- Email: [email protected]
Heavy Spectroscopy at BaBar
Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337 www.elsevierphysics.com
Heavy Spectroscopy at BaBar E. Prencipea a
Laboratoire d’Annecy-le-vieux de Physique des Particules, 9 Chemin de Bellevue - BP 110 Annecy-le-vieux (France) [email protected]
The BaBar experiment, located in SLAC at the PEPII e+ e− asymmetric storage ring, achieved the luminosity of 477 f b−1 , so Spectroscopy studies at the energy in the center of mass of 10.58 GeV/c2 , the threshold of Υ(4S) production, have been possible. The B-Factory BaBar offers an excellent opportunity in searching new states and their decay modes to understand their nature (charm and charmonium physics). From December 2007 the possibility to run at the energy of Υ(3S) and Υ(2S) was opened, in order to search also for bottomonium states and light Higgs. In addition, a scan around Υ(4S), collecting a point every 25 pb−1 , was done until the end of the runs, 10th of April 2008. There are several motivations to perform Spectroscopy studies at B-factories, mainly to do measurements of high precision and try to fully understand QCD. In fact, several resonances observed do not fit theoretical predictions. They can be classified in two main categories: light mesons (like f 0 , K ∗ ,...), and heavy hadrons (e.g. c¯ s and c¯ c mesons, and light baryons). Here below the main results recently observed in the field of Heavy Hadron Physics at BaBar are briefly presented.
The search for new states in BaBar has been done studying the B decays, and ISR events. There are two ways to perform these kind of researches: the inclusive and the exclusive analyses. In this paper the Heavy Hadron Spectroscopy studies at BaBar are presented, using both methods. 1. Charm Spectroscopy Only 4 c¯ s quark bound states were observed before B-factories started to work in this field, in perfect agreement with the theoretical models; after tens of new states were found, and many of them were unexpected. Here below are briefly summarized the main properties of those. 1.1. Charm mesons BaBar observed D∗ (2317)+ and Dsj (2460)+ in the decay modes Ds+ π 0 and Ds∗+ π 0 respectively, at energies where the theory has not done predictions. New non-expected states were observed, making more rich the mass spectrum, 0920-5632/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2008.09.060
most of them decaying to channels where Ds got ∗ involved: Dsj (2317)+ and Ds1 (2536)+ . For these analyses, high precision measurements and high statistics were required[1]. These very narrow states were detected in inclusive decays of the B meson. In the figure, at the end of this paper, you can look at a recent Ds1 (2536)+ study, by analyzing the decay B → D(∗) Ds1 . From this recent study, the mass value was measured: (2534.78 ± 0.31 ± 0.40) MeV/c2 , but nothing we can conclude yet on J P , because of the low statistics[3]. A very interesting contribution of BaBar was given in the measurement of the mass difference of Ds1 and D∗ . In the PDG06[2] the value was: (525.0 ± 0.6 ± 0.1) MeV/c2 ; BaBar obtained: m(Ds1 - m(D∗ )) = (525.85 ± 0.02 ± 0.04) MeV/c2 [4,5], a large improvement in the error measurement. By searching in the inclusive modes: e+ e− → D0,± K 0,± X, BaBar observed on 240 f b−1 the
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E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
values reported in the Tab. 1. A preliminary study performed on the state Dsj (2700) was done, by analyzing the decay B → D(∗) D(∗) K. Recently a full Dalitz plot analysis is ongoing. The values that we had measured in the previous analysis (e+ e− → DKX) are: M = (2688 ± 4 ± 3) MeV/c2 and Γ = 112 ± 7 ± 36 MeV; these values are compatible with the structure Dsj (2700). 1.2. Charmed baryons A new state in the mass spectrum was added: −1 Ω∗0 BaBar searched this css c [6]. On 232 f b 3+ P state, J = 2 , decaying to Ω0c γ, with Ω0c decaying in 4 different modes. By combining them, and Ω0c was meathe mass difference of Ω∗0 c sured: (70.8 ± 1.0 ± 1.1) MeV/c2 , and this is in good agreement with theoretical expectations. In addition, we report the measured value: σ(e+ e− →Ω∗0 c ) σ(e+ e− →Ω0c ) = (1.01 ± 0.23 ± 0.11). Now we have also a first evidence of Ω0c in B decays. Another interesting contribution of BaBar was given in the analysis of the invariant mass of D − proton: a known state was confirmed, Λc (2880)+ , and a new state was observed: Λc (2940)+ [7]. Evidence of excited charmed baryons was found: Ξc (2980)+, Ξc (3077)+ , Ξc (3077)0 , and the recent observations for Ξc (3055)+ and Ξc (3125)+ make this study more interesting[8]. They are in agreement with the corresponding values published by the Belle collaboration, even if the measurements done in Belle show to be slightly overestimated from the corresponding ones measured in BaBar, the smaller values of mass and width in some cases due to the treatment of proximity to the threshold. 