Measurement of the Pion Structure Function

1. Measurement of the Pion Structure Function Lingyan Zhu Physics Opportunities in Hall C at 12 GeV Aug 4-5, 2008

2. Pion’s structure function is not well measured, though pion is the simplese hadron with only two valence quarks. Pion Structure Function • The xp->1 behavior of (1-xp) in Drell-Yan data differs from pQCD prediction of (1-xp)2.

3. Pion Structure Measurement at HERA HERA H1 preliminary, July 2008. Similar results from ZEUS Very small xp

4. Pion Exchange (Sullivan) Process |t| has to be small to enhance contribution from Sullivan process.

5. Pion Form Factor Measurements via p cloud via e-p scattering • Pion form factor can be measured via ELASTIC scattering on the pion cloud, which is consistent with that via e-p scattering. T. Horn et al. PRL97(2006)192001

6. Range of t in Pion Form Factor Measurements T. Horn et al. PRL97(2006)192001 Pion exchange dominates at |t|<0.2, especially at |t| <0.1.

7. CLAS e6 Proton data at 5.7 GeV |t|<0.2 |t|<0.1 • Reaction ep->e’p’X with global cut: Q2>1.0 • No clear resonance structure with MX>1, when the baryon number equals zero. h p w,r MX • Few events with 6 GeV beam can satisfy both |t|<0.2 and MX>1.

8. PAC20 Report on PR-01-110 1: MX>1 cut. 2: on to-do-list. 3: agree. 1[ ] 2{ } 3( )

9. Phase Space for Sullivan Process at 11 GeV |t|<0.2 and Mx>1,Q2>1 RAPGAP is a full Monte Carlo to describe inclusive and diffractive DIS. It was used in HERA to extract pion structure function. Thank Paul Reimer for modifying RAPGAP interface.

10. Possible Channels • Proton target + proton detection, which is sensitive to the p0 cloud of proton. • Proton target + neutron detection, which is sensitive to the p+ cloud of proton. • Deuterium target + two proton detection, which is sensitive to the p- cloud of neutron, referring to Letter-of-intent LOI-01-001.

11. Leading Proton Production at HERA ZEUS, Nucl.Phys.B658(2003)3 IR IP Competing contributions from Reggeon and Pomeron exchange.

12. Pomeron Contribution at 11 GeV with RAPGAP • Loose acceptance cut with 11 GeV beam. • Model for Pomeron distribution Nikolaev&Zakharov, Z.phys.C53(1992)331. Via Pomeron Via p0 cloud

13. Neutron Production via p+ Exchange • Proton target + neutron detection, which is sensitive to the p+ cloud of proton. Charged pion exchange has less background from Pomeron and Reggeon processes. • The p+N cloud doubles p0N cloud in the proton. Regge approach: a=0.105, b=0.015 Nikolaev et al.,PRD60(1999)014004 Chiral approach: a=0.24,b=0.12 Thomas, Melnitchouk & Steffens,PRL85(2000)2892 • This channel was used in HERA to extract pion structure function.

14. Pion Structure Measurement with Hall A BigBite • Basically an extension of 6 GeV proposal PR01- 110. • p(e,e’n)X at Ee=11 GeV. Chose Q2>1 and |t|<0.2 to favor DIS on the charged pion cloud, and MX>1 to be above the resonance region. • BigBite at 30ofor scattered electron detection, the most forward angle. The solid angle Ω=64 msr was used in the simulation. The shower detector should be removed so that it won’t interfere with the neutron detection. The gas cherenkov detector under construction will be used to identify electrons from pion background. • Neutron detector will be placed behind BigBite with reduced background. • High Resolution Spectrometer (HRS) with solid angle of Ω=6 msr can be placed at 30o for systematic study or at 15o for more pion structure data.

15. Kinematics with Hall A BIGBITE |t|<0.2 and Mx>1 |t|<0.1Q2>1 Radiative Corrections?

16. Neutron Detection Efficiency Ramesh Subedi et al, Technical Note For E01-015 (short range correlation) Reducing the Pb shielding and adding two more scintillator planes can increase the neutron detection efficiency.

17. Projected Statistical Uncertainties HERA H1 FermiLab E615 For 0.2<xp<0.6 |t|<0.2: ~2% |t|<0.1: ~5% E615: ~10% JLAB HallA

18. Summary • The knowledge of the pion structure function is very limited due to the lack of stable pion target. The models or global parameterizations can not well describe the Drell-Yan data in the high xp region and the HERA data in the low xp region. • The pion exchange (Sullivan) process can be used to measure pion structure function. This technique was used to get pion structure function in HERA. • The JLab 12 GeV upgrade allows phase space for |t|<0.2, Q2>1 and Mx>1.0 and enables us to measure the pion structure function in the intermediate xp region.

19. Acknowledgements • Hampton University: Eric Christy, Rolf Ent, Thia Keppel, Alberto Accardi, Peter Monaghan, Antje Bruell • PR-01-110: Paul Reimer, Roy Holt • LOI-01-001: Paul King, Jen-Chieh Peng, Dipankar Dutta • BigBite and Neutron Detector: Ramesh Subedi, Doug Higinbotham • CLAS E6 and BONUS collaboration: Narbe Kalantarians, Sebastian Kuhn, Jixie Zhang • RAPGAP: Hannes Jung

20. Backup Slides

21. Kinematics at 11 GeV |t|<0.2 and Mx>1 |t|<0.1 Very loose acceptance cuts

22. Leading Neutron Production at H1 H1 preliminary July 2008. Data agree with the RAPGAP simulation at larger xL.

23. Leading Neutron Production at HERA ZEUS, Nucl.Phys.B776(2007)1

24. Pion Structure Measurement with Hall A HRS • at Ee=11 GeV. Chose Q2>1 and -t<0.2 to favor DIS on the charged pion cloud, and MX>1 to be above the resonance region. • HRS at 15ofor scattered electron detection. The central momentum Pe’ =2.5 GeV. • BigBite at 30ofor scattered electron detection with the solid angle Ω=64 msr. Neutron detector will be placed behind BigBite with reduced background. • High Resolution Spectrometer (HRS) with solid angle of Ω=6 msr can be placed at 30o on the other side of the hall for the systematic/background control.

25. Kinematics with Hall A HRS |t|<0.2 and Mx>1 |t|<0.1