- Email: [email protected]
Heavy flavor production at the next linear collider
Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
Heavy #avor production at the next linear collider Sekazi K. Mtingwa *, Mark Strikman Department of Physics, North Carolina A&T State University, 1601 E. Market Street, Greensboro, NC 27411, USA Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, GA 30314, USA Pennsylvania State University, University Park, PA 16802, USA
Abstract Using the next e>}e\ linear collider, it will be possible to produce, by Compton backscattering, highly monochromatic photons of energy 250 GeV or higher. We describe how to use such photons to photoproduce large quantities of B}B mesons and s>}s\ lepton pairs for studies of CP-violation and s decay. 2000 Elsevier Science B.V. All rights reserved. PACS: 41.80.Ee; 11.80.!m; 13.60.Le; 29.25.!t
1. Introduction The use of high-energy c quanta produced by Compton backscattering for studies in high- and medium-energy nuclear physics has been speculated upon, and even utilized to a limited extent, for a number of years. Perhaps the earliest discussions of the possibility of observing this phenomenon in the laboratory were due to Milburn [1]; Arutyunian et al. [2]; and Arutyunian and Tumanian [3]. Subsequently, Harutyunian et al. [4] suggested using the scattering of Compton backscattered c quanta with low-energy laser photons to observe for the "rst time photon} photon scattering, a strictly quantum mechanical process with no classical analogue. Then, Mikaelian
* Correspondence address: Department of Physics, North Carolina A&T State University, 1601 E. Market Street, Greensboro, NC 27411, USA. Tel.: 1-336-334-7646; fax: 1-336-3347423. E-mail address: [email protected] (S.K. Mtingwa).
[5] advocated producing 19.5 GeV photons via Compton backscattering at the Stanford Linear Accelerator Center (SLAC) for observing photon} photon scattering o! a 4.66 eV laser beam. Others, such as Ginzburg et al. [6,7], Akerlof [8], and Sens [9], have proposed using Compton backscattering to produce two high-energy c beams for doing collider physics. This would be an alternative to standard e>}e\ colliders, with comparable luminosity, depending upon the e$ciency of the e\Pc conversion. Moreover, a high-energy c}c collider would enjoy three major advantages over e>}e\ colliders: (1) There would be no beam-beam radiation at the "nal focus (2) There would be no need for a positron source (3) The cross sections for some reactions are larger at a c}c collider than at a conventional e>}e\ collider. At least, two notable experimental uses of Compton backscattering have been realized.
0168-9002/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 6 9 2 - 6
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
Ballam et al. [10] at SLAC used a nearly monochromatic high-energy photon beam that was produced by Compton backscattering of ruby laser light to study photoproduction in a hydrogen bubble chamber. Their measurements of total and partial hadronic cp cross sections were consistent with other measurements. In another application, the theoretical work of Prescott [11] was used to determine the polarization of electron beams at several facilities. Subsequently, there have been studies and proposals to do the same elsewhere [12}14]. While the use of Compton backscattering in high- and medium-energy nuclear physics is not new, it still has not been fully exploited. In this paper, we describe its usefulness for producing copius B mesons and s leptons. 2. Photoproduction of b mesons As discovered previously [15], it is possible to photoproduce &10 B}B meson pairs per year in a scheme dubbed BACKGAMMON, for BACKscattered GAMMas On Nucleons. To realize this scheme, one needs an electron beam of energy at least &250 GeV or higher, such as is proposed for the next generation linear collider. One also needs a set of high repetition rate lasers and a state-of-the-art detector. The electron beam energy is determined by the fact that the hadronic cross section for b quark photoproduction increases rapidly from 100 to 200 GeV and plateaus at its maximum value about 250}300 GeV [16,17]. Since at these energies essentially all of the electron's energy is transferred to the backscattered photons during Compton scattering, the electron beam must be in the 250}300 GeV range. The energy of the incident laser photons must not be too high, otherwise the incident photons could interact with backscattered c-rays, which then would be lost by pair production. For 250 GeV incident electrons, the optimum laser wavelength is &1 lm. BACKGAMMON proceeds as follows. The 0.250}1.0 TeV electron beam is Compton scattered o! a low-energy laser pulse containing photons of energy several eV. Essentially, all of the scattered
