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Future Measurements at 12 GeV at Jlab

Future Measurements at 12 GeV at Jlab. A. Bruell (Jefferson Lab). 21st Winter Workshop on Nuclear Dynamics Breckenridge, Feb 8, 2005. The 12 GeV upgrade at Jefferson Lab Nuclear effects in hadronisation Transversity and transverse momentum dependent

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Future Measurements at 12 GeV at Jlab

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  1. Future Measurements at 12 GeV at Jlab A. Bruell (Jefferson Lab) 21st Winter Workshop on Nuclear Dynamics Breckenridge, Feb 8, 2005 • The 12 GeV upgrade at Jefferson Lab • Nuclear effects in hadronisation • Transversity and transverse momentum dependent • parton distributions • Summary

  2. Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls Add new hall 12 11 6 GeV CEBAF

  3. Main Physics Topics • Confinement in QCD • search for glueballs and hybrid mesons • Flavour and spin structure of the nucleon • high x behaviour of parton distributions • flavour dependence of spin dependent PDFs • transverse momentum dependent PDFs • Generalised parton distributions (exclusive processes) • Physics of nuclei • origin of EMC effect • hadron attenuation and pT broadening • short range correlations

  4. Enhanced and/or Complementary Equipment in Halls A, B, & C and a New Hall D A B Medium Acceptance Detector (MAD) at high luminosity and intermediate angles CLAS upgraded to higher (1035) luminosity and coverage C D Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles 9 GeV tagged polarized photons and a 4 hermetic detector

  5. Hadronisation in the Nuclear Environment • Nucleus acts as a spatial filter for outgoing hadronisation products determine hadronisation distance scales and reaction mechanisms partonic energy loss via gluon emission ?

  6. Observables

  7. Transverse momentum broadening from Fermilab Drell-Yan Experiments Quark-Gluon Dynamics L • Struck quark emits gluons in vacuum because of confinement • In nuclear medium, multiple scattering will stimulate additional gluon radiation; may vary as L2 (!) – QCD LPM effect • Gluon radiation creates dE/dx that can be connected to transverse momentum broadening (an experimental observable): • Indications from models and data suggest dE/dx may be of measurable size, ~ 1 GeV/fm • There is an associated quark-gluon correlation function (Guo and Qiu, PRD61, 096003, 2000) • Energy loss is proportional to the gluon density of the medium

  8. Recent Model Approaches: Semi-Inclusive DIS on Nuclei The essential reaction mechanism has not been isolated: Hadron forms inside nucleus or outside? or both? • Gluon bremsstrahlung (Kopeliovich) • Gluon radiation of colored quark • Formation of color singlet pre-hadron • Color transparency modulates pre-hadron (color dipole) attenuation • Hadron attenuates in medium • Twist-4 pQCD model (Wang) • Medium-induced gluon radiation modifies fragmentation function • No hadronization • Non-abelian LPM effect predicted • Can extrapolate to predict jet quenching in RHI collisions

  9. Recent Model Approaches: Semi-Inclusive DIS on Nuclei • Semi-Classical Coupled-Channel Transport (Mosel, Falter) • Initial state from Pythia • Detailed final state interactions within a coupled-channel BUU transport model • Tested extensively against many other reactions with leptonic and hadronic probes • Rescaling models (Accardia, Pirner, Muccifora) • Partial deconfinement of nucleon in nucleus (lA>l0) • => PDF’s and frag. fcns. modified The models vary in sophistication, but all can describe the HERMES data! Differentiate among models: extend measurements to more variables and observables

  10. Jefferson Lab Experiments: Next 7 Years • E02-104 (Brooks, CLAS EG2) in Hall B • Took part of data in January-February this year • Hadronization, transverse momentum broadening surveyed over a wide kinematic range • E04-002 (Chen, Norum, Wang) in Hall A • Hadronization in narrow kinematic bins with good particle ID for charged K and p • Waiting to get on the schedule • Interest in Hall C (Ent, Gaskell, Keppel, Kinney) • Transverse momentum broadening in narrow kinematic bins with good particle ID for charged K and p • Proposal under discussion

