Diphoton and diboson probes of fermiophobic Higgs bosons at the LHC

JHEP06(2016)042 Published for SISSA by Springer Received:March 30, 2016 Revised:May 25, 2016 Accepted:May 30, 2016 Published:June 7, 2016 Diphoton and diboson probes of fermiophobic Higgs bosons at the LHC Antonio Delgado,aMateo Garcia-Pepin,bMariano Quir´os,b,c Jos´e Santiagod and Roberto Vega-Moralesd aDepartment of Physics, University of Notre Dame, Notre Dame, IN 46556, U.S.A. bInstitut de F´ısica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), Universitat Aut`onoma de Barcelona, Barcelona, Spain cInstituci´o Catalana de Recerca i Estudis Avan¸cats (ICREA), Barcelona, Spain dDepartamento de F´ısica Te´orica y del Cosmos and CAFPE, Universidad de Granada, Campus de Fuentenueva, E-18071 Granada, Spain E-mail: [email protected],[email protected],[email protected], [email protected],[email protected] Abstract: Extensions of the Standard Model Higgs sector with electroweak charged scalars can possess exotic ‘Higgs’ bosons with vanishing or suppressed couplings to Standard Model fermions. These ‘fermiophobic’ scalars, which cannot be produced via gluon fusion, are constrained by LHC measurements of the 125 GeV Higgs boson to have a small vacuum expectation value. This implies that vector boson fusion and associated vector boson production are in general suppressed rendering conventional Higgs searches insensitive. However, Drell-Yan Higgs pair production, which is not present in the SM, can be sizeable even in the limit of vanishing exotic Higgs vacuum expectation value. We utilize this to show that diphoton searches at 8 TeV LHC already rule out a large class of neutral fermiophobic Higgs bosons below ∼110 GeV. This includes fermiophobic scalars found in two Higgs doublet as well as Higgs triplet and Georgi-Machacek type models. Our results extend the only relevant limit on fermiophobic Higgs bosons obtained by a recent CDF analysis of 4γ+XTevatron data. Furthermore, diphoton limits are independent of the decay of the second Higgs boson and thus apply even for degenerate masses in contrast to the CDF search. We also find that if the fermiophobic Higgs has very enhanced couplings to photons, masses as large as ∼150 GeV can be ruled out while if these couplings are somehow highly suppressed, masses below ∼90 GeV can still be ruled out. Finally, we show that WW and ZZ diboson searches may serve as complementary probes for masses above the diphoton limit up to ∼250 GeV and discuss prospects at 13 TeV LHC. Keywords: Beyond Standard Model, Higgs Physics ArXiv ePrint: 1603.00962 Open Access,c The Authors. Article funded by SCOAP3.doi:10.1007/JHEP06(2016)042 JHEP06(2016)042 Contents 1 Introduction 1 2 Fermiophobic Higgs boson production and decay 3 2.1 Higgs pair production 3 2.2 Fermiophobic Higgs diboson decays 5 3 Probing fermiophobic Higgs bosons at the LHC 9 3.1 Diphoton probes for light masses 9 3.2 Diboson probes of intermediate masses 11 4 Closing the ‘fiveplet window’ 11 5 Summary and conclusions 14 1 Introduction The discovery of the Higgs boson [1,2] has provided the first direct window into the mechanism of electroweak symmetry breaking (EWSB). Many models of EWSB and extensions of the Standard Model (SM) predict enlarged Higgs sectors, in which the spectrum includes extra electroweak charged scalars beyond the SM Higgs doublet. In a number of models, neutral Higgs bosons with suppressed or vanishing couplings to SM fermions are present at the weak scale after EWSB. These ‘fermiophobic’ Higgs bosons have many generic phenomenological features which have been considered for some time [3–15] and searched for previously at LEP [16–19], Tevatron [20,21], and LHC [22]. They can be found in ‘Type I’ two Higgs doublet models [23] in the large tan βlimit [15,24,25] as well as Higgs triplet models [26–33] including the well known Georgi-Macachek (GM) model [34] and its variations [35,36,36,37,37–42] or their supersymmetric incarnations [43–48]. They can also appear in non-minimal composite Higgs models [49,50]. Since these fermiophobic Higgs scalars do not couple to quarks, production via gluon fusion is not available. Furthermore, as pointed out in [13,14], if the vacuum expectation value (vev) of the fermiophobic Higgs is small, vector boson fusion (VBF) and associated Higgs vector boson production (VH) quickly become highly suppressed. Since these are the dominant production mechanisms in the SM, they have been assumed