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Nuclear Physics B (Proc. Suppl.) 56A (1997) 84-88

P R O C E E D I N G S S U P P L E M E N T S

Protonium X-ray spectroscopy

D. Anagnostopoulos 1, M. Augsburger 2, G. Borehert 3, C. Castelli 4, D. ChateUard 2, P. EI-Khoury 5,

J.-P. Egger 2, M. Elble 3, H. Gorke 3, D. Gotta 3, P. Hauser 6, P. Indelicato 5, K. Kirch 6, S. Lenz 3, N. Nelms 4 ,

K. Rashid 7, O.W.B. Schult 3, Th. Siems 3, L.M. Simons 6

presented by D. Gotta

1 Department of Physics, University of Ioannina, Greece

2 Institut de Physique de l'Universit6 de Neuch,qtel, Switzerland

3 Institut for Kernphysik, Forschungszentrum JtUich, Germany;

4 Dep. of Astronomy and Astrophysics, University of Leicester, England

5 Institut du Radium, Universit~ Pierre et Marie Curie, Paris, France

6 Paul-Scherrer-Institut (PSI) ViUigen, Switzerland

7 Quad-I-Azam University, Islamabad, Pakistan

In LEAR experiment PS207, the Balmer o~ radiation from antiprotonic hydrogen has been measured with a focussing crystal spectrometer. Preliminary results for strong interaction effects are reported.

1. INTRODUCTION The aim of LEAR experiment PS207 is to

measure the characteristic Lo~ radiation from antiprotonic hydrogen and deuterium with a high resolution crystal spectrometer and to extract from the line shift and broadening the strong interaction parameters of the 2p levels [1,2]. In this paper, we present preliminary results from our last measuring period in July 1996, where antiprotonic hydrogen was measured with high statistics.

2. EXPERIMENTAL SET-UP The LEAR beam of 105 MeV/c momentum was

injected into the cyclotron trap [3]. In average, an incoming antiproton flux of 106 per second was received, which could be stopped to 90% in the center of the trap. Thus, about 109 antiprotons per hour were stopped in 20 mbar hydrogen gas. The gas volume was separated from the spectrometer vacuum by a 2 ~tm thick mylar window to minimize absorption losses. The diameter of the stop volume is about 20 mm (FWHM) and has been measured in an earlier beam period with the crystal spectrometer using the p4He(5g-4f) transition [4].

0920-5632/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII: S0920-5632(97)00256-9

For the hydrogen measurement, the crystal spectrometer was operated with two arms and three quartz crystals (Fig. 1). The energy resolution AE/E of such a spectrometer in the 2 keV region is of the order of 10 "4 and the overall efficiency for one crystal is about 5-10 -6.

The Bragg crystals are spherically bent to a radius of curvature of 3 m and have a diameter of l0 cm [5-7]. To avoid effects from the boundaries disturbing the resolution the active diameter has been reduced by an aperture to 95 nun.

For each crystal an independent CCD detector was used as position sensitive detector to avoid a reduction in resolution from matching several images. On spectrometer arm I, a CCD of 21 nun × 28 mm active area was mounted having a pixel size of 27 }~m × 27 ~m. For arm II, the active area of the two detectors with a pixel size of 22.5 }~m x 22.5 ~m was 17 nun x 52 nun each. Besides the very good intrinsic position resolution, an energy resolution of better than 200 eV at 2 keV and the pixel structure itself allow an efficient background suppression. All the detectors were equipped with a 2 ttm mylar window.

D. Anagnostopoulos et al. /Nuclear Physics B (Proc. Suppl.) 56,4 (1997) 84-88 85

CRYSTAL SPECTROMETER II

MOS-CCD

valve

beam tube

pn-CCD

~ curved crystal

vacuum tubes

larger chamber

0 5 100cm

X-Ray tube

CYCLOTRON TRAP curved crystal

CRYSTAL SPECTROMETER I valve

MOS-CCD

Figure 1. Set-up at LEAR for the beam period in 1996.

