Study of Neutron Structure with Spectator Tagging via eD e NX in - PowerPoint PPT Presentation

Study of Neutron Structure with Spectator Tagging via eD → e ′ NX in MEIC Kijun Park 1 1 Old Dominion University/Jefferson Lab March 9, 2015 K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 1 / 33

Electron Ion Collider Importance of low x physics - Gluon and sea quark (transverse) imaging of the nucleon - Nucleon Spin (∆ G vs. log Q 2 , transverse momentum) - Nucleon QCD (gluons in nuclei, quark/gluon energy loss) - QCD vacuum and Hadron Structure and formation K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 2 / 33

Electron Ion Collider → Spectator Tagging Figure : A Schematic of Reaction eD → e ′ p s X No Free Neutron Target - Neutron Structure (flavor decomposition of quark spin, sea quarks, gluon pol.) - Spectator Nucleon Tagging (forward detection/unique for collider) - Polarized Deuterium (a simple wave function/pol. neutron spin/limited FSI/coherence N = 2,...) K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 3 / 33

Spectator Tagging → Extrapolating Neutron Structure ��� ��� X ��� ��� ( − M N ) 2 on−shell point ∼ n ��� ��� F 2 n ( x, Q ) 2 D ��� ��� t ��� ��� d [..] ∗ ����� ����� ��� ��� ∼ GeV 2 0.1 ��� ��� p ��� ��� σ/ ��� ��� α , p d R RT = ( p ) t p − 2 m N − t 2 R D [by courtesy of C. Weiss] Light-Cone momentum fraction, Transverse momentum of recoil proton: α R = 2 E R + p z R , � p RT M D Cross-section in the IA d σ � x � , Q 2 = f Flux × S D ( α R , p RT ) × F 2 n dxdQ 2 d α R d 3 p R / E R 2 − α R N ≡ t ′ → 0) On-shell extrapolation: t → M 2 ( t − M 2 N - Free neutron structure at pole - FSI does not affect to pole value - Model-independent method K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 4 / 33

Spectator Tagging: Coherent Effects at x ≪ 0 . 1 ��� ��� X ��� ��� ��� ��� ��� ��� ��� ��� n ��� ��� ��� ��� Shadowing effect important in inclusive ������ ������ ��� ��� p ��� ��� DIS x ≪ 0 . 1 ��� ��� interference Diffractive scattering on single nucleon + Interference between scattered p and n ��� ��� X ��� ��� ��� ��� ��� ��� ��� ��� n ��� ��� ������ ������ ��� ��� ��� ��� p ��� ��� ��� ��� Shadowing in Tagged DIS Coherent effect is clean ( N = 2) ��� ��� X ��� ��� ��� ��� Systematics is important (unpol./pol.) ��� ��� ��� ��� ��� ��� in p - n ����� ����� ��� ��� S ��� ��� p T FSI between p and n → distortion of ��� ��� ��� ��� p T , spin [by courtesy of C. Weiss] K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 5 / 33

Far-forward Detection in EIC Good acceptance for all ion fragments - rigidity different from beam - Large magnet apertures (small gradients a fixed maximum peak field) Good acceptance for low- p T recoils - rigidity similar to beam - Small beam size detection point (downstream focus, efficient cooling) - Large dispersion (generated after the IP, D = D ′ =0 the IP) Good momentum and angular resolution - Longitudinal dp / p ≈ 4 · 10 − 4 - Angular in θ , for all φ : ≈ 0 . 2mrad - p RT ≈ 15MeV/c resolution for tagged nucleon in 100GeV deuterium beam - Long, instrumented drift space (no apertures, magnet, ...) Sufficient beam line separation ( ≈ 1m) K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 6 / 33

MC Simulation Basic configuration: E e = 5 GeV, E D = 100 GeV, p R < 300 MeV, cross-angle: 50 mrad Normal. Emittances: dp / p = 3 × 10 − 4 , d θ = 2 × 10 − 4 , Luminosity= 10 33 cm − 2 sec − 1 , Time= 10 6 ( sec ), [e.g: HERA config.] User inputs: cross-section model - nucleon Struc.Func./deuteron Wav.Func./deuteron Residue Spect.Func. Known facts: Initial State Smearing (ISS) is ≪ ± 1% Intrinsic MC Statistical Uncertainty is ≤ 1% Sufficient t ′ resolution for the extrapolation F 2 D structure function on-shell extrapolation with experimental uncertainty estimation � d σ ∆ σ MC ∆ σ MC � N i ∆ t ′ ∆ σ MC = dxdQ 2 dt ′ Γ · J / N 0 , count = L · T · ∆ σ MC , σ (∆ σ MC ) = √ count = L · T K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 7 / 33

