Publications by Lucian Harland-Lang

Searching for the odderon in ultraperipheral proton-ion collisions at the LHC

PHYSICAL REVIEW D 99 (2019) ARTN 034011

LA Harland-Lang, VA Khoze, AD Martin, MG Ryskin

On the consistent use of scale variations in PDF fits and predictions


LA Harland-Lang, RS Thorne

A fresh look at ALP searches in fixed target experiments

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 793 (2019) 281-289

L Harland–Lang, J Jaeckel, M Spannowsky

© 2019 A significant number of high power proton beams are available or will go online in the near future. This provides exciting opportunities for new fixed target experiments and the search for new physics in particular. In this note we will survey these beams and consider their potential to discover new physics in the form of axion-like particles, identifying promising locations and set ups. To achieve this, we present a significantly improved calculation of the production of axion-like particles in the coherent scattering of protons on nuclei, valid for lower ALP masses and/or beam energies. We also provide a new publicly available tool for this process: the Alpaca Monte Carlo generator. This will impact ongoing and planned searches based on this process.

Ad Lucem: QED parton distribution functions in the MMHT framework


LA Harland-Lang, AD Martin, R Nathvani, RS Thorne

LHC searches for Dark Matter in compressed mass scenarios: challenges in the forward proton mode


LA Harland-Lang, VA Khoze, MG Ryskin, M Tasevsky

Exclusive LHC physics with heavy ions: SuperChic 3.

The European physical journal. C, Particles and fields 79 (2019) 39-39

LA Harland-Lang, VA Khoze, MG Ryskin

We present results of the updated SuperChic 3 Monte Carlo event generator for central exclusive production. This extends the previous treatment of proton-proton collisions to include heavy ion (pA and AA) beams, for both photon and QCD-initiated production, the first time such a unified treatment of exclusive processes has been presented in a single generator. To achieve this we have developed a theory of the gap survival factor in heavy ion collisions, which allows us to derive some straightforward results about the A scaling of the corresponding cross sections. We compare against the recent ATLAS and CMS measurements of light-by-light scattering at the LHC, in lead-lead collisions. We find that the background from QCD-initiated production is expected to be very small, in contrast to some earlier estimates. We also present results from new photon-initiated processes that can now be generated, namely the production of axion-like particles, monopole pairs and monopolium, top quark pair production, and the inclusion of W loops in light-by-light scattering.

Towards ultimate parton distributions at the high-luminosity LHC

European Physical Journal C 78 (2018)

RA Khalek, S Bailey, J Gao, L Harland-Lang, J Rojo

© 2018, The Author(s). Since its start of data taking, the LHC has provided an impressive wealth of information on the quark and gluon structure of the proton. Indeed, modern global analyses of parton distribution functions (PDFs) include a wide range of LHC measurements of processes such as the production of jets, electroweak gauge bosons, and top quark pairs. In this work, we assess the ultimate constraining power of LHC data on the PDFs that can be expected from the complete dataset, in particular after the High-Luminosity (HL) phase, starting in around 2025. The huge statistics of the HL-LHC, delivering L=3ab-1 to ATLAS and CMS and L=0.3ab-1 to LHCb, will lead to an extension of the kinematic coverage of PDF-sensitive measurements as well as to an improvement in their statistical and systematic uncertainties. Here we generate HL-LHC pseudo-data for different projections of the experimental uncertainties, and then quantify the resulting constraints on the PDF4LHC15 set by means of the Hessian profiling method. We find that HL-LHC measurements can reduce PDF uncertainties by up to a factor of 2 to 4 in comparison to state-of-the-art fits, leading to few-percent uncertainties for important observables such as the Higgs boson transverse momentum distribution via gluon-fusion. Our results illustrate the significant improvement in the precision of PDF fits achievable from hadron collider data alone, and motivate the continuation of the ongoing successful program of PDF-sensitive measurements by the LHC collaborations.

The structure of the proton in the LHC precision era


J Gao, L Harland-Lang, J Rojo

MMHT updates, LHC jets and α<inf>S</inf>

Proceedings of Science 316 (2018)

RS Thorne, LA Harland-Lang, AD Martin

© Copyright owned by the author(s) under the terms of the Creative Commons. We summarise the effects of including jet data from the LHC in the MMHT PDF extraction. We also present the latest results on the preferred value of the strong coupling αS(MZ2) in a number of fit variations. The best current value with all new data is αS(MZ2) = 0.1176.

