Studies of Spin-Orbit Correlations with CLAS Harut Avakian (JLab) Deep PWG, Genova, Feb 27 H. Avakian, DPWG, Feb 27

Outline Physics motivation Spin asymmetries from eg1: Summary spin-orbit correlations and widths of PDFs Spin asymmetries from eg1: A1 measurements for pions Extraction of g1 width from pi+ data Summary After an introduction of main transverse momentum dependent parton distributions accessible with transverse target, I’ll discuss run conditions, CLAS configurations and Projected results. In the end I’ll present one example of extraction of the Sivers function from Projected measurements. H. Avakian, DPWG, Feb 27

Transverse Momentum Dependent (TMD) Distributions Quark polarization kT – leads to 3D description with 8PDFs Real and imaginary parts of the DL≠0 interference contributions Nucleon polarization Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al) As discussed in the previous presentation, the introduction of the transverse momentum of quarks, leads to addition transverse degrees of freedom for already existing collinear parton distributions Describing the momentum, helicity and transversity distributions and appearance of 5 new TMD pdfs. Columns in the table show the polarization of the parent nucleon and rows show polarizations of corresponding parton distributions. All off diagonal PDFs describe interference of wavefunctions with different orbital momenta. The new distribution appearing in particular for the longitudinally polarized target, related to the transversely polarized quarks in the longitudinally polarized nucleon describes the real part of the overlap of wave function, while the BM distribution discussed in previous presentation represents its imaginary part. In the factorized picture proved to work for SIDIS at low P_T of hadrons, two structure functions defining the cross section in the leading order factorize respectively to convolution of distribution and fragm. Functions, where D_1 is the unpolarized fragmentation function and H_q the Collins pol. FF. While the contribution involving the helicity distribution was in the focus recent decades, not much is known about the term involving the transverse spin distribution which is the main focus of the current proposal. In addition there are two more structure functions, which in case the factorization works will have contributions from all 4 functions listed here, coupled to some twist-3 distribution and fragmentation functions. While I’ll not covere the higher twist effects in this presentation we will measure also them and expect to get important info out of them as well. Factorization is a major issue and not only for higher twist structure functions but also for Leading order contribution as the energies we use to study them are relatively low. One observable that was suggested to check the factorization of the polarized structure Function was the the P_T-dependence of the double spin asymmetry. Twist-3 H. Avakian, DPWG, Feb 27

Polarized Semi-Inclusive DIS Cross section is a function of scale variables x,y,z U unpolarized L long.polarized T trans.polarized z H. Avakian, DPWG, Feb 27

CLAS configurations with long.polarized target ep→e’pX Inner Calorimeter e p- p+ CLAS detector is uniquely positioned to satisfy requirements of large x coverage and wide acceptance coverage crucial for separation of different azimuthal moments. Shown here is a typical SIDIS event with scattered electron detected in the detector and Identified by its signals in the cherenkov -> and calorimeter. You can see also radiated photon and charged pions. Detection of multiparticle final states in wide range of kinematics, crucial for understanding of background processes. The most prominent being the diffractive rho-0 production. Both target and mini-torus will be located upstream. HD-Ice target (crucial for this experiment) located upstream to increase pi0 detection with ~70cm consistent with DVCS Measurements. The suggested configuration will require measurements with different orientations of spins of H and D to minimize systematics from acceptance. 15days of polarized only D combined with D from 25 days of hydrogen running will provide comparable error bars for H and D. Additional 5 days will take measurements with pure H,D and empty targets to keep under control the dilution factors for H and D. Polarizations: Beam: ~80% NH3 proton 80% Polarized NH3/ND3 (no IC, ~5 days) Polarized NH3 with IC 60 days H. Avakian, DPWG, Feb 27

Target fragmentation in SIDIS Use PEPSI MC to define the kinematic region where the partonic description works Pions from target fragments mainly at low energies, small z and PT H. Avakian, DPWG, Feb 27

SSA with Longitudinal Target quark polarization Higher twist in fragmentation/or distribution In jet SIDIS only contributions ~ D1 survive With H1┴ (p0)≈0 (or measured) Target (Beam) SSA can be a valuable source of info on HT T-odd distribution functions H. Avakian, DPWG, Feb 27

Polarized target: HERMES vs CLAS at 5.7GeV ep → e’ p+ X ( Ee =5.7 GeV, MX > 1.1) x dependence of CLAS A1p (A┴=0) consistent with HERMES data Du/u from CLAS EG1 is consistent with GRV(GRVS) PDFs H. Avakian, DPWG, Feb 27

A1-kinematic dependences inbending outbending Ratio to inclusive asymmetry will account the x-dependence H. Avakian, DPWG, Feb 27

A1 PT-dependence in SIDIS m02=0.25GeV2 mD2=0.2GeV2 M.Anselmino et al hep-ph/0608048 Como-2005 constituent quark model (Pasquini et al). In perturbative limit predicted to be constant p+ ALL can be explained in terms of broader kT distributions for f1 compared to g1 H. Avakian, DPWG, Feb 27

