The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrödinger equation to obtain their mass spectra using only four parameters namely quark mass (mc, mb) and confinement strength (Ac¯c, Ab¯b). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited S, P, D and F states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available experimental observations and results from other theoretical models. We also compute mass spectra and life time of the Bc meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and Bc mesons are in tune with available experimental data and other theoretical approaches.
Mesonic bound states having both heavy quark and anti-quark (c¯c, b¯b and c¯b) are among the best tools for understanding the quantum chromodynamics. Many experimental groups such as CLEO, LEP, CDF/D0 and NA50 have provided data and BABAR, Belle, CLEO-III, ATLAS, CMS and HERA-B are producing and expected to produce more precise data in upcoming experiments. Comprehensive reviews on the status of experimental heavy quarkonium physics are found in literature Eichten:2007; Godfrey:2008; Barnes:2009; Brambilla:2010; Brambilla:2014; Andronic:2016.
Within open flavor threshold, the heavy quarkonia have very rich spectroscopy with narrow and experimentally characterized states. The potential between the interacting quarks within the hadrons demands the understanding of underlying physics of strong interactions. In PDG pdg2016, large amount of experimental data is available for masses along with different decay modes.
There are many theoretical groups viz. the lattice quantum chromodynamics (LQCD) Dudek:2007; Meinel:2009; Burch:2009; Liu:2012; McNeile:2012; Daldrop:2011; Kawanai:2013; Kawanai:2011; Burnier:2015; Kalinowski:2015; Burnier:2016, QCD Hilger:2014; Voloshin:2007,
QCD sum rules Cho:2014; Gershtein:1995, perturbative QCD Kiyo:2013, lattice NRQCD Liu:2016; Dowdall:2013 and
effective field theories Neubert:1993 that have attempted to explain the production and decays of these states.
Others include phenomenological potential models such as
the relativistic quark model based on quasi-potential approach Ebert:2011; Ebert:2009; Ebert:2005; Ebert:2002; Ebert:2003lepton; Ebert:2003gamma, where the relativistic quasi potential including one loop radiative corrections reproduce the mass spectrum of quarkonium states.
The quasi potential has also been employed along with leading order radiative correction to heavy quark potential Gupta:1981; Gupta:1982kp; Gupta:1982; Pantaleone:1985, relativistic potential model Maung:1993; Radford:2007; Radford:2009 as well as semi relativistic potential model Gupta:1986.
In nonrelativistic potential models, there exist several forms of quark anti-quark potentials in the literature. The most common among them is the coulomb repulsive plus quark confinement interaction potential. In our previous work Vinodkumar:1999; Pandya:2001; Rai:2008; Pandya:2014, we have employed the confinement scheme based on harmonic approximation along with Lorentz scalar plus vector potential.
The authors of Devlani:2014; Parmar:2010; Rai:2002; Rai:2005; Rai:2006; Rai:2008prc; Patel:2008 have considered the confinement of power potential Arν with ν varying from 0.1 to 2.0 and the confinement strength A to vary with potential index ν.
Confinement of the order r2/3 have also been attempted FabreDeLaRipelle:1988. Linear confinement (Cornell potential) of quarks has been considered by many groups Eichten:1974; Eichten:1978; Eichten:1979; Quigg:1979; Eichten:1980; Barnes:2005; Sauli:2011; Leitao:2014; Godfrey:1985; Godfrey:2004; Godfrey:2015; Deng:2016cc; Deng:2016bb and they have provided good agreement with the experimental data for quarkonium spectroscopy along with decay properties.
The Bethe-Salpeter approach was also employed for the mass spectroscopy of charmonia and bottomonia Sauli:2011; Leitao:2014; Fischer:2014.
The quarkonium mass spectrum was also computed in the nonrelativistic quark model Lakhina:2006, screened potential model Deng:2016cc; Deng:2016bb and constituent quark model Segovia:2016.
There are also other non-linear potential models that predict the mass spectra of the heavy quarkonia successfully Patel:2015; Bonati:2015; Gutsche:2014; Li:2009; Li:2009bb; Quigg:1977; Martin:1980; Buchmuller:1980.
In 90’s, the nonrelativistic potential models predicted not only the ground state mass of the tightly bound state of c and ¯b in the range of 6.2–6.3 GeV Kwong:1990; Eichten:1994 but also predicted to have very rich spectroscopy.
In 1998, CDF collaboration Abe:1998 reported Bc mesons in p¯p collisions at √s = 1.8 TeV and was later confirmed by D0 Abazov:2008 and LHCb Aaij:2012 collaborations.
The LHCb collaboration has also made the most precise measurement of the life time of Bc mesons Aaij:2014.
The first excited state is also reported by ATLAS Collaborations Aad:2014 in p¯p collisions with significance of 5.2σ.
It is important to show that any given potential model should be able to compute mass spectra and decay properties of Bc meson using parameters fitted for heavy quarkonia. Attempts in this direction have been made in relativistic quark model based on quasi-potential along with one loop radiative correction Ebert:2011, quasistatic and confinement QCD potential with confinement parameters along with quark masses Gupta:1996 and rainbow ladder approximation of Dyson-Schwinger and Bethe-Salpeter equations Fischer:2014.
