PionCT (E01-107) Update

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

2. HMS: 6 GeV SOS: 1.7 GeV Experiment Overview (E01-107) • Took data to the highest possible Q2 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 Q2 • LH2, LD2, 12C, 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 Q2 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 Q2, 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 Q2~8 GeV2 • 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’p+) 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. Nuclear Transparency - Q2 Dependence • 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 B. Clasie et al., PRL 99, 242502 (2007) Covered in Phys. Rev. Focus 6/2006 Inner error bar are statistical uncertainties outer error bar are the quadrature sum of statistical and pt to pt systematic uncertainties.

6. A Dependence of Transparency • Energy dependence of α, which quantifies the A dependence of nuclear transparency, can be viewed as an indication for CT-like effects s (A) = s0 Aa T = Aα-1 Larson, Miller and Strikman, PRC 74, 018201 (2006) Cosyn, Ryckebusch et al., PRC 74, 062201R (2006) • Fits to π-N scattering cross sections give α~0.76 • Energy independent a Fit of T(A) = Aα-1 at fixed Q2 B. Clasie et al., PRL 99, 242502 (2007)

7. `Pp’ Dependence of Transparency • No conflict between pionCT data and recent Hall-B e,e'ρ data • Pπ >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] Inner error bar are statistical uncertainties outer error bar are the quadrature sum of statistical and pt. to pt. systematic uncertainties.

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

9. (GeV/c)2 w(GeV) 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. fq | qq| Transparency to be extracted as dp(%) missmass (GeV) Analysis Plan Data in Red Blue is simulation Slide from D. Dutta 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 . Example for pions, similar procedure will be followed for kaons.

10. Transparency at large missing mass Slide from X. Qian • Q2 scaling predicts that σL scales to leading order as Q-6 • Consistent with JLab σL data at 6 GeV (E01107, E01004, E93021), BUT limited Q2 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 Q2 using π+ and π- electroproduction • Essential for reliable interpretation of results from the JLab GPD program at both 6 and 12 GeV

11. L/T separations nuclear targets Slide from X. Qian • Q2 scaling predicts that σL scales to leading order as Q-6 • Consistent with JLab σL data at 6 GeV (E01107, E01004, E93021), BUT limited Q2 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 Q2 using π+ and π- electroproduction • Essential for reliable interpretation of results from the JLab GPD program at both 6 and 12 GeV

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 Q2 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 Q2 dependence of the πelectroproduction cross section • σL scales to leading order as Q-6 Factorization Q2 ? • Factorization theorems for meson electroproduction have been proven rigorously only for longitudinal photons [Collins et al, Phys. Rev. D56, 2982 (1997)]

13. Q2 dependence of σL and σT Hall C data at 6 GeV: 3 different experiments • The Q-6QCD scaling prediction is consistent with the JLab σL data • Limited Q2 coverage and large uncertainties make it difficult to draw a conclusion • The two additional predictions that σL>>σT and σT~Q-8 are not consistent with the data • Testing the applicability of factorization requires larger kinematic coverage and improved precision Q2=2.7-3.9 GeV2 Q2=1.4-2.2 GeV2 σL σT T. Horn et al., arXiv:0707.1794 (2007)

14. Q2 Scaling of the Interference Terms Preliminary from Fpi1, Fpi2 • Scaling prediction based on transverse content to the amplitude • σLT ~ Q-7 • σTT ~Q-8 • Limited Q2 coverage complicates the interpretation • Interference terms decrease in magnitude as Q2 increases Q2 range is small T. Horn, Ph.D. thesis, University of Maryland (2006)

15. Scaling tests at 12 GeV • Experiment approved for 42 days in Hall C • E12-07-105 (T. Horn et al.) • Measure the Q2 dependence of the p(e,e’π+)n cross section at fixed xB and –t to search for evidence of hard-soft factorization • Separate the cross section components: L, T, LT, TT • The highest Q2 for any L/T separation in π electroproduction • Also determine the L/T ratio for π- production to test the possibility to determine σL without an explicit L/T separation 6 GeV data

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.