- Email: [email protected]
Observation of a K∗ resonance at 2088 MeV
Volume 118B, number 4, 5, 6
PIIYSICS LETTERS
9 December 1982
OBSERVATION OF A K* RESONANCE AT 2088 MeV Birmingham I _ C E R N
Glasgow 1 Michigan State 2 Paris Collaboration
M. BAUBILLIER e, I.J. BLOODWORTH a, A. BURNS b, J.N. CARNEY a, G.F. COX a, U. DORE b,3, J.B. KINSON a, K. KNUDSON b, F. LEVY e, M. MacDERMOTT
a,4,
p.j. NEGUS c, B.Y. OH d,
E. QUERCIGH b, J.M. SCARR c, G.A. SMITH d, O. VILLALOBOS-BAILLIE a, M.F. VOTRUBA a, J. WHITMORE d and R. ZlTOUN b,e a Physics Department, University of Birmingham, Birmingham, United Kingdom b CERN, European Organization for Nuclear Research, Geneva, Switzerland c Department of Natural Philosophy, University of Glasgow, Glasgow, United Kingdom d Michigan State University, East Lansing, MI, USA e LPNHE s, University of Paris VI, Paris, France Received 9 August 1982
In a high statistics (180 events/gb) bubble chamber study of the reaction K-p ~ ~0n-p at 8.25 GeV/c, we observe a K°ir- state at 2088 _+20 MeV with a width 170+ls0°°MeV, produced with a cross section of 3.6 -+ 1.2 ~b. In addition we observe tiffs state in the channels K*(890)nn, oKrr, coKrr with a combined cross section of 7.1 + 2.6/~b, and possibly K*(890)nnn.
Two recent experiments [1,2] have reported the observation of a spin 4 K* resonance in the 2.0-2.1 GeV mass region. This state has been observed in spherical harmonic analyses of the Krr scattering angles, but no significant enhancement was found in the mass spectra. The mass and width of tire state have been measured a s M = 2023 -+ I0, P = 324 +- 45 a n d M = z-~c~c~+lO0 u / u _ 4 0 , F = 240+5%% M e V i n refs. [1] and [2] respectively. An indication of this state has been found in an earlier experiment [3]. We present a clear observation of a K* state [K*(2090) in the following] in the K ° n mass specvn+t00 MeV, trum at 2088 _+ 20 MeV with a width of 1,,,_50 produced in the reaction K p -+ K*p at 8.25 GeV/c with a cross section of 3.6 + 1.2/Jb. In addition, we t Work supported by the Science and Engineering Research Council, United Kingdom. 2 Work supported by the National Science Foundation, USA. 3 And Roma University, Rome, Italy. 4 Now at Rutherford Laboratory, United Kingdom. s Laboratory associated to IN2P3. 0 0 3 1 - 9 1 6 3 / 8 2 / 0 0 0 0 - 0 0 0 0 / $ 0 2 . 7 5 © 1982 North-Holland
observe this state in the inelastic channels K*(890)nn, pKn, coKn and possibly K*(890)TrTrn. In spite of the clear enhancement observed in this experiment, we are unable to determine its spin and parity. The K*(2090) is most naturally interpreted as a member of tire 4++SU(3) nonet which contains tile h(2040) meson v 1 The present analysis is based on a high statistics K - p exposure at 8.25 GeV/c in tire CERN 2 m hydrogen bubble chamber, corresponding to a sensitivity of ~ 1 8 0 events/rib. We have searched for high-nrass Kn states in the 4 constraint reaction K - p -+ K0rr-p ,
(1)
applying a probability cut of P(x 2) > 0.1% at the production vertex. A sample of 15 096 events of this reaction has been identified with negligible background This search has then been extended to the channels K p-+ i(0n -rr0p
(46 600 events),
(2)
*1 For references, see ref. [4]. 447
Volume 118B, number 4, 5, 6
'l .
PHYSICS LETTERS
i
o)
i
r
b)
24C
1780
20C 60016C c ,~ 5 0 0 -
12C 8( ~
4C
E z
30C-
,16
2'o
2:~
L/
20C
I00
O] 04
i 08
K - p -+ K0rr-rr+n
(27 632 e v e n t s ) ,
(3)
K - p -+ K07r-rr+rr-p
(19 504 e v e n t s ) ,
(4)
K p -+ K0rr-lr+rr-Tr0p
(33 668 e v e n t s ) .
