4 pages, 3 figures, to appear in the proceedings of DIS2008, the XVI International Workshop on Deep-Inelastic Scattering and Related Subjects, 7-11 April 2008, University College London
Experimental prospects for studying high-energy photon-photon and photon-proton interactions at the LHC are discussed. Assuming a typical LHC multipurpose detector, various signals and their irreducible backgrounds are presented after applying acceptance cuts. Selection strategies based on photon interaction tagging techniques are presented. Prospects are discussed for the Higgs boson search, detection of SUSY particles and of anomalous quartic gauge couplings, as well as for the top quark physics.
Yield of direct photons in Pb+Pb collisions at SpS and LHC energy is evaluated with emphasis on estimate of possible uncertainty. Possibility of experimental observation of direct photons at LHC is discussed. Predictions of several models at SpS energy are compared with experimental data.
We review various production mechanisms of photons and small mass dileptons at large transverse momentum in heavy ion collisions at the LHC. Their relevance as a signal for quark-gluon plasma formation is discussed.
We present POWHEG predictions for photon-jet correlations at RHIC and the LHC. We show that the total transverse-momentum spectrum of photons and jets is modified not only by medium, but also by higher-order QCD effects, as is the distribution in their relative azimuthal angle. At the LHC, photon-jet measurements in the forward region allow to probe parton momentum fractions of lead ions down to 10$^{-4}$.
In the Randall-Sundrum model there can be a rich new phenomenology associated with Higgs-radion mixing. A photon-photon collider would provide a crucial complement to the LHC and a future ILC collider for fully determining the parameters of the model and definitively testing it.
The search for an intermediate mass Higgs boson at the LHC needs the quantitative understanding of the two-photon background. A calculation of two-photon production in hadronic collisions at full next-to-leading order is described. It includes photons originating from the hadronization of QCD partons which play an important role at the LHC. A prediction for the invariant mass distribution for photon pairs at the LHC is presented and finally the residual scale dependencies are discussed.
We investigate the sensitivity of the heavy ion mode of the LHC to Higgs boson and Radion production via photon-photon fusion through the analysis of the processes photon to photon photon, photon photon to b anti-b, and photon photon to g g in peripheral heavy ion collisions. We suggest cuts to improve the Higgs and Radion signal over standard model background ratio and determine the capability of LHC to detect these particles production.
The exclusive production pp->pXp is known to be one of the most clean channels at the LHC. We investigate the potential of processes pp -> p l-l+ p and pp-> p gamma gamma p to probe scalar and tensor unparticles by considering three different forward detector acceptances; 0.0015<xi<0.15, 0.0015<xi<0.5 and 0.1<xi<0.5. We obtain 95% confidence level sensitivity limits on the unparticle couplings for various integrated luminosities.
We investigate the sensitivity of the heavy ion mode of the LHC to anomalous Higgs boson couplings to photons, H-photon-photon, through the analysis of the processes photon photon to b anti-b and photon photon to photon photon in peripheral heavy ion collisions. We suggest cuts to improve the signal over background ratio and determine the capability of LHC to impose bounds on anomalous couplings by searching for a Higgs boson signal in these modes.
We discuss the complementarity between the LHC and a low energy photon collider. We mostly consider the scenario, where the first linear collider is a photon collider based on dual beam technology like CLIC.
We use the POMWIG Monte Carlo generator to predict the cross-sections for double diffractive higgs and di-photon production at the Tevatron and LHC. We find that the higgs production cross-section is too small to be observable at Tevatron energies, and even at the LHC observation would be difficult. Double diffractive di-photon production, however, should be observable within one year of Tevatron Run II.
The DGLAP improved color dipole approach provides a good description of data for inclusive direct photon spectra at the energies of RHIC and Tevatron. Within the same framework we predict the transverse momentum distribution of direct photons at the CERN LHC energies.
