Harland-Lang, L

Martin, A

Thorne, RS

UCL Discovery

Inclusion of new LHC data in MMHT PDFsR.S. Thorne∗Department of Physics and Astronomy,University College London, WC1E 6BT, UKE-mail: robert.thorne@ucl.ac.ukL.A. Harland-LangDepartment of Physics and Astronomy,University College London, WC1E 6BT, UKE-mail: l.harland-lang@ucl.ac.ukA.D. MartinInstitute for Particle Physics Phenomenology,University of Durham, DH1 3LE, UKE-mail: A.D.Martin@durham.ac.ukI consider the effects of including a variety of new LHC data sets into the MMHT approach forPDF determination. I consider the impact of fitting new LHC and Tevatron data, which leads toclear improvements in some PDF uncertainties. There are specific issues with ATLAS 7 TeV jetdata and I include a discussion of the treatment of correlated uncertainties and briefly the effectsof NNLO corrections. I also present preliminary results with the inclusion of the high precisonfinal ATLAS 7 TeVW,Z rapidity-dependent data.XXV International Workshop on Deep-Inelastic Scattering and Related Subjects3-7 April 2017University of Birmingham, UK∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/MMHT R.S. ThorneThe MMHT2014 parton distributions [1] were the first from our group to include LHC datain their determination. Soon after we considered the effect of updating these to include the finalHERA total cross section measurements [2], noting only minor changes in the central values ofthese PDFs and reductions in uncertainties of up to 10% [3]. I will start from the baseline of thePDFs in [3] when considering the effect of further updates in this account.The MMHT PDF fit has been updated to account for a fit to a wide variety of new hadroncollider data. We include in the PDF determination high rapidity W,Z data from LHCb at 7 and8 TeV [4, 5, 6],W+c jets from CMS [7], which constrains strange quarks, high precision CMS dataon W+,− rapidity distributions [8] which can also be interpreted as an asymmetry measurement,and also the final e asymmetry data from D0 [9]. All these cross sections are calculated at NLOusing MCFM [10] in combination with Applgrid [11] and FEWZ [14].Points NLO χ2 NNLO χ2σtt 18 19.6 (20.5) 14.7 (15.3)LHCb 7 TeVW +Z 33 50.1 (45.4) 46.5 (42.9)LHCb 8 TeVW +Z 34 77.0 (58.9) 62.6 (59.0)LHCb 8 TeV Z→ ee 17 37.4 (33.4) 30.3 (28.9)CMS 8 TeVW 22 32.6 (18.6) 34.9 (20.5)CMS 7 TeVW + c 10 8.5 (10.0) 8.7 (7.8)D0 e asymmetry 13 22.2 (21.5) 27.3 (25.8)Total 3405 (3738) 4375.9 (4336.1) 3741.5 (3723.7)Table 1: χ2 at NLO and NNLO for the prediction (fit) to the new LHC and Tevatron data included in theMMHT – 2016 fit. Also shown is the total number of points without (with) the new data included.The results are shown in Table 1. The predictions from the existing PDFs are generally good,and there is no real tension with other data when refitting (at NLO ∆χ2 = 9 for the remainder ofthe data and at NNLO ∆χ2 = 8). The fit quality is slightly (∼ 10 units) better than in a previousreport [12] due to improvements (and one correction) in NNLO K-factors. The data which requiresmost PDF adjustment is the new 8 TeV CMSW± rapidity and asymmetry data. This is shown inthe left of Figure 1 where good agreement is seen after refitting. (We fit to individual distributionsnot the asymmetry, but it is easier to display the latter.) We have also included further results onσt¯t to those in the MMHT2014 study. The NNLO K-factors are calculated using top++ [13].The fit quality is very good and with αS(M2Z) = 0.118 the fitted mpolet = 173.4 GeV at NNLO,and at NLO mpolet = 170.2 GeV. In contrast the MMHT values were mpolet = 174.2 GeV andmpolet = 171.7 GeV. When the coupling is left free in our new fits then at NLO αS(M2Z) stays veryclose to the MMHT2014 value of 0.120 but at NNLO αS(M2Z) is marginally above 0.118, slightlyhigher than the value of 0.1172 in MMHT2014 [15].We have generated a central set at NLO