2. Charmonium Spectroscopy The c¯ c mass spectrum is not completely understood, and not full-filled yet. In fact, states be¯ threshold are well known, and some low the DD 1−− states above; moreover they fit well theoretical models. Recently, some other states were observed but they do not fit well theoretical predictions. More than one prediction was done from
theorists[13]. Here below are presented the results of the more recent charmonium − like states observed in BaBar. 2.1. X(3872) BaBar searched for the narrow state X(3872)[9] (Γ < 2.3 MeV and M = (3782.4 ± 0.6) MeV/c2 , world average) in B → XK, X → J/ψπ + π − , and also in the decay B → J/ψγK, on 260f b−1. Thanks to this decay mode observed, we could establish that the parity C of this state is positive[10]. In the figure, at the end of this paper, new plots of the X(3872) mass are reported, realized on 413 fb−1 luminosity. The updated mass values measured are: (3871.4 ± 0.6 ± 0.1) MeV/c2 for the charged mode, and (3868.7 ± 1.5 ± 0.2) MeV/c2 for the neutral mode. It is interesting to note that the mass difference is (2.7 ± 1.2 ± 0.4) MeV/c2 , and the ratio between the two B.R. is (0.41 ± 0.24 ± 0.6): these two numbers should be compared with the corresponding values for different theoretical interpretations of X(3872), that actually allow us to say that probably this resonant structure is a state J P C = 1++ or J P C = 2++ [11]. An important implication concerning the decay modes of X → J/ψπ + π − is that the invariant mass of π + π − is compatible with the ρ mass, so we should look at the charged partners of X (I = 1). But the search for X + or X − gave no evidence of signal[12]. So we can conclude that the resonance X is a isospin violating state (I = 0). That is the reason why we observed such a narrow width. Recently, BaBar searched for the decay: ¯ 0 D∗0 K[14]. By studying the invariB → D ¯ 0 D∗0 , with D∗0 → D0 π 0 and ant mass of D D∗0 → D0 γ, we observed an excess of events at (3875.1 ± 0.7 ± 0.5) MeV/c2 . This important result confirms the measurement that Belle per¯ 0 D0 π 0 K, so we also found that formed in B → D the mass value is 4.5 σ above the world average of X → J/ψπ + π − (see the figure at the end of this paper). The X(3872) is probably not a charmonium state; but we cannot exclude other interpretations, yet[13].
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Table 1 Charm mesons table Decay mode D0 → K − π+ D0 → K − π + D0 → K − π+ D proton D proton
State ∗ Ds2 (2573) X(2690) ∗ Dsj (2860) Λc (2880)+ Λc (2940)+
M ass(M eV /c2 ) 2572.2 ± 0.3 ± 1.0 2688 ± 4 ± 3 2856.6 ± 1.5 ± 5.0 2881.9 ± 0.1 ± 0.5 2939.8 ± 1.3 ± 1.0
Γ(M eV ) 27.1 ± 0.6 ± 5.6 112 ± 7 ± 36 47 ± 7 ± 10 5.8 ± 1.5 ± 1.1 17.5 ± 5.2 ± 5.9
Table 2 Υ(nS) transition table Decay mode Υ(4S) → Υ(2S)π + π − Υ(4S) → Υ(1S)π + π −
B.F. (1.29 ± 0.32)10−4 (0.90 ± 0.15)10−4
2.2. X(3940) Searching in the decay B → J/ψωK BaBar confirmed another important result: the discovery of the X(3940)[15]. BaBar analyzed the invariant mass of J/ψω, where ω → π + π − π 0 , and J/ψ → l+ l− , π 0 → γγ, Ks → π + π − . In order to check the purity of the signal sample BaBar weighted each event with the appropriate function (Legendre polynomial of the second order × cosθ, where θ is the ω Dalitzplot helicity angle), so we can be sure that no contribution of non-resonant π + π − π 0 can create a peak in the J/ψω invariant mass. By combining the charged and the neutral modes, BaBar found with 350 f b−1 the mass value M +3.8 = (3914.3−3.4 (stat) ± 1.6(sys)) MeV/c2 and a width: Γ = (33 ± 0.7+12 −8 (stat) ± 0.6(sys)) MeV. The B.R. of the B → J/ψωK was measured, too. It it in good agreement with the Belle measurements, while the measurements of mass and width of the state X(3940) done in Belle are overestimated compared to what we observed in BaBar, because we obtained the measurement of a more narrow state and a mass value being 30 MeV/c2 smaller.
