- Email: [email protected]
φ meson inclusive production by 70 GeVc protons
Volume 110B, number 3,4
PHYSICS LETTERS
1 April 1982
~bMESON INCLUSIVE PRODUCTION BY 70 GeV/c PROTONS Yu.M. ANTIPOV, V.A. BESSUBOV, N.P. BUDANOV, S.P. DENISOV, Yu.P. GORIN, V.G. KARTASHEVA, S.V. KLIMENKO, A.A. LEBEDEV, A.I. PETRUKHIN, S.A. POLOVNIKOV, V.N. ROINISHVILI ~, D.A. STOYANOVA and F.A. YOTCH Institute for High Energy Physics, Serpukhov, USSR Received 14 September 1981
Results of the experimental study of inclusive ~ meson production off berillium nuclei by 70 GeV/c protons in the beam fragmentation region x > 0.41 are presented. Fitting of the measured differential cross sections to the forms do/dx ~ (1 - x)n/x and do/dp~ ~ e x p ( - b p ~ ) gives the parameters n = 6.0 • 1.7 and b = (2.4 + 0.7) (GeV/c) -2. In the framework of a q u a r k - p a r t o n model the measured ~ meson x-distribution suggests that in the region of x > 0.41 nearly 90% of the 0 mesons are produced via a strange sea quark fusion. The ratio of the OZI-forbidden and OZIallowed transition coupling constants has been found to be ten times smaller than the same ratio calculated from the partial decay widths. The total inclusive cross section is estimated to be o(pN --, ~X) = (0.7_+ 0.2) × 10-27 cm 2.
To continue our study of pure neutral vectormeson inclusive production with the "Sigma" spectrometer [1-3] we have investigated q5 meson production in the reaction
tions. The smooth curve in fig. 1 represents the fit with a gaussian of 70 + 4 MeV FWHM and central value 1021 +- 7 MeV for the ~b meson together with
p + Be -~ ~b + anything
p . B e ~ u.'ja- • X 70 GeV/e
L p+pat 70 GeV/c beam momentum. In this experiment the ¢'s were produced in the kinematical region x = 2p[/x/~ >~ 0.4 and pt2 < 1.0 (GeV/c) 2. The sensitivity of the exposure was 18.4 × 10 -33 cm2/ weighted event/Be nucleus. The detected dimuon events have been weighted for geometric acceptance. To calculate it the 4)decay angular distribution was assumed to be isotropic. If instead we used (1 + cos 0~) distributions, then all the cross sections would change by -+20%, however, the changes in the shapes of the differential spectra would be negligible. Fig. 1 shows the weighted p + p - mass spectrum for all the events. A clear ~ signal is seen with the statistical significance of more than 5 standard devia: Institute of Physics, Tbilisi, USSR.
326
XF > 0.43
500C
600
m 4000 U3 Z ~J
> 3000
W
2000
,7, 1000
900
J 500
1000
1100
M ~ , MeV
700
900
1100
1300
DIMUON MASS (MeV) Fig. 1. Weighted dimuon mass spectrum,
0 031-9163/82/0000-0000/$02.75 © 1982 Noah-Holland
Volume 110B, number 3,4 . . . .
PHYSICS LETTERS 1 . . . .
F
'
p÷Be--¢.X
Table 1 Differential cross sections for the reaction pBe ~ 4~Xat 70 GeV/c. p~-interval (GeV/c) 2
0.00-0.05 0,00-0.08 0.05-0.15 0,08-0.15 0.15-0.25 0.25-0.35 0,35-0.45 0.45-0.55 0.55-0.75 0.75-1.00
10
(D
0.5
1.0 p2,(GeV/c) 2
Fig. 2. The ~ meson p~ distribution. an i n c o h e r e n t sum of the sophisticated B r e i t Wigner formulae for the p0 + co peak (for details see ref. [3]) and a second-order p o l y n o m i a l for a n o n r e s o n a n t background. The measured ¢ m e s o n p r o d u c t i o n inclusive cross section for x > 0.41 and pt2 < 1 (GeV/c) 2 was f o u n d to be (15 -+ 3) X 10 - 3 0 cm2/Be nucleus where the error is statistical only. To determine the differential distribution of meson with respect to pt2 or x variable, the data were first divided into suitable bins in p 2 or x, and the ¢ signals were then obtained by fitting the corresponding/2+/2 - mass spectra. The position and the apparent width o f the ¢ peak were k e p t fixed during these fits. The procedure used makes the background subtraction from a neighbouring mass region pleonastic. The p2t distribution of 4~ mesons is presented in fig. 2 and also in table 1. It is fitted b y the exponential f u n c t i o n e x p ( - b p 2) with b = (2.4 + 0.7) (GeV/c) - 2 . This value of b is compatible with those from other experiments on ¢ meson p r o d u c t i o n by non-strange hadrons [4,5].