and NNLO for the fit including these new data –labelled MMHT (2016 fit). We also generate PDF eigenvector sets for uncertainties at NNLOusing the same basis of free PDF parameters as in MMHT2014. Hence, there are 50 eigenvectordirections, and 14 of these are best constrained by one of the new (LHC) data sets. There is alarge reduction in the s+ s¯ uncertainty, but little change in the central value, due to theW + c jetsdata. There is also a significant change in uv−dv at small-x from the CMSW data, and noticeablyreduced uncertainty with the new data inclusion.1MMHT R.S. Thorne0.9511.050 0.5 1 1.5 2 2.50.150.20.25CMS W asym.,ps = 8 TeV, NNLOData/Theory⌘µpredictionfittt, NNLO, Data/TheoryATLAS 8 TeVCMS 8 TeVCMS 7 TeVATLAS 7 TeVTevatron.1.61.41.210.80.60.4Figure 1: Good agreement with new 8 TeV CMSW± rapidity and asymmetry (left). The data/theory ratiofor more up-to-date results on σt¯t (right)We have also attempted a NLO fit including the high luminosity ATLAS 7 TeV inclusivejet data [16]. Full details have already been presented in [17], so we present a brief summaryhere. The MMHT prediction gives χ2/Npts = 413.1/140, and a refit gives an improvement only toχ2/Npts = 400.4/140. We cannot simultaneously fit data in all the rapidity bins. The data set haslarge correlated systematics which dominate over uncorrelated uncertainties. The best possible fitrequires a shift in data against theory which is different from one rapidity bin to another, and hencenot allowed due to the correlations of the uncertainties between bins, but a good fit (χ2/Npts ∼ 1)is possible when fitting each individual rapidity bin separately. Hence, we look at the shifts due toeach source of correlated uncertainty. A small number of sources prefer very different values whenfits to different bins are performed. Hence, we consider fits to all data when decorrelating someerror sources, i.e. making them independent between the 6 rapidity bins. There is a very significantimprovement, particularly from decorrelating source jes21. With correlations between rapidity binsrelaxed for just two sources of systematics, jes21 and jes62, χ2/Npts = 178/140= 1.27.−10−505100.0001 0.001 0.01 0.1Gluon (NLO), percentage difference at Q2 = 104 GeV2xMMHT2014 + HERA IIMMHT (ATLAS jets)MMHT (ATLAS jets 21,62)MMHT (no ATLAS jets)−10−505100.0001 0.001 0.01 0.1Gluon (NNLO), percentage difference at Q2 = 104 GeV2xMMHT2014 + HERA IIMMHT (ATLAS jets)MMHT (ATLAS jets 21,62)Figure 2: The gluon at NLO (left) and NNLO (right) when ATLAS jet data is fit.We also consider the effect of NNLO corrections to jet cross sections [18]. We find a sig-nificant, if not dramatic, deterioration in the fit quality, which might be expected as the NNLOcorrections move the unshifted data and theory slightly further apart. The gluon obtained whenincluding ATLAS jet data at NLO and NNLO is shown in Figure 2. The effect on the best fit gluonis noticeable, but within (or at the boundary) of the uncertainties. It is softer at very high x and thereis a slightly smaller effect at NLO than at NNLO. The result on the gluon is not very dependent onwhether uncertainty sources are decorrelated or not even though the fit quality is vastly different.2MMHT R.S. Thorne0.9911.010 0.5 1 1.5 2 2.5320360400440480ATLAS W−,√s = 7 TeVData/Theory|ηl|dσd|ηl|[pb]predictionfit0.9911.010 0.5 1 1.5 2 2.5560600640ATLAS W+,√s = 7 TeVData/Theory|ηl|dσd|ηl|[pb]predictionfit0.9611.040 0.5 1 1.5 2 2.52345ATLAS Z, 46 <mll < 66GeV,√s = 7 TeVData/Theory|yll|dσd|yll|[pb]predictionfit0.9911.010 0.5 1 1.5 2 2.54080120ATLAS Z, 66 <mll < 116GeV,√s = 7 TeVData/Theory|ηl|dσd|ηl|[pb]predictionfitFigure 3: Fit to ATLASW,Z data. A slight reduction in theory forW− is required (top left) and the oppositeforW+ (top right). There is a significant change in the shape required for Z production (bottom right), i.e.the theory becomes higher at low |η | and