(5)
28C
7> :~ 7 0 0
40C
9 December 1982
l 12
I
IG M ( R ° T r -)
2,0
2,4
2,8
3,2
GeV
Fig. I. (a) The K°rr - mass distribution from reaction (1) with cos 0~¢rr > 0.75 in the K-p cms. (b) The K°rr - mass distribution with resonance curves described in the text.
For reactions (2), (3) and (5), a p r o d u c t i o n probability cut P(X 2) > 5% was applied, while in the case o f reaction (4), a probability cut o f P ( x 2) > 0.1% was used. Reaction ( 1 ) i s well k n o w n to be d o m i n a t e d by K * ( 8 9 0 ) and K * ( 1 4 3 0 ) p r o d u c t i o n . In fig. la we show the mass distrbution o f the K01r system for cos 0* > 0.75 in the K - p centre o f mass system. This cos 0* cut (which corresponds to [tpp[ < i .3 GeV 2 for a KTr mass o f 2090 MeV) selects forwardly produced K*'s and reduces the b a c k g r o u n d ; i t has been applied t h r o u g h o u t the paper. In addition to three well established [4] K*'s (890, 1430 and 1780), a fourth state is clearly seen at a mass o f 2090 MeV (a signal o f ~ 1 0 0 over a background o f ~ 4 0 0 between 2000 and 2160 MeV). Fig. 1b shows the results of a fit using B r e i t - W i g n e r shapes for the Krr resonances and a s m o o t h p o l y n o m i a l background. The resulting mass and width for the K * ( 2 0 9 0 ) a r e M = 2088 + 20 vn+100 MeV. The p r o d u c t i o n cross section, and r = 1/v,_50 based on the fitted n u m b e r of events (200 + 70) o f the K * ( 2 0 9 0 ) , is 3.6 + 1.2/~b, after correcting for geometrical losses and neutral decays o f the K O. No significant structure is observed in the YLM m o m e n t s for Krr masses greater than 1900 MeV.
Table 1 Decay channels and cross sections of K*(2090). Reaction
Channels
Fitted number of events
Cross section a) (~b)
1 4 4 5 5 2
K0rrK*-(890)n+rr oK_OftcoKOrrK*-(890)Tr+rr-rr 0 K*0 (890)rr - or K*-(890)~r 0 K*-(890)Ir + K*0(1430)rr - or K*-(1430)rr ° K*-(1430)rr ÷ p-g0 p°K° f0K°
200 120 114 89 99 <40
3.6±1.2 3.2±1.6 2.1±0.9 1.8±0.9 2.7±1.5
3 2 3 2 3 3
± 70 ± 56 ± 52 ± 43 ± 55
<30 <40 <30 <30 <30 <30
a) The cross sections have been corrected for unseen K0, K* and co° decay modes. 448
Volume 118B, number 4, 5, 6
PHYSICS LETTERS ,
300[-
al 'K*-c89o~ j ~+~r-~ .,, 2~9o
T
b) p R° "rr
1 I
1
3oo
1
200
200
> o
L
c > "S E Z
I00
100
c)
© ,
-
I
K~-(890)
]
i
i
F
__
1
200
40C
IOC
200
O, 16
i
d/ coR° rr-
/r + ~r-Tr
2,0
2,4
2.8
.6
Moss
GeV
20
2,4
2,8
Fig. 2. (a), (b) The K*-~+rr- and pK°~ - distributions from reaction (4); (c), (d) The K*-rr+rr-rr0 and coK°rr- distributions from reaction (5). The curves show the result of fits described in the text.
We now turn to our search for higher multiplicity decays o f the K*(2090) from reactions (2) to (5). The l~0~r-rr° and K°rr-rr + mass spectra (not shown) of reactions (2) and (3) respectively give little indication of the K*(2090) decaying into these channels. We have searched for the K*(2090) decaying into K*(890)rr, K*(1430)rr, p ~ 0 and f0~0. No statistically significant evidence for the K*(2090) is observed in any of these quasi-two-body channels; we quote, in table 1,95% confidence level upper limits of the decays into these channels.
