Precision Measurement of Parity-violation in Deep Inelastic Scattering Over a Broad Kinematic Range P. A. Souder July 28, 2010 PVDIS 1
Outline • Physics potential – Standard Model Test – Charge Symmetry Violation (CSV) – Higher Twist – d/u for the Proton • New Solenoidal Spectrometer (SoLID) • Polarimetry July 28, 2010 PVDIS 2
PV Asymmetries: Any Target and Any Scattering Angle Forward Backward T + g V (g A e g V e g A T ) • The couplings g T depend on electroweak physics as well as on the weak vector and axial-vector hadronic current • For PVDIS, both new physics at high energy scales as well as interesting features of hadronic structure come into play • A program with a broad kinematic range can untangle the physics July 28, 2010 PVDIS 3
PVDIS: Electron-Quark Scattering Many new physics models give rise to neutral ‘contact’ (4 -Fermi) interactions: Heavy Z’s, compositeness, extra dimensions… f 1 f 2 f 1 f 2 1 f 2 f f 1 f or g ij ’s for all f 1 f 2 Consider 2 combinations and L,R combinations A V V A Moller PV is insensitive to the C ij C 2u and C 2d are small and poorly known: one combination can be accessed in PV DIS C 1u and C 1d will be determined to high precision by Q weak , APV Cs July 28, 2010 PVDIS 4
Deep Inelastic Scattering A PV G F Q 2 a (x) and b (x) e - e - a ( x ) Y ( y ) b ( x ) contain quark 2 * Z * distribution functions f i (x) x x Bjorken X N ( x ) + (x) C 1i Q i f i C 2i Q i f i y 1 b ( x ) a (x) = i E / E i 2 f i 2 f i + (x) ( x ) Q i Q i f f f i i i i i at high x For an isoscalar target like 2 H, structure 2 s a ( x ) 3 0 . 6 functions largely cancel in the ratio at high x 10 (2 C 1 u C 1 d ) 1 u d At high x, A PV becomes independent of x, W, 0 10 (2 C 2 u C 2 d ) u v d v b ( x ) 3 with well-defined SM prediction for Q 2 and y u d New combination of: 1 Vector quark couplings C 1q Sensitive to new physics at the TeV scale Also axial quark couplings C 2q Unknown radiative corrections PVDIS: Only way to measure C 2q for coherent processes July 28, 2010 PVDIS 5
Sensitivity: C 1 and C 2 Plots 6 GeV World’s data PVDIS PVDIS Precision Data Qweak Cs July 28, 2010 PVDIS 6
Search for CSV in PV DIS u ( x ) u p ( x ) d n ( x ) • u-d mass difference u p ( x ) d n ( x )? • electromagnetic effects d ( x ) d p ( x ) u n ( x ) d p ( x ) u n ( x )? • Direct observation of parton-level CSV would be very exciting! • Important implications for high energy collider pdfs • Could explain significant portion of the NuTeV anomaly A u d PV 0 . 28 For A PV in electron- 2 H DIS: A u d PV Sensitivity will be further enhanced if u+d falls off more rapidly than u- d as x 1 Strategy: • measure or constrain higher twist effects at x ~ 0.5-0.6 • precision measurement of A PV at x → 0.8 to search for CSV July 28, 2010 PVDIS 7
Sensitivity with PVDIS d x 0.28 u x R CSV A PV x d x A PV x u x July 28, 2010 PVDIS 8
Need Full Phenomenology 2 2 d xyM L ( 1 ) F F R R 2 ( 1 ) xyF y F 1 2 1 2 2 dxdy y E T EM V 2 2 d G xyM Z Z [ { 2 ( 1 ) }] g xyF y F 1 2 A 2 dxdy 2 2 y E Z A 2 There are 5 d G Z [ ( 2 ) ] g x y F relevant structure 3 V dxdy 2 2 functions Z V A Z ( ) Z a x ( ) ( ) f y b x V A Z Z PV A EM EM B Small; use ν data BIG EM (Higher twist workshop at Madison, Wisconsin) July 28, 2010 PVDIS 9
Why HT in PVDIS is Special Bjorken, Start with Lorentz Invariance PRD 18, 3239 (78) 4 iq x | ( ) ( 0 ) ( ) ( 0 ) | l D j x J J x j D e d x A Wolfenstein, 4 iq x | ( ) ( 0 ) | l D j x j D e d NPB146, 477 (78) iq x 4 V u u d d S u u d d | ( ) ( 0 ) | VV l D V x V D e d x 1 ( ) ( ) C C VV C C SS Next use CVC 1 u 1 d 1 u 1 d 3 A Zero in QPM 1 (deuteron only) VV SS 3 4 iq x ( )( ) | ( ) ( ) ( 0 ) ( 0 ) VV SS V S V S l D u x u x d d e d x HT in F 2 is dominated by quark-gluon correlations Higher-Twist valance quark-quark correlations Vector-hadronic piece only July 28, 2010 PVDIS 10
Quark-Quark vs Quark-Gluon PVDIS is the only known way to isolate What is a true Parton Model quark-quark quark-gluon or Quark-gluon operator? leading twist correlations diagram u u u d Di-quarks Quark-gluon operators QCD equations Might be computed correspond to of motion on the lattice transverse momentum July 28, 2010 PVDIS 11
Statistical Errors (%) vs Kinematics Strategy: sub-1% precision over broad kinematic range for sensitive Standard Model test and detailed study of hadronic structure contributions Error bar σ A /A (%) shown at center of bins in Q 2 , x 4 months at 11 GeV 2 months at 6.6 GeV July 28, 2010 PVDIS 12
Coherent Program of PVDIS Study Strategy: requires precise kinematics and broad range 1 Fit data to: 2 1 A A x HT CSV 3 2 ( 1 ) x Q C(x)= β HT /(1-x) 3 • Measure A D in NARROW bins of x, Q 2 with 0.5% precision • Cover broad Q 2 range for x in [0.3,0.6] to constrain HT • Search for CSV with x dependence of A D at high x • Use x>0.4, high Q 2 , and to measure a combination of the C iq ’s Q 2 x y New Physics no yes no CSV yes no no Higher Twist yes no yes July 28, 2010 PVDIS 13
PVDIS on the Proton: d/u at High x ( ) 0 . 91 ( ) u x d x a P ( ) x ( ) 0 . 25 ( ) u x d x Deuteron analysis has large nuclear corrections (Yellow) A PV for the proton has no 3-month run such corrections (complementary to BONUS) The challenge is to get statistical and systematic errors ~ 2% July 28, 2010 PVDIS 14
CSV in Heavy Nuclei: EMC Effect Isovector- Additional 5% vector mean possible field. (Cloet, application of Bentz, SoLID and Thomas) July 28, 2010 PVDIS 15
SoLID Spectrometer Gas Cerenkov Shashlyk Baffles GEM’s July 28, 2010 PVDIS 16
Layout of Moller and PVDIS July 28, 2010 PVDIS 17
Access to the Detectors • End Cap rolls backward along the beam line on Hilman Rollers • 342 metric tons for both end caps with baffles installed • Must allow for 5% rolling resistance July 28, 2010 PVDIS 18
Baffle geometry and support July 28, 2010 PVDIS 19
Error Projections for Moller Polarimetry Table from MOLLER director’s review by E. Chudakov July 28, 2010 PVDIS 20
Summary of Compton Uncertainties July 28, 2010 PVDIS 21
Error Budget in % Statistics 0.3 Polarimetry 0.4 Q2 0.2 Radiative Corrections 0.3 Total 0.6 July 28, 2010 PVDIS 22
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