Parton Distribution Functions Claire Gwenlan (Oxford) and Max Klein (Liverpool+CERN) For the ATLAS PDF Forum PDF Status QCD Fits Data Comparisons Outlook ATLAS Collaboration Week Lecce (Italy) 6 th October, 2015 See Marjorie for PDFs in MCs – links to PMG group See Claire at Sibiu for a complementary summary

PDFs ( )

Gluons and Quarks 1989  2015 arXiv: “Legacy” paper NC/CC HERAPDF2.0 NNLO BCDMS C.Gwenlan+M.Klein, ATLAS, Lecce CDHS gg  H (y=0) High mass HL-LHC fixed target lN to ep collider 

4M.Klein HERA & p Structure

PDF sets and their assumptions V.Radescu 10/15

Parton-Parton “Luminosities” C.Gwenlan+M.Klein, ATLAS, Lecce x 1

Parton-Parton “Luminosities” C.Gwenlan+M.Klein, ATLAS, Lecce x 1

Parton-Parton “Luminosities” C.Gwenlan+M.Klein, ATLAS, Lecce x 1

Parton-Parton “Luminosities” C.Gwenlan+M.Klein, ATLAS, Lecce x 1

Obtaining constraints with ATLAS data QCD fit analyses (jets and W,Z) Comparisons with some PDF sensitive measurements C.Gwenlan+M.Klein, ATLAS, Lecce

Technical Developments Several ATLAS PDF Forum members are main active developers of technical tools APPLGRID: open source package for performing fast (N)NLO convolutions with PDFs. Rich environment of interfaces with (N)NLO calculations currently available: all processes in MCFM (EW,V+jets,HQ) and NLOjet++ for jet production all fixed order NLO processes in using aMCfast interface (arXiv: ) Sherpa for fixed NLO processes using MCgrid (arXiv: ); and an independent native APPLGRID-Sherpa interface available NNLO interface to DYNNLO and to other new codes progressing HERAfitter: based on open source QCD software package; relies on fast tools for theory calculations i.e. APPLGRID, DYTURBO (also developed by ATLAS members) provides means to optimise measurements and assess impact of new data through QCD fits to extract PDFs, α s ; or through (new) profiling method to quantify how much a new measurement would improve a global PDF if included can provide information on consistency of measurements, among themselves and with SM (need detailed exp. uncertainties split into (un)correlated sources, and correlations between datasets) H.o. eweak and QCD corrections - treatment developed with SANC,FEWZ,DYNNLO (cf Les Houches arXiv: and U.K. at PMG )

Inclusive jets JHEP 02(2015)15 p T – y cross section Drops by ~5 orders of magnitude for p T increase TeV Sensitive to q and xg Also published di-jets (JHEP05(14)059 and tri-jets (EPJ C75(15)228) C.Gwenlan+M.Klein, ATLAS, Lecce

Inclusive jets - forward JHEP 02(2015)15 Jet energy scale and large x PDF uncertainties dominant C.Gwenlan+M.Klein, ATLAS, Lecce

Inclusive jets - central JHEP 02(2015)15 A major success of pQCD  Neither ABM nor HERA fit LHC jet data ! C.Gwenlan+M.Klein, ATLAS, Lecce

Fitting inclusive n-Jets Attempt to fit the 7 TeV 1,2,3 jet data together with HERA for a study of xg reveals that we have been unable to obtain respectable Χ 2 values, especially for the central region of the inclusive jets which has been difficult also for the comparison with ABM and HERA1.5 Study ongoing on why that is, as one hardly can use a bad fit to change xg. Study variations of jet radius, scales-jets,h.o., hadronisation and UE (PERUGIA, AUET2B, HERWIG), data correlations, order NLO ? Also looking at effect of HERA jet and to 8 TeV data Initial study showed some sensitivity to xg C.Gwenlan+M.Klein, ATLAS, Lecce j 2j 3j

Determination of the Strange Sea Fraction A. Cooper-Sarkar and V. Radescu PDF forum WZ meeting HERA measures (down+strange) in F 2 and, for Q 2 limited range and luminosity, cannot separate the two. Neutrino di-lepton data suggest(ed) suppression of s/d. Is the strange a ‘heavy quark’? No – WK. Tung Nuclear Corr’s in νN! HERMES obtained a very different x shape in an LO analysis of K multiplicities. Published W,Z QCD analysis – 2 papers found s/d ≈1 ± 0.2 (exp) Note the u,d sea changes then substantially also HERA I+II and WZ2010 add WZ2011 (imminent..) now s/d ≈1 ± 0.06 (exp) extra errors delicate to estimate.. s/d affects y and pT of W – relation to W mass! (parameterisation leads to outside x range covered..) C.Gwenlan+M.Klein, ATLAS, Lecce

Nuclear PDFs Z into di-leptons in pPb Not affected by QGP Sensitive to nPDFs and to nuclear corrections Consistent with pQCD and binding effects as implemented in EPS09 Difficult to constrain PDFs with W,Z because at Q 2 = M W,Z 2 the Q 2 evolution has washed out initial differences in x shape  requires <1% precision.. C.Gwenlan+M.Klein, ATLAS, Lecce