9 December 1982
The K°a-rr+Tr mass distribution for reaction (4), on the other hand, shows a significant structure around 2090 MeV, while for the K0rr-Tr+lr 7r0 mass distribution of reaction (5) a rapidly varying background around 2090 MeV renders a clear cut interpretation difficult. Noting a strong presence of the K*(890) in these reactions, as well as a strong signal o f p and co in reactions (4) and (5) respectively, we have studied the K*(890)rr+Tr - and pK°Tr subchannels in reaction (4) and the K*(890)~r+Tr-rr 0 and coK0rr- subchannels in reaction (5). These mass spectra are shown in fig. 2. In figs. 2a, 2b and 2d, corresponding to K*Tr+rr , p K ° r r - and coK0rr- channels respectively, enhancements are observed at 2090 MeV with widths compatible with that determined for the Ka- mode indicating the decays o f the K*(2090) into these channels, while for K*(890)rr+rr-rr 0 (fig. 2c), there is no clear signal. We have fitted these mass spectra with two resonances (1780 and 2090) with the parameters determined from fig. l b , plus a smooth polynomial background. The results are superimposed on fig. 2. It should be noted that the introduction of the K*(2090) improved fits in all cases. The fitted number of events in these channels are given in table 1 together with the corresponding cross sections. We find no significant evidence for possible ~ * p 0 and K ' c o decays o f the K*(2090) or for K*(2090) decaying into 3 kaons (with or without pions). In conclusion we observe a Klr resonance with mass '~n+100 MeV in the K07r 2088 _+ 20 MeV and width 1.,,_50 decay mode, with a cross section o f 3.6 + 1.2/lb. We further observe this state decaying into K*(890)rr+~r - , pK.0rt-, co0K.°rr - with a combined cross section of 7.1 -+ 2.6/.tb. R eferen ces [1 ] W.E. Cleland et al., Phys. Lett. 97B (1980) 465. [2] D. Aston et al., Phys. Lett. 99B (1981) 502; 106B (1981) 235. [3] D.D.Carmony et al., Phys. Rev. D16 (1977) 1251. [41 R.L. Kelly et al., Rev. Mod. Phys. 52 (1980) S1.
449
PIIYSICS LETTERS
9 December 1982
OBSERVATION OF A K* RESONANCE AT 2088 MeV Birmingham I _ C E R N
Glasgow 1 Michigan State 2 Paris Collaboration
M. BAUBILLIER e, I.J. BLOODWORTH a, A. BURNS b, J.N. CARNEY a, G.F. COX a, U. DORE b,3, J.B. KINSON a, K. KNUDSON b, F. LEVY e, M. MacDERMOTT
a,4,
p.j. NEGUS c, B.Y. OH d,
E. QUERCIGH b, J.M. SCARR c, G.A. SMITH d, O. VILLALOBOS-BAILLIE a, M.F. VOTRUBA a, J. WHITMORE d and R. ZlTOUN b,e a Physics Department, University of Birmingham, Birmingham, United Kingdom b CERN, European Organization for Nuclear Research, Geneva, Switzerland c Department of Natural Philosophy, University of Glasgow, Glasgow, United Kingdom d Michigan State University, East Lansing, MI, USA e LPNHE s, University of Paris VI, Paris, France Received 9 August 1982
In a high statistics (180 events/gb) bubble chamber study of the reaction K-p ~ ~0n-p at 8.25 GeV/c, we observe a K°ir- state at 2088 _+20 MeV with a width 170+ls0°°MeV, produced with a cross section of 3.6 -+ 1.2 ~b. In addition we observe tiffs state in the channels K*(890)nn, oKrr, coKrr with a combined cross section of 7.1 + 2.6/~b, and possibly K*(890)nnn.
