1. A coherent gamma source the GlueX experiment the Hall D photon beam the requirements for diamonds Richard Jones, University of Connecticut presented by GlueX Tagged Photon Beam Working Group University of Glasgow University of Connecticut Catholic University of America

2. Richard Jones, CHESS seminar, Aug. 15, 2006 2 What is GlueX? Forward Calorimeter Cerenkov Counter Time of Flight Solenoid Barrel Calorimeter Tracking Target A new meson spectroscopy experiment at Jefferson Lab which requires: the 12 GeV upgrade  the 12 GeV upgrade  a new experimental hall  a polarized photon beam  a multi-particle spectrometer  a new collaboration, presently ~80 physicists ~30 institutions

3. Richard Jones, CHESS seminar, Aug. 15, 2006 3 Motivation: gluonic excitations Consider QCD with only heavy quarks: the light mesons are glueballs qq mesons have the conventional positronium low-energy spectrum spectrum is distorted at higher excitations by a linear potential for r >> 0.5 fm a tube of gluonic flux forms between q and q 0.40.81.2 1.6 1.0 2.0 0.0 r (fm) V 0 (QQ) (GeV) glueball decay threshold

4. Richard Jones, CHESS seminar, Aug. 15, 2006 4 Motivation: gluonic excitations Consider QCD with only heavy quarks: gluonic excitations give rise to new potential surfaces for r >> r 0 gluonic excitations behave like flux tube oscillations flux tube model inspires the flux tube model

5. Richard Jones, CHESS seminar, Aug. 15, 2006 5 Motivation: normal vs hybrid mesons m=0 CP=(-1) S+1 m=1 CP=(-1) S Flux-tube Model ground-state flux-tube m=0 excited flux-tube m=1 CP = (-1) L+S (-1) L+1 = (-1) S+1 S=0, L=0 J=1 CP=+ J PC =1 ++,1 -- (not exotic) S=1, L=0 J=1 CP=- 0 +- J PC = 0 -+, 0 +- 1 -+ 1 -+, 1 +- 2 +- 2 -+, 2 +-exotic normal mesons 1 -+ 1 +- 1 -+ or 1 +-

6. Richard Jones, CHESS seminar, Aug. 15, 2006 6 Motivation: hybrid masses Flux-tube model: 8 degenerate nonets 1 ++,1 -- 0 -+,0 +-,1 -+,1 +-,2 -+,2 +- ~1.9 GeV/c 2 Lattice calculations --- 1 -+ nonet is the lightest UKQCD (97) 1.87  0.20 MILC (97) 1.97  0.30 MILC (99) 2.11  0.10 Lacock (99) 1.90  0.20 Mei(03) 2.01  0.10 Bernard (04) 1.79  0.14 ~2.0 GeV/c 2 In the charmonium sector: 1 -+ 4.39  0.08 0 +- 4.61  0.11 Splitting = 0.20 1 -+ 0 +- 2 +- Splitting  0.20 S=0 S=1

7. Richard Jones, CHESS seminar, Aug. 15, 2006 7 Lowest mass expected to be  1 (1 −+ ) at 1.9±0.2 GeV Lattice 1 -+ 1.9 GeV 2 +- 2.1 GeV 0 +- 2.3 GeV

8. Richard Jones, CHESS seminar, Aug. 15, 2006 8 Experiment: hybrid searches BNL E852 Most of what is presently known about the hybrid spectrum has come from one experiment: BNL E852  - p X n at 18 GeV   1 (1400) – seen in    1 (1600) – seen in , f 1 , b 1 ,  ’    1 (2000) – seen in f 1  b   General observations regarding these analyses  exotic intensities are typically 1/10 dominant ones  requires large samples (~10 6 in exclusive channels)  requires good acceptance (uniform and well-understood)  requires access to high-multiplicity final states

9. Richard Jones, CHESS seminar, Aug. 15, 2006 9 Experiment: hybrid photoproduction BNL @ 18 GeV Unexplored territory with unique advantages for hybrid search ca. 1998 @ 19 GeV 28 4 Events/50 MeV/c 2 SLAC 1.02.52.01.5 ca. 1993

10. Richard Jones, CHESS seminar, Aug. 15, 2006 10 Almost no data is available in the mass region where we expect to find exotic hybrids when flux tube is excited Experiment: hybrid photoproduction A pion or kaon beam, when scattering occurs, can have its flux tube excited  or  beam Quark spins anti-aligned Data from these reactions show evidence for gluonic excitations (small part of cross section) q q before q q after q q q q before  beam Quark spins aligned _ _ _ _

11. Richard Jones, CHESS seminar, Aug. 15, 2006 11 Experiment: photoproduction phenomemology NN   X final state forward system general framework:  VMD in initial state  t-channel exchange

12. Richard Jones, CHESS seminar, Aug. 15, 2006 12 GlueX Experiment Lead Glass Detector Solenoid Electron Beam from CEBAF Coherent Bremsstrahlung Photon Beam Tracking Target Cerenkov Counter Time of Flight Barrel Calorimeter Note that tagger is 80 m upstream of detector 12 GeV electrons are required In order to produce a 9 GeV photon beam with a significant degree of linear polarization 9 GeV gamma beam MeV energy resolution high intensity (10 8  /s) linear polarization www.gluex.org

