1. Measurement of the Pion Structure Function
Lingyan Zhu
Physics Opportunities in Hall C at 12 GeV
Aug 4-5, 2008
Aug 04, 2008

2. Pion Structure Function
Pion’s structure function is not well measured, though pion is the simplese hadron with only two valence quarks.
The xp->1 behavior of (1-xp) in Drell-Yan data differs from pQCD prediction of (1-xp)2.
Aug 04, 2008

3. Pion Structure Measurement at HERA
HERA H1 preliminary, July 2008.
Similar results from ZEUS
Very small xp
Aug 04, 2008

4. Pion Exchange (Sullivan) Process
|t| has to be small to enhance contribution from Sullivan process.
Aug 04, 2008 4

5. Pion Form Factor Measurements
Pion form factor can be measured via ELASTIC scattering on the pion cloud, which is consistent with that via e-p scattering.
via e-p scattering
via p cloud
T. Horn et al. PRL97(2006)192001
Aug 04, 2008

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.
Aug 04, 2008

7. CLAS e6 Proton data at 5.7 GeV
Reaction ep->e’p’X with global cut: Q2>1.0
No clear resonance structure with MX>1, when the baryon number equals zero. p h
w,r MX
Few events with 6 GeV beam can satisfy both |t|<0.2 and MX>1.
|t|<0.2
|t|<0.1
Aug 04, 2008

8. PAC20 Report on PR-01-110 1: MX>1 cut. 2: on to-do-list. 3: agree.1[ ] 2{ } 3( )
Aug 04, 2008

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.
Aug 04, 2008

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
Aug 04, 2008

11. Leading Proton Production at HERA
ZEUS, Nucl.Phys.B658(2003)3 IR IP
Competing contributions from Reggeon and Pomeron exchange.
Aug 04, 2008

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
Aug 04, 2008

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.
This channel was used in HERA to extract pion structure function.
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
Aug 04, 2008

14. Pion Structure Measurement with Hall A BigBite
Basically an extension of 6 GeV proposal PR
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 30o for 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.
Aug 04, 2008

15. Kinematics with Hall A BIGBITE
and Mx>1
|t|< Q2>1
Radiative Corrections?
Aug 04, 2008

16. Neutron Detection Efficiency
Ramesh Subedi et al, Technical Note For
E (short range correlation)
Reducing the Pb shielding and adding two more scintillator planes can increase the neutron detection efficiency.
Aug 04, 2008

17. Projected Statistical Uncertainties
HERA H1
For 0.2<xp<0.6
|t|<0.2: ~2%
|t|<0.1: ~5%
E615: ~10%
FermiLab E615
JLAB HallA
Aug 04, 2008

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.
Aug 04, 2008

19. Acknowledgements
Hampton University: Eric Christy, Rolf Ent, Thia Keppel, Alberto Accardi, Peter Monaghan, Antje Bruell
PR : Paul Reimer, Roy Holt
LOI : 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
Aug 04, 2008

20. Backup Slides
Aug 04, 2008

21. Kinematics at 11 GeV |t|<0.2 |t|<0.1 Very loose acceptance cuts
and Mx>1
|t|<0.1
Very loose acceptance cuts
Aug 04, 2008

22. Leading Neutron Production at H1
H1 preliminary
July 2008.
Data agree with the RAPGAP simulation at larger xL.
Aug 04, 2008

23. Leading Neutron Production at HERA
ZEUS, Nucl.Phys.B776(2007)1
Aug 04, 2008

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 15o for scattered electron detection. The central momentum Pe’ =2.5 GeV.
BigBite at 30o for 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.
Aug 04, 2008

25. Kinematics with Hall A HRS
and Mx>1
|t|<0.1
Aug 04, 2008