  11. 12 GeV Anticipated Data Bins in yellow are accessible at 6 GeV 12 GeV Anticipated Data

  12. Accessible Hadrons (12 GeV)

  13. Transverse momentum dependent parton distributions and fragmentation functions • transversity, Collins fragmentation function, Sivers functions and friends

  14. SIDIS kinematic plane and relevant variables

  15. Transverse momentum of quarks • kT – crucial for orbital momentum and spin structure studies • lead to SSA in hard scattering processes • kT – lead to 3 dimensional description • lead to introduction of kT dependent/u PDFs • kT - important for cross section description (important also for exclusive production) • PT distributions of hadrons in DIS • exclusive photon production (DVCS) • - hard exclusive vector meson x-section • - pp → p0X (E704,RHIC) x-sections To study orbital motion of quarks in semi-inclusive DIS measurements in a wide range of PT, f and fS are required.

  16. e Unpolarized target e p Longitudinally pol. target Transversely pol. target p SIDIS at leading twist Mulders et al. Boer Mulders e Sivers transversity Off-diagonal PDFs vanish if quarks only in s-state! In addition T-odd PDFs require FSI(Brodsky et al., Collins, Ji et al. 2002) • Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al) • Universality of kT-dependent distribution and fragmentation functions proven (Collins,Mets…)

  17. Universality of Distribution & Fragmentation functions J. Collins kT-dependent distribution and fragmentation functions are universal ! Brodsky et al.→ h┴1 responsible for measured cos2f in DY (CERN 1986-87 , Fermilab 1989)

  18. Wpu(x,k,r) “Parent” Wigner distributions d3r d2kT (FT) TMD PDFs: fpu(x,kT),.. GPDs: Hpu(x,x,t), … x=0,t=0 dx d2kT PDFs fpu(x),… FFs F1pu(t),F2pu(t).. Probability to find a quark u in a nucleon P with a certain polarization in a position r and momentum k GPD Measure momentum transfer to quark kT distributions also important for exclusive studies Measure momentum transfer to target Exclusive meson data important in understanding of SIDIS measurements Some PDFs same in exclusive and semi-inclusive analysis Analysis of SIDIS and DVMP are complementary

  19. ep→e’pX: kinematic coverage at 11 GeV • Acceptance in Q2,Mx,PT gained with high luminosity and energy upgrade (at 6GeV Mx<2.5GeV, Q2<4.5GeV2, PT<1GeV) • test factorization in a wide kinematic range • study the transition between the nonperturbative and perturbative regimes of QCD • measure PDFs and study higher twists

  20. p quark Collinear Fragmentation The only fragmentation function at leading twist for pions in eN→e’pX is D1(z) Ee =5.7 GeV Hall-CEe =5.5 GeV No significant variation observed in p+/p- ratio and in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5)

  21. Sivers AUT ~ Sivers SSA: First measurement f1T┴, requires final state interactions + interference between different helicity states • f1T┴ consistent with large Nc limit • A<0, consistent with predictions of Burkardt based on the link of Sivers PDF and GPD E • Significantly different from pp→pX fit Efremov et al. (hep-ph/0412353)

  22. Collins AUT ~ Interpretation requires large unfavored spin dependent fragmentation. Transversely polarized target SSA transversely polarized quarks in a transversely polarized nucleon. • No success so far in describing consistently Collins SSA for all 3 pions at least in cQSM! • More data needed, new observables GSI, CERN

  23. Collins AUT ~ Sivers AUT ~ Transverse Target SSA @11 GeV CLAS @ 11GeV (NH3) p+ p0 p- f1T┴, requires final state interactions + interference between different helicity states Simultaneous (with pion SIDIS) measurement of, exclusive r,r+,w with a transversely polarized target important to control the background.

