Dihadron production at Jefferson Lab. Sergio Anefalos Pereira - PowerPoint PPT Presentation

XXII. International Workshop on Deep-Inelastic Scattering April 28 – May 2, Warsaw Dihadron production at Jefferson Lab. Sergio Anefalos Pereira (INFN - Frascati)

Physics Motivation Describe complex nucleon structure in terms of partonic degrees of freedom of QCD • ι n the collinear approximation there are 3 leading twist PDFs + 3 twist-3 PDFs which survive the integration over the transverse momentum. They give a detailed picture of the nucleon in longitudinal momentum space; • the goal of the present work is to extract the two twist-3 collinear distribution functions e(x) and h L (x) looking at dihadron SIDIS, where: e (x) : sub-leading twist PDF of transverse polarized quark in an unpolarized nucleon number density h L (x) : sub-leading twist PDF of transverse e polarized quark in a longitudinally polarized nucleon helicity h L transversity g T 04/30/2014 DIS2014 Warsaw 2

Physics Motivation PRD 67, 114014 (2003) The twist-3 PDFs e(x) and h L (x) contains important information on the quark-gluon correlations. The first extraction of e(x) [PRD 67, 114014 (2003)] has been done using single-pion CLAS data [PRD 69, 112004 (2004)] There are also some model predictions: chiral quark soliton (χQSM) spectator model bag model Phys. Rev. D64 (2001) 034013 Nucl. Phys. A626 (1997) 937 Nucl. Phys. B375 (1992) 527 04/30/2014 DIS2014 Warsaw 3

Physics Motivation On the other hand, h L (x) has only some model predictions chiral quark soliton (χQSM) spectator model bag model Phys. Rev. D64 (2001) 034013 Nucl. Phys. A626 (1997) 937 Nucl. Phys. B375 (1992) 527 04/30/2014 DIS2014 Warsaw 4

JLab Accelerator CEBAF • Continuous Electron Beam • Energy up to 6 GeV • 1nA - 200 µ A simultaneous beam in different halls • polarization up to 85% CLAS 04/30/2014 DIS2014 Warsaw 5

Hall B: Cebaf Large Acceptance Spectrometer (CLAS) Torus magnet Electromagnetic calorimeters 6 superconducting Lead/scintillator, 1296 coils photomultipliers Liquid D 2 (H 2 )target + γ start counter; e • Broad angular coverage minitorus (8° - 140° in LAB frame) Drift chambers • Charged particle momentum argon/CO 2 gas, 35,000 resolution ~0.5% forward cells direction CLAS is designed to measure exclusive reactions with multi-particle final states Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/ π separation, 216 PMT s 04/30/2014 DIS2014 Warsaw 6

The eg1-dvcs experiment • beam polarization ~ 85% • proton polarization ~ 80% • used the Inner Calorimeter (in addition to the EC) to detect photons at small angles. NH 3 Hydrogen target (NH 3 ) Part A Beam energy: 5.892 GeV ND 3 4.735 GeV Luminosity: 22.7 fb -1 12 C Hydrogen target (NH 3 ) Part B Empty Beam energy: 5.967 GeV Luminosity: 50.7 fb -1 Runs with 12 C target for Deuterium target (ND 3 ) background evaluation Part C Beam energy: 5.764 GeV Luminosity: 25.3 fb -1 04/30/2014 DIS2014 Warsaw 7

SIDIS observables and kinematical planes ν= E − E' 2 =( k − k ' ) 2 Q y =ν/ E 2 / 2M ν x = Q z = E h / ν the fraction of the virtual-photon energy carried by the two hadrons π x F = 2 p ∥ π X W longitudinal momentum fraction carried by the hadron, where W is the γ *-p center-of-mass energy 04/30/2014 DIS2014 Warsaw 8

Definition of azimuthal and polar angles k k' q the angle between the direction of P 1 in the π + π - center-of-mass frame, and the direction of P h in the photon-target rest frame. 04/30/2014 DIS2014 Warsaw 9

Structure functions in terms of PDF and DiFF q ( x ) D 1 q ( z , cos θ , M h ) F UU ,T = x f 1 F UU , L = 0 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F UU z f 1 D Q cos2 φ R = 0 F UU sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) ̃ q ( x ) H 1 ∢ q ( z , cos θ , M h )] F LU xe z f 1 G Q M h sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) H 1 q ( x ) ̃ ∢ q ( z , cos θ , M h )] F UL x h L z g 1 G Q M h sin2 φ R = 0 F UL q ( x ) D 1 q ( z , cos θ , M h ) F L L = x g 1 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F L L z g 1 D 1 Q 04/30/2014 DIS2014 Warsaw 10

Structure functions in terms of PDF and DiFF q ( x ) D 1 q ( z , cos θ , M h ) F UU ,T = x f 1 F UU , L = 0 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F UU z f 1 D Q cos2 φ R = 0 F UU sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) ̃ q ( x ) H 1 ∢ q ( z , cos θ , M h )] F LU xe z f 1 G Q M h sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) H 1 q ( x ) ̃ ∢ q ( z , cos θ , M h )] F UL x h L z g 1 G Q M h sin2 φ R = 0 F UL q ( x ) D 1 q ( z , cos θ , M h ) F L L = x g 1 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F L L z g 1 D 1 Q 04/30/2014 DIS2014 Warsaw 1 0