2.3. Y(4260) The discovery of the state called Y(4260)[16] came from ISR events, and Belle confirmed by
Γ(keV ) 2.7 ± 0.8 1.8 ± 0.4
2 CLEO. The mass value is (4258 ± 8+6 −4 ) MeV/c +6 and the width is (88 ± 23−4 ) MeV. As it comes from ISR events, its quantum numbers are J P C = 1−− . But in the plot of the ratio R (the ratio between the cross section of e+ e− → hadrons to the cross section of e+ e− → μ+ μ− ) we expected to look at a maximum corresponding to the energy in the center of mass of 4.26 GeV. Indeed, we looked at a local minimum there, that is a very peculiar behaviour. So, in order to reject some possibilities, we searched for the decay ¯ and modes: Y (4260) → π + π − φ, Y (4260) → DD Y (4269) → p¯ p: we observed no yields, so probably it is not a glueball or charmonium state. There is also an evidence of this new state in the charged B decay: the measurement of this B.R. (B → Y (J/ψπ + π − )K) is (2.0 ± 0.7 ± 0.2)10−5 .
The search for the Y(4260) decay modes, and other searches in the inclusive ψ(2S)π + π − led to the discovery of another resonance, whose mass is (4324 ± 24) MeV/c2 [17] and whose width is (172 ± 33) MeV . It is not compatible with the above mentioned Y(4260), neither with Y(4415) or S-waves-three-body-phase space. That is a new peak, confirmed now also from the Belle Collaboration. All the studies performed on ISR events gave very interesting results: the analysis that allowed
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E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
to observe the resonant structure Y(4175), for instance, deserves attention too. It is confirmed now also from the BES Collaboration.
3. Search of bottomonium states We want to introduce a physics case for running PEP-II and BaBar at a center-of-mass energy at the peak of the Υ(3S) resonance. A data sample of about 30 fb−1 would increase the available data at this energy by an order of magnitude and provide physics opportunities ranging from Spectroscopy and discovery of unobserved bottomonium states and transitions within the Standard Model to searches for exotic physics including low-mass Higgs boson and dark matter candidates. We have compared running at the Υ(3S) energy to running at the Υ(2S) energy and conclude that the physics potential at the Υ(3S) is significantly higher than at the lower Υ resonances. The results are not ready yet for this conference. The transitions Υ(4S) → Υ(2S)π + π − and Υ(4S) → Υ(1S)π + π − were studied. You can see in Tab. 2 the values of the Branching Fractions and widths listed. An interesting study was done in analyzing the transition Υ(4S) → Υ(2S)η, that here is presented as preliminary result. The ratio Γ4S→1Sη /Γ4S→1Sπ+ π− was measured and the result is surprising, as we expected a number much smaller than 1, because we are measuring the ratio between a transition E1M2 over E1E1, so we expect a large suppression. Instead, the measured value is: (2.41 ± 0.40 ± 0.12). 4. Conclusion BaBar has given an important contribution in searching for new states and understanding this complex field of physics. With the statistics available BaBar will still continue to perform measurements of high precision, giving its contribution in the Spectroscopy studies. The availability to the Υ(nS) data has opened new possibilities in this researches; the results will be shown soon to the next conferences.
