- Email: [email protected]
KLOE results on φ radiative decays
ELSEVIER
Nuclear Physics A721 (2003) 801~~804~ www.elsevier.com/locate/npe
KLOE Results on 4 Radiative Decays The KLOE Collaboration* presented by S. Giovannella Laboratori Nazionali di Frascati dell’INFN Via E. Fermi 40, I-00044 Frascati (Roma), Italy e-mail address: [email protected] We report the results on the radiative decays 4 -+ q’y, q3 --t 7r07royand 4 + 77”‘~ obtained with the KLOE detector at the DA@NE &factory, using a sample of N 16 pb-r. The value of the branching ratio for the 4 + q’y decay is related to the ss and gluon content of the q’. A fit to the two-pseudoscalar invariant mass for the rr”7roy and nrr’y final states gives the contribution of the direct terms 4 -+ for, 4 + (~7 and 4 -+ as-y, allowing us to investigate the nature of these light scalar mesons. 1. Introduction
Among the measurements performed with the 2000 data sample (- 16 pb-‘) of the KLOE experiment [l] at DAQNE [2], the Frascati q&factory, the radiative decays provide an excellent opportunity to study the nature of light scalar and pseudoscalar mesons. KLOE has been designed to study CP violation in the K”Eo system. The apparatus is inserted in a 0.6 T magnetic field and consists of a 2 m radius drift chamber (DCH) with full stereo geometry in a helium based gas mixture, surrounded by a fine sampling lead/scintillating fibers electromagnetic calorimeter (EMC) with a hermetic coverage and a very high efficiency for low energy photons. The DCH resolutions are vr,,/pt x 0.4%, or4 N 150 pm, a, N 2 mm while the EMC energy and time resolutions can be parametrized and 0~ = 57 pslJE(Gev) @ 50 ps respectively. These as Q/E = 5.7%/$3ii3 performances are also well suited for studying 4 radiative decays. *A. Aloisio, F. Ambrosino, A. Antonelli, M. Antonelli, C. Bacci, G. Bencivenni, S. Bertolucci, C. Bini, C. Bloise, V. Bocci, F. Bossi, P. Branchini, S. A. Bulychjov, R. Caloi, P. Campana, G. Capon, G. Carboni, M. Cssarsa, V. Cssavola, G. Cataldi, F. Ceradini, F. Cervelli, F. Cevenini, G. Chiefari, P. Ciambrone, S. Conetti, E. De Lucia, P. De Simone, G. De Zorzi, S. Dell’Agnello, A. Denig, A. Di Domenico, C. Di Donato, S. Di Falco, B. Di Micco, A. Doria, M. Dreucci, 0. Erriquez, A. Farilla, G. Felici, A. Ferrari, M. L. Ferrer, G. Finocchiaro, C. Forti, A. Franceschi, P. Franzini, C. Gatti, P. Gauzzi, S. Giovannella, E. Gorini, E. Graziani, S. W. Han, M. Incagli, W. Kluge, V. Kulikov, F. Lacava, G. Lanfranchi, J. Lee-Franzini, D. Leone, F. Lu, M. Martemianov, M. Matsyuk, W. Mei, L. Merola, R. Messi, S. Miscetti, M. Moulson, S. Miiller, F. Murtas, M. Napolitano, A. Nedosekin, F. Nguyen, M. Palutan, E. Pasqualucci, L. Passalacqua, A. Passeri, V. Patera, E. Petrolo, L. Pontecorvo, M. Primavera, F. Ruggieri, P. Santangelo, E. Santovetti, G. Saracino, R. D. Schamberger, B. Scisscia, A. Sciubba, F. Scuri, I. Sfiligoi, A. Sibidanov, T. Spadaro, E. Spiriti, G. L. Tong, L. Tortora, P. Valente, B. Valeriani, G. Venanzoni, S. Veneziano, A. Ventura, S. Ventura, R. Versaci, G. W. Yu. 0375-9474/03/$ - see front matter 0 2003 Elsevier Science B.V doi:lO.l016/S0375-9474(03)01185-O
All rights reserved.