Moreover, the mesonic states are identified with masses along with certain decay channels, therefore the test for any successful theoretical model is to reproduce the mass spectrum along with decay properties.
Relativistic as well as nonrelativistic potential models have successfully predicted the spectroscopy but they are found to differ in computation of the decay properties Quigg:1977; Eichten:1978; Martin:1980; Buchmuller:1980; Gershtein:1995; Rai:2002; Rai:2005; Rai:2006; Rai:2008prc; Parmar:2010.
This discrepancy motivates us to employ nonrelativistic potential of the one gluon exchange (essentially Coulomb like) plus linear confinement (Cornell potential) as this form of the potential is also supported by LQCD Bali:2000; Bali:2001; Alexandrou:2002. We solve the Schrödinger equation numerically for the potential to get the spectroscopy of the quarkonia. We first compute the mass spectra of charmonia and bottomonia states to determine quark masses and confinement strengths after fitting the spin-averaged ground state masses with experimental data of respective mesons. Using the potential parameters and numerical wave function, we compute the decay properties such as leptonic decay constants, digamma, dilepton, digluon decay width using the Van-Royen Weiskopf formula. These parameters are then used to compute the mass spectra and life-time of Bc meson. We also compute the electromagnetic (E1 and M1) transition widths of heavy quarkonia and Bc mesons.
Ii Methodology
Basically, the bound state of two body system within relativistic quantum field is described in Bethe-Salpeter formalism. But the Bethe-Salpeter equation is solved only in the ladder approximations. Also Bethe-Salpeter approach in harmonic confinement is successful in low flavor sectors Isgur:1978; VijayaKumar:1997. Therefore the alternative treatment for the heavy bound state is nonrelativistic. Also due to negligible momenta of quark and anti quark compared to mass of quark-antiquark system mQ,¯Q≫ΛQCD∼|→p|, which constitutes the basis of the nonrelativistic treatment for the heavy quarkonium spectroscopy. Here for the study of heavy bound state of mesons such as c¯c, c¯b and b¯b, the nonrelativistic Hamiltonian is given by
H=M+p22Mcm+VCornell(r)+VSD(r)
(1)
where
M=mQ+m¯QandMcm=mQm¯QmQ+m¯Q
(2)
where mQ and m¯Q are the mass of quark and antiquark, →p is the relative momentum of the each quark and Vcornell(r) is the quark-antiquark potential of the type coulomb plus linear confinement (Cornell potential) given by
VCornell(r)=−43αsr+Ar.
(3)
Here, 1/r term is analogous to the Coulomb type interaction corresponding to the potential induced between quark and antiquark through one gluon exchange that dominates at small distances. The second term is the confinement part of the potential where the confinement strength A is the model parameter. The confinement term becomes dominant at the large distances. αs is a strong running coupling constant and can be computed as
αs(μ2)=4π(11−23nf)ln(μ2/Λ2)
(4)
where nf is the numbers of flavors, μ is renormalization scale related to the constituent quark masses as μ=2mQm¯Q/(mQ+m¯Q) and Λ is a QCD scale which is taken as 0.15 GeV by fixing αs = 0.1185 pdg2016 at the Z-boson mass.
The confinement strengths with respective quark masses are fine tuned to reproduce the experimental spin averaged ground state masses of both c¯c and b¯b mesons and are given in Table 1. We compute the masses of higher excited states without any additional parameters. Similar kind of work has been done by Patel:2008; Rai:2008prc; Parmar:2010 and they have considered different values of confinement strengths for different potential indices. The Cornell potential has been shown to be independently successful in computing the spectroscopy of ψ and Υ families. In this article, we compute the mass spectra of the ψ and Υ families along with Bc meson with minimum number of parameters.
