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Overview of recent results from CLAS Marco Mirazita I.N.F.N. – Laboratori Nazionali di Frascati for the CLAS Collaboration Meson Production at Intermediate and High Energies - November 10-11, 2011 – Messina

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Jefferson Lab at Newport News, USA Hall B Hall AHall C CEBAF Large Acceptance Spectrometer CEBAF Energy : GeV Max current : 200 A Polarization : ~80 %

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The CLAS detector Toroidal magnetic field (6 supercond. coils) Drift chambers (argon/CO 2 gas, cells) Time-of-flight scintillators Electromagnetic calorimeters Cherenkov Counters (e/ separation) Performances for charged particles: large acceptance 8°< <142° in LAB frame 60-80% of good momentum and angular resolution p/p ≤0.5%- 1.5%, ≤ 1 mrad ≤ 4 mrad

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JLab physics program quarks gluons From nuclei to quarks: a laboratory from “strong” to perturbative QCD Start physics program in 1996 Distance Energy heavy nuclei few body quarks gluons vacuum Correlations Eff. NN (+ΛN) force n-radii: N Z Hadrons in-medium Hypernuclei Baryon and meson excitation spectrum Missing resonances Exotics Parton D.F. TMD GPD 3D imaging of the nucleon PV e-scattering Strange FF Parton D.F. TMD GPD 3D imaging of the nucleon Baryon and meson excitation spectrum Missing resonances Exotics Correlations Eff. NN (+ΛN) force n-radii: N Z Hadrons in-medium CLAS physics program Talk by D. Watts This talk

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From baryonic to partonic degrees of freedom Hadrons are made by 3 valence quarks, but as the resolution increases, a reach and complicated partonic structure emerges How can hadrons be described in terms of quarks and gluons ? parton distribution functions low Q 2 high Q 2 the “spin crisis” - how the proton spin is made up ? - only ~2% of the proton mass is from bare quarks, the proton mass is generated dinamically baryonic spectrum?

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Parton model in DIS e’ = (E’, k’) e = (E, k) p = (M, 0) * = (,q) W W )Q,x(g 2 2 )Q,x(g 2 1 W W spin )Q,x(F 2 2 )Q,x(F 2 1 Deep Inelastic Scattering (DIS) W 2 M 2 x B > M 2 PDFs have a simple probabilistic interpretation: they encode the distribution of longitudinal momentum and polarization carried by quarks, antiquarks and gluons within a fast moving hadron. x is the fraction of quark momentum in the scaling regime only x-dependence Q 2 corrections can be computed

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Unpolarized and Helicity PDF Unpolarized DF WELL KNOWN Helicity DF KNOWN

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Orbital Angular Momentum SU(6) RCQM broken SU(6) curves: LO pQCD without/with OAM valence quarks: JLab

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From collinear approximation to TMD Three PDFs in collinear approximation in DIS partons move collinearly with the nucleon no angular momentum Transverse Momentum Dependent parton distribution functions more complex dist. functions Access to the transverse momentum requires tagging of the leading quark in the final state

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TMD distributions all functions depend on x and p T of the quark off-diagonal elements from interference between wave functions with different angular momentum 3D picture of quarks inside the nucleon in momentum space Parton Distribution Functions Parton Fragmentation Functions

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Accessing TMDs pp → hX pp → e + e - X ep → ehX e + e - →h 1 h 2 X

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Universality and TMDs Non-zero because of initial or final state interaction Sivers and Boer-Mulders change sign form SIDIS to Drell-Yan Crucial test for the gauge structure of QCD Sivers function: - unpolarized quarks in transversely polarized nucleon - correlation between quark transverse momentum and spin of the nucleon Boer-Mulders function: - transversely polarized quarks in unpolarized nucleon - correlation between quark transverse spin and nucleon momentum TMDs are universal objects - same functions in SIDIS, e+e-, DY,...

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PTPT SIDIS Kinematical Plane and Observables Beam helicityTarget polarization U unpolarized L long.polarized T trans.polarized Extraction of the various terms from moments or asymmetries in = UU + S T UT sin( – S ) + S T LT cos( – S ) +....

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SIDIS cross section 18 structure functions Structure functions decomposition - leading twist (parton model) - higher twist ~M/Q - only f 1 and g 1 survive P T integration

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Observables in SIDIS Observables in SIDIS are the structure function F, not the partonTMD DFs and FFs. Unpolarized structure function: momentum conservation kin. factorDFFF 1.TMD P T = z k T + p T 2.Need models to unfold DFs and FFs - gaussian ansatz for the transverse momentum dependence

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TMD measurements at JLab B large acceptance spectrometer with good resolution lower luminosity cm -2 s -1 asymmetry measurements over a broad kinematical range Hall A high resolution and small acceptance spectrometers high luminosity cm -2 s -1 high polarization 3 He target (long. or transv.) neutron Hall C high resolution and small acceptance spectrometers high luminosity cm -2 s -1 high precision cross section measurements TMDs are studied at JLab through SIDIS scattering on nucleons (and nuclei) with different experimental equipments

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CLAS results

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Factorization at CLAS energies ep→e’ X In the valence region: multiplicity FF Agreement with FF extraction from world data DSS (Q 2 =2.5GeV 2 ) DSS (Q 2 =25GeV 2 )

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smooth dependence for all pions CLAS Double spin asymmetry Same analysis as in the collinear g extraction but now focus on TMD Calculations using gaussian ansatz g / f transverse mom. distribution different for quarks with spin parallel or antiparallel to nucleon spin