802~ 2. The
S. Giooannella/Nuclear Physics A721 (2003) 801~~804~ Pseudoscalar
Decays:
@I +
~7, 4 --f ~‘7
In the pseudoscalar sector, the branching ratio (BR) of the 4 -+ rjy is sensitive to the ss and gluon content of the 7’. Studies based on Chiral Pertubation Theory and phenomenological analysis suggest that the q-r]’ mixing in the quark flavour basis can be parametrized using only one mixing angle (pp [3,4]. Th is angle can be extracted from the ratio of the BR’s for the processes 4 -+ 71’7 and $J -+ ~7, h!,,,,! [5]. At KLOE we have studied these two processes using the decay chains: 4 -+ rfy --+ rpr+vy + yy7r+n-y and 4 + my --) zf~-7roy --t n+~-yyy, thus producing the same final state and leading to a first order cancellation for many of the systematic effects in the &,rt measurement. The separation between the 4 -t n’y and the dominant 4 + ny events (S/B N l/100) is achieved by exploiting the difference in the energy distribution of the photons (Fig. l-left); the resulting nf7r-yyy invariant mass for the 4 -+ $7 candidates is shown in Fig. l-right. The ratio of BR ‘s is then [6]: R,,, = FR;
< ;;;
= ( 4.70 f 0.47,&t f 0.3&t
) x w3,
leading to a mixing angle (pp = (41.8+]::)” and to an absolute branching ratio BR(4 -+ $7) = ( 6.10 f 0.61stat f 0.43,,t ) x 10-5,
(2)
which is the most precise measurement to date. This result limits the gluon content of r]’ to be less than 15%. 3. The Scalar
Decays:
C#J-+ for,
C$ +
~07
Although the existence of the scalar mesons fe(980) and as(980) is well established, their nature is still unclear. The main theoretical hypotheses are: ordinary @ mesons, -qqqq states and K3i; molecules [7-g]. The study of the radiative decays 4 + for, 4 -+ a07 is very important in this framework since both the BR’s and the meson mass spectra are sensitive to the nature of f. and Q [lo]. These two processes have been studied at KLOE by looking at the final states fo --+ z”7ro (a) and as + n7r”, with both 77+ yy (b) and n -+ ?I+~-xO (c). The final event topology is then either five prompt photons or five prompt photons and two tracks. In the 16 pb-’ data sample we count 2438 f. 61,607 f 36, 197 5 15 events for the (a), (b) and (c) decay respectively, corresponding to the following branching ratios [13,14]: BR(4 -+ ~T’O~T’O~) JW4 + W ’Y ; 77--+ YY) BR(@ -+ rj7r”y ; 7 + R+~-T’)
= = =
(1.09 f 0.03&& f 0.05,,&) x 1o-4 (8.51 f 0.51stat f 0.57& x 1O-5 (7.96 f 0.60stat f 0.40,& x 1O-5
(3) (4 (5)
The MT,, M,,, spectra (Fig. 2) are then fitted to extract the fs and ae parameters, including also the other processes that can contribute to the final states: 4 -+ porno(with both p --+ 7r”y and p -+ 77) and 4 -+ ay for the z”7roy final state. The vector meson term parametrization is taken from VMD calculations [ll] while for the v we use the result from Ref. [12]. The fit result is superimposed to the mass spectra in Fig. 2, where
S. Giooannella/Nuclear Physics A721 (2003) 8Olc-804~
h
500
3 2 3
i
2
400
fi A--
--...
300
.. ..*
.. -..
*-
-.
I., '0900
g:'
*
h
. :I??! 200
40 30
.
20
; : 5
. .
200
803c
10
< - . .;
300
, 400
!
E,WV)
u
910 920 930 940 950 960 970 980 990 II JO M Irw (MeV/c')
Figure 1. Selection of 4 -+ $7 + rr+rr-n’y: events inside the ellipse in the plane of the two hardest photons of the event (left) are retained. The two monochromatic bands are due to the 4 -+ qy background. The resulting r]’ invariant mass (right) is compared with the MC expectation for the signal (light grey) and the background (dark grey), whose amount has been evaluated from data itself.
a negligible qS-+ p contribution and a strong destructive interference between 4 ---f for and q!~+ ay can be observed. The resulting BR for the f. meson is then: BR(4 + for + n”7ro) = (1.49 f 0.07) x 10-4.
(6)
For the ae we have: BR(4 ---f a07 ---f 77~‘) = (7.4 f 0.7) x 10-5.
(7)
Concerning the fit parameters, the f. results are compatible with the qqq?j predictions while the a0 values indicate a better agreement with qtj expectations. 4. Conclusions
A sample of N 16 pb-’ of the KLOE data has been analyzed to study 4 radiative decays. We measured the branching ratio for the processes: 4 + $7, Q!J-+ n”7roy and 4 + 77s’~. We also extract the 7-v’ mixing angle and the couplings of fe (aa) to KK and mr (v). At the moment of writing we are analyzing the whole collected statistics, corresponding to an integrated luminosity of N 500 pb-’ These data will allow us to reach a better sensitivity on all reported measurements and distinguish between the recent phenomenological hypotheses interpreting these decays [15-181.