Two recent experiments [1,2] have reported the observation of a spin 4 K* resonance in the 2.0-2.1 GeV mass region. This state has been observed in spherical harmonic analyses of the Krr scattering angles, but no significant enhancement was found in the mass spectra. The mass and width of tire state have been measured a s M = 2023 -+ I0, P = 324 +- 45 a n d M = z-~c~c~+lO0 u / u _ 4 0 , F = 240+5%% M e V i n refs. [1] and [2] respectively. An indication of this state has been found in an earlier experiment [3]. We present a clear observation of a K* state [K*(2090) in the following] in the K ° n mass specvn+t00 MeV, trum at 2088 _+ 20 MeV with a width of 1,,,_50 produced in the reaction K p -+ K*p at 8.25 GeV/c with a cross section of 3.6 + 1.2/Jb. In addition, we t Work supported by the Science and Engineering Research Council, United Kingdom. 2 Work supported by the National Science Foundation, USA. 3 And Roma University, Rome, Italy. 4 Now at Rutherford Laboratory, United Kingdom. s Laboratory associated to IN2P3. 0 0 3 1 - 9 1 6 3 / 8 2 / 0 0 0 0 - 0 0 0 0 / $ 0 2 . 7 5 © 1982 North-Holland
observe this state in the inelastic channels K*(890)nn, pKn, coKn and possibly K*(890)TrTrn. In spite of the clear enhancement observed in this experiment, we are unable to determine its spin and parity. The K*(2090) is most naturally interpreted as a member of tire 4++SU(3) nonet which contains tile h(2040) meson v 1 The present analysis is based on a high statistics K - p exposure at 8.25 GeV/c in tire CERN 2 m hydrogen bubble chamber, corresponding to a sensitivity of ~ 1 8 0 events/rib. We have searched for high-nrass Kn states in the 4 constraint reaction K - p -+ K0rr-p ,
(1)
applying a probability cut of P(x 2) > 0.1% at the production vertex. A sample of 15 096 events of this reaction has been identified with negligible background This search has then been extended to the channels K p-+ i(0n -rr0p
(46 600 events),
(2)
*1 For references, see ref. [4]. 447
Volume 118B, number 4, 5, 6
'l .
PHYSICS LETTERS
i
o)
i
r
b)
24C
1780
20C 60016C c ,~ 5 0 0 -
12C 8( ~
4C
E z
30C-
,16
2'o
2:~
L/
20C
I00
O] 04
i 08
K - p -+ K0rr-rr+n
(27 632 e v e n t s ) ,
(3)
K - p -+ K07r-rr+rr-p
(19 504 e v e n t s ) ,
(4)
K p -+ K0rr-lr+rr-Tr0p
(33 668 e v e n t s ) .
(5)
28C
7> :~ 7 0 0
40C
9 December 1982
l 12
I
IG M ( R ° T r -)
2,0
2,4
2,8
3,2
GeV
Fig. I. (a) The K°rr - mass distribution from reaction (1) with cos 0~¢rr > 0.75 in the K-p cms. (b) The K°rr - mass distribution with resonance curves described in the text.
For reactions (2), (3) and (5), a p r o d u c t i o n probability cut P(X 2) > 5% was applied, while in the case o f reaction (4), a probability cut o f P ( x 2) > 0.1% was used. Reaction ( 1 ) i s well k n o w n to be d o m i n a t e d by K * ( 8 9 0 ) and K * ( 1 4 3 0 ) p r o d u c t i o n . In fig. la we show the mass distrbution o f the K01r system for cos 0* > 0.75 in the K - p centre o f mass system. This cos 0* cut (which corresponds to [tpp[ < i .3 GeV 2 for a KTr mass o f 2090 MeV) selects forwardly produced K*'s and reduces the b a c k g r o u n d ; i t has been applied t h r o u g h o u t the paper. In addition to three well established [4] K*'s (890, 1430 and 1780), a fourth state is clearly seen at a mass o f 2090 MeV (a signal o f ~ 1 0 0 over a background o f ~ 4 0 0 between 2000 and 2160 MeV). Fig. 1b shows the results of a fit using B r e i t - W i g n e r shapes for the Krr resonances and a s m o o t h p o l y n o m i a l background. The resulting mass and width for the K * ( 2 0 9 0 ) a r e M = 2088 + 20 vn+100 MeV. The p r o d u c t i o n cross section, and r = 1/v,_50 based on the fitted n u m b e r of events (200 + 70) o f the K * ( 2 0 9 0 ) , is 3.6 + 1.2/~b, after correcting for geometrical losses and neutral decays o f the K O. No significant structure is observed in the YLM m o m e n t s for Krr masses greater than 1900 MeV.
