QCD analysis of the CMS inclusive differentialZproduction data ats=8  TeV

Abstract

The parton distribution functions (PDFs) of the proton are one of the essential ingredients to describe physics processes at hadron colliders. The Z boson production data at the LHC have a potential to constrain PDFs, especially the gluon distribution. In this study the CMS measurement of the inclusive double differential Z boson production cross section in terms of transverse momentum and rapidity are compared to the next-to-leading order theory predictions at the center of mass energy, √ s=8 TeV with an integrated luminosity of 19.71 f b −1 . In addition, the sensitivity of this measurement to PDFs is studied within the framework of the HERAFitter. A moderate improvement to the gluon distribution is observed at the Bjorken x ≈ 0.1 region. However, in order to obtain further improvement to the gluon distribution in the global fits, the higher-order theory calculations accessible via fast techniques are necessary.The precision measurements of the Standard Model (SM) of particle physics are one of the top priority programmes at the LHC. The accurate theory predictions are necessary in order to completely exploit the potential of the SM measurements. Importantly, in the hadron colliders parton distribution functions (PDFs) are one of the necessary ingredients for theory predictions. Naively, the PDF f i (x, Q 2 ) represent the probability of finding a parton of flavour i (where i: g(gluons),q (quarks); q=u,d,c,s..) inside a proton carrying a fraction x of the momentum of the proton at the scale Q, called the factorization scale related with the hard scale of the involved physical process. The PDFs cannot be derived from the first principles of Quantum Chromodynamics (QCD) [1] and have to be constrained experimentally. The PDFs are constrained primarily by the Deep Inelastic Scattering (DIS) data. Additional constraints come from the Fixed-target, Tevatron and LHC measurements [for more details, see for example, the reviews in Ref. [2,3] and references therein].Currently, various published SM measurements at the LHC with the center of mass energies 7 and 8 TeV are already used in the global PDF fits [4][5][6][7]. Besides these global PDF fitting efforts, the sensitivity of the particular LHC measurement to PDFs are also studied. For example, PDFs are constrained using the measurement of the W and Z production to strange quark distribution in ATLAS [8], the CMS W charge asymmetry [9] and W in association with the charm quark measurements at 7 TeV [10], W boson production in association with a single charm quark in ATLAS [11], the inclusive jet cross sections from the LHC [12][13][14][15], top quark pair production [16,17] etc. In this current analysis, the impact to the PDFs of the CMS production cross section measurement of the Z boson decaying to a pair of muons [18,19] is studied. This measurement is performed in various bins of transverse momentum (p T (Z)) and rapidity (Y (Z)) of the Z boson. The QCD analysis is performed at the Next-to-Leading order(NLO) in the framework of the HERAFitter [20]. Along with the C...

The impact of the LHC Z-boson transverse momentum data on PDF determinations

“…The potential for p Z T measurements to provide valuable constraints on PDF determinations has been considered previously, both on general grounds [6,7], and when considering a recent measurement performed by the CMS collaboration [8]. Both of these studies, which are based on NLO QCD, show the potential of these measurements.…”

Pinning down the large-x gluon with NNLO top-quark pair differential distributions

“…LHC measurements on inclusive electroweak vector boson and jet production are routinely included in most of the modern PDF determinations [6][7][8][9]. Furthermore, several dedicated analyses have demonstrated the constraining power of many other LHC processes, including W +charm production [10,11], the transverse momentum distribution of W and Z bosons [12,13], prompt photons [14] and charm production in the forward region [15][16][17][18].…”

xFitter project

“…On the theory side, these are QED PDF evolution via QCDNUM [18] or APFEL [19], an interface to the N-space evolution using MELA [20], an interface to APFEL [19] which provides access to the FONLL scheme as used for NNPDF, MNR caclulations [38] for heavy-flavour production in pp collisions as used for [39]. On the technical side, the most important improvements include a full installation script, stand-alone scripts for downloading data and theory files, unified theory interface for expression between fastNLO and APPLGRID, HERA data using the FONLL general-mass variable-flavour-number scheme [40], QCD analysis of the CMS W ± charge asymmetry data [41], combined QCD and electroweak analysis of HERA data [42], QCD analysis of CMS inclusive differential Z production data [43], study of the impact of heavy-flavour production masurements by LHCb on PDFs at low x [39].…”