New ColorOctet Vector Boson Revisit
Abstract
Motivated by CDF recent measurements on dijet invariant mass spectrum where dijet is associated production with charged leptons () and missing energy, we reexamine the previous proposed massive coloroctet axialvectorlike boson . Our simulation showed that the dijet bump around 120160 GeV can be induced by with effective coupling (q represents the quark other than top and is the strong coupling constant). Moreover our numerical investigation indicated that the top quark forwardbackward asymmetry can be reproduced without distorting shape of differential cross section , provided that the and top quark coupling is appropriately chosen (). Our results also showed that the theoretical as functions of and can be consistent with data within and respectively.I Introduction
In the previous work Xiao:2010ph , part of authors proposed a new massive coloroctet vector boson just above in order to account for the top quark forwardbackward asymmetry at Tevatron. Just after Xiao:2010ph posted, a new analysis on appeared Aaltonen:2011kc . The analysis indicated that, in the rest frame, increase with the rapidity difference , and with the invariant mass of the system. In order to satisfy the measured for GeV which is consistent with standard model (SM) prediction, must be adjusted very carefully to ensure the cancelation of contributions to asymmetric cross section. This feature makes the idea less attractive. However the alternative proposals to account for anomalous , for example the tchannel flavor changing contribution and a generic schannel heavy color octet, will have a risk to distort the shape of , especially for the high energy regime. This disadvantage is, in fact, one of our primary motivations to introduce the light coloroctet axiallike vector boson.
Recently CDF at Tevatron released their measurements on WW/WZ cross sections via the electron/muon + missing energy + dijet channel Aaltonen:2009vh ; CDFemu2jetlatest ; cdflatest . The cross sections are in agreement with the SM prediction. However there seems an unexpected bump in the dijet spectrum around 120160 GeV, though the significance ( cdflatest ) is not significant. The instant investigations showed that the extra vector bosons Wang:2011uq ; Cheung:2011zt , as well as the new resonance in Technicolor models Eichten:2011sh , can account for such bump with appropriate parameters. However the new particles prefer to couple with quarks instead of leptons provided that the severe constraints from other measurements at LEP, Tevatron and even the UA2 experiments. Such feature motivates us to pursue the possibility that the new bump is actually the coloroctet axial vector. The obvious reason is that the coloroctet does not couple with leptons.
The interaction Lagrangian of and quarks can be written as
(1) 
and are vector and axialvector couplings among quarks and . In order to ensure the successful prediction on in the SM, the extra contribution to the total cross section should be limited. Thus for simplicity we choose , same with the choice in Ref. Xiao:2010ph . This point can be understood from the amplitude squared for the process
(2) 
where , , and are vector and axialvector couplings among light quarks (top) and . Here the terms at rhs represent QCD amplitude squared, interference between QCD and amplitudes and amplitude squared respectively.
Why can such light particle escape the constraints from (1) new resonance search using dijet invariant mass distributions; (2) quark composite scale limits which are derived from the deviation from the background (mainly from QCD processes) shape of or ? The reasons are as following.

Jet is usually not measured so well as that of charged leptons and the dijet mass peak can be buried by large mass resolution if the contribution is less than the huge QCD backgrounds. As the consequence, the Tevatron constraints on new particle less than 200 GeV are quite weak Buckley:2011vc . The UA2 experiment can only effectively constrain such light particle with the coupling strength larger than . The required parameter to account for the new bump is only , as shown below, which is permitted by direct searches of past experiments.