Using the parameters defined in Table 1, we compute the spin averaged masses of quarkonia. In order to compute masses of different nmLJ states according to different JPC values, we use the spin dependent part of one gluon exchange potential (OGEP) VSD(r) perturbatively. The OGEP includes spin-spin, spin-orbit and tensor terms given by Gershtein:1995; Barnes:2005; Lakhina:2006; Voloshin:2007{dmath}
V_SD (r) = V_SS (r) [S(S+1) - 32] + V_LS(r) (→L⋅→S) + V_T(r) [S(S+1)-3(S⋅^r) (S⋅^r)]
mc
mc
Acc
Abb
1.317 GeV
4.584 GeV
0.18 GeV2
0.25 GeV2
Table 1: Parameters for quarkonium spectroscopy
The spin-spin interaction term gives the hyper-fine splitting while spin-orbit and tensor terms gives the fine structure of the quarkonium states. The coefficients of spin dependent terms of the Eq. (II) can be written as Voloshin:2007
State
Present
PDG pdg2016
Ebert:2011
Deng:2016cc
Patel:2015
Fischer:2014
LQCD Kalinowski:2015
11S0
2.989
2.984
2.981
2.984
2.979
2.925
2.884
13S1
3.094
3.097
3.096
3.097
3.096
3.113
3.056
21S0
3.602
3.639
3.635
3.637
3.600
3.684
3.535
23S1
3.681
3.686
3.685
3.679
3.680
3.676
3.662
31S0
4.058
4.039
3.989
4.004
4.011
–
–
33S1
4.129
–
4.039
4.030
4.077
3.803
–
41S0
4.448
4.421
4.401
4.264
4.397
–
–
43S1
4.514
–
4.427
4.281
4.454
–
–
51S0
4.799
–
4.811
4.459
–
–
–
53S1
4.863
–
4.837
4.472
–
–
–
61S0
5.124
–
5.155
–
–
–
–
63S1
5.185
–
5.167
–
–
–
–
13P0
3.428
3.415
3.413
3.415
3.488
3.323
3.412
13P1
3.468
3.511
3.511
3.521
3.514
3.489
3.480
11P1
3.470
3.525
3.525
3.526
3.539
3.433
3.494
13P2
3.480
3.556
3.555
3.553
3.565
3.550
3.536
23P0
3.897
3.918
3.870
3.848
3.947
3.833
–
23P1
3.938
–
3.906
3.914
3.972
3.672
–
21P1
3.943
–
3.926
3.916
3.996
3.747
–
23P2
3.955
3.927
3.949
3.937
4.021
–
4.066
33P0
4.296
–
4.301
4.146
–
–
–
33P1
4.338
–
4.319
4.192
–
3.912
–
31P1
4.344
–
4.337
4.193
–
–
–
33P2
4.358
–
4.354
4.211
–
–
–
43P0
4.653
–
4.698
–
–
–
–
43P1
4.696
–
4.728
–
–
–
–
41P1
4.704
–
4.744
–
–
–
–
43P2
4.718
–
4.763
–
–
–
–
53P0
4.983
–
–
–
–
–
–
53P1
5.026
–
–
–
–
–
–
51P1
5.034
–
–
–
–
–
–
53P2
5.049
–
–
–
–
–
–
Table 2: Mass spectrum of S and P wave charmonia (in GeV)
VSS(r)=13mQm¯Q∇2VV(r)=16παs9mQm¯Q
(5)
VLS(r)=12mQm¯Qr(3dVV(r)dr−dVS(r)dr)
(6)
VT(r)=16mQm¯Q(3dV2V(r)dr2−1rdVV(r)dr)
(7)
Where VV(r) and VS(r) correspond to the vector and scalar part of the Cornell potential in Eq. (3) respectively. Using all the parameters defined above, the Schrödinger equation is numerically solved using Mathematica notebook utilizing the Runge-Kutta method Lucha:1998. The computed mass spectra of heavy quarkonia and Bc mesons are listed in Table 2–7
State
Present
Ebert:2011
Deng:2016cc
Patel:2015
Fischer:2014
13D3
3.755
3.813
3.808
3.798
3.869
11D2
3.765
3.807
3.805
3.796
3.739
13D2
3.772
3.795
3.807
3.794
3.550
13D1
3.775
3.783
3.792
3.792
–
23D3
4.176
4.220
4.112
4.425
3.806
21D2
4.182
4.196
4.108
4.224
–
23D2
4.188
4.190
4.109
4.223
–
23D1
4.188
4.105
4.095
4.222
–
33D3
4.549
4.574
4.340
–
–
31D2
4.553
3.549
4.336
–
–
33D2
4.557
4.544
4.337
–
–
33D1
4.555
4.507
4.324
–
–
43D3
4.890
4.920
–
–
–
41D2
4.892
4.898
–
–
–
43D2
4.896
4.896
–
–
–
43D1
4.891
4.857
–
–
–
13F2
3.990
4.041
–
–
–
13F3
4.012
4.068
–
–
3.999
11F3
4.017
4.071
–
–
4.037
13F4
4.036
4.093
–
–
–
23F2
4.378
4.361
–
–
–
23F3
