A
bstract
The existence of an axion-like particle (ALP) would induce anomalous scattering of light by light. This process can be probed at the Large Hadron Collider in central exclusive production of ...photon pairs in proton-proton collisions by tagging the surviving protons using forward proton detectors. Using a detailed simulation, we estimate the expected bounds on the ALP-photon coupling for a wide range of masses. We show that the proposed search is competitive and complementary to other collider bounds for masses above 600 GeV, especially for resonant ALP production between 600 GeV and 2 TeV. Our results are also valid for a CP-even scalar, and the efficiency of the search is independent of the width of the ALP.
We consider the possibility that the diphoton excess at 750 GeV is caused by a new scalar resonance produced in photon fusion. This scenario is parametrized by only one relevant effective couplings ...and is thus minimal. We show that this setup can reproduce both the production rate and width of the resonance, and is not in conflict with the 8 TeV limits on the diphoton cross section. The scenario also predicts event rates for WW, ZZ, Zgamma final states. We suggest for one to perform precision measurements by studying light-by-light scattering with intact protons detected in forward detectors. We construct a simple model that shows that the required couplings can be achieved with new vectorlike, uncolored fermions (with a strong Yukawa coupling to the resonance) which may also account for the required width.
We study the discovery potential of axion-like particles (ALP), pseudo-scalars weakly coupled to Standard Model fields, at the Large Hadron Collider (LHC). Our focus is on ALPs coupled to the ...electromagnetic field, which would induce anomalous scattering of light-by-light. This can be directly probed in central exclusive production of photon pairs in ultra-peripheral collisions at the LHC in proton and heavy-ion collisions. We consider non-standard collision modes of the LHC, such as argon-argon collisions at sNN=7 TeV and proton-lead collisions at sNN=8.16 TeV, to access regions in the parameter space complementary to the ones previously considered for lead-lead and proton-proton collisions. In addition, we show that, using laser beam interactions, we can constrain ALPs as resonant deviations in the refractive index induced by anomalous light-by-light scattering effects. If we combine the aforementioned approaches, ALPs can be probed in a wide range of masses from the eV scale up to the TeV scale.
A slight excess has been observed in the first data of photon-photon events at the 13 TeV Large Hadron Collider that might be interpreted as a hint of physics beyond the standard model. We show that ...a completely model-independent measurement of the photon-photon coupling of a putative 750 GeV resonance is possible using the forward proton detectors scheduled at ATLAS and CMS.
A
bstract
The sensitivities to the anomalous quartic gauge boson coupling
γγγZ
are estimated via
γZ
production with intact protons in the forward region at the LHC. Proton tagging proves to be a ...powerful tool to suppress the background, which allows consideration of the hadronic decays of the
Z
boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of 300 fb
−1
and 3000 fb
−1
. The sensitivity we obtain at 300 fb
−1
goes beyond the one expected from LHC bounds on the
Z
→
γγγ
decay by about three orders of magnitude. The
γZ
channel provides important discriminatory information with respect to the exclusive
γγ
channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.
A
bstract
We present a phenomenology study on central exclusive production of
W
+
W
−
boson pairs in proton-proton collisions at the Large Hadron Collider at 14 TeV using the forward proton ...detectors, such as the ATLAS Forward Proton or the CMS-TOTEM Precision Proton Spectrometer detectors. Final states where at least one of the
W
bosons decay hadronically in a large-radius jet are considered. The latter extends previous efforts that consider solely leptonic final states. A measurement of exclusive
W
+
W
−
also allows us to further constrain anomalous quartic gauge boson interactions between photons and
W
bosons. Expected limits on anomalous quartic gauge couplings
a
0
,
C
W
associated to dimension-six effective operators are derived for the hadronic, semi-leptonic, and leptonic final states. It is found that the couplings can be probed down to one-dimensional values of
a
0
W
=
3.7
×
10
−
7
GeV
−
2
and
a
C
W
=
9.2
×
10
−
7
GeV
−
7
at 95% CL at an integrated luminosity of 300 fb
−
1
by combining all final states, compared to values of about
a
0
W
=
4
×
10
−
6
GeV
−
2
and
a
C
W
=
1
×
10
−
5
GeV
−
2
at 95% CL expected for the leptonic channel alone.
A
bstract
We present a phenomenological analysis of events with two high transverse momentum (
p
T
) jets separated by a large (pseudo-)rapidity interval void of particle activity, also known as ...jet-gap-jet events. In the limit where the collision energy
s
is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between partons within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) limit of perturbative quantum chromodynamics (QCD). The BFKL pomeron exchange amplitudes, with resummation at the next-to-leading logarithmic approximation, have been embedded in the PYTHIA8 Monte Carlo event generator. Standard QCD dijet events are simulated at next-to-leading order in
α
s
matched to parton showers with POWHEG+PYTHIA8. We compare our calculations to measurements by the CDF, D0, and CMS experiments at center-of-mass energies of 1.8, 7 and 13 TeV. The impact of the theoretical scales, the parton densities, final- and initial-state radiation effects, multiple parton interactions, and
p
T
thresholds and multiplicities of the particles in the rapidity gap on the jet-gap-jet signature is studied in detail. With a strict gap definition (no particle allowed in the gap), the shapes of most distributions are well described except for the CMS azimuthal-angle distribution at 13 TeV. The survival probability is surprisingly well modelled by multiparton interactions in PYTHIA8. Without multiparton interactions, theoretical predictions based on two-channel eikonal models agree qualitatively with fits to the experimental data.
The TOTEM Collaboration has measured the differential cross section of elastic proton-proton scattering dσ/d|t| at s=2.76, 7, 8, and 13 TeV. It is observed that all dσ/d|t| data points vary in the ...same way as a function of the center-of-mass energy in the so-called “dip” and “bump” regions. These features hint at possible universal properties of elastic scattering. Based on these empirical observations, and taking inspiration from saturation models, we propose a simple scaling law for proton-proton elastic scattering at LHC energies. We find that the dσ/d|t| at LHC energies fall onto a universal curve when they are mapped to the scaling variables dσ/d|t|×(s/TeV2)−0.305 versus (s/TeV2)0.065(|t|/GeV2)0.72. Some implications of this scaling law in the impact parameter picture of the scattering amplitudes are explored.
The sensitivities to anomalous quartic photon couplings at the Large Hadron Collider are estimated using diphoton production via photon fusion. The tagging of the protons proves to be a very powerful ...tool to suppress the background and unprecedented sensitivities down to 7 x 10 super(-15) GeV-4 are obtained, providing a new window on extra dimensions and strongly interacting composite states in the multi-TeV range. Generic contributions to quartic photon couplings from charged and neutral particles with arbitrary spin are also presented.
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