51
photons are scattered through 1803 and assume approximately the full energy from the electrons o! which they scatter. This hot photon beam has several advantages over those produced by Bremsstrahlung, most notably it is highly monochromatic and uncontaminated by other particles, such as neutrons and neutral kaons. Finally, the hot photons strike a nuclear target to produce the B mesons. To better organize the detector part of the scheme, the original idea was to allow each electron bunch to convert 100 laser beams into 100 highenergy photon minibeams, each containing 10 photons. These minibeams travel approximately 100 m downstream to the target. After each electron}laser crossing, the electron bunch is de#ected 10\ rad by a trim dipole before scattering with the next laser. These dipoles are oriented randomly so that the hits at the target are scattered in the transverse plane and separated by &1 cm. Since each photon minibeam has an angular divergence of 410\, the strikes on the target are separated nicely. This scheme produces &10 B}B meson pairs per year, an excellent number for studying CP violation and rare B decays. To avoid swamping the detector, we limit the intensity of the hot photon minibeams so that, at the location of each hit on the target, only about one hadronic interaction per hot photon pulse occurs (&10 photons;10% hadronic interaction length ;10\ fraction of total events that are hadronic). We get the following number of meson pairs per year: N
&10 hot photons per minibeam ;100 minibeams ;2;10\ branching ratio to b quarks ;2;10 electron bunch rep rate ;3;10 seconds per year
N
See Refs. [18,19] for N &;10\
&;10\ and Ref. [18] for
LASER COMPTON SCATTERING
52
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
;10\ hadronic length of target [18,19] ;10\ fraction of photon}nucleon interactions that are hadronic [18] &10.
(1)
With the recent advances in particle detection, it is possible to avoid using the 100 laser scatterings per electron bunch. First of all, if one wanted to convert each electron in the collider bunch to a hot c, as proposed for c}c colliders, one could use the Thomson cross section to estimate that about 10 photons need to collide with each electron. Therefore, for the 10 electrons of a typical collider bunch, one would need 10 photons, corresponding to about a 1 J laser #ash, which is not excessive and possible nowadays with lasers. Hence, for 10\ of the maximum conversion e$ciency, one could create one hot c pulse containing 10 photons for each electron bunch. Thus, one could trade 100 minibeams containing 10 hot photons per minibeam for one beam with 10 hot photons. Whether this second option leads to undesirable nonlinear QED e!ects will have to be studied further. This alternative yields &10 B}B meson pairs per year. Finally, the B mesons are produced with about equal large momenta &E /2 and at large transc verse momenta P &m , leaving a nice signal in the detector. We know that most of the reactions on the target will be electromagnetic, with the b quark contributions being down by a factor of &2;10\. Since we have discussed only the production mechanism and not a detection system at this time, more studies need to be performed on specifying a system of detectors and performing Monte Carlo simulations to understand better background rates and signal-to-noise ratios.
3. Photoproduction of s leptons Using the second scheme for BACKGAMMON involving one hot photon pulse per electron bunch, one can revisit a previous calculation of the photoproduction of s>}s\ lepton pairs [20]. One starts
with the ratio of s>}s\ to e>}e\ photoproduction cross sections p(cPs>s\) [log (2u/m )!109/42] r s s " (2) p(cPe>e\) [log (2u/m )!109/42] r where r is the classical lepton radius, m is the lepton mass, and u is the backscattered photon energy. At 250 GeV, this ratio is &2;10\ and varies slowly with u. Thus, we arrive at the following per year:
p(cPs>s\) p(cPbb ) N > \& N s s p(cPe>e\) p(cPe>eN ) &[2;10\/(2;10\;10\)]10 &10.
(3)
In BACKGAMMON, the s>}s\ #y at relatively large angles &m /E and the decay lengths are of s c the order of 1 cm. Finally, Refs. [1,3] point out that if polarized laser light is used, the Compton backscattered photons will preserve to a high degree the polarization of the incident laser light. However, to optimize the Compton scattering cross section, one may want to choose the electron helicity opposite to that of the laser photons. Thus, we have a real opportunity to photoproduce polarized s leptons and study in a detailed way the polarization e!ects in s decay.
