[Paper Review] Constraining the Charm Yukawa and Higgs-quark Universality

Gilad Perez, Yotam Soreq+2 more|arXiv (Cornell University)|Mar 1, 2015

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents four data-driven analyses to constrain the Higgs-charm Yukawa coupling, using Vh→bb̄, J/ψγ, and global signal strength fits. It finds y_c/y_c^{SM} < 6.2 from a global fit, and shows that current data rules out quark universality in Higgs couplings, with charm-tagging offering potential for a tenfold improvement in sensitivity.

ABSTRACT

We introduce four different types of data-driven analyses with different level of robustness that constrain the size of the Higgs-charm Yukawa coupling: (i) recasting the vector-boson associated, Vh, analyses that search for bottom-pair final state. We use this mode to directly and model independently constrain the Higgs to charm coupling, y_c/y_c^{SM} J/\psi\gamma, y_c/y_c^{SM} < 220; (iv) a global fit to the Higgs signal strengths, y_c/y_c^{SM} < 6.2. A comparison with t\bar{t}h data allows us to show that current data eliminates the possibility that the Higgs couples to quarks in a universal way, as is consistent with the Standard Model (SM) prediction. Finally, we demonstrate how the experimental collaborations can further improve our direct bound by roughly an order of magnitude by charm-tagging, as already used in new physics searches.

Motivation & Objective

• To directly and model-independently constrain the Higgs to charm quark Yukawa coupling using existing LHC data.
• To test the hypothesis of Higgs-quark coupling universality predicted by the Standard Model.
• To evaluate the robustness of different analysis approaches in constraining y_c/y_c^{SM} across multiple final states.
• To demonstrate the potential for future improvements in sensitivity through charm-tagging techniques already used in new physics searches.

Proposed method

• Recasting existing vector-boson associated Higgs production (Vh) analyses targeting bottom-quark final states to extract constraints on the Higgs-charm Yukawa coupling.
• Analyzing the J/ψγ final state to obtain a direct, model-independent bound on y_c/y_c^{SM} < 220.
• Performing a global fit to all Higgs signal strength measurements to derive a combined constraint on y_c/y_c^{SM} < 6.2.
• Comparing constraints from t̄th and Vh data to test the validity of quark coupling universality.
• Assessing the potential for sensitivity improvement via charm-tagging, which could enhance bounds by roughly an order of magnitude.

Experimental results

Research questions

• RQ1 What is the most robust direct constraint on the Higgs-charm Yukawa coupling using existing LHC data?
• RQ2 Can the Higgs coupling to charm quarks be constrained independently of theoretical models?
• RQ3 Does current data support the assumption of universal Higgs couplings to quarks as predicted by the Standard Model?
• RQ4 How much could sensitivity to the Higgs-charm coupling improve with the implementation of charm-tagging in experimental analyses?
• RQ5 What is the relative strength of constraints from different final states such as bb̄, J/ψγ, and global signal strengths?

Key findings

• The analysis of the J/ψγ final state yields a direct, model-independent bound: y_c/y_c^{SM} < 220.
• The global fit to Higgs signal strengths gives a combined upper limit of y_c/y_c^{SM} < 6.2.
• Comparison of t̄th and Vh data rules out quark coupling universality at the current level of precision.
• The current data disfavor the Standard Model prediction of universal Higgs couplings to quarks.
• The inclusion of charm-tagging in future analyses could improve the sensitivity to the Higgs-charm Yukawa coupling by approximately an order of magnitude.