that is mostly dependent just on kinematic variables Setting A and A to cancel by rotating target pol. angle reduces uncertainties contributed by scaling effects in asymmetry such as target and beam polarization Need to know GE n a priori to do it correctly, only for low Q Seamus Riordan SBS 16 G n E 1/1

18 Assuming Galster for G n E, Kelly for G n M : Q [GeV ] time [days] stat [%] sys [%] Systematic uncertainties to asymmetries at highest Q Quantity Expected Value Rel. Uncertainty Beam polarization P e.85.4% Target polarization P He.6.% Neutron polarization P n.86.% Nitrogen dilution D N.94.1% Background dilution D back.95 < 1% Final state interactions.95.1% Inelastic correction % Angular error from A < 1% Systematic error in GE n/g M n 6.6% Seamus Riordan SBS 16 G n E 1/1

19 DIS - W δt = 1. ns W, Q = 1.5 GeV, He QE Cuts, DIS inelastic 1 W, Q =.7 GeV, He QE Cuts, DIS inelastic 5 4 Cont = 1% 5 Cont = 4% W [GeV ] W, Q = 6.7 GeV, He QE Cuts, DIS inelastic W, Q W [GeV ] = 1. GeV, He QE Cuts, DIS inelastic 18 Cont = 5% Cont = 15% W [GeV ] W [GeV ] Adjusting cuts so contamination is about the same, loss of statisics is about % Seamus Riordan SBS 16 G n E 1/1

20 DIS - W δt = 1.5 ns W, Q = 1.5 GeV, He QE Cuts, DIS inelastic Cont = 1% W [GeV ] W, Q = 6.7 GeV, He QE Cuts, DIS inelastic W, Q W, Q 18 =.7 GeV, He QE Cuts, DIS inelastic Cont = 4% W [GeV ] = 1. GeV, He QE Cuts, DIS inelastic Cont = 6% Cont = 16% W [GeV ] W [GeV ] Adjusting cuts so contamination is about the same, loss of statisics is about 5% Seamus Riordan SBS 16 G n E 1/1

21 Trigger Trigger Rate [khz] Trigger Rate vs. Threshold, G n E Q = 1.5 GeV Q = 4 GeV Q = 7 GeV Q = 1 GeV Threshold [GeV] Rates above include elastic e, DIS e, and π + Single arm shower/preshower (with ps cut) keeps will have < khz trigger rate without affecting QE cuts Need to allow some inelastic in trigger - prescale lower threshold Seamus Riordan SBS 16 G n E 1/1

22 Trigger Trigger Rate vs. Threshold, G, Q = 1 GeV n E Elastic Inelastic - π π + π γ Trigger Rate [khz] Threshold [GeV] Rates above include elastic e, DIS e, and π + Single arm shower/preshower (with ps cut) keeps will have < khz trigger rate without affecting QE cuts Need to allow some inelastic in trigger - prescale lower threshold Seamus Riordan SBS 16 G n E 1/1

23 Smearing and Photons Momentum Smearing, p = 1.4 GeV, δt =.5 ns Momentum Smearing, p =.7 GeV, δt =.5 ns Raw p 1 Raw p 14 Smeared p 1 Smeared p 1 1 Smeared γ 8 Smeared γ p [GeV] p [GeV] Momentum Smearing, p = 4.4 GeV, δt =.5 ns 5 Momentum Smearing, p = 6. GeV, δt =.5 ns 5 4 Raw p Smeared p Raw p Smeared p Smeared γ 15 Smeared γ p [GeV] p [GeV] Smearing ToF is asymmetric in p For highest momentum transfers β = 1 particles can get smeared in (from small p m, ) 48D48 and energy resolution of HCAL should suppress π production could contribute - need to study responses, rates Seamus Riordan SBS 16 G n E 1/1