Structure functions in terms of PDF and DiFF q ( x ) D 1 q ( z , cos θ , M h ) F UU ,T = x f 1 F UU , L = 0 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F UU z f 1 D Q cos2 φ R = 0 F UU sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) ̃ q ( x ) H 1 ∢ q ( z , cos θ , M h )] F LU xe z f 1 G Q M h sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) H 1 q ( x ) ̃ ∢ q ( z , cos θ , M h )] F UL x h L z g 1 G Q M h sin2 φ R = 0 F UL q ( x ) D 1 q ( z , cos θ , M h ) F L L = x g 1 cos φ R =− x ∣ R ∣ sin θ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h ) F L L z g 1 D 1 Q 04/30/2014 DIS2014 Warsaw 10

Strategy behind the extraction of e(x) and h L (x) sin φ R =− x ∣ R ∣ sin θ [ M ∢ q ( z , cos θ , M h )+ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h )] q ( x ) H 1 F LU xe z f 1 G Q M h ~ 0 sin φ R =− x ∣ R ∣ sin θ [ M q ( x ) H 1 ∢ q ( z , cos θ , M h )+ 1 q ( x ) ̃ ∢ q ( z , cos θ , M h )] F UL x h L z g 1 G Q M h ~ 0 in the Wandzura-Wilczek approx. for fragmentation functions Phys. Lett. B72 (1977) 195 ∢ q The interference H 1 Fragmentation Function has been recently extracted by the Belle Collaboration from e + /e − data PRD 85, 114023 (2012) ∢ u ( z , M h ;Q 0 2 ) H 1 R ( z , M h )= ∣ R ∣ where M h u ( z , M h ;Q 0 2 ) D 1 04/30/2014 DIS2014 Warsaw 11

Analysis procedure  semi-inclusive channel  two topologies will be analyzed:  e p → e’ π + π - X π π X  e p → e’ π + π 0 X → e’ π + γ γ X - π 0 is identified as M ( γ γ ) 04/30/2014 DIS2014 Warsaw 12

Current fragmentation region and SIDIS cut π ± > π + x ( ) 0 F the CFR comprise hadrons produced in the forward hemisphere (along the virtual photon) π - the final sample will be then binned in three variables: x , z , M h MM > 1.1 GeV 04/30/2014 DIS2014 Warsaw 13

Beam-Spin Asymmetry (BSA)  − N – ) P t – +( N – − N – – ) P t  ( N A LU = – + N  ) P t – +( N – – + N – ) P t  ) P B (( N ∢ q ( z , cos θ , M h ) A LU ∝ e ( x ) H 1 ● significantly non-zero asymmetries ● gives access to the sub-leading twist PDF e (x) 04/30/2014 DIS2014 Warsaw 14

Beam-Spin Asymmetry (BSA)  − N – ) P t – +( N – − N – – ) P t  ( N A LU = – + N  ) P t – +( N – – + N – ) P t  ) P B (( N ∢ q ( z , cos θ , M h ) A LU ∝ e ( x ) H 1 ● Two independent analysis ● Two different experiments (unpolarized H 2 target (e1f) and longitudinally polarized NH 3 target (eg1-dvcs)) ● Good agreement between the two analysis ● No nuclear effects observed 04/30/2014 DIS2014 Warsaw 15

Target-Spin Asymmetry (TSA) – – + N – − N – + N  A UL = 1 − N – + N  ) P t – +( N – – + N – ) P t  D f ( N ● significantly non-zero asymmetries ∢ q ( z , cos θ , M h ) A UL ∝ h L ( x ) H 1 ● DF = 0.18 has been used ● sin 2 φ compatible with zero ● gives access to the sub-leading twist PDF h L (x) 04/30/2014 DIS2014 Warsaw 16

Beam- and Target-Spin Asymmetry comparison ● Similar behavior for z and M h dependence ● Opposite trend in the x dependence ● TSA higher than BSA, in some cases up to 5 times higher ● In the present approximation, the ratio A LU /A UL can provide information about the relative weights ∢ q ( z , cos θ , M h ) A LU ∝ e ( x ) H 1 of e(x) and h L (x) ∢ q ( z , cos θ , M h ) A UL ∝ h L ( x ) H 1 04/30/2014 DIS2014 Warsaw 17

Double-Spin Asymmetry (DSA) – – − N – − N – + N  1 N A L L = – + N  ) P t – +( N – – + N – ) P t  D f P B ( N ● Significantly non-zero A LL const asymmetries const ∝ g 1 ( x ) D 1 q ( z , cos θ , M h ) A L L ● DF = 0.18 has been used cos ϕ R ∝ g 1 ( x ) ̃ ∢ q ( z , cos θ , M h ) A L L D 04/30/2014 DIS2014 Warsaw 18

Extracting A 1 from dihadron A LL const as a sanity check ● A 1 can be calculated as 2 g 2 A 1 ≈ g 1 −γ f 1 ● In this check, A 1 was calculated assuming g 2 = 0 const ≈ F UU ● We measure A L L F L L q ( x ) D 1 q ( z , cos θ , M h ) g 1 ≈ q ( x ) D 1 q ( z , cos θ , M h ) f 1 04/30/2014 DIS2014 Warsaw 19