We report on recent studies of photon-induced (PI) contributions to di-lepton production and their implications for Beyond Standard Model (BSM) $Z^\prime$-bosons searches at the LHC.
The capability of the LHC to study the electromagnetic dipole moments of the top quark is discussed. In particular, the process $pp\to pγγp\to pt\bar{t}p$, which is supposed to be tagged by the forward/backward detectors at the LHC experiments, is used to explore the top quark electric and magnetic moments. We perform analytical calculations and then a numerical analysis on the sensitivity of the total cross section of the top quark pair production in $γγ$ scattering at the LHC to the anomalous top quark couplings with photon. It is shown that improvements in the bounds on the electromagnetic …
We present some physics topics that can be studied at the LHC using proton tagging. We distinguish the QCD (Pomeron structure, BFKL analysis...) from the exploratory physics topics (HIggs boson, anomalous couplings between photons and $W/Z$ bosons)
Transverse momentum imbalance between a jet produced with a hard photon is considered as a signal of medium-induced partonic energy loss in ultrarelativistic heavy ion collisions. We analyze photon-jet correlation in the context of a real experimental situation at the LHC, the problem of neutral pion background being discussed.
Many extensions of the SM contain hidden sectors which are uncharged under the SM gauge group. The simplest model with an additional $U(1)$ group predicts the existence of the new gauge boson, dark photon $Z_D$. In this work we consider single production of dark photon $Z_D$ at the LHC and study its discovery potential via the process $pp\rightarrow Z_Dγ\rightarrow llγ$. After simulating the signal as well as the relevant backgrounds, the numerical results show that the signal of $Z_D$ might be detected at the 14TeV LHC.
Due to coherence, there are strong electromagnetic fields of short duration in very peripheral heavy ion collisions. They give rise to photon-photon and photon-nucleus collisions with high flux. Photon-photon and photon-hadron physics at various invariant mass scales are discussed.
We show the SM prediction of di-lepton production at the LHC where to the usual Drell-Yan production we add the contribution from Photon-Initiated processes. We discuss the effects of the inclusion of photon interactions in the high invariant mass region (TeV region) and their consequences on BSM heavy Z'-boson searches.
We study the W/Z pair production via two-photon exchange at the LHC and give the sensitivities on trilinear and quartic gauge anomalous couplings between photons and W/Z bosons for an integrated luminosity of 30 and 200 fb^{-1}. For simplicity and to obtain lower backgrounds, only the leptonic decays of the electroweak bosons are considered.
The cross sections for the reaction $γγ\rightarrow 4\ell$ in proton--proton collisions are calculated at the LHC energies. We show that the purely electroweak process $γγ\rightarrow 4\ell$ can be studied at the LHC and can constitute a background to other processes with $4\ell$ or $2\ell$ final states.
The photon-induced processes at the $LHC$ provide clean experimental conditions due to absence of the proton remnants, which might produce complementary and interesting results for tests of the standard model and for searching of new physics. In the context of the littlest $Higgs$ model with T-parity, we consider the photon-induced production of the mirror quarks at the $LHC$. The cross sections for various production channels are calculated and a simply phenomenology analysis is performed by assuming leptonic decays.
We provide a discussion of the impact of a subset of Drell-Yan data from LHC on the determination of the photon parton distribution function (PDF), using the NNPDF methodology. In previous work we have shown that the photon PDF determined from deep-inelastic scattering (DIS) data only has large uncertainties, suggesting the need for more data from other processes such as Drell-Yan, which unlike DIS, includes photon-induced contributions at leading order in QED. We describe the inclusion of ATLAS Drell-Yan W, Z data, which is a subset of the LHC data used in a final photon PDF determination, by…
We discuss the potential of the photon-induced two lepton final states at the LHC to explore the phenomenology of the Kaluza-Klein (KK) tower of gravitons in the scenarios of the Arkani-Hamed, Dimopoulos and Dvali(ADD) model and Randall-Sundrum (RS) model. The sensitivity to model parameters can be improved compared to the present LEP or Tevatron sensitivity.