4.396
4.400
–
–
–
21F3
4.400
4.406
–
–
–
23F4
4.415
4.434
–
–
–
33F2
4.730
–
–
–
–
33F3
4.746
–
–
–
–
31F3
4.749
–
–
–
–
33F4
4.761
–
–
–
–
Table 3: Mass spectrum of D and F wave charmonia (in GeV)
State
Present
PDG pdg2016
Godfrey:2015
Ebert:2011
Deng:2016bb
Segovia:2016
Fischer:2014
11S0
9.428
9.398
9.402
9.398
9.390
9.455
9.414
13S1
9.463
9.460
9.465
9.460
9.460
9.502
9.490
21S0
9.955
9999
9.976
9.990
9.990
9.990
9.987
23S1
9.979
10.023
10.003
10.023
10.015
10.015
10.089
31S0
10.338
–
10.336
10.329
10.326
10.330
–
33S1
10.359
10.355
10.354
10.355
10.343
10.349
10.327
41S0
10.663
–
10.523
10.573
10.584
–
–
43S1
10.683
10.579
10.635
10.586
10.597
10.607
–
51S0
10.956
–
10.869
10.851
10.800
–
–
53S1
10.975
10.876
10.878
10.869
10.811
10.818
–
61S0
11.226
–
11.097
11.061
10.997
–
–
63S1
11.243
11.019
11.102
11.088
10.988
10.995
–
13P0
9.806
9.859
9.847
9.859
9.864
9.855
9.815
13P1
9.819
9.893
9.876
9.892
9.903
9.874
9.842
11P1
9.821
9.899
9.882
9.900
9.909
9.879
9.806
13P2
9.825
9.912
9.897
9.912
9.921
9.886
9.906
23P0
10.205
10.232
10.226
10.233
10.220
10.221
10.254
23P1
10.217
10.255
10.246
10.255
10.249
10.236
10.120
21P1
10.220
10.260
10.250
10.260
10.254
10.240
10.154
23P2
10.224
10.269
10.261
10.268
10.264
10.246
–
33P0
10.540
–
10.552
10.521
10.490
10.500
–
33P1
10.553
–
10.538
10.541
10.515
10.513
10.303
31P1
10.556
–
10.541
10.544
10.519
10.516
–
33P2
10.560
–
10.550
10.550
10.528
10.521 –
43P0
10.840
–
10.775
10.781
–
–
–
43P1
10.853
–
10.788
10.802
–
–
–
41P1
10.855
–
10.790
10.804
–
–
–
43P2
10.860
–
10.798
10.812
–
–
–
53P0
11.115
–
11.004
–
–
–
–
53P1
11.127
–
11.014
–
–
–
–
51P1
11.130
–
11.016
–
–
–
–
53P2
11.135
–
11.022
–
–
–
–
Table 4: Mass spectrum of S and P wave bottomonia (in GeV)
State
Present
PDG pdg2016
Godfrey:2015
Ebert:2011
Deng:2016bb
Segovia:2016
Fischer:2014
13D3
10.073
–
10.115
10.166
10.157
10.127
10.232
11D2
10.074
–
10.148
10.163
10.153
10.123
10.194
13D2
10.075
10.163
10.147
10.161
10.153
10.122
10.145
13D1
10.074
–
10.138
10.154
10.146
10.117
–
23D3
10.423
–
10.455
10.449
10.436
10.422
–
21D2
10.424
–
10.450
10.445
10.432
10.419
–
23D2
10.424
–
10.449
10.443
10.432
10.418
–
23D1
10.423
–
10.441
10.435
10.425
10.414
–
33D3
10.733
–
10.711
10.717
–
–
–
31D2
10.733
–
10.706
10.713
–
–
–
33D2
10.733
–
10.705
10.711
–
–
–
33D1
10.731
–
10.698
10.704
–
–
–
43D3
11.015
–
10.939
10.963
–
–
–
41D2
11.015
–
10.935
10.959
–
–
–
43D2
11.016
–
10.934
10.957
–
–
–
43D1
11.013
–
10.928
10.949
–
–
–
13F2
10.283
–
10.350
10.343
10.338
10.315
–
13F3
10.287
–
10.355
10.346
10.340
10.321
10.302
11F3
10.288
–
10.355
10.347
10.339
10.322
10.319
13F4
10.291
–
10.358
10.349
10.340
–
–
23F2
10.604
–
10.615
10.610
–
–
–
23F3
10.607
–
10.619
10.614
–
–
–
21F3
10.607
–
10.619
10.647
–
–
–
23F4
10.609
–
10.622
10.617
–
–
–
33F2
10.894
–
10.850
–
–
–
–
33F3
10.896
–
10.853
–
–
–
–
31F3
10.897
–
10.853
–
–
–
–
33F4
10.898
–
10.856
–
–
–
–
Table 5: Mass spectrum of D and F wave bottomonia (in GeV)
State
Present
Devlani:2014
Ebert:2011
Godfrey:2004
Monteiro:2016
PDG pdg2016
11S0
6.272
6.278
6.272
6.271
6.275
6.275
13S1
6.321
6.331
6.333
6.338
6.314
–
21S0
6.864
6.863
6.842
6.855
6.838
6.842
23S1
6.900
6.873
6.882
6.887
6.850
–
31S0
7.306
7.244
7.226
7.250
–
–
33S1
7.338
7.249
7.258