4. Conclusion We have discussed the possibility to photoproduce &10 B}B meson pairs and &10 s>}s\ lepton pairs per year. These possibilities have arisen due to the unique properties of Compton backscattered photon beams. This scheme in its original form was proposed about ten years ago when the state of the technology for the next linear collider was in its infancy. Since that time, the next linear collider seems to be approaching realization. Furthermore, laser technology has progressed considerably. Hirose [21], Pogorelsky [21], and Telnov [21] have considered laser con"gurations for other
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
applications, such as positron sources and c}c colliders, at the next linear collider. Since their schemes involve roughly 100% conversion of the electrons to photons, the requirements on the laser systems are more stringent. In BACKGAMMON, the required backscattered photon #ux is only &10\ of that for these other applications; thus, for example, BACKGAMMON could utilize the scheme of Hirose and Pogorelsky, involving several tens of CO multi-bunch lasers with 0.25 J/bunch, each with 85 bunches at 150 Hz. However, there is still considerable research and development that must be done before any of these laser systems are used. Finally, Compton backscattering o!ers highly energetic, monochromatic, polarized, and pure (uncontaminated by other neutral particles) photon beams that leave relatively clean signals in detectors. Thus, BACKGAMMON o!ers excellent opportunities to do interesting "xed target physics at the next linear collider.
References [1] R.H. Milburn, Phys. Rev. Lett. 10 (1963) 75. [2] F.R. Arutyunian, I.I. Goldman, V.A. Tumanian, Zh. Eksp. Teor. Fiz. 45 (1963) 312 [Sov. Phys. JETP 18 (1964) 218]. [3] F.R. Arutyunian, V.A. Tumanian, Phys. Lett. 4 (1963) 176.
53
[4] V.M. Harutyunian, F.R. Harutyunian, K.A. Ispirian, V.A. Tumanian, Phys. Lett. 6 (1963) 175. [5] K.O. Mikaelian, Phys. Lett. B 115 (1982) 267. [6] I.F. Ginzburg, G.L. Kotkin, V.G. Serbo, V.I. Telnov, Nucl. Instr. and Meth. 205 (1983) 47. [7] I.F. Ginzburg, G.L. Kotkin, S.L. Pan"l, V.G. Serbo, V.I. Telnov, Nucl. Instr. and Meth. 219 (1984) 5. [8] C. Akerlof, Preprint UM HE 81-59, University of Michigan, 1981. [9] J.C. Sens, CERN-EP/88-99, 1988. [10] J. Ballam et al., Phys. Rev. Lett. 23 (1969) 498. [11] C. Prescott, SLAC internal report, SLAC-TN-73-1, 1973. [12] S. Kerhoas, SACLAY internal report, 1994. [13] G. Bardin et al., SACLAY report, DAPHNIA-SPhN-9614, 1996. [14] G. Bardin, C. Cavata, J.-P. Jorda, SACLAY internal report, 1997. [15] S.K. Mtingwa, M. Strikman, Phys. Rev. Lett. 64 (1990) 1522. [16] J.J. Aubert et al., Nucl. Phys. B 213 (1983) 1. [17] J.J. Aubert et al., Phys. Lett. B 89 (1980) 267. [18] D. Harding, Fermilab Experiment E687, private communication. [19] P. Frabetti et al., Fermilab internal report, FERMILABPub-90/258-E [E687], 1990. [20] S.K. Mtingwa, M. Strikman, in Rare and Exclusive B&K Decays and Novel Flavor Factories, American Institute of Physics Publication, Conference Proceedings Vol. 261, AIP, New York, 1992, p. 236. [21] Proceedings of the Symposium, New Visions in LaserBeam Interactions: Fundamental Problems and Applications of Laser-Compton Scattering, Tokyo Metropolitan University and High Energy Accelerator Research Organization (KEK), Tokyo, Japan, 1999 Nucl. Instr. and Meth. A 455 (2000).
