Dimuon production in proton-copper collisions at sqrt s =38.8 GeV

Parton distributions with small-x resummation: evidence for BFKL dynamics in HERA data

We present a determination of the parton distribution functions of the proton in which NLO and NNLO fixed-order calculations are supplemented by NLLx small-x resummation. Deep-inelastic structure functions are computed consistently at NLO+NLL x or NNLO+NLL x , while for hadronic processes small-x resummation is included only in the PDF evolution, with kinematic cuts introduced to ensure the fitted data lie in a region where the fixed-order calculation of the hard cross-sections is reliable. In all other respects, the fits use the same methodology and are based on the same global dataset as the recent NNPDF3.1 analysis. We demonstrate that the inclusion of small-x resummation leads to a quantitative improvement in the perturbative description of the HERA inclusive and charm-production reduced cross-sections in the small x region. The impact of the resummation in our fits is greater at NNLO than at NLO, because fixed-order calculations have a perturbative instability at small x due to large logarithms that can be cured by resummation. We explore the phenomenological implications of PDF sets with small-x resummation for the longitudinal structure function F L at HERA, for parton luminosities and LHC benchmark cross-sections, for ultra-high-energy neutrino-nucleus cross-sections, and for future high-energy lepton-proton colliders such as the LHeC.

Parton distributions from high-precision collider data: NNPDF Collaboration

We present a new set of parton distributions, NNPDF3.1, which updates NNPDF3.0, the first global set of PDFs determined using a methodology validated by a closure test. The update is motivated by recent progress in methodology and available data, and involves both. On the methodological side, we now parametrize and determine the charm PDF alongside the light-quark and gluon ones, thereby increasing from seven to eight the number of independent PDFs. On the data side, we now include the D0 electron and muon W asymmetries from the final Tevatron dataset, the complete LHCb measurements of W and Z production in the forward region at 7 and 8 TeV, and new ATLAS and CMS measurements of inclusive jet and electroweak boson production. We also include for the first time top-quark pair differential distributions and the transverse momentum of the Z bosons from ATLAS and CMS. We investigate the impact of parametrizing charm and provide evidence that the accuracy and stability of the PDFs are thereby improved. We study the impact of the new data by producing a variety of determinations based on reduced datasets. We find that both improvements have a significant impact on the PDFs, with some substantial reductions in uncertainties, but with the new PDFs generally in agreement with the previous set at the one-sigma level. The most significant changes are seen in the light-quark flavor separation, and in increased precision in the determination of the gluon. We explore the implications of NNPDF3.1 for LHC phenomenology at Run II, compare with recent LHC measurements at 13 TeV, provide updated predictions for Higgs production cross-sections and discuss the strangeness and charm content of the proton in light of our improved dataset and methodology. The NNPDF3.1 PDFs are delivered for the first time both as Hessian sets, and as optimized Monte Carlo sets with a compressed number of replicas.

A determination of the charm content of the proton: The NNPDF Collaboration

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the NLO calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced. We then find that the fitted charm PDF vanishes within uncertainties at a scale [Formula: see text] GeV for all [Formula: see text], independent of the value of [Formula: see text] used in the coefficient functions. We also find some evidence that the charm PDF at large [Formula: see text] and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of [Formula: see text], carrying less than [Formula: see text] of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on [Formula: see text] is reduced. The increased stability with respect to [Formula: see text] persists at high scales and is the main implication of our results for LHC phenomenology. Our results show that if the EMC data are correct, then the usual approach in which charm is perturbatively generated leads to biased results for the charm PDF, though at small x this bias could be reabsorbed if the uncertainty due to the charm mass and missing higher orders were included. We show that LHC data for processes, such as high [Formula: see text] and large rapidity charm pair production and [Formula: see text] production, have the potential to confirm or disprove the implications of the EMC data.

