mfb said:DId you check the public pages of ATLAS and CMS? They have the best studies of Higgs self-interaction so far. It has not been discovered yet, if it is SM-like the experiments will need huge datasets (hundreds of 1/fb) to have a chance to see it.
Probing the Higgs self coupling via single Higgs production at the LHC
Giuseppe Degrassi, Pier Paolo Giardino, Fabio Maltoni, Davide Pagani
(Submitted on 14 Jul 2016)
We propose a method to determine the trilinear Higgs self coupling alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production (ggF, VBF, WH, ZH, tt¯H) and decay (γγ, WW∗/ZZ∗→4f, gg) modes at the LHC and then estimate the sensitivity to the trilinear coupling via a one-parameter fit to the single Higgs measurements at LHC 8 TeV. We find that the bounds on the self coupling are already competitive with those coming from Higgs pair production and will be further improved in the current and next LHC runs.
Comments: 34 pages, 13 figures, 5 tables
[P]resent estimates [8, 9], suggest that at the end of Run II the Higgs boson couplings to the vector bosons are expected to reach a ∼ 5% precision with 300 fb−1 luminosity, while the corresponding ones for the heavy fermions can reach ∼ 10 − 15% precision. Similar estimates for the end of the HL option indicate a reduction of these numbers by at least a factor ∼ 2.
The study of the trilinear (λ3) and quartic (λ4) Higgs self couplings in the scalar potential V (H) = m2 H 2 H2 + λ3vH3 + λ4H4 2 is in a completely different situation. In the SM, the potential is fully determined by only two parameters, v = (√ 2Gµ) −1/2 and λ, the coefficient of the (Φ†Φ)2 interaction Φ being the Higgs doublet field (m2 H = 2λv2 , λ3 = λ, λ4 = λ/4).
In the case of extended scalar sectors or in presence of new dynamics at higher scales the trilinear and quartic coupling become independent from the Higgs mass and their values can depart from the SM predictions [10,11].
At the Leading Order (LO) the cross sections corresponding to the main single Higgs production processes, i.e., gluon gluon fusion (ggF), vector boson fusion (VBF), W and Z associated production (ZH, V H) and production in association with a top quark pair (ttH¯ ), as well as the Higgs decay widths depend on the couplings of the Higgs boson to the other particles of the SM, yet they are insensitive to λ3 and λ4. Information on λ3 can be directly obtained at LO only from final states featuring at least two Higgs bosons. However, the cross sections corresponding to these processes are much smaller than those for single Higgs production due to the suppression induced by a heavier final state and an additional weak coupling.
At √ s = 13 TeV the single Higgs gluon-gluon-fusion production cross section in the SM is around 50 pb [12] while the double Higgs cross section is around 35 fb in the gluon-gluon-fusion channel [13–15] and even smaller in other production mechanisms [16, 17]. A plethora of perspective studies performed at √ s = 13 TeV suggest that it should be possible to detect the production of a Higgs pair via b ¯bγγ [16,18– 22], b ¯bτ τ¯ [16, 23], b ¯bW+W− [24] and b ¯bb¯b [25–27] final states. However, the ultimate precision with which λ3 could then be extracted is much less clear.
Even with an integrated luminosity of 3000 fb−1 , experimental analyses suggest that it will be possible to exclude at the LHC only values in the range λ3 < −1.3 λ SM 3 and λ3 > 8.7 λ SM 3 via the b ¯bγγ signatures [28] or λ3 < −4 λ SM 3 and λ3 > 12 λ SM 3 even including also b ¯bτ τ¯ signatures [29], i.e., a much more pessimistic perspective than the results reported in the phenomenological explorations.
The current experimental bounds on nonresonant Higgs pair production cross sections as obtained at 8 TeV are rather weak: ATLAS has been able to exclude only a signal up to 70 times larger than the SM one [30, 31], which we can be roughly translated to excluding λ3 < −12 λ SM 3 and λ3 > 17 λ SM 3 while CMS puts a 95% C.L. exclusion limit on λ3 < −17.5 λ SM 3 and λ3 > 22.5 λ SM 3 assuming changes only in the trilinear Higgs boson coupling, with all other parameters fixed to their SM values [32]. Thus, alternative strategies in the determination of the trilinear Higgs self coupling λ3 other than the constrains from Higgs pair production would be certainly helpful. Finally, the perspectives of determining the quartic Higgs self-coupling λ4 via measurements in triple Higgs production seems quite 3 bleak at the LHC [33, 34] due to the smallness of the corresponding cross section [14]. In this work we explore the possibility of constraining the trilinear Higgs self coupling with a different approach, namely, via precise measurements of processes featuring single Higgs production and decay at the LHC. Indeed, although single Higgs production does not depend on λ3 at LO or at higher orders in QCD, it does depend on it via weak loops, namely at Next-to-Leading (NLO) in the electroweak (EW) interactions. We therefore extract the λ3-dependent part from the corresponding NLO EW corrections for all phenomenologically relevant single Higgs production cross sections (ggF, VBF, W H, ZH, ttH¯ ) and branching ratios, (H → γγ, H → ZZ, WW → 4f, H → f ¯f, H → gg). By varying the value of λ3 we evaluate the impact of an anomalous trilinear Higgs self coupling on the predictions for the aforementioned cross sections and decay widths. A distinctive pattern of deformations of the SM predictions for the rates (σ(i) · BR(f)) is obtained that can be compared to the experimental data.
The Higgs self interaction is a fundamental force that allows the Higgs boson particle to interact with itself and give mass to other particles.
Understanding the strength and behavior of the Higgs self interaction is crucial for confirming the validity of the Standard Model of particle physics and for furthering our understanding of the fundamental forces and particles that make up the universe.
The Higgs self interaction is typically measured through experiments at particle colliders, such as the Large Hadron Collider (LHC). These experiments involve colliding particles at high energies and analyzing the resulting data to look for evidence of Higgs self interactions.
The main challenge in measuring the Higgs self interaction is the incredibly small probability of these interactions occurring. This requires highly sensitive detectors and precise experimental techniques to detect and analyze the data.
Previous measurements of the Higgs self interaction have confirmed the existence of the Higgs boson and its role in giving mass to other particles. They have also provided evidence for the validity of the Standard Model and have opened up new avenues for research into the origins of mass and the fundamental forces of nature.