S. Giooannella /Nuclear
m (MeV)
Figure 2. Unfolded dBR/dM spectra for 4 -+ rr”7roy (left) and 4 + q7r”y (right). The fit results are superimposed as solid lines; single contributions are also shown (4 -+ ~7rO-r: 4 + a07 dashed, 4 4 pro dotted).
REFERENCES 1. 2. 3. 4. 5. 6. 7.
8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
The KLOE Collaboration (A. Aloisio et al.), LNF-92/019 (IR) (1992) and LNF-93/002 (IR) (1993). S. Guiducci et al., Proc. of the 2001 Particle Accelerator Conference (Chicago, Illinois, USA), P. Lucas S. Webber Eds. (2001) 353. Th. Feldmann and P. Kroll, Phys. Rev. D 58 (1998) 057501. F. De Fazio and M. R. Pennington, JHEP 0007 (2000) 51. A. Bramon, R. Escribano and M. D. Scadron, Eur. Phys. J. C 7 (1999) 271. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 541 (2002) 45. N. A. Tornqvist, Phys. Rev. Lett. 49 (1982) 624. R. L. Jaffe, Phys. Rev. D 15 (1997) 267. J. Weinstein and N. Isgur, Phys. Rev. Lett. 48 (1982) 659. N. N. Achasov and V. N. Ivanchenko, Nucl. Phys. B 315 (1989) 465. N. N. Achasov and V. V. Gubin, Phys. Rev. D 63 (2001) 094007. E. M. Aitala et al., Phys. Rev. Lett. 86 (2001) 770. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 537 (2002) 21. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 536 (2002) 209. F. E. Close and A. Kirk, Phys. Lett. B 515 (2001) 515. A. Bramon, R. Escribano, J. L. Lucia M., M. Napsuciale and G. Pancheri, hepph/0204339. N. A. Tornqvist, hep-ph/0204215 J. A. Oller, hep-ph/0205121.
Nuclear Physics A721 (2003) 801~~804~ www.elsevier.com/locate/npe
KLOE Results on 4 Radiative Decays The KLOE Collaboration* presented by S. Giovannella Laboratori Nazionali di Frascati dell’INFN Via E. Fermi 40, I-00044 Frascati (Roma), Italy e-mail address: [email protected] We report the results on the radiative decays 4 -+ q’y, q3 --t 7r07royand 4 + 77”‘~ obtained with the KLOE detector at the DA@NE &factory, using a sample of N 16 pb-r. The value of the branching ratio for the 4 + q’y decay is related to the ss and gluon content of the q’. A fit to the two-pseudoscalar invariant mass for the rr”7roy and nrr’y final states gives the contribution of the direct terms 4 -+ for, 4 + (~7 and 4 -+ as-y, allowing us to investigate the nature of these light scalar mesons. 1. Introduction
Among the measurements performed with the 2000 data sample (- 16 pb-‘) of the KLOE experiment [l] at DAQNE [2], the Frascati q&factory, the radiative decays provide an excellent opportunity to study the nature of light scalar and pseudoscalar mesons. KLOE has been designed to study CP violation in the K”Eo system. The apparatus is inserted in a 0.6 T magnetic field and consists of a 2 m radius drift chamber (DCH) with full stereo geometry in a helium based gas mixture, surrounded by a fine sampling lead/scintillating fibers electromagnetic calorimeter (EMC) with a hermetic coverage and a very high efficiency for low energy photons. The DCH resolutions are vr,,/pt x 0.4%, or4 N 150 pm, a, N 2 mm while the EMC energy and time resolutions can be parametrized and 0~ = 57 pslJE(Gev) @ 50 ps respectively. These as Q/E = 5.7%/$3ii3 performances are also well suited for studying 4 radiative decays. *A. Aloisio, F. Ambrosino, A. Antonelli, M. Antonelli, C. Bacci, G. Bencivenni, S. Bertolucci, C. Bini, C. Bloise, V. Bocci, F. Bossi, P. Branchini, S. A. Bulychjov, R. Caloi, P. Campana, G. Capon, G. Carboni, M. Cssarsa, V. Cssavola, G. Cataldi, F. Ceradini, F. Cervelli, F. Cevenini, G. Chiefari, P. Ciambrone, S. Conetti, E. De Lucia, P. De Simone, G. De Zorzi, S. Dell’Agnello, A. Denig, A. Di Domenico, C. Di Donato, S. Di Falco, B. Di Micco, A. Doria, M. Dreucci, 