7.272
–
–
41S0
7.684
7.564
7.585
–
–
–
43S1
7.714
7.568
7.609
–
–
–
51S0
8.025
7.852
7.928
–
–
–
53S1
8.054
7.855
7.947
–
–
–
61S0
8.340
8.120
–
–
–
–
63S1
8.368
8.122
–
–
–
–
13P0
6.686
6.748
6.699
6.706
6.672
–
13P1
6.705
6.767
6.750
6.741
6.766
–
11P1
6.706
6.769
6.743
6.750
6.828
–
13P2
6.712
6.775
6.761
6.768
6.776
–
23P0
7.146
7.139
7.094
7.122
6.914
–
23P1
7.165
7.155
7.134
7.145
7.259
–
21P1
7.168
7.156
7.094
7.150
7.322
–
23P2
7.173
7.162
7.157
7.164
7.232
–
33P0
7.536
7.463
7.474
–
–
–
33P1
7.555
7.479
7.510
–
–
–
31P1
7.559
7.479
7.500
–
–
–
33P2
7.565
7.485
7.524
–
–
–
43P0
7.885
–
7.817
–
–
–
43P1
7.905
–
7.853
–
–
–
41P1
7.908
–
7.844
–
–
–
43P2
7.915
–
7.867
–
–
–
53P0
8.207
–
–
–
–
53P1
8.226
–
–
–
–
51P1
8.230
–
–
–
–
53P2
8.237
–
–
–
–
Table 6: Mass spectrum of S and P wave Bc meson (in GeV)
State
Present
Devlani:2014
Ebert:2011
Godfrey:2004
Monteiro:2016
13D3
6.990
7.026
7.029
7.045
6.980
11D2
6.994
7.035
7.026
7.041
7.009
13D2
6.997
7.025
7.025
7.036
7.154
13D1
6.998
7.030
7.021
7.028
7.078
23D3
7.399
7.363
7.405
–
–
21D2
7.401
7.370
7.400
–
–
23D2
7.403
7.361
7,399
–
–
23D1
7.403
7.365
7.392
–
–
33D3
7.761
–
7.750
–
–
31D2
7.762
–
7.743
–
–
33D2
7.764
–
7.741
–
–
33D1
7.762
–
7.732
–
–
43D3
8.092
–
–
–
–
41D2
8.093
–
–
–
–
43D2
8.094
–
–
–
–
43D1
8.091
–
–
–
–
13F2
7.234
–
7.273
7.269
–
13F3
7.242
–
7.269
7.276
–
11F3
7.241
–
7.268
7.266
–
13F4
7.244
–
7.277
7.271
–
23F2
7.607
–
7.618
–
–
23F3
7.615
–
7.616
–
–
21F3
7.614
–
7.615
–
–
23F4
7.617
–
7.617
–
–
33F2
7.946
–
–
–
–
33F3
7.954
–
–
–
–
31F3
7.953
–
–
–
–
33F4
7.956
–
–
–
–
Table 7: Mass spectrum of D and F wave Bc meson (in GeV)
Iii Decay properties
The mass spectra of the hadronic states are experimentally determined through detection of energy and momenta of daughter particles in various decay channels. Generally, most phenomenological approaches obtain their model parameters like quark masses and confinement/Coulomb strength by fitting with the experimental ground states. So it becomes necessary for any phenomenological model to validate their fitted parameters through proper evaluation of various decay rates in general and annihilation rates in particular.
In the nonrelativistic limit, the decay properties are dependent on the wave function. In this section, we test our parameters and wave functions to determine various annihilation widths and electromagnetic transitions.
iii.1 Leptonic decay constants
The leptonic decay constants of heavy quarkonia play very important role in understanding the weak decays. The matrix elements for leptonic decay constants of pseudoscalar and vector mesons are given by
⟨0|¯Qγμγ5Q|Pμ(k)⟩=ifPkμ
(8)
⟨0|¯QγμQ|Pμ(k)⟩=ifVMVϵ∗μ
(9)
where k is the momentum of pseudoscalar meson, ϵ∗μ is the polarization vector of meson. In the nonrelativistic limit, the decay constants of pseudoscalar and vector mesons are given by Van Royen-Weiskopf formula VanRoyen:1967
f2P/V=3|RnsP/V(0)|2πMnsP/V¯C2(αS).
(10)
Here the QCD correction factor ¯C2(αS)Braaten:1995; Berezhnoy:1996
¯C2(αS)=1−αsπ(δP,V−mQ−m¯QmQ+m¯QlnmQm¯Q).
(11)
With δP = 2 and δV = 8/3.
Using the above relations, we compute the leptonic decay constants fp and fv for charmonia, bottomonia and Bc mesons and are listed in Table 8 – 13.