Recent comparisons – High Mass Drell Yan 8 TeV Quite evolved PDF analysis. Photon induced contribution rises with M. High mass interesting. ATL-COM-PHYS C.Gwenlan+M.Klein, ATLAS, Lecce Cross section decreases by 5 orders of magnitude in covered range. Study cares for 1-10% effects Consistent with 7 TeV paper PLB:

Recent comparisons – W,Z - 13 TeV First tests of cross sections measured for W,Z with 0.1fb -1 of 13 TeV data against modern PDF sets. W+/W- W/Z C.Gwenlan+M.Klein, ATLAS, Lecce

Recent comparisons – tt/Z - 13 TeV tt/Z “profiling”: use PDFset (here CT10) to represent “the world” and add ATLAS (simulated) data to estimate sensitivity With ttbar+Z can improve on the gluon and, correlated, also the low x sea. indico.cern.ch/event/395434/ A.Glazov C.Gwenlan+M.Klein, ATLAS, Lecce

top-top Sensitive to generators, tunes, IFSR PDF sets, perturbative series and electroweak corrections, top mass.. Draft conclusion of 8 TeV paper draft ____ 7 TeV 8 TeV see also C.Gwenlan+M.Klein, ATLAS, Lecce

Prompt Photons Work in progress, 8 TeV STDM Amazing agreement with theory (JetPhox, NLO, CT10) over 10 orders of magnitude 10-20% uncertainties from CT10, coupling, scales Sensitive to gluon distribution (renewal ? -- photons had been abandened from QCD fits for kt effects in fixed target data description, long ago..) cf eg Aurenche et al, PRD39(89)3275 C.Gwenlan+M.Klein, ATLAS, Lecce

Outlook Some observations C.Gwenlan+M.Klein, ATLAS, Lecce

Gluon at High x ? Gluon prior to LHC data (2011) Gluon with (first) LHC data (2015) used by CT14,NNPDF,MMHT Related to quark distributions, low x, α s, heavy flavour treatment, to resummation A QCD problem by itself and a key question for searches as luminosity increases … C.Gwenlan+M.Klein, ATLAS, Lecce

Rising PDF uncertainties at high mass SUSY Juan Rojo PDF forum C.Gwenlan+M.Klein, ATLAS, Lecce

Large Bjorken x CC at HERA reached at best x=0.5. The luminosity was while > is required as xq ~ (1-x) k for x  1 Fixed target DIS data suffer from TMC, HT, nuclear corrections and inconsistencies  There is no reliable base for predictions at large x C.Gwenlan+M.Klein, ATLAS, Lecce Final HERA data on charged currents

Valence quarks up down C.Gwenlan+M.Klein, ATLAS, Lecce Related to DY, W mass etc Recall xq v ~ (1-x) 3 d/u  1 a classic question

Approaching 10 TeV From Dave Charlton C.Gwenlan+M.Klein, ATLAS, Lecce

Very High Mass Dell Yan 13 TeV - σ(PDF)/σ(CT14) VRAP calculation, U.Klein NNPDF3  ABM12   MMHT14 CT10 JR14 HERA2.0 C.Gwenlan+M.Klein, ATLAS, Lecce

Future ultra-high precision demands on PDFs Higgs theory uncertainties in HL LHC Need high precision on W,Z, +c data to constrain uv,dv,s,c.. e.g. W mass measurement Maarten B at Moriond 15: δM W ≈ MeV Flavour decomposition crucial. C.Gwenlan+M.Klein, ATLAS, Lecce

Final Remarks pQCD has a major success in broadly describing our measurements. High precision is required to interprete the measurements in terms of PDFs, to derive constraints on the PDFs. Important areas are the constraints on the strange quark (W,Z, W+c) and the gluon (jets, tt). First interesting comparisons have been made of 13 TeV data with new sets. Higgs, M W,.. measurements will demand maximum possible precision. We need to think of how we master the high x challenge where new phenomena are expected which may not be confused with PDFs. There is a close collaboration with the PDF4LHC forum (new paper today). The Forum, with the analysis groups, provides a rather professional base for treating PDFs as appropriate as possible. Besides the data, we face many calculational challenges on which important work is being done as a collaborative effort, with also theorists. C.Gwenlan+M.Klein, ATLAS, Lecce

PDFs need Thanks to Amanda Cooper-Sarkar, Monica D’Onofrio, Claire Gwenlan, Uta Klein, Kristin Lohwasser, Voica Radescu Stefano Camarda, Zvi Citron, Sasha Glazov, Jan Kretzschmar, Misha Lishevoy, Pavel Starovoitov, Mark Sutton… Sergey Alekhin, Dmitry Bardin, Johannes Bluemlein, Stefano Forte, Fred Olness, Juan Rojo, Robert Thorne and many others. C.Gwenlan+M.Klein, ATLAS, Lecce

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top-top Sensitive to generators, tunes, IFSR PDF sets, perturbative series and electroweak corrections, top mass.. Draft conclusion of 8 TeV paper draft ____

35 high x PDFs: link to LHC large uncertainties in high x PDFs limit searches for new physics at high scales many interesting processes at LHC are gluon-gluon initiated: top, Higgs, … and BSM processes, such as gluino pair production current BSM search in dilepton final state; uncertainties on high-x (anti)quarks dominate LHeC PDF arXiv: arXiv: C. Gwenlan, PDFs and QCD at the LHeC

more on PDFs … High x HERA Neutral Current