Helicity distributions: Diquark model Jakob, Mulders, Rodrigues, Nucl. Phys. A 1997 q Dq Du/u (dipole formfactor), J.Ellis, D-S.Hwang, A.Kotzinian JMR model MR, R=s,a Indeed the k For given x the sign of the polarization is changing at large kT Difference in q+=f1+g1 (quark aligned with proton spin) and q-=f1-g1 - (anti-aligned) kT-dependences may lead to observable effects H. Avakian, DPWG, Feb 27

A1 PT-dependence in SIDIS 0.4<z<0.7 M.Anselmino et al hep-ph/0608048 m02=0.25GeV2 mD2=0.2GeV2 more data in 2009! p+ A1 suggests broader kT distributions for f1 compared to g1 p- A1 may require non-Gaussian kT-dependence for different helicities and/or flavors H. Avakian, DPWG, Feb 27

cosf moment in A1-PT-dependence hep-ph/0608048 m02=0.25GeV2 mD2=0.2GeV2 CLAS PRELIMINARY PT-dependence of cosf moment of double spin asymmetry is most sensitive to kT-distributions of quarks with spin orientations along and opposite to the proton spin. H. Avakian, DPWG, Feb 27

Extracting widths from ALL Assuming the widths of f1/g1 x,z and flavor independent Anselmino et al Collins et al Fits to unpolarized data H. Avakian, DPWG, Feb 27

A1 PT-dependence Anselmino Collins CLAS data suggests that width of g1 is less than the width of f1 H. Avakian, DPWG, Feb 27

Summary double spin asymmetries measured at CLAS are consistent with HERMES and fits to world data, assuming the factorized picture PT-dependence of the double spin asymmetry provides access to kT-widths of transverse momentum dependent distributions of quarks. CLAS data suggests that the kT-width of the momentum distribution is wider than the width of the helicity distribution The suggestions of the review committee have been applied and the analysis note has been prepared for the next round of review. H. Avakian, DPWG, Feb 27

Support slides…. H. Avakian, DPWG, Feb 27

IC Experimental Setup (CLAS EG1+IC) Polarized target (eg1) solid NH3 polarized target proton polarization ~80% high lumi ~ 21034 s-1cm-2 13o 50o Major componnents of the proposed experimental setup are the Polarized target used in the Eg1 run with polarized solid ammonia (${}^{14}$NH$_{3}$), polarized via Dynamic Nuclear Polarization, which requires cooling the target to 1 K, and holding it in a uniform ($\Delta B/B=10^{-4}$) magnetic field of 5T. The polarized target magnetic field shields the detector from the Moller electrons produced in the target by focusing them onto the beam line, allowing lumi as high as 2x10^34 The IC designed for the e1-DVCS experiment, used with polarized target will significantly increase the kinematic coverage for the direct detection of high-energy photons from the decay of high momentum $\pi^0$. **The target polarization direction will bereversed many times during the experiment by changing the frequency **of the microwaves used to polarize the target. **The cooling system is a ${}^{4}$He evaporation refrigerator. **The ${}^{4}$He, $N$, and Al endcap contributions to the cross sections and asymmetries will be **determined using data from the ${}^{12}C$ and empty cell targets. **Approximately 7 daysof running on these targets will be needed for accurate measurements of the dilution factor **and background asymmetries. For a more accurate determination of the product of target and beam polarizations, **$P_e P_t$, we will use the well-known $ep$ elastic scattering asymmetry, as was done in Eg1b. **To minimize radiation damage to the target the beam will be rastered over the target surface in a spiral pattern. ** The beam motion is indirectly recorded in the data stream by storing the ADC values of the raster magnet. ** M{\o}ller electrons, which are the vastly dominating source of electromagnetic background, will pass through the ** central penetration in the lead-tungstate wall, and be absorbed in the downstream shielding pipe. The shielding ** arrangement is very similar to the one used during Eg1. IC Inner Calorimeter (424 PbWO4 crystals) for the detection of high energy photons at forward lab angles (e1-DVCS). H. Avakian, DPWG, Feb 27

Collinear Fragmentation p quark Collinear Fragmentation The only fragmentation function at leading twist for pions in eN→e’pX is D1(z) Ee =5.7 GeV No significant variation observed in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT H. Avakian, DPWG, Feb 27

p0 multiplicities ep→e’p0X M.Aghasyan DSS (Q2=2.5GeV2) DSS (Q2=25GeV2) p0 multiplicities consistent with SIDIS predictions H. Avakian, DPWG, Feb 27

sinf SSA analysis for pi0 Measure both for 3 pions and combine to separate different contributions. With H1┴ (p0)≈0 (or measured) Target (Beam) SSA can be a valuable source of info on HT T-odd distribution functions H. Avakian, DPWG, Feb 27

Dilution factor in SIDIS Fraction of events from polarized hydrogen in NH3 Nu,Np -total counts from NH3 and carbon normalized by lumi ru, rp -total areal thickness of hydrogen (in NH3), and carbon target Cn=Nitr/Carbon ratio (~0.98) Diff. symbols for diff x-bins p- Nuclear targed introduces in addition to significant nuclear background, also attennuation effects, which have to be studied separately. Multiple scattering and attenuation in nuclear environment introduces additional PT-dependence for hadrons H. Avakian, DPWG, Feb 27