as the production mechanisms in almost all Higgs boson searches regardless of if they are fermiophobic or not. On the other hand since LHC measurements of the 125 GeV Higgs boson couplings [51] seem to indicate a SM-like Higgs boson [52], this implies a small vev for any additional exotic Higgs boson. As these measurements increase in precision without observing a deviation from the SM prediction, previous collider searches for fermiophobic Higgs bosons, which assumed SM-like production mechanisms, become increasingly obsolete. – 1 – JHEP06(2016)042 However, Drell-Yan (DY) Higgs pair production, which is not present in the SM, can be sizable even in the limit of small exotic Higgs vev [13,14]. Furthermore, as pointed out many times [10,24,53–55], since there is no b¯ bdecay to compete with, neutral fermiophobic Higgs scalars (which we refer to as H0 F) at low masses can have large branching ratios to vector boson pairs and in particular photons. This can be combined with DY pair production to place stringent constraints on light fermiophobic Higgs bosons using multiphoton final states. In particular, the Wboson mediated H±H0 Fproduction channel (see figure 1), followed by H±→W±H0 Fand H0 F→γγ decays, leads to a 4γ+Xfinal state, which has been proposed as a probe [13,14] of fermiophobic Higgs bosons at high energy colliders. Clearly the H±→W±H0 Fdecay requires a mass splitting between the charged and neutral Higgs and, in particular, MH±> MH0 F. The lone experimental search to utilize this DY pair production to multi-photon channel to search for a fermiophobic Higgs is a very recent CDF analysis of previously collected Tevatron data [56]. This was applied to fermiophobic Higgs bosons found in Type I two Higgs doublet models to put constraints for the first time and, in particular, rule out a neutral fermiophobic Higgs boson below 100 GeV. Constraints in the two dimensional plane of the charged and neutral Higgs boson masses were also obtained. Of course in the limit where the mass splitting goes to zero this multiphoton search can be evaded. In models with custodial symmetry [57] in the Higgs sector, which are motivated by electroweak precision data, degenerate masses between the neutral and charged Higgs is commonly found (at tree level). This makes CDF searches in the 4γ+Xchannel insensitive to these fermiophobic custodial Higgs scalars.1Clearly these searches are also insensitive when MH±< MH0. In this paper we emphasize that the Wmediated H±H0 Fpair production can also be combined with conventional diphoton searches to probe neutral fermiophobic Higgs bosons. While the signal to background ratio is worse than in 4γ+X[56], diphoton searches have the advantage that, being more inclusive, are more model independent and can probe neutral fermiophobic Higgs bosons without any reference to the second Higgs boson decay. In particular, they can be applied even in the custodial limit of degenerate masses as well as when MH±< MH0or if the charged Higgs decays in a way that is difficult to observe. We find that while Tevatron diphoton searches are not sensitive to fermiophobic Higgs bosons, the larger production cross sections at 8 TeV LHC allow a neutral fermiophobic Higgs boson below 90–150 GeV to be ruled out depending on particular model assumptions. For similar assumptions, we find that stronger bounds than those obtained in 4γ+Xsearches at Tevatron can be obtained with 8 TeV diphoton searches at LHC. We also examine, combining the Higgs pair production with WW and ZZ diboson searches as a complementary probe to diphoton searches, for larger fermiophobic Higgs masses up to ∼250 GeV. Finally, we pay particular attention to the specific case of a fermiophobic custodial fiveplet scalar found in all incarnations of custodial Higgs triplet models [34,41,43] in which the neutral and charged Higgs scalars are predicted to be degenerate. Thus the CDF 4γ+Xsearch [56] cannot be applied to this case. We show for the first time that 1Of course if there are additional Higgs scalars which are in different custodial representations than H0 F, additional Higgs pair production mechanisms with non-degenerate masses can become available allowing for 4γ+Xlimits to again be applied. – 2 – JHEP06(2016)042 W± H0 F H± N Figure 1. The dominant contribution to Higgs pair production in extensions of the Standard Model Higgs sector. when the Wboson loop (see figure 3) dominates the effective couplings to photons, a custodial