State
fp
fp(corr)
Patel:2008
Krassnigg:2016
Lakhina:2006
LQCDBecirevic:2013
QCDSR Becirevic:2013
1S
440.406
350.314
363
378
402
387(7)(2)
309 ± 39
2S
350.056
278.447
275
82
240
–
–
3S
313.354
249.253
239
206
193
–
–
4S
290.673
231.211
217
82
–
–
–
5S
274.367
218.241
202
–
–
–
–
6S
261.698
208.163
197
–
–
–
–
Table 8: Pseudoscalar decay constant of charmonia (in MeV)
State
fv
fv(corr)
Patel:2008
Krassnigg:2016
Lakhina:2006
LQCDBecirevic:2013
QCDSR Becirevic:2013
1S
448.096
325.876
338
411
393
418(8)(5)
401 ± 46
2S
353.855
257.34
254
155
293
–
–
3S
316.064
229.857
220
188
258
–
–
4S
292.829
212.959
200
262
–
–
–
5S
276.177
200.848
186
–
–
–
–
6S
263.266
191.459
175
–
–
–
–
Table 9: Vector decay constant of charmonia (in MeV)
State
fp
Patel:2008
Krassnigg:2016
Pandya:2001
Lakhina:2006
1S
646.025
744
756
711
599
2S
518.803
577
285
–
411
3S
474.954
511
333
–
354
4S
449.654
471
40
–
–
5S
432.072
443
–
–
–
6S
418.645
422
–
–
–
Table 10: Pseudoscalar decay constant of bottomonia (in MeV)
State
fv
Patel:2008
Krassnigg:2016
Lakhina:2006
Wang:2005
LQCDColquhoun:2014
1S
647.250
706
707
665
498±(20)
649(31)
2S
519.436
547
393
475
366±(27)
481(39)
3S
475.440
484
9
418
304±(27)
–
4S
450.066
446
20
388
259±(22)
–
5S
432.437
419
–
367
228±(16)
–
6S
418.977
399
–
351
–
–
Table 11: Vector decay constant of bottomonia (in MeV)
State
fp
Patel:2008
Ebert:2002
Gershtein:1995
Eichten:1994
Monteiro:2016
1S
432.955
465
503
460±(60)
500
554.125
2S
355.504
361
–
–
–
3S
325.659
319
–
–
–
4S
307.492
293
–
–
–
5S
294.434
275
–
–
–
6S
284.237
261
–
–
–
Table 12: Pseudoscalar decay constant of Bc meson (in MeV)
State
fv
Patel:2008
Ebert:2002
Gershtein:1995
Eichten:1994
1S
434.642
435
433
460±(60)
500
2S
356.435
337
–
–
–
3S
326.374
297
–
–
–
4S
308.094
273
–
–
–
5S
294.962
256
–
–
–
6S
284.709
243
–
–
–
Table 13: Vector decay constant of Bc meson (in MeV)
iii.2 Annihilation of heavy quarkonia
Digamma, digluon and dilepton annihilation decay rates of heavy quarkonia are very important in understanding the dynamics of heavy quarks within the mesons. The measurement of digamma decay widths provides the information regarding the internal structure of meson.
The decay ηc→γγ, χc0,2→γγ was reported by CLEO-c Ecklund:2008, BABARLees:2010 and then BESIII Ablikim:2012 collaboration have reported high accuracy data. LQCD is found to underestimate the decay widths of ηc→γγ and χc0→γγ when compared to experimental data Dudek:2006; ChenT:2016.
Other approaches to attempt computation of annihilation rates of heavy quarkonia include NRQCD Bodwin:1994; Khan:1995; Schuler:1997; Bodwin:2006; Bodwin:2007,
relativistic quark model Ebert:2003gamma; Ebert:2003lepton,
effective Lagrangian Lansberg:2009; Lansberg:2006 and next-to-next-to leading order QCD correction to χc0,2→γγ in the framework of nonrelativistic QCD factorization Sang:2015.
The meson decaying into digamma suggests that the spin can never be one Landau:1948; Yang:1950. Corresponding digamma decay width of a pseudoscalar meson in nonrelativistic limit is given by Van Royen-Weiskopf formula VanRoyen:1967
Γn1S0→γγ=12α2ee4Q|nsP(0)|2M2ηQ[1+αsπ(π2−203)]
(12)
Γn3P0→γγ=27α2e|R′nP(0)|2e4QM4χQ0[1+αsπ(3π2−289)]
(13)
Γn3P2→γγ=36α2e|R′nP(0)|2e4QM4χc2[1−163αsπ]
(14)
where the bracketed quantities are QCD next-to-leading order radiative corrections Kwong:1988; Barbieri:1981.
Digluon annihilation of quarkonia is not directly observed in detectors as digluonic state decays into various hadronic states making it a bit complex to compute digluon annihilation widths from nonrelativistic approximations derived from first principles. The digluon decay width of pseudoscalar meson along with the QCD leading order radiative correction is given by Lansberg:2009; Kwong:1988; Barbieri:1981; Mangano:1995
Γn1S0→gg=α2sMηQ|RnsP(0)|23m3Q[1+CQ(αs/π)]
(15)
Γn3P0→gg=3α2sMχc0|R′nP(0)|2m5Q[1+C0Q(αs/π)]
(16)
Γn3P2→gg=4153α2sMχc2|R′nP(0)|2m5Q[1+C2Q(αs/π)]
(17)
The vector mesons have quantum numbers 1−− and can annihilate into dilepton. The dileptonic decay of vector meson along with one loop QCD radiative correction is given by VanRoyen:1967; Kwong:1988
Γn3S1→ℓ+ℓ−=4α2ee2Q|nsV(0)|2M2V[1−16αs3π]
(18)
Here, αe is the electromagnetic coupling constant, αs is the strong running coupling constant in Eq. (4) and eQ is the charge of heavy quark in terms of electron charge.
In above relations, |RnsP/V(0)| corresponds to the wave function of S wave at origin for pseudoscalar and vector mesons while |R′nP(0)| is the derivative of P wave wave function at origin.