86 D. Anagnostopoulos et al./Nuclear Physics B (Proc. SuppL) 56A (1997) 84-88

Table 1 Electromagnetic transition energies, crystal properties, and measured line widths. For the electromagnetic energies of the antiprotonic transitions, a recent calculation of Boucard and Indelicato was used [8]. The values for the fluorescence X-rays are from [9]. The narrow antiprotonic transitions from 3He and 2°Ne were used both for the energy calibration and the determination of the experimental resolution. The intrinsic rocking curve widths wf of the Bragg crystals at the Bragg angle ®B have been calculated for plane crystals with the code XDF of Brennan and Cowan [10]. The expected experimental line width AEMc was obtained from of a Monte-

_:C:~_10__my_-~ging c~9_=___AE,~ ! s ~ e ~ d t h obtained bya singl e linefit tp..t!Le m__eas~ed s l~a__ _~__::_ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

transition energy OB crystal order of wf AE Mc AE ,~p reflection

/ eV /meV /meV /meV

~ I (3-2) 1736.756 57.06 ° quartz 100 130 225+__20 ~3He (5g-4f) en. cal. & resp. f. 1686.477 59.74 ° quartz 100 135 170+_10 180+30 Si Kot~ energy cal. 1739.986 56.85 ° quartz 100 129

+0.019

ISD (3-2) 2316.420 58.57 ° silicon 111 272 570+90 ~2°Ne(13-12) en. cal. & resp. f. 2444.035 53.99 ° silicon 111 304 320_+_20 360+40 S Kot~ energy cal. 2307.89 58.94 ° silicon 111 170

+ 0.03

3. CALIBRATION In order to extract the strong interaction

parameters, both the energy calibration and the determination of the spectrometer response function have to be performed with high accuracy.

For the calibration of the Bragg angle, two possibilities exist: (i) Kot fluorescence X-rays, (ii) antiprotonic transitions, which are not affected by strong interaction.

The experimental line width, however, can only be obtained from narrow antiprotonic transitions, because their natural line width of a few meV is negligible compared to the spectrometer resolution. The natural line widths of the Kot~ fluorescence radiation from Si and S are 524-t-19 meV and 769+30meV [91 and thus exceed the crystal resolution by more than a factor of two (table 1). Therefore, fluorescence lines cannot be used to extract the experimental line width.

In principle, the purely electromagnetic transition energies can be calculated precisely from QED. However, the existing calculations are not fully consistent. The results for antiprotonic hydrogen deviate up to 80 meV from calculations published earlier [8,11,12]. We use here the most recent calculation of [8].

In the case of antiprotonic hydrogen, the resolution at 1.7 keV was measured with the ~3He(5g-4f) transition. The line is of almost symmetrical shape and the parallel transition ~3He(5f-4d) is clearly resolved from the main line.

4. RESULTS The Balmer ~ transitions of the hydrogen

isotopes and the corresponding calibration transitions 153He(5g-4f) and ]52°Ne(13-12) are shown in Fig. 2. An additional broadening for the Lot lines is observed which is attributed to the hyperfine structure and the strong interaction broadening.

For pH, an increase of the total width of 45 meV compared to the instrumental line width is observed (table 1). The tail on the high energy side may be attributed to the 23Po hyperfine level. The energy difference to the center of gravity of the main line is about 330 meV. Using the predicted value of 249 meV for the purely electromagnetic shift [13], we obtain a strong shift of the order of 80 meV. Such an attractive strong interaction shift is in agreement with models using the Dover-Richard potential [14]. It is an imperative consequence of the meson exchange picture.

D. Anagnostopoulos et al./Nuclear Physics B (Proc. Suppl.) 56,4 (1997) 84-88 8 7

n

lOO

80

GO

40

20

0 0

p3Het.b-4) "~ quartz 10o

1,687 key spher. R : 2.99 m

channels im~'gy

~2°Ne(13-121

2.444 keV

Si 111

sph~. R : 2.98 m

¢, 10,0

1 eV

chahnets ener~'-~-

n~ ~ •H13-2} quartz 100 i

l~ ~- 1.737 keV spher.