E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
Acknowledgments We are grateful for the excellent luminosity and machine conditions provided by our PEP-II colleagues, and for the substantial dedicated effort from the computing organizations that support BaBar. REFERENCES 1. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 74 032007; 2. D. E. Groom et al. [Particle Data Group Coll.], “ Review of particle physics,” Eur. Phys. J. C 15; 3. BABAR Collaboration, B. Aubert et al. Phys. Rev. D. 97 011102; 4. BABAR Collaboration, B. Aubert et al. hepex/0607084 ; 5. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 97 222001; 6. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 97 232001; 7. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 98 012001; 8. BABAR Collaboration, B. Aubert et al. hepex/0607042; 9. Belle Collaboration, Phys. Rev. Lett. 91 262003; BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 73 011101; Phys. Rev. Lett. 74 071101; 10. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 71 031501; 11. BABAR Collaboration, B. Aubert et al. hepex. arXiv:0803.2838; 12. BABAR Collaboration, B. Aubert et al. hepex. arXiv:0708.1565; 13. Phys. Rev. D. 71 074005; Phys. Rev. D. 71 014028; 14. BABAR Collaboration, B. Aubert et al. arXiv: hep-ex/0708.1565 15. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 95 142001; 16. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 73 011101; Phys. Rev. Lett. 73 012005; 17. BABAR Collaboration, B. Aubert et al. Phys. Rev. Lett. 98 212001.
337
Heavy Spectroscopy at BaBar E. Prencipea a
Laboratoire d’Annecy-le-vieux de Physique des Particules, 9 Chemin de Bellevue - BP 110 Annecy-le-vieux (France) [email protected]
The BaBar experiment, located in SLAC at the PEPII e+ e− asymmetric storage ring, achieved the luminosity of 477 f b−1 , so Spectroscopy studies at the energy in the center of mass of 10.58 GeV/c2 , the threshold of Υ(4S) production, have been possible. The B-Factory BaBar offers an excellent opportunity in searching new states and their decay modes to understand their nature (charm and charmonium physics). From December 2007 the possibility to run at the energy of Υ(3S) and Υ(2S) was opened, in order to search also for bottomonium states and light Higgs. In addition, a scan around Υ(4S), collecting a point every 25 pb−1 , was done until the end of the runs, 10th of April 2008. There are several motivations to perform Spectroscopy studies at B-factories, mainly to do measurements of high precision and try to fully understand QCD. In fact, several resonances observed do not fit theoretical predictions. They can be classified in two main categories: light mesons (like f 0 , K ∗ ,...), and heavy hadrons (e.g. c¯ s and c¯ c mesons, and light baryons). Here below the main results recently observed in the field of Heavy Hadron Physics at BaBar are briefly presented.
The search for new states in BaBar has been done studying the B decays, and ISR events. There are two ways to perform these kind of researches: the inclusive and the exclusive analyses. In this paper the Heavy Hadron Spectroscopy studies at BaBar are presented, using both methods. 1. Charm Spectroscopy Only 4 c¯ s quark bound states were observed before B-factories started to work in this field, in perfect agreement with the theoretical models; after tens of new states were found, and many of them were unexpected. Here below are briefly summarized the main properties of those. 1.1. Charm mesons BaBar observed D∗ (2317)+ and Dsj (2460)+ in the decay modes Ds+ π 0 and Ds∗+ π 0 respectively, at energies where the theory has not done predictions. New non-expected states were observed, making more rich the mass spectrum, 0920-5632/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2008.09.060
most of them decaying to channels where Ds got ∗ involved: Dsj (2317)+ and Ds1 (2536)+ . For these analyses, high precision measurements and high statistics were required[1]. These very narrow states were detected in inclusive decays of the B meson. In the figure, at the end of this paper, you can look at a recent Ds1 (2536)+ study, by analyzing the decay B → D(∗) Ds1 . From this recent study, the mass value was measured: (2534.78 ± 0.31 ± 0.40) MeV/c2 , but nothing we can conclude yet on J P , because of the low statistics[3]. A very interesting contribution of BaBar was given in the measurement of the mass difference of Ds1 and D∗ . In the PDG06[2] the value was: (525.0 ± 0.6 ± 0.1) MeV/c2 ; BaBar obtained: m(Ds1 - m(D∗ )) = (525.85 ± 0.02 ± 0.04) MeV/c2 [4,5], a large improvement in the error measurement. By searching in the inclusive modes: e+ e− → D0,± K 0,± X, BaBar observed on 240 f b−1 the