  24. Longitudinally polarized Target SSA for p+ Measurement of kT dependent twist-2 distribution provides an independent test of the Collins fragmentation. Real part of interfe-rence of wave functions with L=0 and L=1 In noncollinear single-hadron fragmentation additional FF H1(z,kT) Efremov et al. p • Study the PT – dependence of AULsin2f • Study the possible effect of large unfavored Collins function. kT quark

  25. PT-dependence of beam SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) In the perturbative limit 1/PT behavior expected Perturbative region Nonperturbative TMD Asymmetries from kT-odd and kT-even (g1) distribution functions are expected to have a very different behavior (flat A1p(PT) observed at 5.7 GeV).

  26. Transversity in double pion production h1 “Collinear” dihadron fragmentation described by two functions at leading twist: D1(z,cosqR,Mpp),H1R(z,cosqR,Mpp) RT quark h2 The angular distribution of two hadrons is sensitive to the spin of the quark • Collins et al, Ji, Jaffe et al, • Radici et al. relative transverse momentum of the two hadrons replaces the PT in single-pion production (No transverse momentum of the pair center of mass involved ) Dihadron production provides an alternative, “background free” access to transversity

  27. Summary • Jlab upgrade to 12 GeV will allow to • (amongst many other things) • measure the hadron attenuation ratio for many hadrons with high precision and as function of all relevant kinematic variables • investigate the pTbroadening in nuclei • determine the essentially unknown transversity and Sivers functions with high precision and in a variety of channels • sensitivity to orbital motion of quarks Essential for understanding the structure of the nucleon and its modification in the nuclear environment

  28. support slides…..

  29. Hayk Hakobyan, Yerevan State U. CLAS EG2, very preliminary, 5% of total data set DIS kinematics, Q2>1, all n Carbon Iron Lead • No acceptance correction (small, two targets in the beam) • Not final calibrations (should be nearly irrelevant, bins are huge) • No fiducial cuts (probably ok, two targets in beam) • No radiative correction (effect primarily cancels in ratios) • No correction for pi+ from rho (need full statistics to correct for this)*** • Few-percent kaon contamination in region 2-2.7 GeV • No isospin correction for heavy targets(~5%?) • No xF cuts

  30. Semi-Inclusive Deep Inelastic Scattering (SIDIS) DIS: Major source of QCD tests and PDF studies • Probes only the sum of quarks and anti-quarks • Requires assumptions on sea • No access to transversity effect in LO SIDIS: “Tagging” to distinguish different quark flavors. • Provide access to quark distributions with fragmentation acting as a weight factor: • Probes orbital motion of quarks. Main focus of SIDIS studies: • orbital angular momentum of quarks • parton distributions at large x

  31. Hayk Hakobyan, Yerevan State U. CLAS EG2, very preliminary, 5% of total data set DIS kinematics, Q2>1, all n Carbon Iron Lead • No acceptance correction (small, two targets in the beam) • Not final calibrations (should be nearly irrelevant, bins are huge) • No fiducial cuts (probably ok, two targets in beam) • No radiative correction (effect primarily cancels in ratios) • No correction for pi+ from rho (need full statistics to correct for this)*** • Few-percent kaon contamination in region 2-2.7 GeV • No isospin correction for heavy targets(~5%?) • No xF cuts

  32. Polarized PDFs Ee =11 GeV NH3+He3 g1u=u,g1d=d…. Jlab @11 GeV • Asymmetry measurements with different hadrons (p+p-) and targets (p,n) allow flavor separation

  33. JLab @11 GeV Flavor decomposition: polarized sea • Predictions: • Instantons (QSM): • First data from HERMES •  0 More data expected from RHIC W± production in future

  34. SIDIS: target fragmentation xF>0 (current fragmentation) xF- momentum in the CM frame xF<0 (target fragmentation, TFR) Wide kinematic coverage at 11 GeV allows studies of hadronization in the target fragmentation region