LASER COMPTON SCATTERING
Heavy #avor production at the next linear collider Sekazi K. Mtingwa *, Mark Strikman Department of Physics, North Carolina A&T State University, 1601 E. Market Street, Greensboro, NC 27411, USA Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, GA 30314, USA Pennsylvania State University, University Park, PA 16802, USA
Abstract Using the next e>}e\ linear collider, it will be possible to produce, by Compton backscattering, highly monochromatic photons of energy 250 GeV or higher. We describe how to use such photons to photoproduce large quantities of B}B mesons and s>}s\ lepton pairs for studies of CP-violation and s decay. 2000 Elsevier Science B.V. All rights reserved. PACS: 41.80.Ee; 11.80.!m; 13.60.Le; 29.25.!t
1. Introduction The use of high-energy c quanta produced by Compton backscattering for studies in high- and medium-energy nuclear physics has been speculated upon, and even utilized to a limited extent, for a number of years. Perhaps the earliest discussions of the possibility of observing this phenomenon in the laboratory were due to Milburn [1]; Arutyunian et al. [2]; and Arutyunian and Tumanian [3]. Subsequently, Harutyunian et al. [4] suggested using the scattering of Compton backscattered c quanta with low-energy laser photons to observe for the "rst time photon} photon scattering, a strictly quantum mechanical process with no classical analogue. Then, Mikaelian
* Correspondence address: Department of Physics, North Carolina A&T State University, 1601 E. Market Street, Greensboro, NC 27411, USA. Tel.: 1-336-334-7646; fax: 1-336-3347423. E-mail address: [email protected] (S.K. Mtingwa).
[5] advocated producing 19.5 GeV photons via Compton backscattering at the Stanford Linear Accelerator Center (SLAC) for observing photon} photon scattering o! a 4.66 eV laser beam. Others, such as Ginzburg et al. [6,7], Akerlof [8], and Sens [9], have proposed using Compton backscattering to produce two high-energy c beams for doing collider physics. This would be an alternative to standard e>}e\ colliders, with comparable luminosity, depending upon the e$ciency of the e\Pc conversion. Moreover, a high-energy c}c collider would enjoy three major advantages over e>}e\ colliders: (1) There would be no beam-beam radiation at the "nal focus (2) There would be no need for a positron source (3) The cross sections for some reactions are larger at a c}c collider than at a conventional e>}e\ collider. At least, two notable experimental uses of Compton backscattering have been realized.
0168-9002/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 6 9 2 - 6
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
Ballam et al. [10] at SLAC used a nearly monochromatic high-energy photon beam that was produced by Compton backscattering of ruby laser light to study photoproduction in a hydrogen bubble chamber. Their measurements of total and partial hadronic cp cross sections were consistent with other measurements. In another application, the theoretical work of Prescott [11] was used to determine the polarization of electron beams at several facilities. Subsequently, there have been studies and proposals to do the same elsewhere [12}14]. While the use of Compton backscattering in high- and medium-energy nuclear physics is not new, it still has not been fully exploited. In this paper, we describe its usefulness for producing copius B mesons and s leptons. 2. Photoproduction of b mesons As discovered previously [15], it is possible to photoproduce &10 B}B meson pairs per year in a scheme dubbed BACKGAMMON, for BACKscattered GAMMas On Nucleons. To realize this scheme, one needs an electron beam of energy at least &250 GeV or higher, such as is proposed for the next generation linear collider. One also needs a set of high repetition rate lasers and a state-of-the-art detector. The electron beam energy is determined by the fact that the hadronic cross section for b quark photoproduction increases rapidly from 100 to 200 GeV and plateaus at its maximum value about 250}300 GeV [16,17]. Since at these energies essentially all of the electron's energy is transferred to the backscattered photons during Compton scattering, the electron beam must be in the 250}300 GeV range. The energy of the incident laser photons must not be too high, otherwise the incident photons could interact with backscattered c-rays, which then would be lost by pair production. For 250 GeV incident electrons, the optimum laser wavelength is &1 lm. BACKGAMMON proceeds as follows. The 0.250}1.0 TeV electron beam is Compton scattered o! a low-energy laser pulse containing photons of energy several eV. Essentially, all of the scattered