fiveplet scalar below ∼110 GeV is ruled out by 8 TeV LHC diphoton searches independently of the Higgs triplet vev. Larger masses possibly up to ∼150 GeV can also be ruled out if charged scalar loops produce large constructive contributions to the effective photon couplings. We also find that diboson searches, and in particular ZZ searches, may be useful for higher masses allowing us to potentially obtain limits again for custodial fiveplet masses up to ∼250 GeV independently of the Higgs triplet vev. The paper is organized as follows: in section 2we review the relevant aspects of fermiophobic production and decay for LHC diboson searches. In section 3we examine diphoton and diboson searches at 8 TeV LHC for generic fermiophobic Higgs scenearios. Finally in section 4we examine the particular case of a custodial fiveplet scalar before summarizing our conclusions in section 5. 2 Fermiophobic Higgs boson production and decay Here we review production and decay of fermiophobic Higgs bosons focusing on the aspects most relevant for LHC diphoton and diboson searches. In particular we focus on the limit of small exotic Higgs vev in which the DY Higgs pair production mechanism is dominant. A more detailed discussion of fermiophobic Higgs production and decays can be found in [4–8,10–14], and references therein, to which we refer the reader for details. 2.1 Higgs pair production Any extension of the SM Higgs sector by electroweak charged scalars will possess the pair production channel mediated by a Wboson shown in figure 1. Here we take H0 Fto generically represent our neutral fermiophobic Higgs boson and assume it to be CP even while H± Nis in an arbitrary SU(2)L⊗U(1)Yrepresentation labeled by Nwhich may (or may not) be the same representation which H0 Fbelongs to. The corresponding diagram involving aZboson can arise when H± Nis replaced by a neutral CP odd scalar, but is subdominant to the Wmediated channel [13]. In general the neutral and charged components in figure 1 can have different masses, but as long as the mass splitting is not too large and both are sufficiently light to be produced on-shell, it will not qualitatively affect our discussion since we will only be concerned with the neutral fermiophobic Higgs decay. We can write the WHH vertex schematically as, VW HH ≡igCN(p1−p2)µ(2.1) – 3 – JHEP06(2016)042 8 TeV H N ± H F 0 H N ± H F 0 , H N 0 H F 0 , Δ M H = 100 GeV H N ± H F 0 , ( 13 TeV ) s θ = 0.03 s θ = 0.1 s θ = 0.4 s θ = 1 ( H F 0 VBF ) Δ M H = 100 GeV 50 100 150 200 250 1 5 10 50 100 500 1000 MHF 0[GeV] σ(pp →HF 0HN)[fb] Figure 2. Various Drell-Yan Higgs pair production cross sections for a neutral fermiophobic Higgs boson (H0 F) at the LHC with √s= 8 TeV (thick solid curves) and √s= 13 TeV (black dotted curve). The black curves show the production cross section for H0 FH± Nassuming degenerate masses. Cross sections for DY Higgs pair production mediated by a W(orange solid) or Z(blue solid) when there is 100 GeV mass splitting (MH± N> MH0 F) are also shown. For comparison we show in the shaded gray region contours of the ‘vev mixing angle’ sθas defined in eq. (2.2) for the VBF production channel where we have rescaled the 8 TeV SM cross sections [60–62] by s2 θ. where CNis fixed by the SU(2)Lrepresentation and p1, p2are the four momenta of the incoming and outgoing scalar momenta. Once EWSB occurs there may (or may not) be a dependence on the exotic Higgs vev and mass mixing angles introduced into the vertex, depending on if the gauge and mass eigenstates are ‘aligned’. The key point is that, unlike the terms which generate the Wand Zmasses or the single coupling of Hto pairs of electroweak vector bosons, VW HH does not necessarily depend on the exotic Higgs vev and, more importantly, does not go to zero in the limit of vanishing vev. A more detailed discussion of how the vertex in eq. (2.1) can depend on these various mixing angles in the context of the two Higgs doublet or Higgs triplet models can be found in [11,15,34,41,43] and references therein. To see roughly how large these Higgs pair production cross sections are, we show in figure 2leading order cross sections for various channels (thick solid curves) involving H0 Fat the LHC with √s= 8 TeV in the mass range 45–250 GeV. In these curves we have factored out any group theory factors or mass mixing angles which could enter in the vertex in eq. (2.1) so that the coefficient is simply given by the SU(2) gauge coupling g. The