MC Simulation → F 2 D ( x , Q 2 , α R , t ′ ) Actual Distribution htS htS 2.2 of tPrime at vertex Entries Entries 26880 26880 Mean -0.0003975 Mean -0.0003975 2 Intrinsic momentum spread in Ion beam RMS RMS 0.005271 0.005271 1.8 smears recoil momentum 1.6 Dominant uncertainty for MEIC 1.4 Effect on t ′ (angular spread) x=0.01-0.05 1.2 Q2=15-20GeV2 Smearing < t ′ bin-size 1 0.8 0.6 0.4 0.2 0 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 Delta tPrime F 2 D vs. t ′ : take out f Flux α R : cut around 1.0 ± 0.02 Excellent resolution allows to reach smaller t ′ Feasible on-shell extrapolation blue vertical dash line: t ′ min = 0 . 00416 GeV 2 K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 8 / 33

MC Simulation → Detector Simulation [GEMC] Sample Tracks in Detector Simulation Figure : Examples of 10 physics events from eD → e ′ p s X , red color rays: spectator protons, light-blue rays: scattered electrons. This configuration has no solenoid field. K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 9 / 33

e , � Polarization ( � D ), hel = ± 1 along each beam � � A || = N + − N − � 1 − A 2 and A 1 (= A || / D ′ ), δ A = Asymmetry N + + N − N + + N − D ′ = 1 − ǫ � � 1 + y · γ s = (1 − ǫ )(2 − y ) � � �� 2 − y : Depolarization, or y 2 y (1+ ǫ R ) , where γ s = 4 x 2 D M 2 D / Q 2 , y = Q 2 / x D / ( s eD − M 2 D ), R = σ L /σ T K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 10 / 33

Depolarization dependence x BJ , Q 2 Simple Check with certain variables at x BJ = 0 . 06 − 0 . 08, Q 2 = 15 − 20 GeV 2 D ′ = 1 − ǫ 1 + y · γ s � � �� 2 − y y 2 γ s = 4 x 2 D M 2 D / Q 2 , y = Q 2 / x D / ( s eD − M 2 D ) D ′ in given x BJ , Q 2 bins K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 11 / 33

Diffractive Effects Kinematics I : x BJ = 0 . 01 − 0 . 02, Q 2 = 15 − 20 GeV 2 Diffractive Effect shows a stronger impact in large t ′ than low − 9% , t ′ = 0 . 08 GeV 2 +1% , t ′ = 0 . 01 GeV 2 Kinematics II : x BJ = 0 . 0009 − 0 . 0012, Q 2 = 15 − 20 GeV 2 Diffractive Effect shows a stronger impact in smaller x BJ − 19% , t ′ = 0 . 08 GeV 2 and − 1 . 8% , t ′ = 0 . 01 GeV 2 [Vadim’s shadowing corrections] K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 12 / 33

Systematic uncertainty: momentum smearing effect x BJ =0.04-0.06, Q 2 =30-40 GeV 2 , S eD =2002.442 GeV 2 Exact calculation (Red) and nominal smearing (Black) Up to 30% difference at lower p RT Fixed Point p RT = 0 . 45 GeV (vertical dashed line) Difference between no-smearing and nominal smearing of Ion beam Trans. emittances K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 13 / 33

Global systematic uncertainty: p RT smearing x BJ =0.0499-0.0501, Q 2 =34.99-35.01 GeV 2 The systematic uncertainty from the uncertainty in the beam rms is ± 2.5% Check the relation between t ′ and p RT in Code (make sure print out same values) � � M 2 P R | 2 = − t ′ | � t ′ D − M 2 1 − + N , 2 2 M 2 4 D where t ′ = M 2 N − t � � | � P R | 2 − pSpec Rest 2 P RT = z = invts . pPerpS Relative Error (Rel.Err.)   � � d σ d σ  −  dxdQ 2 ,.., pnom + δ dxdQ 2 ,.., pnom R R = � � d σ dxdQ 2 ,.., pnom R ** Random number seed is randomized each Figure : Using correct p RT definition in the collinear frame. run, the ran.num.seed error ≪ 1% K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 14 / 33

F 2 D · Spec( RES , ( t ′ ) 2 ) as a function of t ′ Systematic uncertainty is dominated at lower t ′ On-shell extrapolation is about 0.5% change Extrapolation fitting uncertainty gets larger factor of ∼ 2.4 K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 15 / 33

On-shell extrapolation F 2 n as a function of x BJ , Q 2 E e = 5 GeV, E D = 100 GeV, s eD = 2002.442 GeV 2 L = 10 33 cm − 2 s − 1 , T = 3 × 10 6 s Figure : (Left) Kinematic map of F 2 n (ˆ z -axis) in terms of x BJ , Q 2 , (right) F 2 n vs. Q 2 . Band-(a): x BJ dependence at fixed Q 2 = 10 . 0 − 12 . 58 GeV 2 , band-(b): Q 2 dependence at fixed x BJ = 0 . 1 − 0 . 126 K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 16 / 33

Extrapolation F 2 n : x BJ -dependence at fixed � Q 2 � = 11 . 29GeV 2 Kinematic Band-(a) K.Park (ODU/JLAB) High Energy Physics with Spectator Tagging March 9, 2015 17 / 33