1 April 1982
do/dp~
x-interval
do/dx ~ub/Be nucleus
0.41-0.43 0.43-0.45 0.45-0.47 0.47-0.50 0.50-0.52 0.50-0.55 0.52-0.55 0.52-0.60 0.55-0.60 0.60-0.80 0.60-1.00 0.80-1.00
179 -+ 89 166 -+ 79 156 -+ 58 71 -+ 40 72 ,+ 41 60 ,+ 25 45 -+ 26 26 ,+ 19 15 ,+ 12 4.4 ,+ 3.7 2.1 ,+ 1.7 1.4 ,+ 1.5
izb(GeV/e)2/ Be nucleus 43 _+ 22 27 -+ 14 24 -+ 14 38 ,+ 16 26 ,+ 13 25 ,+ 11 16 ,+ 12 15 -+ 9 7.7 -+ 4.6 4.3 _+ 3.5
The differential cross section do/dx for ¢ production is presented in fig. 3 and also in table 1. Fitting this do/dx distribution to the forms (1 - x)n/x and (1 - x) n' we o b t a i n e d the values o f n = 6.0 -+ 1.7 (the solid curve in fig. 3) and n ' = 7.0 -+ 1.8 for x > 0.41. These values of the e x p o n e n t are comparable
p* B e ~ ¢ . X 70 GeV]c p2 < 0.75(GeV/c )2
¢, c
~3c :I, x7
F'x.\
015
0!6
0!7
Fig. 3, The C-meson x = 2PL/x/sdistribution. Smooth curves are different kinds of fits described in the text. 327
Volume 110B, number 3,4
PHYSICS LETTERS
to those of the experiment [4] at 150 GeV/c (n = 4.1 -+ 0.4) but there is a contradiction with the measurements from ref. [6] at ~/s-= 63 GeV (the dashed curve in fig. 3 corresponds to their n = 2.4 --- 0.9 and is normalized to our number o f events). To understand the mechanism o f the ~ meson production in the non-strange hadron collisions we used the q u a r k - p a r t o n model to fit the do/dx distributions. According to ref. [7] for small p2 one has x R da/dx ~ F l ( X ) + ~F2(x ) ,
whe re: x R = (x 2 +
4M2/s)l/2,
F2(X ) = u 1 s2 +
F l ( X ) = 2X2SlS2 ,
SlU2 + l ( d l S
2 + Sld2) + 2SlS 2 ,
Ul, u 2, d l , d 2 are the valence quark distributions, Sl, s2, the sea quark distributions, Xs = 0.43, the strange sea suppression factor. The term F l ( X ) corresponds to the OZI-allowed strange sea quark fusion, F 2 ( x ) describes the contribution of the OZI-forbidden non-strange valence and sea quark annihilation, the free parameter a = g2/g2 represents the coupling constant ratio. Using the quark distribution parametrization from ref. [8] and our d e / d x data we estimated a<~ 10 - 3 , which should be compared with a "~ 0.02, calculated from the ~b-+ 37r and the w -+ 37r partial width ratio [9] (the d a s h e d - d o t t e d curve in fig. 3 corresponds to a = 0.02). Thus the Zweig-suppression factor in the ~ production is an order o f magnitude lower than that in its decay. After integration of F 1(x) and F 2 ( x ) over x for x > 0.41 we have found that only 10% of the ~ mesons in this region o f x are produced via the OZIforbidden process. This result is in qualitative agreement with the experiment [10] where the associated
328
1 April 1982
production of strange particles and q~ mesons have been observed. Different kinematical regions in our experiment and in ref. [10] do not allow further comparison. To obtain the integrated cross section per nucleon and for all x we used the q u a r k - p a t t o n model xdistribution with a = 0 and assumed the A-dependence of the cross section in the form a A ~ A 0.7, as was measured by us for K - A interactions [2]. The result is o(pN -+ ~bX) = (0.7 -+ 0.2) × 10 -27 cm 2 with an additional systematic error of 30%. To conclude, the above results provide further information on the ~b production mechanism. In particular, the ratio o f the OZl-forbidden and OZIallowed transition coupling constants has been found to be ten times smaller than the same ratio calculated from the partial decay widths. We thank V.V. Ezhela, A.K. Likhoded, V.F. Obrastsov and S.R. Slabospitsky for useful discussions.