Ad Lucem: The photon in the MMHT PDFs

Proceedings of Science 316 (2018)

R Nathvani, R Thorne, L Harland-Lang, A Martin

© Copyright owned by the author(s) under the terms of the Creative Commons. We describe the inclusion of the photon as an additional component of the proton's Parton Distribution Functions (PDFs) in the MMHT framework. The input for the photon is adopted from the recent LUXqed determination. We describe the similarities and differences above the input scale with other photon PDF determinations and the contributions to the MMHT photon from both leading twist and higher twist contributions, and their uncertainties. We study the impact of QED effects on the quark and gluon PDFs and the fit quality, and outline our development of an equivalent set of neutron PDFs.

The impact of LHC jet data on the MMHT PDF fit at NNLO

European Physical Journal C Springer 78 (2018) 248-

LA Harland-Lang, AD Martin, RS Thorne

We investigate the impact of the high precision ATLAS and CMS 7 TeV measurements of inclusive jet production on the MMHT global PDF analysis at next-to-next-to-leading order (NNLO). This is made possible by the recent completion of the long-term project to calculate the NNLO corrections to the hard cross section. We find that a good description of the ATLAS data is not possible with the default treatment of experimental systematic errors, and propose a simplified solution that retains the dominant physical information of the data. We then investigate the fit quality and the impact on the gluon PDF central value and uncertainty when the ATLAS and CMS data are included in a MMHT fit. We consider both common choices for the factorization and renormalization scale, namely the inclusive jet transverse momentum, p⊥, and the leading jet p⊥, as well as the different jet radii for which the ATLAS and CMS data are made available. We find that the impact of these data on the gluon is relatively insensitive to these inputs, in particular the scale choice, while the inclusion of NNLO corrections tends to improve the data description somewhat and has a qualitatively similar though not identical impact on the gluon in comparison to NLO.

Parton distributions and lattice QCD calculations: A community white paper

Progress in Particle and Nuclear Physics Elsevier 100 (2018) 107-160

H-W Lin, ER Nocera, F Olness, K Orginos, J Rojo, A Accardi, C Alexandrou, G Bozzi, J-W Chen, S Collins, AM Cooper-Sarkar, M Constantinou, L Del Debbio, M Engelhardt, J Green, R Gupta, LA Harland-Lang, T Ishikawa, A Kusina, P Nadolsky, J-W Qiu, I Schienbein, G Schierholz, RS Thorne, W Vogelsang

In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this document we present an overview of lattice-QCD and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. This document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.

Chi(c) decays and the gluon component of the eta', eta mesons

Physics Letters B Elsevier 770 (2017) 88-92

LA Harland-Lang, VA Khoze, AG Shuvaev

The large mass of the η′meson indicates that a sizeable gluon component is present in the meson wave function. However, the χc0and χc2decays to η′mesons, which proceed via a purely gluonic intermediate state and we would therefore naïvely expect to be enhanced by such a component, are in fact relatively suppressed. We argue that this apparent contradiction may be resolved by a proper treatment of interference effects in the decay. In particular, by accounting for the destructive interference between the quark and gluon components of the η′distribution function, in combination with a model for strange quark mass effects, we demonstrate that the observed χc(0,2)→η(′)η(′) branching ratios can be reproduced for a reasonable gluon component of the η′, η mesons.