334
E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
values reported in the Tab. 1. A preliminary study performed on the state Dsj (2700) was done, by analyzing the decay B → D(∗) D(∗) K. Recently a full Dalitz plot analysis is ongoing. The values that we had measured in the previous analysis (e+ e− → DKX) are: M = (2688 ± 4 ± 3) MeV/c2 and Γ = 112 ± 7 ± 36 MeV; these values are compatible with the structure Dsj (2700). 1.2. Charmed baryons A new state in the mass spectrum was added: −1 Ω∗0 BaBar searched this css c [6]. On 232 f b 3+ P state, J = 2 , decaying to Ω0c γ, with Ω0c decaying in 4 different modes. By combining them, and Ω0c was meathe mass difference of Ω∗0 c sured: (70.8 ± 1.0 ± 1.1) MeV/c2 , and this is in good agreement with theoretical expectations. In addition, we report the measured value: σ(e+ e− →Ω∗0 c ) σ(e+ e− →Ω0c ) = (1.01 ± 0.23 ± 0.11). Now we have also a first evidence of Ω0c in B decays. Another interesting contribution of BaBar was given in the analysis of the invariant mass of D − proton: a known state was confirmed, Λc (2880)+ , and a new state was observed: Λc (2940)+ [7]. Evidence of excited charmed baryons was found: Ξc (2980)+, Ξc (3077)+ , Ξc (3077)0 , and the recent observations for Ξc (3055)+ and Ξc (3125)+ make this study more interesting[8]. They are in agreement with the corresponding values published by the Belle collaboration, even if the measurements done in Belle show to be slightly overestimated from the corresponding ones measured in BaBar, the smaller values of mass and width in some cases due to the treatment of proximity to the threshold. 2. Charmonium Spectroscopy The c¯ c mass spectrum is not completely understood, and not full-filled yet. In fact, states be¯ threshold are well known, and some low the DD 1−− states above; moreover they fit well theoretical models. Recently, some other states were observed but they do not fit well theoretical predictions. More than one prediction was done from
theorists[13]. Here below are presented the results of the more recent charmonium − like states observed in BaBar. 2.1. X(3872) BaBar searched for the narrow state X(3872)[9] (Γ < 2.3 MeV and M = (3782.4 ± 0.6) MeV/c2 , world average) in B → XK, X → J/ψπ + π − , and also in the decay B → J/ψγK, on 260f b−1. Thanks to this decay mode observed, we could establish that the parity C of this state is positive[10]. In the figure, at the end of this paper, new plots of the X(3872) mass are reported, realized on 413 fb−1 luminosity. The updated mass values measured are: (3871.4 ± 0.6 ± 0.1) MeV/c2 for the charged mode, and (3868.7 ± 1.5 ± 0.2) MeV/c2 for the neutral mode. It is interesting to note that the mass difference is (2.7 ± 1.2 ± 0.4) MeV/c2 , and the ratio between the two B.R. is (0.41 ± 0.24 ± 0.6): these two numbers should be compared with the corresponding values for different theoretical interpretations of X(3872), that actually allow us to say that probably this resonant structure is a state J P C = 1++ or J P C = 2++ [11]. An important implication concerning the decay modes of X → J/ψπ + π − is that the invariant mass of π + π − is compatible with the ρ mass, so we should look at the charged partners of X (I = 1). But the search for X + or X − gave no evidence of signal[12]. So we can conclude that the resonance X is a isospin violating state (I = 0). That is the reason why we observed such a narrow width. Recently, BaBar searched for the decay: ¯ 0 D∗0 K[14]. By studying the invariB → D ¯ 0 D∗0 , with D∗0 → D0 π 0 and ant mass of D D∗0 → D0 γ, we observed an excess of events at (3875.1 ± 0.7 ± 0.5) MeV/c2 . This important result confirms the measurement that Belle per¯ 0 D0 π 0 K, so we also found that formed in B → D the mass value is 4.5 σ above the world average of X → J/ψπ + π − (see the figure at the end of this paper). The X(3872) is probably not a charmonium state; but we cannot exclude other interpretations, yet[13].