References [1] Yu.M. Antipov et al., Phys. Lett. 60B (1976) 309; 72B (1977) 278; 76B (1978) 235; preprint IHEP 80-97 (Serpukhov, 1980). [2] Yu.M. Antipov et al., Yad. Fiz. 28 (1978) 1299. [3] Yu.M. Antipov et al., Yad. Fiz. 32 (1980) 676. [4] K.J. Anderson et al., Phys. Rev. Lett. 37 (1976) 799. [5] B. Ghidini et al., Phys. Lett. 68B (1977) 186. [6] M.M. Block et al., preprint CERN/EP 79-82 (Geneva, 1979). [7] V.V. Kniazev et al., preprint IHEP 77-106 (Serpukhov, .1977). [8] R.Mc Elhaney and S.F. Tuan, Phys. Rev. D8 (1973) 2267. [9] R.P. Feynman, Photon-hadron interactions (Benjamin, New York, 1972). [10] C. Daum et aL, Phys. Lett. 98B (1981) 313.
PHYSICS LETTERS
1 April 1982
~bMESON INCLUSIVE PRODUCTION BY 70 GeV/c PROTONS Yu.M. ANTIPOV, V.A. BESSUBOV, N.P. BUDANOV, S.P. DENISOV, Yu.P. GORIN, V.G. KARTASHEVA, S.V. KLIMENKO, A.A. LEBEDEV, A.I. PETRUKHIN, S.A. POLOVNIKOV, V.N. ROINISHVILI ~, D.A. STOYANOVA and F.A. YOTCH Institute for High Energy Physics, Serpukhov, USSR Received 14 September 1981
Results of the experimental study of inclusive ~ meson production off berillium nuclei by 70 GeV/c protons in the beam fragmentation region x > 0.41 are presented. Fitting of the measured differential cross sections to the forms do/dx ~ (1 - x)n/x and do/dp~ ~ e x p ( - b p ~ ) gives the parameters n = 6.0 • 1.7 and b = (2.4 + 0.7) (GeV/c) -2. In the framework of a q u a r k - p a r t o n model the measured ~ meson x-distribution suggests that in the region of x > 0.41 nearly 90% of the 0 mesons are produced via a strange sea quark fusion. The ratio of the OZI-forbidden and OZIallowed transition coupling constants has been found to be ten times smaller than the same ratio calculated from the partial decay widths. The total inclusive cross section is estimated to be o(pN --, ~X) = (0.7_+ 0.2) × 10-27 cm 2.
