REVIEW
Single Top-Quark Production in Flavor-Changing Z' Models
High Energy Physics - Phenomenology · Submitted 20 Feb 2006 · 35 references
Pith's reading: For a 1 TeV Z' with family non-universal couplings, flavor-changing t-c production is about 1 fb at the LHC (background-limited) and over 100 fb at the ILC resonance, making the ILC the better probe.
The paper
The paper claims
For a 1 TeV Z' with family non-universal couplings, flavor-changing t-c production is about 1 fb at the LHC (background-limited) and over 100 fb at the ILC resonance, making the ILC the better probe.
The reading
The authors first check whether D0-D0 mixing (mixing of the two neutral D mesons) rules out the coupling; they find the constraint is weak. Then they compute production of a top plus anti-charm pair at the LHC and at a proposed ILC electron-positron collider. At the LHC with a 1 TeV Z' and a moderate non-universality parameter x=0.1, the cross section is about 1 fb, but the Standard Model single-top background is roughly five times larger after basic cuts, so detecting the signal requires good charm tagging. At the ILC the signal is almost background-free and reaches more than 100 fb on the Z' resonance.
The paper concludes that the ILC is much better suited to finding this effect and that the ratio of top-charm to top-antitop production could measure the new parameter x. The results are model-dependent estimates with no error bars and no full detector simulation, so they should be read as a guide for search strategies rather than a definitive prediction.
Extended reading notes
Core claim
For a typical value of M_Z'=1 TeV, the production cross section at the LHC can be of the order of 1 fb, but the SM single top-quark background makes it difficult to detect the flavor-changing Z' signal unless with a decent charm tagging method; at the ILC, the cross section at the resonance energy sqrt(s) ≈ M_Z' can reach more than 100 fb, and even away from resonance it exceeds the 0.01 fb observability threshold. (Abstract and Sec. V.)
Load-bearing premise
The model assumes the left-handed down-type quark sector is already diagonal, so V_CKM = V_uL^dagger, and that all right-handed Z' couplings are family-universal. This fixes the flavor-changing t-c-Z' coupling to be purely left-handed and proportional to (x-1) Q_uL V_cb V_tb^*. If the down-type rotations or right-handed couplings are not negligible, the size and even the chirality of the FCNC could differ, changing the cross sections and the LHC/ILC conclusions. The assumption is introduced in Sec. II after Eq. (4) to increase predictive power and is load-bearing for the numerical results.
Original abstract
In some models with an extra U(1) gauge boson Z', the gauge couplings of the Z' to different generations of fermions may not be universal. Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. In this work, we concentrate on the flavor mixing in the up-type quark sector. We deduce a constraint from D0-D0bar mixing. We study in detail single top-quark production via flavor-changing Z' exchange at the LHC and the ILC. We found that for a typical value of M_{Z'}=1 TeV, the production cross section at the LHC can be of the order of 1 fb. However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z' signal unless with a decent charm tagging method. On the other hand, at the ILC, the production cross section at the resonance energy of \sqrt{s} \approx M_{Z'} can reach a size of more than 100 fb. Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
In some models with an extra U(1) gauge boson Z', the gauge couplings of the Z' to different generations of fermions may not be universal. Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. In this work, we concentrate on the flavor mixing in the up-type quark sector. We deduce a constraint from D0-D0bar mixing. We study in detail single top-quark production via flavor-changing Z' exchange at the LHC and the ILC. We found that for a typical value of M_{Z'}=1 TeV, the production cross section at the LHC can be of the order of 1 fb. However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z' signal unless with a decent charm tagging method. On the other hand, at the ILC, the production cross section at the resonance energy of \sqrt{s} \approx M_{Z'} can reach a size of more than 100 fb. Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | In some models with an extra U(1) gauge boson Z', the gauge couplings of the Z' to different generations of fermions may not be universal. | background 1.00 | 0.04 | 0.02 | hedged possibility 1.00 |
| s1 | Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. | background 1.00 | 0.07 | 0.02 | hedged possibility 0.56 |
| s2 | In this work, we concentrate on the flavor mixing in the up-type quark sector. | contribution 0.81 | 0.49 | 0.03 | asserted 0.91 |
| s3 | We deduce a constraint from D0-D0bar mixing. | contribution 0.54 | 0.94 | 0.05 | asserted 1.00 |
| s4 | We study in detail single top-quark production via flavor-changing Z' exchange at the LHC and the ILC. | contribution 1.00 | 0.92 | 0.08 | asserted 0.94 |
| s5 | We found that for a typical value of M_{Z'}=1 TeV, the production cross section at the LHC can be of the order of 1 fb. | result 1.00 | 0.94 | 0.17 | asserted 0.85 |
| s6 | However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z' signal unless with a decent charm tagging method. | limitation 0.52 | 0.69 | 0.13 | asserted 0.97 |
| s7 | On the other hand, at the ILC, the production cross section at the resonance energy of \sqrt{s} \approx M_{Z'} can reach a size of more than 100 fb. | result 1.00 | 0.91 | 0.22 | asserted 0.97 |
| s8 | Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb. | result 0.99 | 0.90 | 0.18 | asserted 1.00 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:hep-ph/0602175 by the authors.
Human review
References
How the literature uses it
7 arXiv papers cite this in 11 sentences
Papers citing it · 9 sentences without a confident label
Compares with it 1 paper
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This process has a smaller cross-section than the one discussed in Ref. [ref] , but it also has significantly lower background.
Flavor changing Z' couplings at the LHC · Introduction · 0.94
Cites it as background 1 paper
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While the discussion presented here is quite general, many string-inspired models have extra $U(1)$ gauge symmetries that lead to extra $Z'$-bosons with possible flavor-changing couplings [ref] .
Implications of D^0-\bar D^0 Mixing for New Physics · Generic $Z'$ Models · 0.82
Discussion
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