335
E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
Table 1 Charm mesons table Decay mode D0 → K − π+ D0 → K − π + D0 → K − π+ D proton D proton
State ∗ Ds2 (2573) X(2690) ∗ Dsj (2860) Λc (2880)+ Λc (2940)+
M ass(M eV /c2 ) 2572.2 ± 0.3 ± 1.0 2688 ± 4 ± 3 2856.6 ± 1.5 ± 5.0 2881.9 ± 0.1 ± 0.5 2939.8 ± 1.3 ± 1.0
Γ(M eV ) 27.1 ± 0.6 ± 5.6 112 ± 7 ± 36 47 ± 7 ± 10 5.8 ± 1.5 ± 1.1 17.5 ± 5.2 ± 5.9
Table 2 Υ(nS) transition table Decay mode Υ(4S) → Υ(2S)π + π − Υ(4S) → Υ(1S)π + π −
B.F. (1.29 ± 0.32)10−4 (0.90 ± 0.15)10−4
2.2. X(3940) Searching in the decay B → J/ψωK BaBar confirmed another important result: the discovery of the X(3940)[15]. BaBar analyzed the invariant mass of J/ψω, where ω → π + π − π 0 , and J/ψ → l+ l− , π 0 → γγ, Ks → π + π − . In order to check the purity of the signal sample BaBar weighted each event with the appropriate function (Legendre polynomial of the second order × cosθ, where θ is the ω Dalitzplot helicity angle), so we can be sure that no contribution of non-resonant π + π − π 0 can create a peak in the J/ψω invariant mass. By combining the charged and the neutral modes, BaBar found with 350 f b−1 the mass value M +3.8 = (3914.3−3.4 (stat) ± 1.6(sys)) MeV/c2 and a width: Γ = (33 ± 0.7+12 −8 (stat) ± 0.6(sys)) MeV. The B.R. of the B → J/ψωK was measured, too. It it in good agreement with the Belle measurements, while the measurements of mass and width of the state X(3940) done in Belle are overestimated compared to what we observed in BaBar, because we obtained the measurement of a more narrow state and a mass value being 30 MeV/c2 smaller.
2.3. Y(4260) The discovery of the state called Y(4260)[16] came from ISR events, and Belle confirmed by
Γ(keV ) 2.7 ± 0.8 1.8 ± 0.4
2 CLEO. The mass value is (4258 ± 8+6 −4 ) MeV/c +6 and the width is (88 ± 23−4 ) MeV. As it comes from ISR events, its quantum numbers are J P C = 1−− . But in the plot of the ratio R (the ratio between the cross section of e+ e− → hadrons to the cross section of e+ e− → μ+ μ− ) we expected to look at a maximum corresponding to the energy in the center of mass of 4.26 GeV. Indeed, we looked at a local minimum there, that is a very peculiar behaviour. So, in order to reject some possibilities, we searched for the decay ¯ and modes: Y (4260) → π + π − φ, Y (4260) → DD Y (4269) → p¯ p: we observed no yields, so probably it is not a glueball or charmonium state. There is also an evidence of this new state in the charged B decay: the measurement of this B.R. (B → Y (J/ψπ + π − )K) is (2.0 ± 0.7 ± 0.2)10−5 .
The search for the Y(4260) decay modes, and other searches in the inclusive ψ(2S)π + π − led to the discovery of another resonance, whose mass is (4324 ± 24) MeV/c2 [17] and whose width is (172 ± 33) MeV . It is not compatible with the above mentioned Y(4260), neither with Y(4415) or S-waves-three-body-phase space. That is a new peak, confirmed now also from the Belle Collaboration. All the studies performed on ISR events gave very interesting results: the analysis that allowed
336
E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
to observe the resonant structure Y(4175), for instance, deserves attention too. It is confirmed now also from the BES Collaboration.
3. Search of bottomonium states We want to introduce a physics case for running PEP-II and BaBar at a center-of-mass energy at the peak of the Υ(3S) resonance. A data sample of about 30 fb−1 would increase the available data at this energy by an order of magnitude and provide physics opportunities ranging from Spectroscopy and discovery of unobserved bottomonium states and transitions within the Standard Model to searches for exotic physics including low-mass Higgs boson and dark matter candidates. We have compared running at the Υ(3S) energy to running at the Υ(2S) energy and conclude that the physics potential at the Υ(3S) is significantly higher than at the lower Υ resonances. The results are not ready yet for this conference. The transitions Υ(4S) → Υ(2S)π + π − and Υ(4S) → Υ(1S)π + π − were studied. You can see in Tab. 2 the values of the Branching Fractions and widths listed. An interesting study was done in analyzing the transition Υ(4S) → Υ(2S)η, that here is presented as preliminary result. The ratio Γ4S→1Sη /Γ4S→1Sπ+ π− was measured and the result is surprising, as we expected a number much smaller than 1, because we are measuring the ratio between a transition E1M2 over E1E1, so we expect a large suppression. Instead, the measured value is: (2.41 ± 0.40 ± 0.12). 4. Conclusion BaBar has given an important contribution in searching for new states and understanding this complex field of physics. With the statistics available BaBar will still continue to perform measurements of high precision, giving its contribution in the Spectroscopy studies. The availability to the Υ(nS) data has opened new possibilities in this researches; the results will be shown soon to the next conferences.
E. Prencipe / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 333–337
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