0. Erriquez, A. Farilla, G. Felici, A. Ferrari, M. L. Ferrer, G. Finocchiaro, C. Forti, A. Franceschi, P. Franzini, C. Gatti, P. Gauzzi, S. Giovannella, E. Gorini, E. Graziani, S. W. Han, M. Incagli, W. Kluge, V. Kulikov, F. Lacava, G. Lanfranchi, J. Lee-Franzini, D. Leone, F. Lu, M. Martemianov, M. Matsyuk, W. Mei, L. Merola, R. Messi, S. Miscetti, M. Moulson, S. Miiller, F. Murtas, M. Napolitano, A. Nedosekin, F. Nguyen, M. Palutan, E. Pasqualucci, L. Passalacqua, A. Passeri, V. Patera, E. Petrolo, L. Pontecorvo, M. Primavera, F. Ruggieri, P. Santangelo, E. Santovetti, G. Saracino, R. D. Schamberger, B. Scisscia, A. Sciubba, F. Scuri, I. Sfiligoi, A. Sibidanov, T. Spadaro, E. Spiriti, G. L. Tong, L. Tortora, P. Valente, B. Valeriani, G. Venanzoni, S. Veneziano, A. Ventura, S. Ventura, R. Versaci, G. W. Yu. 0375-9474/03/$ - see front matter 0 2003 Elsevier Science B.V doi:lO.l016/S0375-9474(03)01185-O
All rights reserved.
802~ 2. The
S. Giooannella/Nuclear Physics A721 (2003) 801~~804~ Pseudoscalar
Decays:
@I +
~7, 4 --f ~‘7
In the pseudoscalar sector, the branching ratio (BR) of the 4 -+ rjy is sensitive to the ss and gluon content of the 7’. Studies based on Chiral Pertubation Theory and phenomenological analysis suggest that the q-r]’ mixing in the quark flavour basis can be parametrized using only one mixing angle (pp [3,4]. Th is angle can be extracted from the ratio of the BR’s for the processes 4 -+ 71’7 and $J -+ ~7, h!,,,,! [5]. At KLOE we have studied these two processes using the decay chains: 4 -+ rfy --+ rpr+vy + yy7r+n-y and 4 + my --) zf~-7roy --t n+~-yyy, thus producing the same final state and leading to a first order cancellation for many of the systematic effects in the &,rt measurement. The separation between the 4 -t n’y and the dominant 4 + ny events (S/B N l/100) is achieved by exploiting the difference in the energy distribution of the photons (Fig. l-left); the resulting nf7r-yyy invariant mass for the 4 -+ $7 candidates is shown in Fig. l-right. The ratio of BR ‘s is then [6]: R,,, = FR;
< ;;;
= ( 4.70 f 0.47,&t f 0.3&t
) x w3,
leading to a mixing angle (pp = (41.8+]::)” and to an absolute branching ratio BR(4 -+ $7) = ( 6.10 f 0.61stat f 0.43,,t ) x 10-5,
(2)
which is the most precise measurement to date. This result limits the gluon content of r]’ to be less than 15%. 3. The Scalar
Decays:
C#J-+ for,
C$ +
~07
Although the existence of the scalar mesons fe(980) and as(980) is well established, their nature is still unclear. The main theoretical hypotheses are: ordinary @ mesons, -qqqq states and K3i; molecules [7-g]. The study of the radiative decays 4 + for, 4 -+ a07 is very important in this framework since both the BR’s and the meson mass spectra are sensitive to the nature of f. and Q [lo]. These two processes have been studied at KLOE by looking at the final states fo --+ z”7ro (a) and as + n7r”, with both 77+ yy (b) and n -+ ?I+~-xO (c). The final event topology is then either five prompt photons or five prompt photons and two tracks. In the 16 pb-’ data sample we count 2438 f. 61,607 f 36, 197 5 15 events for the (a), (b) and (c) decay respectively, corresponding to the following branching ratios [13,14]: BR(4 -+ ~T’O~T’O~) JW4 + W ’Y ; 77--+ YY) BR(@ -+ rj7r”y ; 7 + R+~-T’)
= = =
(1.09 f 0.03&& f 0.05,,&) x 1o-4 (8.51 f 0.51stat f 0.57& x 1O-5 (7.96 f 0.60stat f 0.40,& x 1O-5
(3) (4 (5)
The MT,, M,,, spectra (Fig. 2) are then fitted to extract the fs and ae parameters, including also the other processes that can contribute to the final states: 4 -+ porno(with both p --+ 7r”y and p -+ 77) and 4 -+ ay for the z”7roy final state. The vector meson term parametrization is taken from VMD calculations [ll] while for the v we use the result from Ref. [12]. The fit result is superimposed to the mass spectra in Fig. 2, where
S. Giooannella/Nuclear Physics A721 (2003) 8Olc-804~
h
500
3 2 3
i
2
400
fi A--
--...