curves for any particular model can be obtained by trivial rescaling with (CN)2 and will not qualitatively change this discussion which is largely for intuition purposes. Our results are obtained from Madgraph [58] using a modified version of the GM model implementation of [59] and rescaling appropriately. The main focus of this study will be the pp →W±→H0 FH± Nproduction channel for which we show the cross section (solid black) as a function of H0 Fmass assuming degenerate masses. We see that it can be &O(100) fb all the way up to ∼200 GeV at 8 TeV while at 13 TeV (black dotted) it will be increased by roughly a factor of ∼2. If there is a 100 GeV splitting between the neutral and charged scalars (solid orange) and assuming – 4 – JHEP06(2016)042 MH± N> MH0 Fthe cross section is considerably reduced, but still &O(100) fb all the way up to ∼150 GeV. We also show for comparison the Zmediated H0 FH0 Nchannel (blue solid curve) for the same mass splitting which we see is significantly smaller than the W mediated channels, but again may be relevant for light masses. Note there are also NLO contributions which may generate &O(1) K-factors for Higgs pair production [63–65], but we do not explore this issue here as it does not qualitatively affect our discussion. We also show for comparison in the gray shaded region the VBF cross section for H0 F, which depends on the exotic Higgs vev. We can parametrize this dependence generically through a SM doublet-exotic Higgs ‘vev mixing angles’ (cθ≡cos θ, sθ≡sin θ), cθ=vh v, sθ=vex v(v= 246 GeV),(2.2) where vhis the vev of the mostly SM Higgs doublet observed at 125 GeV and vex represents schematically the sum (in quadrature), which may also include group theory factors, over all exotic Higgs vev contributions to EWSB. So sθessentially parametrizes the relative contribution to the electroweak scale from the exotic Higgs sector. With the definition in eq. (2.2) we can then obtain the VBF cross section by simply rescaling the 8 TeV SM prediction [60–62] by s2 θfor which we show various contours. These curves implicitly assume that the ratios of the H0 Fcouplings to WW and ZZ pairs equal those of the SM Higgs. This will not be true for all Higgs bosons found in exotic Higgs sectors such as for example the custodial fiveplet in custodial Higgs triplet models [34,41,43] to be examined in more detail below. We see clearly that once the measurements of the Higgs boson at 125 GeV constrain sθ1, the VBF production channel quickly becomes highly suppressed relative to the DY Higgs pair production channels. Similar behavior can be seen for the V H production channels which are typically smaller than the VBF cross sections except at very low masses [60–62]. To summarize, we see that &O(100) fb cross sections are obtained for the pp →H0 FH± N Higgs pair production channel in the mass range 45–250 GeV. Crucially this production mechanism is present even in the limit of vanishing exotic Higgs vev unlike VBF and VH production. As we will see, diphoton and diboson searches at the 8 TeV are sensitive to .O(100) fb cross section times branching ratios. Thus if the branching ratios to dibosons are large, searches at the LHC for pairs of photons or Zand Wbosons should be able to probe fermiophobic Higgs bosons in this mass range. 2.2 Fermiophobic Higgs diboson decays In addition to the WHH vertex in eq. (2.1), H0 Fwill have couplings to W W and ZZ pairs which are generated during EWSB and which will be proportional to the exotic Higgs vev [11,15,34,41,43]. We can parametrize these couplings generically with the following lagrangian, L ⊃ sθ H0 F vgZm2 ZZµZµ+ 2gWm2 WWµ+W− µ,(2.3) where gZand gWare fixed by the SU(2)L⊗U(1)Yrepresentation to which H0 Fbelongs. The factor of sθdefined in eq. (2.2) ensures that as the exotic Higgs vev tends to zero – 5 – JHEP06(2016)042 (i.e. sθ→0) the H0 FV V couplings vanish along with the VBF and VH production mechanisms. Again we assume we are in an ‘alignment’ limit so that no Higgs mass mixing angles enter into eq. (2.3). However, even in the case where they do, this dependence largely cancels when considering branching ratios since it enters as an overall factor along with the ‘vev mixing angle’ sθ. The ratio of the gZand gWcouplings, λW Z =gW/gZ,(2.4) is an important quantity and is fixed by custodial symmetry at tree level to be |λW Z|= 1 or |λW Z |= 1/2 for a custodial singlet and fiveplet respectively [66]. Though sizeable deviations from