We present a new method to test the Standard Model expectations at the LHC using photon-induced $WW$ production. Both $W$ decay in the main ATLAS or CMS detectors while scattered protons are measured in forward detectors. The sensitivity to anomalous $WWγ$ triple gauge coupling can be improved by more than a factor 5 or 30 compared to the present LEP or Tevatron sensitivity respectively.
We compute the QCD corrections to the gluon fusion subprocess gg to gamma gamma, which forms an important component of the background to the search for a light Higgs boson at the LHC. We study the dependence of the improved pp to gamma gamma X background calculation on the factorization and renormalization scales, on various choices for photon isolation cuts, and on the rapidities of the photons. We also investigate ways to enhance the statistical significance of the Higgs signal in the di-photon channel.
In "$η_c$ production in photon-induced interactions at the LHC," \cite{Goncalves:2018yxc} Goncalves and Moreira discuss inclusive and exclusive $η_c$ production at $pp$ and $pA$ collisions at LHC energies. The exclusive channels are via two-photon and photon-Odderon interactions. This comment points out that there is a large additional source of almost-exclusive $η_c$ in ultra-peripheral collisions: from the radiative decay of $J/ψ$ that are produced in photon-nucleon interactions. Although the $J/ψ\rightarrowγη_c$ branching ratio is small, the $J/ψ$ production cross-section is large enough th…
LHC collisions can act as a source of photons in the initial state. This mechanism plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme. I will discuss the possibility of modelling PI processes directly via the structure function approach. This can provide percent level precision in the production cross sections, and is therefore well positioned to account for LHC precision requirements. This formalism in addition allows one to make use o…
The LHC potential for a measurement of the Higgs boson coupling to the b quark in the standard model is not well established yet. We show that requiring a large transverse momentum photon in the light Higgs boson production via vector-boson fusion (with subsequent H->bb decay) could provide a further handle on the Hbb coupling determination, and on the measurement of the HWW coupling as well.
We review several most recent prompt-photon measurements at HERA and the Tevatron and discuss their implication for future measurements at the LHC. A comparison to Monte Carlo models, as well as to NLO QCD predictions based on the standard DGLAP and the kT-factorization approaches is discussed. Effects from renormalization and factorization scale uncertainties, as well as uncertainties on the gluon density distribution inside a proton are discussed.
We show how the well studied $γγ$ inclusive Higgs signal can be used at the Large Hadron Collider to test Gauge Mediated Supersymmetry Breaking scenarios in which a rather heavy Higgs boson decays into two light neutralinos, the latter yielding two photons and missing (transverse) energy
In this contribution, we review the results of the recent paper "The photon PDF from high-mass Drell Yan data at the LHC" (arXiv:1701.08553), where a determination of the photon PDF from fits to recent ATLAS measurements of high-mass Drell-Yan dilepton production at centre-of-mass energy of 8 TeV is presented.
The associated production of direct photons and heavy quarks at the LHC is presented. Predictions for the nuclear modification factor to the cross-section at ALICE are shown. It is demonstrated that this process is a great probe of the gluon and heavy quark nuclear PDFs, as over 80 % of its nPDF dependence at NLO comes from those nPDFs. Therefore measurements of this process will provide an excellent constraint on the gluon nPDF, and will distinguish between different nPDF sets currently out on the market.