To continue our study of pure neutral vectormeson inclusive production with the "Sigma" spectrometer [1-3] we have investigated q5 meson production in the reaction
tions. The smooth curve in fig. 1 represents the fit with a gaussian of 70 + 4 MeV FWHM and central value 1021 +- 7 MeV for the ~b meson together with
p + Be -~ ~b + anything
p . B e ~ u.'ja- • X 70 GeV/e
L p+pat 70 GeV/c beam momentum. In this experiment the ¢'s were produced in the kinematical region x = 2p[/x/~ >~ 0.4 and pt2 < 1.0 (GeV/c) 2. The sensitivity of the exposure was 18.4 × 10 -33 cm2/ weighted event/Be nucleus. The detected dimuon events have been weighted for geometric acceptance. To calculate it the 4)decay angular distribution was assumed to be isotropic. If instead we used (1 + cos 0~) distributions, then all the cross sections would change by -+20%, however, the changes in the shapes of the differential spectra would be negligible. Fig. 1 shows the weighted p + p - mass spectrum for all the events. A clear ~ signal is seen with the statistical significance of more than 5 standard devia: Institute of Physics, Tbilisi, USSR.
326
XF > 0.43
500C
600
m 4000 U3 Z ~J
> 3000
W
2000
,7, 1000
900
J 500
1000
1100
M ~ , MeV
700
900
1100
1300
DIMUON MASS (MeV) Fig. 1. Weighted dimuon mass spectrum,
0 031-9163/82/0000-0000/$02.75 © 1982 Noah-Holland
Volume 110B, number 3,4 . . . .
PHYSICS LETTERS 1 . . . .
F
'
p÷Be--¢.X
Table 1 Differential cross sections for the reaction pBe ~ 4~Xat 70 GeV/c. p~-interval (GeV/c) 2
0.00-0.05 0,00-0.08 0.05-0.15 0,08-0.15 0.15-0.25 0.25-0.35 0,35-0.45 0.45-0.55 0.55-0.75 0.75-1.00
10
(D
0.5
1.0 p2,(GeV/c) 2
Fig. 2. The ~ meson p~ distribution. an i n c o h e r e n t sum of the sophisticated B r e i t Wigner formulae for the p0 + co peak (for details see ref. [3]) and a second-order p o l y n o m i a l for a n o n r e s o n a n t background. The measured ¢ m e s o n p r o d u c t i o n inclusive cross section for x > 0.41 and pt2 < 1 (GeV/c) 2 was f o u n d to be (15 -+ 3) X 10 - 3 0 cm2/Be nucleus where the error is statistical only. To determine the differential distribution of meson with respect to pt2 or x variable, the data were first divided into suitable bins in p 2 or x, and the ¢ signals were then obtained by fitting the corresponding/2+/2 - mass spectra. The position and the apparent width o f the ¢ peak were k e p t fixed during these fits. The procedure used makes the background subtraction from a neighbouring mass region pleonastic. The p2t distribution of 4~ mesons is presented in fig. 2 and also in table 1. It is fitted b y the exponential f u n c t i o n e x p ( - b p 2) with b = (2.4 + 0.7) (GeV/c) - 2 . This value of b is compatible with those from other experiments on ¢ meson p r o d u c t i o n by non-strange hadrons [4,5].
1 April 1982
do/dp~
x-interval
do/dx ~ub/Be nucleus
0.41-0.43 0.43-0.45 0.45-0.47 0.47-0.50 0.50-0.52 0.50-0.55 0.52-0.55 0.52-0.60 0.55-0.60 0.60-0.80 0.60-1.00 0.80-1.00
179 -+ 89 166 -+ 79 156 -+ 58 71 -+ 40 72 ,+ 41 60 ,+ 25 45 -+ 26 26 ,+ 19 15 ,+ 12 4.4 ,+ 3.7 2.1 ,+ 1.7 1.4 ,+ 1.5
izb(GeV/e)2/ Be nucleus 43 _+ 22 27 -+ 14 24 -+ 14 38 ,+ 16 26 ,+ 13 25 ,+ 11 16 ,+ 12 15 -+ 9 7.7 -+ 4.6 4.3 _+ 3.5
The differential cross section do/dx for ¢ production is presented in fig. 3 and also in table 1. Fitting this do/dx distribution to the forms (1 - x)n/x and (1 - x) n' we o b t a i n e d the values o f n = 6.0 -+ 1.7 (the solid curve in fig. 3) and n ' = 7.0 -+ 1.8 for x > 0.41. These values of the e x p o n e n t are comparable