51
photons are scattered through 1803 and assume approximately the full energy from the electrons o! which they scatter. This hot photon beam has several advantages over those produced by Bremsstrahlung, most notably it is highly monochromatic and uncontaminated by other particles, such as neutrons and neutral kaons. Finally, the hot photons strike a nuclear target to produce the B mesons. To better organize the detector part of the scheme, the original idea was to allow each electron bunch to convert 100 laser beams into 100 highenergy photon minibeams, each containing 10 photons. These minibeams travel approximately 100 m downstream to the target. After each electron}laser crossing, the electron bunch is de#ected 10\ rad by a trim dipole before scattering with the next laser. These dipoles are oriented randomly so that the hits at the target are scattered in the transverse plane and separated by &1 cm. Since each photon minibeam has an angular divergence of 410\, the strikes on the target are separated nicely. This scheme produces &10 B}B meson pairs per year, an excellent number for studying CP violation and rare B decays. To avoid swamping the detector, we limit the intensity of the hot photon minibeams so that, at the location of each hit on the target, only about one hadronic interaction per hot photon pulse occurs (&10 photons;10% hadronic interaction length ;10\ fraction of total events that are hadronic). We get the following number of meson pairs per year: N
&10 hot photons per minibeam ;100 minibeams ;2;10\ branching ratio to b quarks ;2;10 electron bunch rep rate ;3;10 seconds per year
N
See Refs. [18,19] for N &;10\
&;10\ and Ref. [18] for
LASER COMPTON SCATTERING
52
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
;10\ hadronic length of target [18,19] ;10\ fraction of photon}nucleon interactions that are hadronic [18] &10.
(1)
With the recent advances in particle detection, it is possible to avoid using the 100 laser scatterings per electron bunch. First of all, if one wanted to convert each electron in the collider bunch to a hot c, as proposed for c}c colliders, one could use the Thomson cross section to estimate that about 10 photons need to collide with each electron. Therefore, for the 10 electrons of a typical collider bunch, one would need 10 photons, corresponding to about a 1 J laser #ash, which is not excessive and possible nowadays with lasers. Hence, for 10\ of the maximum conversion e$ciency, one could create one hot c pulse containing 10 photons for each electron bunch. Thus, one could trade 100 minibeams containing 10 hot photons per minibeam for one beam with 10 hot photons. Whether this second option leads to undesirable nonlinear QED e!ects will have to be studied further. This alternative yields &10 B}B meson pairs per year. Finally, the B mesons are produced with about equal large momenta &E /2 and at large transc verse momenta P &m , leaving a nice signal in the detector. We know that most of the reactions on the target will be electromagnetic, with the b quark contributions being down by a factor of &2;10\. Since we have discussed only the production mechanism and not a detection system at this time, more studies need to be performed on specifying a system of detectors and performing Monte Carlo simulations to understand better background rates and signal-to-noise ratios.
3. Photoproduction of s leptons Using the second scheme for BACKGAMMON involving one hot photon pulse per electron bunch, one can revisit a previous calculation of the photoproduction of s>}s\ lepton pairs [20]. One starts
with the ratio of s>}s\ to e>}e\ photoproduction cross sections p(cPs>s\) [log (2u/m )!109/42] r s s " (2) p(cPe>e\) [log (2u/m )!109/42] r where r is the classical lepton radius, m is the lepton mass, and u is the backscattered photon energy. At 250 GeV, this ratio is &2;10\ and varies slowly with u. Thus, we arrive at the following per year:
p(cPs>s\) p(cPbb ) N > \& N s s p(cPe>e\) p(cPe>eN ) &[2;10\/(2;10\;10\)]10 &10.
(3)
In BACKGAMMON, the s>}s\ #y at relatively large angles &m /E and the decay lengths are of s c the order of 1 cm. Finally, Refs. [1,3] point out that if polarized laser light is used, the Compton backscattered photons will preserve to a high degree the polarization of the incident laser light. However, to optimize the Compton scattering cross section, one may want to choose the electron helicity opposite to that of the laser photons. Thus, we have a real opportunity to photoproduce polarized s leptons and study in a detailed way the polarization e!ects in s decay.