In this contribution we study for the first time the prompt photon production in single and double diffractive processes considering the resolved Pomeron model. We estimate the rapidity and transverse momentum dependence of the cross section for the production of two photons and of a photon and a jet. We show that these processes are sensitive to the pomeron structure. In contrast with the dijet and heavy quark production, which are dominated by gluon-gluon interactions, in prompt photon production, Compton like processes are dominant for single photon plus jet events. This gives a unique opor…
Within the resolved Pomeron model of hard diffractive scattering, we compute prompt photon production in double-Pomeron-exchange events in proton-proton collisions. Using specific kinematical constraints chosen according to the acceptances of the forward proton detectors of experiments at the Large Hadron Collider, we provide estimates for inclusive and isolated photon production. This is done using the JetPhox program. We find that next-to-leading order corrections to the hard process are important and must be included in order to correctly constrain the quark and gluon content of the Pomeron…
Exclusive production of neutrinos via photon-photon fusion provides an excellent opportunity to probe electromagnetic properties of the neutrinos at the LHC. We explore the potential of processes pp-> p gamma gamma p -> p nu anti-nu p and pp -> p gamma gamma p -> p nu anti-nu Z p to probe neutrino-photon and neutrino-two photon couplings. We show that these reactions provide more than seven orders of magnitude improvement in neutrino-two photon couplings compared to LEP limits.
The standard model production of two photons is one of the most important backgrounds to light Higgs boson production at the LHC. In this talk we discuss the di-photon background, with emphasis on the effects of the recently calculated next-to-leading-order (NLO) corrections to the gluon-gluon-initiated component. We find that the $K$-factor for this component is smaller than that for the analogous $gg\to H$ process, and that the correction to the total irreducible di-photon production is modest. We also investigate ways to enhance the statistical significance of the Higgs signal in the $γγ$ c…
I present a determination of the photon PDF from a fit to the recent ATLAS measurements of high-mass Drell-Yan lepton-pair production at $\sqrt{s} = 8$ TeV. This analysis is based on the {\tt xFitter} framework interfaced to the {\tt APFEL} program, that accounts for NLO QED effects, and to the {\tt aMCfast} code to account for the photon-initiated contributions within {\tt MadGraph5\_aMC@NLO}. The result is compared with other recent determinations of the photon PDF finding a general good agreement.
In this paper we investigate the hadron and photon production at forward rapidities in $pp$ and $pA$ collisions considering two phenomenological models based on the Color Glass Condensate formalism. The predictions of these models for the hadron spectra are compared with the dAu and pp RHIC data and the nuclear modification factor $R_{hA}$ is estimated. Our results demonstrate that the analysis of the transverse momentum dependence of this factor allows to discriminate between the phenomenological models. Furthermore, we predict $R_{hA}$ for photon production at forward rapidities at RHIC and …
We study the possibility to analyse the data on inclusive prompt photon production at first LHC runs in the framework of the kt-factorization QCD approach. Our consideration is based on the amplitude for the production of a single photon associated with a quark pair in the fusion of two off-shell gluons. The quark component is taken into account separately using the quark-gluon Compton scatterring and quark-antiquark annihilation QCD subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin (KMR) prescription as well as the CCFM evolution equatio…
We first report on possible measurements at the LHC using the first data and a luminosity of 10 pb$^{-1}$ of $W$ and $Z$ pair production via two-photon exchange. This measurement allows in particular to increase the present sensitivity on $WWγγ$ and $ZZγγ$ quartic anomalous couplings from the LEP experiments by almost three orders of magnitude. We also discuss the possible improvements on quartic and trilinear anomalous couplings at high luminosity at the LHC using new forward proton taggers to be installed at 220 and 420 m from the CMS or ATLAS detectors.
The rates for diffractive quarkonium plus prompt-photon associated production at the LHC are estimated. The theoretical framework considered in the J/Psi (or Upsilon) production associated with a direct photon at the hadron collider is the non-relativistic QCD (NRQCD) factorization formalism. The corresponding single diffractive cross section is computed based on the hard diffractive scattering factorization supplemented by absorptive corrections. Such processes are sensitive to the gluon content of the Pomeron at small Bjorken-x and they may also be a good place to test the different availabl…
We present updated predictions on the inclusive total cross sections, including the complete next-to-leading order QCD corrections, for the graviton and photon associated production process in the large extra dimensions model at the LHC with a center-of-mass energy of 7 and 8 TeV, using the parameters according to the requirements of the ATLAS and CMS Collaborations. Moreover, we also discuss in detail the dependence on the transverse momentum cut and uncertainties due to the choices of scales and parton distribution functions.