these two values are in principle possible, they are difficult to reconcile with electroweak precision data in a natural way. Therefore, in what follows we will consider only these two cases. Note also that a factor of sθhas been implicitly canceled in eq. (2.4). At one loop the gWcouplings in eq. (2.3) will also generate effective couplings to γγ and Zγ pairs via the Wboson loops shown in figure 3. We can parametrize these couplings with the effective operators, L ⊃ H0 F vcγγ 4FµνFµν +cZγ 2ZµνFµν,(2.5) where Vµν =∂µVν−∂νVµ. We again define similar ratios, λV γ =cV γ/gZ,(2.6) where V=Z, γ and we have implicitly absorbed a factor of sθinto gZ. There are also contributions to the effective couplings in eq. (2.5) from the additional charged Higgs bosons which are necessarily present. Depending on the Higgs potential, there may be dimensional parameters entering in the trilinear scalar couplings [11,15,34,41,43] which contribute to the charged scalar loop amplitude and which are independent of the exotic vev (sθ). In these cases one can easily obtain larger values of λV γ either by taking this new mass scale large compared to the weak scale or by taking the limit sθ1, thus suppressing the tree level coupling to ZZ and W W. In this case loop induced decays to W W and ZZ can also become relevant. The effective couplings in eq. (2.5) can also be enhanced when the loop particles carry large charges and interfere constructivly with the Wboson loop contribution [55]. However, these contributions could in principle conspire to cancel [67,68] leading to small cV γ effective couplings. If there are no exotic states light enough to decay into, and since there is no b¯ bdecay to compete with, the neutral fermiophobic Higgs bosons will decay almost entirely into electroweak gauge boson pairs and in particular photons at low masses [10,24,53–55]. Loop mediated decays to light SM fermions can occur thus violating the fermiophobic condition, but will be suppressed by the fermion masses and furthermore must be fixed by renormalization [5,6] in certain cases. Here we will assume the fermiophobic condition is maintained by either an appropriately chosen renormalization condition [8,9] or via a symmetry [15] such as custodial symmetry [34,41,43]. Under these assumptions the branching ratios of H0 Fwill only depend on the ratios in eq. (2.4) and eq. (2.6), and in some cases only on λW Z if the Wloop (see figure 3) dominates the H0 FV γ effective couplings. In this case any sθdependence in λV γ cancels explicitly. – 6 – JHEP06(2016)042 H0 F W± W± V γ W± V γ W± W± H0 F H0 F Z,W± Z,W∓ Figure 3. One loop contributions from Wboson loops to the H0 FV γ (V=Z, γ) effective couplings defined in eq. (2.5). Since the qualitative behavior of the branching ratios is largely dominated by phase space considerations, they will share many features in any fermiophobic Higgs model. At low masses, below ∼120–150 GeV, the branching ratio into pairs of photons starts to become significant and quickly dominant below the Wmass, or at higher masses if the couplings to photons are enhanced. At larger masses the three and four body decays involving Wand Zbosons become relevant and eventually completely dominant above the WW and ZZ thresholds. At even higher masses, either the ZZ or W W branching ratio can be the largest decay mode depending on the value of the ratio of the couplings, λW Z . We illustrate these features in figure 4where we show branching ratios for two different fermiophobic Higgs scenarios in the mass range 45–150 GeV. In both cases we take |λW Z|= 1, which is possible in all two Higgs doublet as well as Higgs triplet models. To obtain the three and four body decays we have integrated the analytic expressions for the H0 F→ V γ →2`γ and H0 F→V V →4`fully differential decay widths computed and validated in [69–71]. For the explicit Wloop functions which contribute to the effective couplings we use the parametrization and implementation found in [72]. The first scenario (solid curves) assumes the fermiophobic Higgs interactions are dominated by the couplings in eq. (2.3). In this case the effective couplings to Zγ and γγ are generated only by the Wloop shown in figure 3. This case has been considered previously in [4,5], but did not explicitly include the virtual photon contribution in H0 F→V∗γ→2fγ (purple curves) which is dominated by the γ∗γcomponent at low masses and can be as large as O(20%). While the size of this contribution