120t00 F" ~ ~ 8 ~: 1002"98 rn

1 eg

'°i 0 = l I ' ' ' l ! I I I f = l " l I '

300 350 400 ~ 500 channels w~r~

~o i pD(3-2) ~Oto0 '~! 2.317 key ~t'

2O

0 40 50 6(1 70

channels

Si 111

R s--phi'8 m ¢,100

go 90 10o 110

m.,w~

Figure 2. Measured line shapes of the Balmer ~ transitions of antiprotonic hydrogen and deuterium and the corresponding narrow antiprotonic calibration transitions. The deuterium spectrum was measured in an earlier beam period and is described in detail in [4].

In antiprotonic deuterium, the predicted electromagnetic splitting causes the 5 sublevels to form two groups being separated by about 0.5 eV. We observe, however, that the best approximation is obtained by a single line fit. Unfolding the experimental line width as obtained from ~2°Ne, we extract a Lorentz width of 570+85 meV [4] which is attributed to a very strong 2p level absorption. Such a hadronic width is almost a factor of 20 larger than in the case of antiprotonic hydrogen. From simple scaling laws, only a factor of about 6 is expected compared to pH. A multiple scattering approach as

used for pionic atoms predicts a mean hadronic width of 420 meV for the 2p sublevels, which almost describes the observed broadening [15].

5. S U M M A R Y The 2p levels of antiprotonic hydrogen and deuterium show significant effects as compared to the purely electromagnatic values. In hydrogen, there is evidence that the parameters of the 23po h~erfine state can be separated from the 3 other transitions. In deuterium, the hypertine structure is covered completely by the large line broadening.

88 D. Anagnostopoulos et al./Nuclear Physics B (Proc. Suppl.) 56A (1997) 8 4 4 8

REFERENCES

[1] D. Anagnostopoulos et al., CERN/PSCC/90- 9/P124, 1990; G. Borchert et al., SPSLC/93- 17/P124 Add. 3, 1993 (PS207)

[2] D. Gotta, Nucl. Phys. A 558 (1993) 645c, and ref. therein

[3] L. Simons, Phys. Scr. T22 (1988) 90 [4] D. Anagnostopoulos et al., Proc. of the 3 rd

Int. Workshop on Nucleon-Antinucleon Physics (NAN'95) ITEP, Moscow, September 1995, in press

[5] We are very grateful to Dr. A. Freund and his group at ESRF, Grenoble, that we could use his facilities for crystal tests.

[6] We are very grateful to Prof. F6rster and his group at FSU, Jena, for the determination of crystal properties.

[7] The Bragg crystals were polished and mounted in collaboration with Carl Zeiss GmbI-I, 73446 Oberkochen, Germany

[8] S. Boudard and P. Indelicato, 1996, priv. COml11.

[9] R. Deslattes and T. Mooney, 1990, priv. Comln.

[10] S. Breunan and P. L. Cowan1", Rev. Sci. Instr. 63 (1992) 850

[11] S. Barmo, H. Pilkuhn, and G. Schlaile, Z. Phys. A 301 (1981) 283

[12] E. Boric and B. J6dicke, Comp. Phys. vol.2, no. 6 (1988) 61

[13] E. Borie, Proc. of Phys. at LEAR with Low Energy Cooled Antiprotons, eds. U. Gastaldi and R. Klapisch, Erice, 1982, Plenum Press, New York, 1983 (The signs of the spin orbit + spin-spin contributions have to be changed.)

[14] J. Carbonell, G. Ihle, and J.-M.Richard, Z. Phys. A 344 (1989) 329 and ref. therein

[15] S. Wycech, A.M. Green, and J. A. Niskanen, Phys. Lett 152 B (1985) 308