lower at high |η |.Finally, we consider the inclusion of recent high precision ATLAS W,Z data at 7 TeV [19].We obtain χ2/Npts ∼ 400/61 from MMHT14 PDFs at NNLO (though the χ2 lowers significantlywhen PDF errors are included [19]). For PDFs with final HERA combined data (and some new σtt¯data points) we obtain χ2/Npts ∼ 387/61. We use this as our “baseline”. Including the ATLASW,Z data in our fit the quality reduces to χ2/Npts ∼ 130/61, similar to the result for MMHT PDFsin [19] when PDF profiling is used. The comparison of theory to data is shown in Figure 3. Thedeterioration in the fit to other data is ∆χ2 = 54. This is worst for CMS double differential Z/γdata (∆χ2 = 17) and CCFR/NuTeV dimuon data (∆χ2 = 16). For the latter the charm meson tomuon branching ratio requires a 25% shift, but this is not exceptional as the uncertainty is 15%.Other data sets showing deterioration are fixed target DIS data, E866 Drell-Yan asymmetry andCDF W -asymmetry data. We also increase the weight of new ATLAS data by a factor of 10,and the χ2 improves to χ2/Npts ∼ 121/61. The deterioration in the fit to other data becomes∆χ2 = 92. There is a further increase in CMS double differential Z/γ data (∆χ2 = 24) and E866Drell-Yan asymmetry (the dimuon data is not any worse). There is now also a deterioration inHERA combined data and CDF differential Z/γ data. We also perform a fit with scales set toµR,F =MW,Z/2 rather than µR,F =MW,Z . As in [19] we find a reduction in χ2 to χ2/Npts ∼ 106/61,spread over data subsets. There is most noticeable improvement for W+ data, with some smallimprovement for the lower mass Z/γ data and less fluctuation for the Z peak rapidity distribution.3MMHT R.S. ThorneWe also perform a fully updated fit with all the new LHC data mentioned (except the jet data).The simultaneous inclusion of the ATLAS W,Z data lowers the χ2 for the other new LHC (plusfinal D0) data by ∆χ2 =−10, while the other data in the fit sees little change, i.e. ∆χ2 = 3 in total,with essentially no change in ATLASW,Z data. Hence, the ATLASW,Z data and other new LHCdata are fully compatible and any pulls tend to be in the same direction. Only the CMSW + c fitdeteriorates very slightly. We generate PDF eigenvector sets for uncertainties at NNLO using thesame basis as in MMHT2014. Of the 50 eigenvector directions, 21 are best constrained by one ofthe new LHC data sets. There is a large increase in s+ s¯ and a decrease in its uncertainty. Thecorrelation with the fit to dimuon data (i.e. lower branching ratio) leads to a necessary increasein the cross section at all x. For x > 0.1 this process has a significant down quark contributiondespite Cabibbo suppression since d(x > 0.1,Q2) s(x > 0.1,Q2). Since the down quark is wellconstrained, the enhanced cross section is obtained by a very large increase in strange quark forx∼ 0.1. The large change in the charm meson to muon branching ratio may, however, be mitigatedby NNLO corrections to dimuon production, which appear to be negative, particularly at smaller x[20]. Implementing these corrections in a PDF fit will be an important development.00.20.40.60.811.21.41.61.820.0001 0.001 0.01 0.1(s+ s)/(u+ d) (NNLO), Q2 = 1.9GeV2xMMHTMMHT16 + ATLAS WZMMHT + ATLAS WZ (µ)MMHT + ATLAS WZ (µ/2)−60−40−20020400.0001 0.001 0.01 0.1x(uV − dV ) (NNLO), percentage difference at Q2 = 104 GeV2xMMHTMMHT16 + ATLAS WZMMHT + ATLAS WZ (µ)MMHT + ATLAS WZ (µ/2)Figure 4: The comparison of NNLOMMHT PDFs including the new ATLASW,Z data and other new LHCdata to the existing PDFs for the strange to light sea ratio (left) and for uV −dV (right).The ratio of (s+ s¯) to u¯+ d¯, i.e. Rs at Q2 = 1.9 GeV2 is shown in Figure 4. At x = 0.023Rs ∼ 0.83± 0.15, compared to the ATLAS result [19] of Rs = 1.13+0.08−0.13. Conversely, we are alittle larger than the NNPDF result in [21]. Our value of Rs exceeds unity at lower x, but this isessentially an