1. PionCT (E01-107) Update Tanja Horn JLab JLab Hall C meeting 18 January 2008 Overview of current analysis results Planned analyses Future measurements

2. Experiment Overview (E01-107) Took data to the highest possible Q 2 with 6 GeV electron beam at JLab in 2004 Main goal: measurement of the nuclear transparency of pions Also: full L/T/LT/TT separation in π + production at two values of Q 2 HMS: 6 GeVSOS: 1.7 GeV Q 2 (GeV 2 ) W (GeV)|t| (Gev) 2 E e (GeV) ε 1.12.30.054.00.50 2.152.20.164.0,5.00.27,0.56 3.02.10.295.00.45 4.02.20.445.0,5.80.25,0.39 4.82.20.525.80.26 LH 2, LD 2, 12 C, Cu, and Au targets at each kinematic setting

3. Nuclear Transparency Color transparency (CT) is a phenomenon predicted by QCD in which hadrons produced at large Q 2 can pass through nuclear matter with little or no interaction [A.H.Mueller, Proc. 17th rec. de Moriond, Moriond, p13 (1982), S.J.Brodsky, Proc. 13th intl. Symp. on Multip. Dyn., p963 (1982)] –At high Q 2, hadron can be created with a small transverse size (PLC) –Hadron can propagate through the nucleus before assuming its equilibrium size Currently no conclusive evidence of the onset of CT at intermediate energies –Proton results negative up to Q 2 ~8 GeV 2 Advantage of using pions: simple qq system –Easier to produce a point-like configuration (PLC) of two quarks rather than three –Coherence lengths are small (~1 fm)

4. The A(e,e’   ) Reaction If π + production from a nucleus is similar to that from a proton we can determine nuclear transparency of pions Other mechanisms: NN final state interactions, pion excess, medium modifications, etc. Assumption is verified by L/T separations –Extracted average results over the acceptance Analysis by X. Qian S(E,p) = Spectral function for proton

5. Inner error bar are statistical uncertainties outer error bar are the quadrature sum of statistical and pt to pt systematic uncertainties. Nuclear Transparency - Q 2 Dependence B. Clasie et al., PRL 99, 242502 (2007) Covered in Phys. Rev. Focus 6/2006 Larson et al., [Phys. Rev. C74, 018201 (2006)] –Semiclassical Glauber multiple scattering approximation –Dashed: includes CT Cosyn et al., [Phys. Rev. C74, 062201R (2006)] –Relativistic Glauber multiple scattering theory –Dash-dot: includes CT+SRC

6.   A  T = A α-1 Fit of T(A) = A α-1 at fixed Q 2 A Dependence of Transparency Larson, Miller and Strikman, PRC 74, 018201 (2006) Cosyn, Ryckebusch et al., PRC 74, 062201R (2006)  B. Clasie et al., PRL 99, 242502 (2007) Fits to π -N scattering cross sections give α~0.76 –Energy independent Energy dependence of α, which quantifies the A dependence of nuclear transparency, can be viewed as an indication for CT-like effects

7. `P  ’ Dependence of Transparency Inner error bar are statistical uncertainties outer error bar are the quadrature sum of statistical and pt. to pt. systematic uncertainties. No conflict between pionCT data and recent Hall-B e,e'ρ data –P π >2.5 GeV for all pionCT kinematics while for the Hall B e,e'ρ the highest ρ momentum is <2.5 GeV Solid/Dashed lines are predictions with and without CT [A. Larson, G. Miller and M. Strikman, nuc-th/0604022]

8. Kaon Transparency π K+K+ p Coincidence time (ns) Raw Coincidence time without PID Typical coincidence time spectrum showing the different particles detected Kaon transparency from electro-production has never been measured before!!! Kaons contain strange quarks and thus have a very long mean free path this makes kaons an unique probe of the nuclear force. Will also help verify the anomalous strangeness transparency seen in K-Nuclei scattering [ S.M. Eliseev, NPA 680, 258c (2001 )] Significant sample of kaon data Slide from D. Dutta

9. Analysis Plan  GeV) (GeV/c) 2  q | qq  p  %)missmass (GeV) Build a model for p(e,e’  K +  ) using the hydrogen data. Obtained by iterating a Monte Carlo simulation of the experiment until it agrees with data. Data in RedBlue is simulation Example for pions, similar procedure will be followed for kaons. This new parametrization of the kaon electroproduction cross-section from the nucleon is used as an input for the quasi-free model for the rest of the target nuclei. Transparency to be extracted as Slide from D. Dutta

10. Transparency at large missing mass Q 2 scaling predicts that σ L scales to leading order as Q -6 –Consistent with JLab σ L data at 6 GeV (E01107, E01004, E93021), BUT limited Q 2 coverage and large uncertainties Approved experiment E12-01-105 (T. Horn et al.) will search for the onset of hard-soft factorization over a larger range of Q 2 using π + and π - electroproduction –Essential for reliable interpretation of results from the JLab GPD program at both 6 and 12 GeV Slide from X. Qian