LHC forward physics


K Akiba, M Akbiyik, M Albrow, M Arneodo, V Avati, J Baechler, OV Baillie, P Bartalini, J Bartels, S Baur, C Baus, W Beaumont, U Behrens, D Berge, M Berretti, E Bossini, R Boussarie, S Brodsky, M Broz, M Bruschi, P Bussey, W Byczynski, JC Cabanillas Noris, E Calvo Villar, A Campbell, F Caporale, W Carvalho, G Chachamis, E Chapon, C Cheshkov, J Chwastowski, R Ciesielski, D Chinellato, A Cisek, V Coco, P Collins, JG Contreras, B Cox, D de Jesus Damiao, P Davis, M Deile, D D'Enterria, D Druzhkin, B Ducloue, R Dumps, R Dzhelyadin, P Dziurdzia, M Eliachevitch, P Fassnacht, F Ferro, S Fichet, D Figueiredo, B Field, D Finogeev, R Fiore, J Forshaw, A Gago Medina, M Gallinaro, A Granik, G von Gersdorff, S Giani, K Golec-Biernat, VP Goncalves, P Goettlicher, K Goulianos, J-Y Grosslord, LA Harland-Lang, H Van Haevermaet, M Hentschinski, R Engel, G Herrera Corral, J Hollar, L Huertas, D Johnson, I Katkov, O Kepka, M Khakzad, L Kheyn, V Khachatryan, VA Khoze, S Klein, M van Klundert, F Krauss, A Kurepin, N Kurepin, K Kutak, E Kuznetsova, G Latino, P Lebiedowicz, B Lenzi, E Lewandowska, S Liu, A Luszczak, M Luszczak, JD Madrigal, M Mangano, Z Marcone, C Marquet, AD Martin, T Martin, MI Martinez Hernandez, C Martins, C Mayer, R Mc Nulty, P Van Mechelen, R Macula, E Melo da Costa, T Mertzimekis, C Mesropian, M Mieskolainen, N Minafra, IL Monzon, L Mundim, B Murdaca, M Murray, H Niewiadowski, J Nystrand, EG de Oliveira, R Orava, S Ostapchenko, K Osterberg, A Panagiotou, A Papa, R Pasechnik, T Peitzmann, LA Perez Moreno, T Pierog, J Pinfold, M Poghosyan, ME Pol, W Prado, V Popov, M Rangel, A Reshetin, J-P Revol, M Rijssenbeek, M Rodriguez, B Roland, C Royon, M Ruspa, M Ryskin, A Sabio Vera, G Safronov, T Sako, H Schindler, D Salek, K Safarik, M Saimpert, A Santoro, R Schicker, J Seger, S Sen, A Shabanov, W Schafer, G Gil Da Silveira, P Skands, R Soluk, A van Spilbeeck, R Staszewski, S Stevenson, WJ Stirling, M Strikman, A Szczurek, L Szymanowski, JDT Takaki, M Tasevsky, K Taesoo, C Thomas, SR Torres, A Tricomi, M Trzebinski, D Tsybychev, N Turini, R Ulrich, E Usenko, J Varela, M Lo Vetere, A Villatoro Tello, A Vilela Pereira, D Volyanskyy, S Wallon, G Wilkinson, H Woehrmann, KC Zapp, Y Zoccarato

The production of a diphoton resonance via photon-photon fusion


LA Harland-Lang, VA Khoze, MG Ryskin

Jet activity as a probe of high-mass resonance production

European Physical Journal C Springer 76 (2016) 623-

LA Harland-Lang, VA Khoze, M Spannowsky

We explore the method of using the measured jet activity associated with a high-mass resonance state to determine the corresponding production modes. To demonstrate the potential of the approach, we consider the case of a resonance of mass MRdecaying to a diphoton final state. We perform a Monte Carlo study, considering three mass points MR= 0.75 , 1.5 , 2.5 TeV, and show that the γγ, WW, gg and light and heavy qq¯ initiated cases lead to distinct predictions for the jet multiplicity distributions. As an example, we apply this result to the ATLAS search for resonances in diphoton events, using the 2015 data set of 3.2fb-1 at s=13 TeV. Taking the spin-0 selection, we demonstrate that a dominantly gg-initiated signal hypothesis is mildly disfavoured, while the γγ and light quark cases give good descriptions within the limited statistics, and a dominantly WW-initiated hypothesis is found to be in strong tension with the data. We also comment on the bb¯ initial state, which can already be constrained by the measured b-jet multiplicity. Finally, we present expected exclusion limits with integrated luminosity, and demonstrate that with just a few 10s of fb- 1we can expect to constrain the production modes of such a resonance.

Photon-initiated processes at high mass

PHYSICAL REVIEW D 94 (2016) ARTN 074008

LA Harland-Lang, VA Khoze, MG Ryskin

Sudakov effects in photon-initiated processes

Physics Letters B Elsevier 761 (2016) 20-24

LA Harland-Lang, VA Khoze

We consider the effect of the Sudakov factor in photon-initiated processes, corresponding to the no branching probability for the initial-state photon. We demonstrate how such a factor follows simply from the solution of the DGLAP equation for the photon PDF, and is therefore included automatically by this. We use this result to argue that the appropriate scale for the QED coupling α associated with an initial-state photon is not the virtuality of the photon, but rather the factorization scale at which the photon PDF is evaluated, and therefore that the use of the on-shell renormalization scheme is not appropriate for such processes. We also discuss exclusive photon-initiated processes, and demonstrate that no explicit Sudakov factor is required in this case.

The photon PDF in events with rapidity gaps


LA Harland-Lang, VA Khoze, MG Ryskin

Charm and beauty quark masses in the MMHT2014 global PDF analysis


LA Harland-Lang, AD Martin, P Motylinski, RS Thorne