extrapolation and it is very consistent with a value of 1. Our final fit also shows asignificant impact on the shape of the valence quarks. The ATLAS W,Z data pulls in the samedirection as the other new LHC data. The significant change in uV − dV is also shown in Fig. 4.The change in the strange quark affects the entire sea, making it generally larger, but the new fitshows rather little impact on the gluon distribution.AcknowledgementsWe thank the Science and Technology Facilities Council (STFC) for support via grant awardST/L000377/1. We thank A.M. Cooper-Sarkar and V. Radescu for supplying K-factors for theNNLO ATLASW,Z cross sections.References[1] L. A. Harland-Lang, A. D. Martin, P. Motylinski and R. S. Thorne, Eur. Phys. J. C 75 (2015) no.5,204 doi:10.1140/epjc/s10052-015-3397-6 [arXiv:1412.3989 [hep-ph]].4MMHT R.S. Thorne[2] H. Abramowicz et al. [H1 and ZEUS Collaborations], Eur. Phys. J. C 75 (2015) no.12, 580doi:10.1140/epjc/s10052-015-3710-4 [arXiv:1506.06042 [hep-ex]].[3] L. A. Harland-Lang, A. D. Martin, P. Motylinski and R. S. Thorne, Eur. Phys. J. C 76 (2016) no.4,186 doi:10.1140/epjc/s10052-016-4020-1 [arXiv:1601.03413 [hep-ph]].[4] R. Aaij et al. [LHCb Collaboration], JHEP 1508 (2015) 039 doi:10.1007/JHEP08(2015)039[arXiv:1505.07024 [hep-ex]].[5] R. Aaij et al. [LHCb Collaboration], JHEP 1601 (2016) 155 doi:10.1007/JHEP01(2016)155[arXiv:1511.08039 [hep-ex]].[6] R. Aaij et al. [LHCb Collaboration], JHEP 1505 (2015) 109 doi:10.1007/JHEP05(2015)109[arXiv:1503.00963 [hep-ex]].[7] S. Chatrchyan et al. [CMS Collaboration], JHEP 1402 (2014) 013 doi:10.1007/JHEP02(2014)013[arXiv:1310.1138 [hep-ex]].[8] V. Khachatryan et al. [CMS Collaboration], Eur. Phys. J. C 76 (2016) no.8, 469doi:10.1140/epjc/s10052-016-4293-4 [arXiv:1603.01803 [hep-ex]].[9] V. M. Abazov et al. [D0 Collaboration], Phys. Rev. D 91 (2015) no.3, 032007 Erratum: [Phys. Rev. D91 (2015) no.7, 079901] doi:10.1103/PhysRevD.91.032007, 10.1103/PhysRevD.91.079901[arXiv:1412.2862 [hep-ex]].[10] J. M. Campbell, R. K. Ellis and W. T. Giele, Eur. Phys. J. C 75 (2015) no.6, 246doi:10.1140/epjc/s10052-015-3461-2 [arXiv:1503.06182 [physics.comp-ph]].[11] T. Carli, D. Clements, A. Cooper-Sarkar, C. Gwenlan, G. P. Salam, F. Siegert, P. Starovoitov andM. Sutton, Eur. Phys. J. C 66 (2010) 503 doi:10.1140/epjc/s10052-010-1255-0 [arXiv:0911.2985[hep-ph]].[12] L. A. Harland-Lang, A. D. Martin and R. S. Thorne, AIP Conf. Proc. 1819 (2017) no.1, 030001doi:10.1063/1.4977119 [arXiv:1610.04393 [hep-ph]].[13] M. Czakon and A. Mitov, Comput. Phys. Commun. 185 (2014) 2930 doi:10.1016/j.cpc.2014.06.021[arXiv:1112.5675 [hep-ph]].[14] Y. Li and F. Petriello, Phys. Rev. D 86 (2012) 094034 doi:10.1103/PhysRevD.86.094034[arXiv:1208.5967 [hep-ph]].[15] L. A. Harland-Lang, A. D. Martin, P. Motylinski and R. S. Thorne, Eur. Phys. J. C 75 (2015) no.9,435 doi:10.1140/epjc/s10052-015-3 630-3 [arXiv:1506.05682 [hep-ph]].[16] G. Aad et al. [ATLAS Collaboration], JHEP 1502 (2015) 153 Erratum: [JHEP 1509 (2015) 141]doi:10.1007/JHEP02(2015)153, 10.1007/JHEP09(2015)141 [arXiv:1410.8857 [hep-ex]].[17] L. A. Harland-Lang, A. D. Martin, R. Nathvani and R. S. Thorne, arXiv:1704.00162 [hep-ph].[18] J. Currie, E. W. N. Glover and J. Pires, Phys. Rev. Lett. 118 (2017) no.7, 072002doi:10.1103/PhysRevLett.118.072002 [arXiv:1611.01460 [hep-ph]].[19] M. Aaboud et al. [ATLAS Collaboration], Eur. Phys. J. C 77 (2017) no.6, 367doi:10.1140/epjc/s10052-017-4911-9 [arXiv:1612.03016 [hep-ex]].[20] E. L. Berger, J. Gao, C. S. Li, Z. L. Liu and H. X. Zhu, Phys. Rev. Lett. 116 (2016) no.21, 212002doi:10.1103/PhysRevLett.116.212002 [arXiv:1601.05430 [hep-ph]].[21] R. D. Ball et al. [NNPDF Collaboration], arXiv:1706.00428 [hep-ph].5

Inclusion of new LHC data in MMHT PDFs

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Inclusion of new LHC data in MMHT PDFs

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