Table 1 Decay channels and cross sections of K*(2090). Reaction
Channels
Fitted number of events
Cross section a) (~b)
1 4 4 5 5 2
K0rrK*-(890)n+rr oK_OftcoKOrrK*-(890)Tr+rr-rr 0 K*0 (890)rr - or K*-(890)~r 0 K*-(890)Ir + K*0(1430)rr - or K*-(1430)rr ° K*-(1430)rr ÷ p-g0 p°K° f0K°
200 120 114 89 99 <40
3.6±1.2 3.2±1.6 2.1±0.9 1.8±0.9 2.7±1.5
3 2 3 2 3 3
± 70 ± 56 ± 52 ± 43 ± 55
<30 <40 <30 <30 <30 <30
a) The cross sections have been corrected for unseen K0, K* and co° decay modes. 448
Volume 118B, number 4, 5, 6
PHYSICS LETTERS ,
300[-
al 'K*-c89o~ j ~+~r-~ .,, 2~9o
T
b) p R° "rr
1 I
1
3oo
1
200
200
> o
L
c > "S E Z
I00
100
c)
© ,
-
I
K~-(890)
]
i
i
F
__
1
200
40C
IOC
200
O, 16
i
d/ coR° rr-
/r + ~r-Tr
2,0
2,4
2.8
.6
Moss
GeV
20
2,4
2,8
Fig. 2. (a), (b) The K*-~+rr- and pK°~ - distributions from reaction (4); (c), (d) The K*-rr+rr-rr0 and coK°rr- distributions from reaction (5). The curves show the result of fits described in the text.
We now turn to our search for higher multiplicity decays o f the K*(2090) from reactions (2) to (5). The l~0~r-rr° and K°rr-rr + mass spectra (not shown) of reactions (2) and (3) respectively give little indication of the K*(2090) decaying into these channels. We have searched for the K*(2090) decaying into K*(890)rr, K*(1430)rr, p ~ 0 and f0~0. No statistically significant evidence for the K*(2090) is observed in any of these quasi-two-body channels; we quote, in table 1,95% confidence level upper limits of the decays into these channels.
9 December 1982
The K°a-rr+Tr mass distribution for reaction (4), on the other hand, shows a significant structure around 2090 MeV, while for the K0rr-Tr+lr 7r0 mass distribution of reaction (5) a rapidly varying background around 2090 MeV renders a clear cut interpretation difficult. Noting a strong presence of the K*(890) in these reactions, as well as a strong signal o f p and co in reactions (4) and (5) respectively, we have studied the K*(890)rr+Tr - and pK°Tr subchannels in reaction (4) and the K*(890)~r+Tr-rr 0 and coK0rr- subchannels in reaction (5). These mass spectra are shown in fig. 2. In figs. 2a, 2b and 2d, corresponding to K*Tr+rr , p K ° r r - and coK0rr- channels respectively, enhancements are observed at 2090 MeV with widths compatible with that determined for the Ka- mode indicating the decays o f the K*(2090) into these channels, while for K*(890)rr+rr-rr 0 (fig. 2c), there is no clear signal. We have fitted these mass spectra with two resonances (1780 and 2090) with the parameters determined from fig. l b , plus a smooth polynomial background. The results are superimposed on fig. 2. It should be noted that the introduction of the K*(2090) improved fits in all cases. The fitted number of events in these channels are given in table 1 together with the corresponding cross sections. We find no significant evidence for possible ~ * p 0 and K ' c o decays o f the K*(2090) or for K*(2090) decaying into 3 kaons (with or without pions). In conclusion we observe a Klr resonance with mass '~n+100 MeV in the K07r 2088 _+ 20 MeV and width 1.,,_50 decay mode, with a cross section o f 3.6 + 1.2/lb. We further observe this state decaying into K*(890)rr+~r - , pK.0rt-, co0K.°rr - with a combined cross section of 7.1 -+ 2.6/.tb. R eferen ces [1 ] W.E. Cleland et al., Phys. Lett. 97B (1980) 465. [2] D. Aston et al., Phys. Lett. 99B (1981) 502; 106B (1981) 235. [3] D.D.Carmony et al., Phys. Rev. D16 (1977) 1251. [41 R.L. Kelly et al., Rev. Mod. Phys. 52 (1980) S1.
449