depends on experimental phase space cuts, as emphasized in [69–75], virtual diphoton effects can provide valuable information in scalar decays. Note there is also the two body H0 F→Zγ decay, but it is less than 1% over this mass range. We also emphasize that in this case all of the H→V V decay amplitudes depend linearly on the exotic Higgs vev (or sθ) and thus the branching fractions will be independent of the vev. As we will discuss below, in some cases this vev independence of the branching ratios can be utilized, along with the Higgs pair production mechanism, to obtain constraints on fermiophobic scalars which are independent of the vev. – 7 – JHEP06(2016)042 γγ WW ZZ V γ ( V = Z , γ ) 50 100 150 200 0.01 0.05 0.10 0.50 1 MHF 0[GeV] BR(HF 0→VV) Figure 4. Branching ratios for H0 Fas a function of its mass where for all curves we have set |λW Z |= 1 (see eq. (2.4)). For the solid curves we have assumed the couplings to γγ and Zγ are generated only by the Wboson loop in figure 3. For the dashed curves we have taken the effective couplings to γγ and Zγ as free paramaters and set λγγ =λZγ = 0.05 (see eq. (2.6)). In the second scenario (dashed curves) we consider the possibility of generating large effective coupling to γγ and Zγ by taking λV γ =λγγ =λZγ = 0.05. This is to be compared to λV γ ∼0.005–0.01 from only the Wloop contribution which depends on the mass of H0 F. As discussed above, such large values for this ratio can easily be obtained2in the limit sθ1 if there exist additional mass scales apart from the Higgs vevs in the scalar potential or if the loop particles carry large charges. We see that in this case of enhanced couplings to photons the diphoton channel can be sizable all the way up to the WW threshold. We also see the H0 F→V γ →2fγ three body decay through an off-shell photon or Zcan also be sizable for masses up to ∼130 GeV and may be interesting to study further. Depending on how these large effective couplings are generated, there may be a dependence on the exotic Higgs vev introduced into the branching ratios. However, even in this case the branching ratios are still largely independent of the vev since over much of the mass range either the γγ (and γ∗γ) decay dominates, or W W and ZZ decays dominate. The same holds true if the effective couplings to γγ and Zγ are highly suppressed due to cancellations. Thus one can again obtain limits on fermiophobic Higgs bosons which are independent of their vevs. However, it would be interesting to consider a detailed analysis of H0 Fmasses above the Zmass and below the WW threshold where all decays can in principle be sizeable simultaneously and where the vev dependence can be non-negligible. In both cases considered in figure 4we see the universal features of a fermiophobic Higgs boson. Namely, large branching ratios into photons at lower masses and large branching ratios to WW and ZZ at larger masses. As we will demonstrate below, these diboson decays can be combined along with the Higgs pair production mechanism to provide strin2As an explicit example if we take H0 Fto be ∼160 GeV and to be the neutral component of the custodial fiveplet scalar found in custodial Higgs triplet models [11,15,34,41,43], we find that for trilinear couplings A∼15 sθTeV, ratios of λγγ ∼0.05 can be easily obtained via the contribution from its (degenerate) doubly charged component. Note that such light masses are not ruled out by previous searches for the doubly (or singly) charged component when sθ.0.3 [42]. – 8 – JHEP06(2016)042 extensions of the SM Higgs sector and generally the dominant DY Higgs pair production mechanism. We have emphasized that this production mechanism does not vanish in the limit of small exotic Higgs vacuum expectation value, unlike vector boson fusion and associated vector boson production. Since measurements of the SM-like 125 GeV Higgs boson imply small exotic Higgs vacuum expectation values, previous searches for fermiophobic Higgs bosons which assumed vector boson fusion and associated vector boson production are now obsolete. We have shown that by combining the Higgs pair production mechanism with diphoton searches, one can put stringent and rather generic bounds on fermiophobic Higgs bosons already with 8 TeV LHC diphoton data. These limits are stronger and more general than those obtained in a very recent CDF 4γ+Xsearch [56] which are currently the only other relevant direct constraints on a fermiophobic Higgs boson in