The reconstruction of non pointing photons is a key feature for studying gauge mediated supersymmetry breaking (GMSB) models at the LHC. In this article the angular resolution of the ATLAS electromagnetic calorimeter is characterized from a detailed simulation of the detector. Resulting performances are used to reconstruct GMSB events with a fast simulation program, taking into account reconstruction effects. Finally, the sensitivity to extract the sparticles masses and the lightest neutralino lifetime is estimated.
We consider a color octet scalar particle and its exotic decay in the channel gluon-$γ$ using an effective Lagrangian description for its strong and electromagnetic interactions. Such a state is present in many extensions of the Standard Model, and in particular in composite Higgs models with top partial compositeness, where couplings to photons arise via the Wess-Zumino-Witten term. We find that final states with one or two photons allow for a better reach at the LHC, even for small branching ratios. Masses up to $1.2$ TeV can be probed at the HL-LHC by use of all final states. Finally, we es…
Little Higgs theory naturally predicts a light Higgs boson whose most important discovery channel at the LHC is the di-photon signal $pp\to h\to γγ$. In this work we perform a comparative study for this signal in some typical little Higgs models, namely the littlest Higgs model (LH), two littlest Higgs models with T-parity (named LHT-I and LHT-II) and the simplest little Higgs modes (SLH). We find that compared with the Standard Model prediction, the di-photon signal rate is always suppressed and the suppression extent can be quite different for different models. The suppression is mild ($\lsi…
We study the hadron collider phenomenology of (1,0) Kaluza-Klein modes along two universal extra dimensions compactified on the chiral square. Cascade decays of spinless adjoints proceed through tree-level 3-body decays involving leptons as well as one-loop 2-body decays involving photons. As a result, spectacular events with as many as six charged leptons, or one photon plus four charged leptons are expected to be observed at the LHC. Unusual events with relatively large branching fractions include three leptons of same charge plus one lepton of opposite charge, or one photon plus two leptons…
The recent results of 13 TeV ATLAS and CMS di-photon searches show an excess at di-photon invariant mass of 750 GeV. We look for possible explanation of this within minimal left right symmetric model (MLRSM). The possible candidate is a neutral Higgs of mass 750 GeV that can decay to di-photon via charged Higgs and right handed gauge boson loop. However, the cross-section is not consistent with the ATLAS and CMS results. We then discuss one possible variation of this model with universal seesaw for fermion masses that can explain this excess.
In this paper we explore the use of results on forward particle production at the LHC to constrain nuclear Parton Density Functions (nPDFs). The case study here is based on a possible future measurement of forward photon production with the Forward Calorimeter that is currently under discussion as an upgrade of the ALICE experiment. As a starting point, we use the recent nNNPDF 1.0 nuclear PDFs, which have been determined using fixed target neutral-current DIS data, which constrain the gluon density at x > $10^{-2}$. The Bayesian reweighting technique is used to include the constraints from th…
We present Next-to-Leading Order (NLO) predictions for $γγγγ$ final states, including the effects of photon fragmentation. Our results are calculated fully analytically using the techniques of $D$-dimensional unitarity, and we discuss some refinements to existing methods, focusing particularly on the role of three-mass triangle coefficients. Using these techniques we are able to produce a numerically stable Monto Carlo code that runs fully in double precision. We investigate the $4γ$ signal at colliders, both for Run II of the LHC and at future machines. Our results are implemented in MCFM.
Using a momentum space model for the dipole scattering amplitude we present an analysis of the saturation effects at LHC energies, describing the data on proton-proton and proton-lead collisions. The model is based on the asymptotic solutions of the Balitsky-Kovchegov equation, being ideal in the saturation domain where the target wave function has a high occupation number. We also make predictions for the nuclear modification ratios on charged hadron and prompt photon production in the forward region, where the high parton density effects are important.