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leading term higher twist Target single spin asymmetry H 1 : Collins FF of transverse polarized quark in unpol. hadron h 1L : correlation between transverse spin of quarks and longitudinal spin of nucleon + - 0 HT terms can be important at JLab

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higher twist Beam single spin asymmetry Non-zero P T dependence dominant contribution from g ? g ~ HT correction of Sivers DF no x B dependence same size as +

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Hall A and C results

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phenomenological fit no sea quark contribution (x>0.3) dominance of favoured FF u + d - gaussian k T shape larger k T width for d quark than for u in DF and FF u and d quarks have different momentum distributions Unpol. cross section on H and D Similar shape for both pions Smaller slope for D than H data Hall C

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Small (zero?) Collins Larger Sivers for + than for - Hall A Collins effect Sivers effect Opposite behaviour with respect to proton data HERMES proton data Transverse target SSA on neutron

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Summary of experimental results the effect of the transverse momentum of quarks can be observed - TMD DFs and FFs are non-zero (Hermes+Compass+JLab+...) - how much does parton angular momentum contribute to the nucleon spin? first information on TMD DFs and FFs - non-zero Collins FF (SIDIS, e+e-) - non zero Sivers and Boer-Mulders DF (Hermes+Compass, JLab for the neutron) - first extraction of transversity (BELLE + HERMES) - possibility to access HT terms at JLab

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Open issues strange quark distributions are basically unknown - inconsistency between extractions from DIS and SIDIS experiments - s distributions different from sbar? kaon puzzle - Sivers and Collins for K + twice as biggere as + favoured FF u + u K + TMD extractions largely depend on the gaussian ansatz for the transverse momentum dependences - spin-dependent TMD are differences of probability, they don’t need to be positive analysis of exp. data is complicated due to convolution of DFs and FFs - multidimensional extraction of TMDs - new analysis techniques need to be implemented Need more data, especially on kaons

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End physics 6 GeV in GeV CEBAF CHL-2 Upgrade magnets and power supplies 12 GeV CEBAF Enhance equipment in existing halls add Hall D (and beam line) Beam Power: 1MW Beam Current: 90 µA Max Pass energy: 2.2 GeV Max Enery Hall A-C: 10.9 GeV Max Energy Hall D: 12 GeV May 2013 Accelerator Commissioning starts October 2013 Hall Commissioning starts

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R. De Vita, INFN – Genova Workshop sulle prospettive di fisica adronica a Jefferson Lab Genova, 27 Febbraio 2008CLAS12

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CLAS12 in Hall B Polarimeters Beam monitors, Raster system,.. Faraday cup, Beam monitors CLAS12

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Q2Q2 Kinematic coverage extending to higher x means lower cross sections need high luminosity cm -2 s -1

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GeV/c /K /p K/p TOF LTCC HTCC LTCC TOF LTCC TOF scintillators Low Threshold Cerenkov High Threshold Cerenkov charged particle radiator Photodetectors Proximity gap RICH detector to replace LTCC - good PID of kaons over the whole kinematics range - challenging project because of the large area for photodetectors need mirrors to reduce the area PID in CLAS12 no kaon ID

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Physics program with CLAS12 Experiments for the first 5 years of data taking already approved

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Conclusions Study of TMDs is one of the main items in the JLab physics program They provide a novel insight into the rich nucleon structure The first generation of experiments have shown evidence of sizeable effects due to TMDs but also open questions A new generation of experiments is in preparation at JLab with higher luminosity and improved detectors to test fundamental properties of TMDs universality test of gauge structure of QCD

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Hall A L[cm -2 s -1 ] = Pol. 3 He (neutron) target. =0.5 Longitudinal, transverse pol. Hall B-CLAS L[cm -2 s -1 ] = Pol. NH 3, ND 3 targets =0.8, =0.3 Longitudinal polarization High Momentum Spectrometer (HMS) Short Orbit Spectrometer (SOS) Hall C L[cm -2 s -1 ] = Pol. NH 3, ND 3 targets =0.8, =0.3 Longitudinal, transverse polarization

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Structure of the nucleon The complex structure of the nucleon can be described through a large variety of functions elastic FF charge and current distributions elastic scattering transition FF inelastic scattering GPD longitudinal momentum distributions at a given transverse point exclusive reactions PDF longitudinal momentum distributions of partons inclusive scattering TMD longitudinal and transverse momentum distributions of partons semi-inclusive scattering JLab main program: determination of multi-dimensional parton distribution functions in a large kinematics range

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z-dependence of SIDIS proton g 1 /F 1 37 CLAS 5.7 GeV PRELIMINARY No significant z-dependence for 0.3

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Double spin asymmetry on the neutron Evidence for non zero g1T opposite sign between p+ and p- consistent in sign with models but larger effect

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Single spin asymmetry – new data

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multiplicities in SIDIS ep→e’ X +/- multiplicities at large z diverge from SIDIS predictions 0 multiplicities less affected by higher twists 0.4

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JLab Physics 12 GeV Hall A – form factors, SRC, GPDs & TMDs, Low-energy tests of the SM and Fund. Symmetry Exp. Hall C – precision determination of valence quark properties in nucleons and nuclei Hall B - understanding 3-D nucleon structure via GPDs & TMDs - Search of new form of hadronic matter via Meson Spectroscopy Hall D - exploring origin of confinement by studying exotic mesons using real photons

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