The shapes and magnitudes of and after including the contributions are not distorted severely, especially at high energy region (much larger than ). As such the quark composite scale limit is not applicable to .
The paper is organized as following. Section II showed that associated production can account for the dijet invariant mass distribution observed by CDF cdflatest . In section III we presented the results for and compared with measurements by CDF Aaltonen:2011kc . Section IV contained our conclusions and discussions.
Ii Dijet associated production with and missing energy at Tevatron
In order to account for the CDF data, we simulate the dijet invariant distribution arising from as well as production with GeV. We choose the benchmark parameter set as and as discussed above, which do not contradict with other measurements. The dijet invariant distribution is shown in Fig. 2 after imposing the same cuts with those of cdflatest . The events are generated by MadGraph Maltoni:2002qb , then the initial state radiation, final state radiation and fragmentation are carried out by Pythia Sjostrand:2006za . The detector response is simulated by PGS. We corrected the jet energy according to Ref. phdthesis . From the Fig. 2, we can see that the new contribution arising from the extra can excellently fit the data. Generally speaking, the new contributions from mainly depends on the magnitude of . For specific choice of righthanded coupling, namely , the cross section is zero if parton mass is neglected. Such kind of signal is not difficult to be examined at current running LHC, similar to the case of deciweak Wang:2011uq .
Iii Top Quark Forwardbackward Asymmetry at Tevatron
Now that we know roughly the coupling among and quarks, we switch to discuss whether the same parameters can account for top quark forwardbackward asymmetry at Tevatron. Since the choice of affects insignificantly, we don’t show the numerical results here. Instead we will focus on the as functions of and .
The numerical investigation indicated that if we choose , we can’t obtain the observed . Instead if we choose
. For comparison the experimental measurement is . In Fig. 3 and 4, we also present as functions of and . From the figures, we can see that data and theory is in agreement within for distribution while about for distribution. It is obvious that the plus SM contributions can improve the agreement between theory and data greatly.
Iv Conclusions and discussions
Motivated by recent measurement of dijet distribution associated with and missing energy by CDF, we reexamine the previous idea, namely the new massive coloroctet axialvectorlike boson , to account for observation. Our numerical results showed that can explain the new dijet bump within allowed parameters. We also investigated whether such can account for . We found that if the theory and data is in excellent agreement. Moreover the distributions as functions of and are consistent with data within and about respectively.
At the LHC, the new can be easily discovered via the associated production. Once is discovered the detailed properties, such as spin, coupling structure etc., can also be studied in top pair production processes. Here the observables of oneside forwardbackward asymmetry Wang:2010du and/or edge charge asymmetry Xiao:2011kp can be utilized to analyze the event samples.
Acknowledgment
We would like to thank Jia Liu for the stimulating discussion. This work was supported in part by the Natural Sciences Foundation of China (No 11075003).
References
 (1) B. Xiao, Y. k. Wang and S. h. Zhu, arXiv:1011.0152 [hepph].
 (2) T. Aaltonen et al. [CDF Collaboration], arXiv:1101.0034 [hepex].
 (3) T. Aaltonen et al. [CDF Collaboration], Phys. Rev. Lett. 104, 101801 (2010) [arXiv:0911.4449 [hepex]].
 (4) http://wwwcdf.fnal.gov/physics/ewk/2010/WW_WZ/index.html.
 (5) T. Aaltonen et al. [CDF Collaboration], arXiv:1104.0699 [hepex].
 (6) X. P. Wang, Y. K. Wang, B. Xiao, J. Xu and S. h. Zhu, arXiv:1104.1161 [hepph].
 (7) K. Cheung and J. Song, arXiv:1104.1375 [hepph].
 (8) E. J. Eichten, K. Lane and A. Martin, arXiv:1104.0976 [hepph].
 (9) M. R. Buckley, D. Hooper, J. Kopp and E. Neil, arXiv:1103.6035 [hepph].
 (10) F. Maltoni and T. Stelzer, JHEP 0302, 027 (2003) [arXiv:hepph/0208156].
 (11) T. Sjostrand, S. Mrenna and P. Z. Skands, JHEP 0605, 026 (2006) [arXiv:hepph/0603175].

(12)
V. Cavaliere (2010), Fermilab Ph.D Thesis 201051,
http://www.slac.stanford.edu/spires/find/hep/www?r=FERMILABTHESIS2010051.  (13) Y. k. Wang, B. Xiao and S. h. Zhu, Phys. Rev. D 82, 094011 (2010) [arXiv:1008.2685 [hepph]]; Y. k. Wang, B. Xiao and S. h. Zhu, Phys. Rev. D 83, 015002 (2011) [arXiv:1011.1428 [hepph]].
 (14) B. Xiao, Y. K. Wang, Z. Q. Zhou and S. h. Zhu, Phys. Rev. D 83, 057503 (2011) [arXiv:1101.2507 [hepph]].