the small vev limit. In particular, we find that while Tevatron diphoton searches are not sensitive to fermiophobic Higgs bosons, the larger Higgs pair production cross sections at 8 TeV LHC allow us to already generically rule out a neutral fermiophobic Higgs boson below ∼110 GeV for degenerate masses and under the assumption that the couplings to photons are generated dominantly by a Wboson loop. We have also emphasized that this degenerate mass scenario is not ruled out by Tevatron data. If there is a mass splitting as large as ∼100 GeV, we find masses below ∼100 GeV can be excluded. Furthermore, we find that if the couplings to photons are enhanced, masses up to ∼150 GeV can be ruled out, while if cancellations conspire to give very small effective coupling to photons, fermiophobic Higgs scalars below ∼90 GeV can still be ruled out by diphoton searches at 8 TeV. This makes diphoton searches a robust and sensitive probe of lighter fermiophobic scalars. Of course a dedicated multiphoton search at the LHC including the charged Higgs decay, as done at Tevatron, should improve limits further and is an important complementary probe. We have also combined the H±H0 F Higgs pair production channel with WW and ZZ diboson searches to probe fermiophobic Higgs masses up to ∼250 GeV. We find that while 8 TeV searches are not yet sensitive, the prospects for 13 TeV LHC are very promising if current limits can be improved by about an order of magnitude with future data. The inclusion of NLO Higgs pair production effects as well as other subdominant production mechanisms may also further improve the limits discussed in this study. Finally, we have examined the particular case of a custodial fiveplet scalar found in all incarnations of custodial Higgs triplet models [34,41,43] in which the neutral and charged component are predicted to be degenerate. Thus the CDF 4γ+Xsearch [56] cannot be applied to this case. We have shown for the first time that a custodial fiveplet scalar below ∼110 GeV is ruled out by 8 TeV diphoton searches and possibly up to higher masses if charged scalar loops produce large constructive contributions to the effective photon couplings. These limits are also largely independent of the Higgs triplet vev and so robustly close the ‘fiveplet window’ at masses below ∼110 GeV [42], still allowed by electroweak precision and 125 GeV Higgs boson data. We also find that diboson searches, and in particular ZZ searches, may be useful for larger fiveplet masses, allowing us to potentially obtain limits again independently of the Higgs triplet vev. – 15 – JHEP06(2016)042 To summarize, by combining the pp →W±→H±H0 FHiggs pair production mechanism with H0 F→V V diphoton and diboson decays, one obtains a powerful probe at the LHC of fermiophobic Higgs bosons for masses up to ∼250 GeV. These searches are sensitive even in the limit of vanishing exotic Higgs vev and open a yet to be explored avenue to search for fermiophobic Higgs bosons at the LHC in both current and future data. Acknowledgments We would like to thank Yi Chen, Jorge de Blas, Francisco del Aguila, Adam Falkowski, Heather Logan, Javi Serra, Daniel Stolarski, and Roberto Vega for helpful discussions. R.V.M. would like to especially thank Kunal Kumar for help with Madgraph/Feynrules model implementations. We also would like to thank the Ecole de Physique des Houches for creating a stimulating atmosphere where this project was started. The work of A.D. is partly supported by the National Science Foundation under grant PHY-1520966. The work of J.S. and R.V.M. is supported by MINECO, under grant number FPA2013-47836-C32-P. J.S. is also supported by the European Commission contract PITN-GA-2012-316704 (HIGGSTOOLS) and by Junta de Andaluc´ıa grants FQM 101 and FQM 6552. The work of M.G. P. and M.Q. is partly supported by MINECO under Grant CICYT-FEDER-FPA201455613-P, by the Severo Ochoa Excellence Program of MINECO under Grant SO-2012-0234, and by Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya under Grant 2014 SGR 1450. Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. References [1] CMS collaboration, Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC,Phys. Lett. B 716 (2012) 30 [arXiv:1207.7235] [INSPIRE]. [2] ATLAS collaboration, Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC,Phys. Lett. B 716 (2012) 1 [arXiv:1207.7214] [INSPIRE]. [3] H. Pois, T.J. Weiler and T.C. 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