The annihilation rates of heavy quarkonia are listed in Table 14 - 19.
State
Γγγ
Γγγ(corr)
Li:2009
Ebert:2003gamma
Lakhina:2006
Kim:2004
PDG pdg2016
11S0
8.582
5.618
8.5
5.5
7.18
7.14±0.95
5.1±0.4
21S0
4.498
2.944
2.4
1.8
1.71
4.44±0.48
2.15±1.58
31S0
3.200
2.095
0.88
–
1.21
–
–
41S0
2.512
1.644
–
–
–
–
–
51S0
2.074
1.358
–
–
–
–
–
61S0
1.768
1.158
–
–
–
–
–
13P0
11.477
11.687
2.5
2.9
3.28
–
2.34±0.19
13P2
3.107
1.412
0.31
0.50
–
–
0.53±0.4
23P0
13.235
13.477
1.7
1.9
–
–
–
23P2
3.582
1.628
0.23
0.52
–
–
–
33P0
14.580
14.847
1.2
–
–
–
–
33P2
3.944
1.792
0.17
–
–
–
–
43P0
15.746
16.034
–
–
–
–
–
43P2
4.257
1.935
–
–
–
–
–
53P0
16.807
17.114
–
–
–
–
–
53P2
4.541
2.064
–
–
–
–
–
Table 14: Digamma decay width of S and P wave charmonia (in keV)
State
Γγγ
Li:2009bb
Godfrey:1985
Ebert:2003gamma
Lakhina:2006
Kim:2004
11S0
0.366
0.527
0.214
0.35
0.23
0.384 ± 0.047
21S0
0.223
0.263
0.121
0.15
0.07
0.191 ± 0.025
31S0
0.180
0.172
0.906
0.10
0.04
–
41S0
0.157
0.105
0.755
–
–
–
51S0
0.141
0.121
–
–
–
–
61S0
0.129
0.050
–
–
–
–
13P0
0.021
0.050
0.0208
0.038
–
–
13P2
0.0060
0.0066
0.0051
0.008
–
–
23P0
0.022
0.037
0.0227
0.029
–
–
23P2
0.0058
0.0067
0.0062
0.006
–
–
33P0
0.022
0.037
–
–
–
–
33P2
0.0059
0.0064
–
–
–
–
43P0
0.023
–
–
–
–
–
43P2
0.0061
–
–
–
–
–
53P0
0.023
–
–
–
–
–
53P2
0.0062
–
–
–
–
–
Table 15: Digamma decay width of S and P wave bottomonia (in keV)
State
Γgg
Γgg(corr)
Patel:2015
Kim:2004
PDG pdg2016
11S0
27.325
40.741
22.37
19.60
26.7±3.0
21S0
25.081
37.394
16.74
12.1
14.7±0.7
31S0
25.502
38.022
14.30
–
–
41S0
26.365
39.310
–
–
–
51S0
27.345
40.711
–
–
–
61S0
28.353
42.273
–
–
–
13P0
25.022
47.468
9.45
–
10.4±0.7
13P2
6.775
3.430
2.81
–
2.03±0.12
23P0
28.855
54.738
10.09
–
–
23P2
7.810
3.954
7.34
–
–
33P0
31.788
60.302
–
–
–
33P2
8.599
4.353
–
–
–
43P0
34.330
65.125
–
–
–
43P2
9.281
4.699
–
–
–
53P0
36.642
69.511
–
–
–
53P2
9.900
5.012
–
–
–
Table 16: Digluon decay width of S and P wave charmonia (in MeV)
State
Γgg
Parmar:2010
Gupta:1996gg
11S0
5.602
17.945
12.46
21S0
4.029
–
–
31S0
3.641
–
–
41S0
3.473
–
–
51S0
3.385
–
–
61S0
3.336
–
–
13P0
0.295
5.250
2.15
13P2
0.079
0.822
0.22
23P0
0.306
–
–
23P2
0.082
–
–
33P0
0.314
–
–
33P2
0.084
–
–
43P0
0.320
–
–
43P2
0.085
–
–
53P0
0.326
–
–
53P2
0.087
–
–
Table 17: Digluon decay width of S and P wave bottomonia (in MeV)
State
Γℓ+ℓ−
Γℓ+ℓ−(corr)
Shah:2012
Patel:2008
Radford:2007
Ebert:2003lepton
PDG pdg2016
1S
6.437
2.925
4.95
6.99
1.89
5.4
5.547 ± 0.14
2S
3.374
1.533
1.69
3.38
1.04
2.4
2.359 ± 0.04
3S
2.400
1.091
0.96
2.31
0.77
–
0.86 ± 0.07
4S
1.884
0.856
0.65
1.78
0.65
–
0.58 ± 0.07
5S
1.556
0.707
0.49
1.46
–
–
–
6S
1.326
0.602
0.39
1.24
–
–
–
Table 18: Dilepton decay width of charmonia (in kev)
State
Γℓ+ℓ−
Shah:2012
Radford:2009
Patel:2008
Ebert:2003lepton
Gonzalez:2003
PDGpdg2016
1S
1.098
1.20
1.33
1.61
1.3
0.98
1.340 ± 0.018
2S
0.670
0.52
0.62
0.87
0.5
0.41
0.612 ± 0.011
3S
0.541
0.33
0.48
0.66
–
0.27
0.443 ± 0.008
4S
0.470
0.24
0.40
0.53
–
0.20
0.272 ± 0.029
5S
0.422
0.19
–
0.44
–
0.16
–
6S
0.387
0.16
–
0.39
–
0.12
–
Table 19: Dilepton decay width of bottomonia (in keV)
iii.3 Electromagnetic transition widths
The electromagnetic transitions can be determined broadly in terms of electric and magnetic multipole expansions and their study can help in understanding the non-perturbative regime of QCD.