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V, Weinberg M, Baarmand MM, Hohlmann M, Kalakhety H, Yumiceva F, Adams MR, Apanasevich L, Berry D, Betts RR, Bucinskaite I, Cavanaugh R, Evdokimov O, Gauthier L, Gerber CE, Hofman DJ, Kurt P, O’Brien C, Sandoval Gonzalez ID, Silkworth C, Turner P, Varelas N, Bilki B, Clarida W, Dilsiz K, Haytmyradov M, Merlo JP, Mermerkaya H, Mestvirishvili A, Moeller A, Nachtman J, Ogul H, Onel Y, Ozok F, Penzo A, Rahmat R, Sen S, Tan P, Tiras E, Wetzel J, Yi K, Anderson I, Barnett BA, Blumenfeld B, Bolognesi S, Fehling D, Gritsan AV, Maksimovic P, Martin C, Swartz M, Baringer P, Bean A, Benelli G, Bruner C, Gray J, Kenny RP, Majumder D, Malek M, Murray M, Noonan D, Sanders S, Sekaric J, Stringer R, Wang Q, Wood JS, Chakaberia I, Ivanov A, Kaadze K, Khalil S, Makouski M, Maravin Y, Saini LK, Skhirtladze N, Svintradze I, Gronberg J, Lange D, Rebassoo F, Wright D, Baden A, Belloni A, Calvert B, Eno SC, Gomez JA, Hadley NJ, Kellogg RG, Kolberg T, Lu Y, Mignerey AC, Pedro K, Skuja A, Tonjes MB, Tonwar SC, Apyan A, Barbieri R, Busza W, Cali IA, Chan M, Di Matteo L, Gomez Ceballos G, Goncharov M, Gulhan D, Klute M, Lai YS, Lee YJ, Levin A, Luckey PD, Paus C, Ralph D, Roland C, Roland G, Stephans GSF, Sumorok K, Velicanu D, Veverka J, Wyslouch B, Yang M, Yoon AS, Zanetti M, Zhukova V, Dahmes B, De Benedetti A, Gude A, Kao SC, Klapoetke K, Kubota Y, Mans J, Nourbakhsh S, Pastika N, Rusack R, Singovsky A, Tambe N, Turkewitz J, Acosta JG, Cremaldi LM, Kroeger R, Oliveros S, Perera L, Sanders DA, Summers D, Avdeeva E, Bloom K, Bose S, Claes DR, Dominguez A, Gonzalez Suarez R, Keller J, Knowlton D, Kravchenko I, Lazo-Flores J, Meier F, Ratnikov F, Snow GR, Zvada M, Dolen J, Godshalk A, Iashvili I, Jain S, Kharchilava A, Kumar A, Rappoccio S, Alverson G, Barberis E, Baumgartel D, Chasco M, Massironi A, Nash D, Orimoto T, Trocino D, Wood D, Zhang J, Anastassov A, Hahn KA, Kubik A, Lusito L, Mucia N, Odell N, Pollack B, Pozdnyakov A, Schmitt M, Stoynev S, Sung K, Velasco M, Won S, Brinkerhoff A, 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J, Hirosky R, Ledovskoy A, Li H, Lin C, Neu C, Wood J, Clarke C, Harr R, Karchin PE, Kottachchi Kankanamge Don C, Lamichhane P, Sturdy J, Belknap DA, Carlsmith D, Cepeda M, Dasu S, Dodd L, Duric S, Friis E, Hall-Wilton R, Herndon M, Hervé A, Klabbers P, Lanaro A, Lazaridis C, Levine A, Loveless R, Mohapatra A, Ojalvo I, Perry T, Pierro GA, Polese G, Ross I, Sarangi T, Savin A, Smith WH, Taylor D, Vuosalo C, Woods N, Collaboration [ACMS. Measurements of differential and double-differential Drell-Yan cross sections in proton-proton collisions at [Formula: see text][Formula: see text]

Measurements of the differential and double-differential Drell-Yan cross sections in the dielectron and dimuon channels are presented. They are based on proton-proton collision data at [Formula: see text] recorded with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7[Formula: see text]. The measured inclusive cross section in the [Formula: see text] peak region (60-120[Formula: see text]), obtained from the combination of the dielectron and dimuon channels, is [Formula: see text], where the statistical uncertainty is negligible. The differential cross section [Formula: see text] in the dilepton mass range 15-2000[Formula: see text] is measured and corrected to the full phase space. The double-differential cross section [Formula: see text] is also measured over the mass range 20 to 1500[Formula: see text] and absolute dilepton rapidity from 0 to 2.4. In addition, the ratios of the normalized differential cross sections measured at [Formula: see text] and 8[Formula: see text] are presented. These measurements are compared to the predictions of perturbative QCD at next-to-leading and next-to-next-to-leading (NNLO) orders using various sets of parton distribution functions (PDFs). The results agree with the NNLO theoretical predictions computed with fewz 3.1 using the CT10 NNLO and NNPDF2.1 NNLO PDFs. The measured double-differential cross section and ratio of normalized differential cross sections are sufficiently precise to constrain the proton PDFs.

The quark and gluon structure of the proton

In this paper we present a review of the structure of the proton and the current status of our knowledge of the parton distribution functions (PDFs). The lepton-nucleon scattering experiments which provide the main constraints in PDF extractions are introduced and their measurements are discussed. Particular emphasis is given to the HERA data which cover a wide kinematic region. Hadron-hadron scattering measurements which provide supplementary information are also discussed. The methods used by various groups to extract the PDFs in QCD analyses of hard scattering data are presented and their results are compared. The use of existing measurements allows predictions for cross sections at the LHC to be made. A comparison of these predictions for selected processes is given. First measurements from the LHC experiments are compared to predictions and some initial studies of the impact of this new data on the PDFs are presented.

Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0<x(F)<0.6, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio sigma(p+d)(DY)/2sigma(p+p)(DY). This result shows that the gluon distributions in the proton and neutron are very similar. The Upsilon production cross sections are also compared with the p+d and p+Cu cross sections from earlier measurements.

J/psi polarization in 800-GeV p-Cu interactions

We present measurements of the polarization of the J/psi produced in 800-GeV proton interactions with a copper target. Polarization of the J/psi is sensitive to the ccmacr; production and hadronization processes. A longitudinal polarization is observed at large x(F), while at small x(F) the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus p(T).

Observation of polarization in bottomonium production at square root of s = 38.8 GeV

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.