4. Conclusion We have discussed the possibility to photoproduce &10 B}B meson pairs and &10 s>}s\ lepton pairs per year. These possibilities have arisen due to the unique properties of Compton backscattered photon beams. This scheme in its original form was proposed about ten years ago when the state of the technology for the next linear collider was in its infancy. Since that time, the next linear collider seems to be approaching realization. Furthermore, laser technology has progressed considerably. Hirose [21], Pogorelsky [21], and Telnov [21] have considered laser con"gurations for other
S.K. Mtingwa, M. Strikman / Nuclear Instruments and Methods in Physics Research A 455 (2000) 50}53
applications, such as positron sources and c}c colliders, at the next linear collider. Since their schemes involve roughly 100% conversion of the electrons to photons, the requirements on the laser systems are more stringent. In BACKGAMMON, the required backscattered photon #ux is only &10\ of that for these other applications; thus, for example, BACKGAMMON could utilize the scheme of Hirose and Pogorelsky, involving several tens of CO multi-bunch lasers with 0.25 J/bunch, each with 85 bunches at 150 Hz. However, there is still considerable research and development that must be done before any of these laser systems are used. Finally, Compton backscattering o!ers highly energetic, monochromatic, polarized, and pure (uncontaminated by other neutral particles) photon beams that leave relatively clean signals in detectors. Thus, BACKGAMMON o!ers excellent opportunities to do interesting "xed target physics at the next linear collider.
References [1] R.H. Milburn, Phys. Rev. Lett. 10 (1963) 75. [2] F.R. Arutyunian, I.I. Goldman, V.A. Tumanian, Zh. Eksp. Teor. Fiz. 45 (1963) 312 [Sov. Phys. JETP 18 (1964) 218]. [3] F.R. Arutyunian, V.A. Tumanian, Phys. Lett. 4 (1963) 176.
53
[4] V.M. Harutyunian, F.R. Harutyunian, K.A. Ispirian, V.A. Tumanian, Phys. Lett. 6 (1963) 175. [5] K.O. Mikaelian, Phys. Lett. B 115 (1982) 267. [6] I.F. Ginzburg, G.L. Kotkin, V.G. Serbo, V.I. Telnov, Nucl. Instr. and Meth. 205 (1983) 47. [7] I.F. Ginzburg, G.L. Kotkin, S.L. Pan"l, V.G. Serbo, V.I. Telnov, Nucl. Instr. and Meth. 219 (1984) 5. [8] C. Akerlof, Preprint UM HE 81-59, University of Michigan, 1981. [9] J.C. Sens, CERN-EP/88-99, 1988. [10] J. Ballam et al., Phys. Rev. Lett. 23 (1969) 498. [11] C. Prescott, SLAC internal report, SLAC-TN-73-1, 1973. [12] S. Kerhoas, SACLAY internal report, 1994. [13] G. Bardin et al., SACLAY report, DAPHNIA-SPhN-9614, 1996. [14] G. Bardin, C. Cavata, J.-P. Jorda, SACLAY internal report, 1997. [15] S.K. Mtingwa, M. Strikman, Phys. Rev. Lett. 64 (1990) 1522. [16] J.J. Aubert et al., Nucl. Phys. B 213 (1983) 1. [17] J.J. Aubert et al., Phys. Lett. B 89 (1980) 267. [18] D. Harding, Fermilab Experiment E687, private communication. [19] P. Frabetti et al., Fermilab internal report, FERMILABPub-90/258-E [E687], 1990. [20] S.K. Mtingwa, M. Strikman, in Rare and Exclusive B&K Decays and Novel Flavor Factories, American Institute of Physics Publication, Conference Proceedings Vol. 261, AIP, New York, 1992, p. 236. [21] Proceedings of the Symposium, New Visions in LaserBeam Interactions: Fundamental Problems and Applications of Laser-Compton Scattering, Tokyo Metropolitan University and High Energy Accelerator Research Organization (KEK), Tokyo, Japan, 1999 Nucl. Instr. and Meth. A 455 (2000).
LASER COMPTON SCATTERING