13. Richard Jones, CHESS seminar, Aug. 15, 2006 13 GlueX Experiment: beam polarization Suppose we want to distinguish the exchange: O + from 0 - ( A N from A U ) For circular polarization:  With linear polarization we can isolate A N from A U  Circular polarization gives access to their interference R J=0 – or 0 + X photon for R with J = 0 Gottfried-Jackson frame exchange particle

14. Richard Jones, CHESS seminar, Aug. 15, 2006 14 GlueX Experiment: photon beam flux photon energy (GeV) 12 GeV electrons The coherent bremsstrahlung technique provides requisite energy, flux and polarization collimated Incoherent & coherent spectrum tagged with 0.1% resolution 40% polarization in peak electrons in photons out spectrometer diamond crystal

15. Richard Jones, CHESS seminar, Aug. 15, 2006 15 Requirements for photon beam Energy 9 GeV Linear polarization High rates (consistent with tagging)  Initial running at 10 7  /s in the coherent peak  Design system with a clear path to 10 8  /s Energy resolution   E/E ~ 0.1% for use in event reconstruction

16. Richard Jones, CHESS seminar, Aug. 15, 2006 16 6 GeV CEBAF CHL-2 Upgrade magnets and power supplies 12 Enhance equipment in existing halls add Hall D (and beam line)

17. Richard Jones, CHESS seminar, Aug. 15, 2006 17 1. energy    2. polarization    3. rate    4. resolution (  ) (  ) (  ) 5. background    The generic photon source Techniques: A. Compton backscatter B. Bremsstrahlung C. Coherent bremsstrahlung ABC (  ) with tagging

18. Richard Jones, CHESS seminar, Aug. 15, 2006 18 Incoherent vs coherent bremsstrahlung Consider the electromagnetic form-factor of the target in q-space  q no enhancement  q strong enhancement

19. Richard Jones, CHESS seminar, Aug. 15, 2006 19 Kinematics of Coherent Bremsstrahlung effects of collimation at 80 m distance from radiator incoherent (black) and coherent (red) kinematics effects of collimation: to enhance high-energy flux and increase polarization

20. Richard Jones, CHESS seminar, Aug. 15, 2006 20 No other solution was found that could meet all of these requirements at an existing or planned nuclear physics facility. Coherent Bremsstrahlung with Collimation A laser backscatter facility would need to wait for new construction of a new multi-G$ 20GeV+ storage ring (XFEL?). Even with a future for high-energy beams at SLAC, the low duty factor < 10 -4 essentially eliminates photon tagging there. The continuous beams from CEBAF are essential for tagging and well-suited to detecting multi-particle final states. By upgrading CEBAF to 12 GeV, a 9 GeV polarized photon beam can be produced with high polarization and intensity. Unique:

21. Richard Jones, CHESS seminar, Aug. 15, 2006 21 circular polarization  transfer from electron beam  reaches 100% at end-point linear polarization  determined by crystal orientation  vanishes at end-point  not affected by electron polarization Polarization from Coherent Bremsstrahlung Linear polarization arises from the two-body nature of the CB kinematics Linear polarization has unique advantages for GlueX physics: a requirement Changes the azimuthal  coordinate from a uniform random variable to carrying physically rich information.

22. Richard Jones, CHESS seminar, Aug. 15, 2006 22 Photon Beam Intensity Spectrum 4 nominal tagging interval Rates based on: 12 GeV endpoint 20  m diamond crystal 100nA electron beam Leads to 10 7  /s on target (after the collimator) Design goal is to build an experiment with ultimate rate capability as high as 10 8  /s on target.

23. Richard Jones, CHESS seminar, Aug. 15, 2006 23 II. Optimization photon energy vs. polarization crystal radiation damage vs. multiple scattering collimation enhancement vs. tagging efficiency Understanding competing factors is necessary to optimize the design

24. Richard Jones, CHESS seminar, Aug. 15, 2006 24 Optimization: chosing a photon energy 8 GeV;9-10 GeV A minimum useful energy for GlueX is 8 GeV; 9-10 GeV is better for several reasons, peak polarization coherent gain factor steep functions of peak energy for a fixed endpoint of 12 GeV, the peak polarization and the coherent gain factor are both steep functions of peak energy. CB polarization is a key factor in the choice of a energy range of 8.4-9.0 GeV for GlueX but

25. Richard Jones, CHESS seminar, Aug. 15, 2006 25 Optimization: choice of diamond thickness 20  m 10 -4 rad.len Design calls for a diamond thickness of 20  m which is approximately 10 -4 rad.len. thinning Requires thinning: special fabrication steps and $$. Impact from multiple- scattering is significant. up to a point… Loss of rate is recovered by increasing beam current, up to a point… The choice of 20  m is a trade-off between MS and radiation damage. -3 -4