Considering the experimental constraints given by CMS collaboration at $\sqrt{s} = 8$ TeV on the strength of top quark flavour-changing neutral-current (FCNC) couplings $tqγ$ and $tqg$, we investigate the production of top quark in association with a photon and carry out a full simulation for the signals $\ellνbγ$ and $jjbγ$ at 14 TeV LHC. In our numerical analysis, the contributions of single top production with a photon radiation off the top decay products are also included. The discovery potential for anomalous couplings $tqγ$ and $tqg$ with an integrated luminosity of 100 fb$^{-1}$ are exa…
We investigate the rapidity and transverse momentum distributions of the prompt photon production at the CERN LHC energies considering the current perturbative QCD approaches for this scattering process. Namely, we compare the predictions from the usual NLO pQCD calculations to the the color dipole formalism, using distinct dipole cross sections. Special attention is paid to parton saturation models at high energies, which are expected to be important at the forward rapidities in pp collisions at the LHC.
We reconsider the inclusive production of isolated prompt photons in $pp$ collisions at the LHC energies in the framework of $k_T$-factorization approach. Our analysis is based on the ${\cal O}(αα_s)$ off-shell (depending on the transverse momenta of initial quarks and gluons) production amplitudes of $q^* g^* \to γq$ and $q^* \bar q^* \to γg$ partonic subprocesses and transverse momentum dependent (or unintegrated) quark and gluon densities in a proton, which are chosen in accordance with the Kimber-Martin-Ryskin prescription. We show that the sub-leading high-order ${\cal O}(αα_s^2)$ contrib…
We reexamine the prospects of searching for a neutral Higgs boson in the intermediate-mass range, using the proton- and ion-beam facilities of the LHC to study coherent two-photon processes. Considering realistic design luminosities for the different ion beams, we find that beams of light-to-medium size ions like calcium will give the highest production rates. With a suitable trigger and assuming a b-quark identification efficiency of $30\%$ and a $b{\bar b}$ mass resolution of 10 GeV one could expect to see a Higgs signal in the $b{\bar b}$ channel with a 3-4 $σ$ statistical significance in t…
LHC has reported tantalizing hints for a Higgs boson of mass 125 GeV decaying into two photons. We focus on two-Higgs-doublet Models, and study the interesting possibility that the heavier scalar (H) has been seen, with the lightest scalar (h) having thus far escaped detection. Non-observation of h at LEP severely constrains the parameter-space of two-Higgs-doublet models. We analyze cases where the decay H --> h h is kinematically allowed, and cases where it is not, in the context of type I, type II, lepton-specific, and flipped models.
Probing the Axion--Photon--Dark Photon Interaction with LHC Mono-Photons and Fermi-LAT Gamma-Ray Lines
National Taiwan Normal University（台湾师范大学）；Sichuan University（四川大学）；National Center for Theoretical Sciences, National Taiwan University（台湾大学理论科学中心）；Phenikaa Institute for Advanced Study, Phenikaa University（菲尼亚卡大学先进研究院）
We show that the photon-photon fusion process contributes significantly to the pair production of doubly charged Higgs bosons at the LHC at a level comparable to the Drell-Yan production. We reinterpret the ATLAS lower limit of 570 GeV (420 GeV) on the mass of $Δ_{L}^{\pm\pm}$ ($Δ_{R}^{\pm\pm}$) arising from $SU(2)_L$ triplet (singlet) scalar by including the photon initiated process and derive a new lower limit of 748 GeV (570 GeV), assuming that $Δ^{\pm \pm}$ decays into $e^\pm e^\pm$ 100% of the time. We have also shown that the 5$σ$ discovery reach for ${Δ_{L}^{\pm\pm}}$ (${Δ_{R}^{\pm\pm}}…