11. L/T separations nuclear targets Q 2 scaling predicts that σ L scales to leading order as Q -6 –Consistent with JLab σ L data at 6 GeV (E01107, E01004, E93021), BUT limited Q 2 coverage and large uncertainties Approved experiment E12-01-105 (T. Horn et al.) will search for the onset of hard-soft factorization over a larger range of Q 2 using π + and π - electroproduction –Essential for reliable interpretation of results from the JLab GPD program at both 6 and 12 GeV Slide from X. Qian

12. Hard-Soft Factorization To access physics contained in GPDs, one is limited to the kinematic regime where hard-soft factorization applies –No single criterion for the applicability, but tests of necessary conditions can provide evidence that the Q 2 scaling regime has been reached Factorization is not rigorously possible without the onset of CT [Burkhardt et al., Phys.Rev.D74:034015,2006] One of the most stringent tests of factorization is the Q 2 dependence of the π electroproduction cross section –σ L scales to leading order as Q -6 Factorization Factorization theorems for meson electroproduction have been proven rigorously only for longitudinal photons [Collins et al, Phys. Rev. D56, 2982 (1997)] Q 2 ?

13. Q 2 dependence of σ L and σ T The Q -6 QCD scaling prediction is consistent with the JLab σ L data –Limited Q 2 coverage and large uncertainties make it difficult to draw a conclusion The two additional predictions that σ L >>σ T and σ T ~Q -8 are not consistent with the data Testing the applicability of factorization requires larger kinematic coverage and improved precision T. Horn et al., arXiv:0707.1794 (2007) Hall C data at 6 GeV: 3 different experiments Q 2 =1.4-2.2 GeV 2 Q 2 =2.7-3.9 GeV 2 σLσL σTσT

14. Q 2 Scaling of the Interference Terms Scaling prediction based on transverse content to the amplitude –σ LT ~ Q -7 –σ TT ~Q -8 Limited Q 2 coverage complicates the interpretation –Interference terms decrease in magnitude as Q 2 increases Preliminary from Fpi1, Fpi2 Q 2 range is small T. Horn, Ph.D. thesis, University of Maryland (2006)

15. Scaling tests at 12 GeV 6 GeV data xQ 2 (GeV 2 ) W (GeV) -t (GeV/c) 2 0.311.5-4.02.0-3.10.1 0.402.1-5.52.0-3.00.2 0.554.0-9.12.0-2.90.5 Experiment approved for 42 days in Hall C –E12-07-105 (T. Horn et al.) Measure the Q 2 dependence of the p(e,e’ π + )n cross section at fixed x B and –t to search for evidence of hard-soft factorization –Separate the cross section components: L, T, LT, TT –The highest Q 2 for any L/T separation in π electroproduction Also determine the L/T ratio for π - production to test the possibility to determine σ L without an explicit L/T separation

16. E01-107 collaboration Y. Liang American University, Washington, DC J. Arrington, L. El Fassi, X. Zheng Argonne National Laboratory, Argonne, IL T. Mertens, D. Rohe Basel Univeristy, Basel, Switzerland R. Monson Central Michigan University, Mount Pleasant, MI C. Perdrisat College of William and Mary, Williamsburg, VA D. Dutta (Spokesperson), H. Gao, K. Kramer, X. Qian Duke University, Durham, NC W. Boeglin, P. Markowitz Florida International University, Miami, FL M. E. Christy, C. E. Keppel, S. Malace, E. Segbefia, L. Tang, L. Yuan Hampton University, Hampton, VA J. Ferrer, G. Niculescu, I. Niculescu James Madison University, Harrisonburg, VA P. Bosted, A. Bruell, R. Carlini, E. Chudakov, V. Dharmawardane, R.Ent (Spokesperson), H. Fenker. D. Gaskell, M. K. Jones, A. Lung, D. G. Meekins, G. Smith, W. F. Vulcan, S. A. Wood Jefferson Laboratory, Newport News, VA B. Clasie, J. Seely Massachusetts Institute of Technology, Cambridge, MA V. Punjabi Norfolk State University, Norfolk, VA A. K. Opper George Washington University, Washington, DC A. Villano Rensselaer Polytechnic Institute, Troy, NY F. Benmokhtar Rutgers University, Piscataway, NJ and Universite' des Sciences et de la Technologie, Algiers, Algeria Y. Okayasu, A. Matsumura, T. Miyoshi, M. Sumihama Tohoku University, Sendai, Japan K. Garrow (Spokesperson) TRIUMF, Vancouver, British Columbia, Canada A. Daniel, N. Kalantarians, Y. Li, V. Rodriguez University of Houston, Houston, TX A. W. Rauf University of Manitoba, Winnipeg, Manitoba, Canada T. Horn University of Maryland, College Park, MD G. M. Huber University of Regina, Regina, Saskatchewan, Canada D. Day, N. Fomin University of Virginia, Charlottesville, VA M. Dalton, C. Gray University of the Witwatersrand, Johannesburg, South Africa R. Asaturyan, H. Mkrtchyan, T. Navasardyan, V. Tadevosyan Yervan Physics Institute, Yervan, Armenia

17. LD2 L/T L/T separation from nuclear targets MC model including a parameterization in Mx using the data.