26. Richard Jones, CHESS seminar, Aug. 15, 2006 26 Electron Beam Emittance <10 -8 m r requirement : < 10 -8 m r emittances are r.m.s. values derivation :  virtual spot size: 500  m  radiator-collimator: 76 m  crystal dimensions: 5 mm In reality, one dimension (y) is much better than the other ( x 2.5) This is a key issue for achieving the requirements for the GlueX Photon Beam Optics study: goal is achievable, but close to the limits according to 12 GeV machine models

27. Richard Jones, CHESS seminar, Aug. 15, 2006 27 V. Diamond crystal requirements orientation requirements limitations from mosaic spread radiation damage assessment

28. Richard Jones, CHESS seminar, Aug. 15, 2006 28 Diamond crystal: goniometer mount temperature profile of crystal at full operating intensity oCoC

29. Richard Jones, CHESS seminar, Aug. 15, 2006 29 Diamond Orientation 3 mr orientation angle is relatively large at 9 GeV: 3 mr initial setup takes place at near-normal incidence goniometer precision requirements for stable operation at 9 GeV are not severe. alignment zone operating zone fixed hodoscope microscope (mr)

30. Richard Jones, CHESS seminar, Aug. 15, 2006 30 Driven by beam emittance and spot size at collimator X: r.m.s. = 1.7mm Y: r.m.s. = 0.7mm Minimum acceptable size: 5mm x 3mm How large a diamond is needed?

31. Richard Jones, CHESS seminar, Aug. 15, 2006 31 Mosaic spread goal: Adds in quadrature with beam divergence 50µr r.m.s. 25µr r.m.s. How perfect a crystal is needed?

32. Richard Jones, CHESS seminar, Aug. 15, 2006 32 A HTHP diamond ingot seed slice 1 slice 2 slice 3 We brought samples from 3 ingots to Daresbury January 2002  Stone 1407  Stone 1485A  Stone 1532 SRS measurements (January, 2002)

33. Richard Jones, CHESS seminar, Aug. 15, 2006 33  Stone 1407 slice 1 2mm 4mm x 4mm X-ray beam rocking curve

34. Richard Jones, CHESS seminar, Aug. 15, 2006 34  Stone 1407 slice 1 2mm 0.5mm x 0.5mm X-ray beam rocking curve

35. Richard Jones, CHESS seminar, Aug. 15, 2006 35  Stone 1482A slice 1 2mm 3mm x 5mm X-ray beam rocking curve

36. Richard Jones, CHESS seminar, Aug. 15, 2006 36  Stone 1482A slice 2 4mm 5mm x 5mm X-ray beam rocking curve

37. Richard Jones, CHESS seminar, Aug. 15, 2006 37  Stone 1482A slice 2 (rotated) 4mm 10mm x 10mm X-ray beam rocking curve

38. Richard Jones, CHESS seminar, Aug. 15, 2006 38  Stone 1482A slice 3 4mm 10mm x 10mm X-ray beam rocking curve

39. Richard Jones, CHESS seminar, Aug. 15, 2006 39 13  Stones not looked at Stone 1407 slice 2 Stone 1407 slice 3

40. Richard Jones, CHESS seminar, Aug. 15, 2006 40 Diamond Crystal Quality rocking curve from X-ray scattering natural fwhm (Univ. of Glasgow contact) reliable source of high-quality synthetics from industry (Univ. of Glasgow contact) established procedure in place for selection and assessment using X-rays (Hall B) R&D is ongoing towards reliable operation of one 20  m crystal (Hall B)

41. Richard Jones, CHESS seminar, Aug. 15, 2006 41 conservative estimate (SLAC) for useful lifetime (before significant degradation): during initial running at 10 7  /s this gives 600 hrs of running before a spot move a “good” crystal accommodates 5 spot moves R&D is planned that will improve the precision of this estimate. Diamond Crystal Lifetime 0.25 C / mm 2

42. Richard Jones, CHESS seminar, Aug. 15, 2006 42 14 Conclusions oDoing X-ray topographs is not sufficient. îTopographs are relatively fast and easy to set up. îRocking curves tell us what we need to know. îIt is hard to tell from looking at the topograph what the rocking curve will look like. oLarge and high quality crystals are available. îBased on an example of 1. oNew X-ray tests are needed after thinning, rad. damage.

43. Richard Jones, CHESS seminar, Aug. 15, 2006 43

44. Richard Jones, CHESS seminar, Aug. 15, 2006 44 GlueX Reviews December 1999: PAC Requested Review of the GlueX Project D. Cassel (chair), J. Domingo, W. Dunwoodie, D. Hitlin, G. Young. April 2001: NSAC Long Range Plan Committee. July 2003: Electronics Review of the GlueX Project J. Domingo, A. Lankford (chair), G. Young October 2004: Detector Review M. Albrow, J. Alexander (Chair), W. Dunwoodie, B. Mecking. December 2004: Solenoid Assessment J. Alcorn, B. Kephart (Chair), C. Rode. January 2006: Photon Beam and Tagger Review J. Ahrens (chair), B. Mecking, A. Nathan