  35. e e’ Λ in target fragmentation 1 Λ p 2 π L – unique tool for polarization study due to self-analyzing parity violating decay (ud)-diquark is a spin and isospin singlet → s-quark carries whole spin of L L polarization in TFR provides information on contribution of strange sea to proton spin 6 Polarized beam gives unique possibility to perform an “acceptance independent” measurement of L polarization in electroproduction. W.Melnitchouk and A.W.Thomas ‘96 J.Ellis, D.Kharzeev, A. Kotzinian ‘96

  36. JLab at 12 GeV Wide physics acceptance (exclusive, semi-inclusive current and target fragmentation) Complementarity of high luminosity and wide geometric acceptance halls High luminosity polarised CW beam

  37. Measuring the Q2 dependence of SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) For fixed x, 1/Q behavior expected Wide kinematic coverage allows to check the higher twist nature of beam and longitudinal target SSAs

  38. g1/f1: PT-dependence Constant in perturbative limit Asymmetries from kT-odd (f1┴, h1┴, gT..) and kT-even (g1) distribution functions are expected to have a very different behavior

  39. Transversity Sub-leading pion opposite to leading (into page) Simple string fragmentation (Artru model) L=1 Leading r opposite to leading p(into page) r production may produce an opposite sign AUT r SIDIS @11 GeV: 2 pions p+p0(r+) Understanding of 2 pion asymmetries will help to understand transversity mesurements p+p-(r0)

  40. e e’ Λs in target fragmentation 1 Λ p 2 π P and p- kinematics 6

  41. SSA: PT-dependence of sinf moment ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) CLAS @5.7 GeV CLAS @4.3 GeV Beam and target SSA for p+ are consistent with increase with PT at low PT

  42. Ap1 for p+/-/0 : z-dependence CLAS 5.7 GeV No significant Q2 dependence for A1 No significant z-dependence of A1 in the range 0.4<z<0.7 Data consistent with PEPSI-MC (curves)

  43. SIDIS vs DIS DIS: probes only the sum of quarks and anti-quarks SIDIS: alows for a separation of contributions with fragmentation acting as a weight factor fraction of a parton in total(“purity”) Different hadrons sensitive to different PDFs

  44. r+ pion SSA from r(p+p-/p+p0) (CLAS @5.7GeV) PYTHIA at 5.7 GeV r0 Larger fraction of p+ from r at low x and large z p+ SSA at large z may also have a significant (~20%) contribution from r Exclusiver (higher twist for SIDIS) crucial for pX and ppX studies

  45. e- p e-nr+ π+π0 Exclusive p+p- and p+p0 e p e p π+ π- n r+ r0 r0 PID by Mpp and missing π- r+ PID by Mpp and missing neutron Fit Mpp with a BW + polinomial background.

  46. Photon Sivers Effect Afanasev & Carlson, Metz & Schlegel Beam SSA analyzed in terms of the Sivers effect by F.Yuan using h1┴ from MIT bag model ALU x-dependence: CLAS @ 4.3 and 5.7 GeV 0.5<z<0.8 Beam SSA analyzed in terms of the Collins effect by Schweitzer et al. using e(x) from cQSM Separation of different HT contribution will require independent measurements of separate contributions

  47. Collins AUT ~ Transversity: First measurement Describes spin distribution of a valence quark “switching off the contribution of gluons and of the vacuum”. Requires large unfavored spin dependent fragmentation. No success so far in describing consistently Collins SSA at least in cQSM!

  48. Contamination of SIDIS p+ from PYTHIA-MC In the range 0.5<z<0.8 ~15-20% of p+ from r

  49. A1p data vs PEPSI-MC ep → e’ p+ X ( Ee =5.7 GeV, MX > 1.1) • No z-dependence of A1p observed above z=0.4

  50. SIDIS kinematics Unpolarized Long. pol Trans. pol Kinematic pre-factors depend on the beam energy y=n/E CLAS12

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