300
.. ..*
.. -..
*-
-.
I., '0900
g:'
*
h
. :I??! 200
40 30
.
20
; : 5
. .
200
803c
10
< - . .;
300
, 400
!
E,WV)
u
910 920 930 940 950 960 970 980 990 II JO M Irw (MeV/c')
Figure 1. Selection of 4 -+ $7 + rr+rr-n’y: events inside the ellipse in the plane of the two hardest photons of the event (left) are retained. The two monochromatic bands are due to the 4 -+ qy background. The resulting r]’ invariant mass (right) is compared with the MC expectation for the signal (light grey) and the background (dark grey), whose amount has been evaluated from data itself.
a negligible qS-+ p contribution and a strong destructive interference between 4 ---f for and q!~+ ay can be observed. The resulting BR for the f. meson is then: BR(4 + for + n”7ro) = (1.49 f 0.07) x 10-4.
(6)
For the ae we have: BR(4 ---f a07 ---f 77~‘) = (7.4 f 0.7) x 10-5.
(7)
Concerning the fit parameters, the f. results are compatible with the qqq?j predictions while the a0 values indicate a better agreement with qtj expectations. 4. Conclusions
A sample of N 16 pb-’ of the KLOE data has been analyzed to study 4 radiative decays. We measured the branching ratio for the processes: 4 + $7, Q!J-+ n”7roy and 4 + 77s’~. We also extract the 7-v’ mixing angle and the couplings of fe (aa) to KK and mr (v). At the moment of writing we are analyzing the whole collected statistics, corresponding to an integrated luminosity of N 500 pb-’ These data will allow us to reach a better sensitivity on all reported measurements and distinguish between the recent phenomenological hypotheses interpreting these decays [15-181.
S. Giooannella /Nuclear
m (MeV)
Figure 2. Unfolded dBR/dM spectra for 4 -+ rr”7roy (left) and 4 + q7r”y (right). The fit results are superimposed as solid lines; single contributions are also shown (4 -+ ~7rO-r: 4 + a07 dashed, 4 4 pro dotted).
REFERENCES 1. 2. 3. 4. 5. 6. 7.
8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
The KLOE Collaboration (A. Aloisio et al.), LNF-92/019 (IR) (1992) and LNF-93/002 (IR) (1993). S. Guiducci et al., Proc. of the 2001 Particle Accelerator Conference (Chicago, Illinois, USA), P. Lucas S. Webber Eds. (2001) 353. Th. Feldmann and P. Kroll, Phys. Rev. D 58 (1998) 057501. F. De Fazio and M. R. Pennington, JHEP 0007 (2000) 51. A. Bramon, R. Escribano and M. D. Scadron, Eur. Phys. J. C 7 (1999) 271. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 541 (2002) 45. N. A. Tornqvist, Phys. Rev. Lett. 49 (1982) 624. R. L. Jaffe, Phys. Rev. D 15 (1997) 267. J. Weinstein and N. Isgur, Phys. Rev. Lett. 48 (1982) 659. N. N. Achasov and V. N. Ivanchenko, Nucl. Phys. B 315 (1989) 465. N. N. Achasov and V. V. Gubin, Phys. Rev. D 63 (2001) 094007. E. M. Aitala et al., Phys. Rev. Lett. 86 (2001) 770. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 537 (2002) 21. The KLOE Collaboration (A. Aloisio et al.), Phys. Lett. B 536 (2002) 209. F. E. Close and A. Kirk, Phys. Lett. B 515 (2001) 515. A. Bramon, R. Escribano, J. L. Lucia M., M. Napsuciale and G. Pancheri, hepph/0204339. N. A. Tornqvist, hep-ph/0204215 J. A. Oller, hep-ph/0205121.