p* B e ~ ¢ . X 70 GeV]c p2 < 0.75(GeV/c )2
¢, c
~3c :I, x7
F'x.\
015
0!6
0!7
Fig. 3, The C-meson x = 2PL/x/sdistribution. Smooth curves are different kinds of fits described in the text. 327
Volume 110B, number 3,4
PHYSICS LETTERS
to those of the experiment [4] at 150 GeV/c (n = 4.1 -+ 0.4) but there is a contradiction with the measurements from ref. [6] at ~/s-= 63 GeV (the dashed curve in fig. 3 corresponds to their n = 2.4 --- 0.9 and is normalized to our number o f events). To understand the mechanism o f the ~ meson production in the non-strange hadron collisions we used the q u a r k - p a r t o n model to fit the do/dx distributions. According to ref. [7] for small p2 one has x R da/dx ~ F l ( X ) + ~F2(x ) ,
whe re: x R = (x 2 +
4M2/s)l/2,
F2(X ) = u 1 s2 +
F l ( X ) = 2X2SlS2 ,
SlU2 + l ( d l S
2 + Sld2) + 2SlS 2 ,
Ul, u 2, d l , d 2 are the valence quark distributions, Sl, s2, the sea quark distributions, Xs = 0.43, the strange sea suppression factor. The term F l ( X ) corresponds to the OZI-allowed strange sea quark fusion, F 2 ( x ) describes the contribution of the OZI-forbidden non-strange valence and sea quark annihilation, the free parameter a = g2/g2 represents the coupling constant ratio. Using the quark distribution parametrization from ref. [8] and our d e / d x data we estimated a<~ 10 - 3 , which should be compared with a "~ 0.02, calculated from the ~b-+ 37r and the w -+ 37r partial width ratio [9] (the d a s h e d - d o t t e d curve in fig. 3 corresponds to a = 0.02). Thus the Zweig-suppression factor in the ~ production is an order o f magnitude lower than that in its decay. After integration of F 1(x) and F 2 ( x ) over x for x > 0.41 we have found that only 10% of the ~ mesons in this region o f x are produced via the OZIforbidden process. This result is in qualitative agreement with the experiment [10] where the associated
328
1 April 1982
production of strange particles and q~ mesons have been observed. Different kinematical regions in our experiment and in ref. [10] do not allow further comparison. To obtain the integrated cross section per nucleon and for all x we used the q u a r k - p a t t o n model xdistribution with a = 0 and assumed the A-dependence of the cross section in the form a A ~ A 0.7, as was measured by us for K - A interactions [2]. The result is o(pN -+ ~bX) = (0.7 -+ 0.2) × 10 -27 cm 2 with an additional systematic error of 30%. To conclude, the above results provide further information on the ~b production mechanism. In particular, the ratio o f the OZl-forbidden and OZIallowed transition coupling constants has been found to be ten times smaller than the same ratio calculated from the partial decay widths. We thank V.V. Ezhela, A.K. Likhoded, V.F. Obrastsov and S.R. Slabospitsky for useful discussions.
References [1] Yu.M. Antipov et al., Phys. Lett. 60B (1976) 309; 72B (1977) 278; 76B (1978) 235; preprint IHEP 80-97 (Serpukhov, 1980). [2] Yu.M. Antipov et al., Yad. Fiz. 28 (1978) 1299. [3] Yu.M. Antipov et al., Yad. Fiz. 32 (1980) 676. [4] K.J. Anderson et al., Phys. Rev. Lett. 37 (1976) 799. [5] B. Ghidini et al., Phys. Lett. 68B (1977) 186. [6] M.M. Block et al., preprint CERN/EP 79-82 (Geneva, 1979). [7] V.V. Kniazev et al., preprint IHEP 77-106 (Serpukhov, .1977). [8] R.Mc Elhaney and S.F. Tuan, Phys. Rev. D8 (1973) 2267. [9] R.P. Feynman, Photon-hadron interactions (Benjamin, New York, 1972). [10] C. Daum et aL, Phys. Lett. 98B (1981) 313.