We consider the leading order terms i.e. electric (E1) and magnetic (M1) dipoles with selection rules ΔL=±1 and ΔS=0 for the E1 transitions while ΔL=0 and ΔS=±1 for M1 transitions.
We now employ the numerical wave function for computing the electromagnetic transition widths among quarkonia and Bc meson states in order to test parameters used in present work. For M1 transition, we restrict our calculations for transitions among S waves only.
In the nonrelativistic limit, the radiative E1 and M1 widths are given by Eichten:1974; Eichten:1978; Radford:2009; Brambilla:2010; Li:2010{dmath}
Γ(n^2S+1L_iJ_i →n^,2S+1L_fJ_f + γ) = 4 αe⟨eQ⟩2ω33 (2 J_f + 1) S_if^E1 —M_if^E1—^2
{dmath}
Γ(n^3S_1 →n^,1S_0+ γ) = αeμ2ω33 (2 J_f + 1) S_if^M1 —M_if^M1—^2
where, mean charge content ⟨eQ⟩ of the Q¯Q system, magnetic dipole moment μ and photon energy ω are given by
⟨eQ⟩=∣∣∣m¯QeQ−e¯QmQmQ+m¯Q∣∣∣
(19)
μ=eQmQ−e¯Qm¯Q
(20)
and
ω=M2i−M2f2Mi
(21)
respectively. Also the symmetric statistical factors are given by
SE1if=max(Li,Lf){Ji1JfLfSLi}2
(22)
and
SM1if=6(2Si+1)(2Sf+1){Ji1JfSfℓSi}2{1121212SfSi}2.
(23)
The matrix element |Mif| for E1 and M1 transition can be written as
∣∣ME1if∣∣=3ω⟨f∣∣∣ωr2j0(ωr2)−j1(ωr2)∣∣∣i⟩
(24)
and
∣∣MM1if∣∣=⟨f∣∣∣j0(ωr2)∣∣∣i⟩
(25)
The electromagnetic transition widths are listed in Table 20 - 25 and also compared with experimental results as well as theoretical predictions.
Transition
Present
Radford:2007
Ebert:2002
Li:2009
Deng:2016cc
PDG pdg2016
23S1→13P0
21.863
45.0
51.7
74
22
26.3 ± 2.6
23S1→13P1
43.292
40.9
44.9
62
42
25.5± 2.8
23S1→13P2
62.312
26.5
30.9
43
38
25.2± 2.9
21S0→11P1
36.197
8.3
8.6
146
49
–
33S1→23P0
31.839
87.3
–
–
–
–
33S1→23P1
64.234
65.7
–
–
–
–
33S1→23P2
86.472
31.6
–
–
–
–
31S0→21P1
51.917
–
–
–
–
–
33S1→13P0
46.872
1.2
–
–
–
–
33S1→13P1
107.088
2.5
–
–
–
–
33S1→13P2
163.485
3.3
–
–
–
–
31S0→11P1
178.312
–
–
–
–
–
13P0→13S1
112.030
142.2
161
167
284
371 ± 34
13P1→13S1
146.317
287.0
333
354
306
285 ± 14
13P2→13S1
157.225
390.6
448
473
172
133 ± 8
11P1→11S0
247.971
610.0
723
764
361
257 ± 2.80
23P0→23S1
70.400
53.6
–
61
–
–
23P1→23S1
102.672
208.3
–
103
–
–
23P2→23S1
116.325
358.6
–
225
–
–
21P1→21S0
163.646
–
–
309
–
–
23P0→13S1
173.324
20.8
–
74
–
–
23P1→13S1
210.958
28.4
–
83
–
–
23P2→13S1
227.915
33.2
–
101
–
–
21P1→11S0
329.384
–
–
134
–
–
13D1→13P0
161.504
–
423
486
272
202 ± 42
13D1→13P1
93.775
–
142
150
138
81 ± 27
13D1→13P2
5.722
–
5.8
5.8
7.1
≤ 24.8
13D2→13P1
165.176
317.3
297
342
285
–
13D2→13P2
50.317
65.7
62
70
91
–
13D3→13P2
175.212
62.7
252
284
350
–
11D2→11P1
205.93
–
335
575
362
–
Table 20: E1 transition width of charmonia (in keV)