A M Cooper-Sarkar
Charm production data from HERA can be used to determine the charm quark mass and jet production data from HERA can be used to detrmine $α_s(M_Z)$. recent results are summarised.
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We compute the predictions of intrinsic charm for deep-inelastic scattering at high-Q^2 and compare to HERA data. With the inclusion of constraints from low-energy data, enhancements beyond the predictions of standard structure functions are very modest, but peaking in the leptoquark mass variable is present near 200 GeV. Ultimately, the ability of HERA to probe the intrinsic charm hypothesis could be very substantial.
PDF fits in the HERAPDF1.0 formalism have been made to the combined HERA-I inclusive data and the newly combined $F_2$(charm) data from the H1 and ZEUS experiments. The charm data are found to be sensitive to the value of the charm mass and the choice of the heavy quark scheme. This has consequences for the predictions of $W$ and $Z$ cross sections at the LHC.
Results on open charm and beauty production and on the search for top production in high-energy electron-proton collisions at HERA are reviewed. This includes a discussion of relevant theoretical aspects, a summary of the available measurements and measurement techniques, and their impact on improved understanding of QCD and its parameters, such as parton density functions and charm- and beauty-quark masses. The impact of these results on measurements at the LHC and elsewhere is also addressed.
We determine the charm-quark mass mc(mc) in the MS-bar scheme using measurements of charm production in deep-inelastic ep scattering at HERA in the kinematic range of photon virtuality from 5 to 1000 GeV squared and Bjorken scaling variable from 0.0001 to 0.5. The extraction of charm quark mass from this process with space-like kinematics provides complementary information to results from hadronic processes. The QCD analysis of the HERA data yields a value of mc(mc) of 1.27 plus minus 0.05(exp) plus 0.06 minus 0.01(scale) GeV at next-to-leading order and mc(mc) of 1.36 plus minus 0.04(exp) plu…
Heavy quark structure functions from HERA provide a direct handle on the medium and small-x gluon PDF. In this contribution, we discuss ongoing progress on the implementation of the FONLL General-Mass scheme with running heavy quark masses, and of its benchmarking with the HOPPET and OpenQCDrad codes, and then present the impact of the recently released combined HERA charm production cross sections in the NNPDF2.3 analysis. We find that the combined charm data contribute to constraining the gluon and quarks at small values of Bjorken-x.
We apply the method of ratios to search for geometrical scaling in the charm production in deep inelastic scattering. To this end we use recent combined data from H1 and ZEUS experiments. Two forms of geometrical scaling are tested: originally proposed scaling which results from Golec-Biernat-Wusthoff model and scaling motivated by a dipole representation which takes into account charm mass. It turns out that in both cases some residual scaling is present and charm mass inclusion improves scaling quality.
This review is devoted to the study of charm production in ep and pp collisions. The total set of measurements obtained by the two collaborations H1 and ZEUS from HERA and their combination is outlined, as well as complementary data obtained by the LHCb collaboration at the LHC. After fitting the parton distribution functions the charm production cross sections are predicted within perturbative QCD at next-to-leading order using the fixed-flavour-number scheme. Agreement with the data is found. The combined HERA charm data are sensitive to the $c$-quark mass and enabled its accurate determinat…
The ZEUS data on the charm structure function F_2^c at small x fit well to a single power of x, corresponding to the exchange of a hard pomeron that is flavour-blind. When combined with the contribution from the exchange of a soft pomeron, the hard pomeron gives a good description of elastic $J/ψ$ photoproduction.
The HERAPDF1.0 PDF set, which was an NLO QCD analysis based on H1 and ZEUS combined inclusive cross section data from HERA-I, has been updated to HERAPDF1.5 by including preliminary inclusive cross section data from HERA-II running. Studies have also been made by adding various other HERA data sets: combined charm data, combined low energy run data and H1 and ZEUS jet data. These data give information on the treatment of charm and the charm quark mass and on the value of $α_s(M_Z)$. The PDF analysis has also been extended to NNLO. The PDFs give a good description of Tevatron and early LHC data…
One of the most popular definition for the charm-quark mass is the charm-quark pole mass $m_c^{\rm pole}$. In this contribution, we extract the charm-quark pole mass through perturbative Quantum Chromo Dynamics (pQCD) analysis up to the next-to-next-to-leading order (NNLO) corrections from HERA Combined and LHCb charm production recent data sets. Then, we investigate for the first time the charm-quark pole mass $m_c^{\rm pole}$ pure impact, as an extra pQCD parameter on the proton Parton Distribution Functions (PDFs) at the NNLO corrections.
Measurements of open charm and beauty production cross sections in deep inelastic $ep$ scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections are obtained in the kinematic range of negative four-momentum transfer squared of the photon $2.5$ GeV$^2<Q^2<2000$ GeV$^2$ and Bjorken scaling variable $3\cdot10^{-5}<x_{\text{Bj}}<5\cdot10^{-2}$. The combination method accounts for the correlations of the statistical and systematic uncertainties among the different datasets. Perturbative QCD calculations are compared to the combined data. A next-to-leading order QCD…
An introduction and overview of charm production in deep inelastic scattering at HERA is given. The existing next-to-leading order perturbative QCD calculations are then reviewed, and key results are summarized. Finally, comparisons are made with the most recent HERA data, and unresolved issues are highlighted.
In the framework of the semi-hard (k_t-factorization) approach, we analyze the various charm production processes in the kinematic region covered by the HERA experiments.
We review the theoretical and experimental status of heavy-flavour production at HERA. The results presented include some outstanding issues in charm and beauty photoproduction, charm production in DIS and quarkonium production.
We explore the possibility that the excess neutral and charged current events seen by the H1 and ZEUS Collaborations at HERA at large x and Q^2 could arise from a hard charm component of the nucleon. While the symmetric intrinsic charm hypothesis is unable to account for the HERA anomaly, a non-symmetric charm distribution generated non-perturbatively, for which c-bar is much harder than c, can produce significant enhancement of cross sections at the HERA kinematics.
The cross section of the $D^*$-meson diffractive photoproduction at the HERA collider has been calculated in the framework of perturbatively motivated model for the different kinematic regions. The camparison between the different Pomeron models has been performed.
The measurements of inclusive charm and beauty cross sections in deep-inelastic scattering $ep$ collisions at HERA are compared with the predictions of perturbative quantum chromodynamics from the CTEQ and MRST fitting groups, employing a range of theoretical schemes. The differences in the theoretical predictions are discussed and the theoretical uncertainties investigated.
Approximately taking into account the higher-order effects due to multiple-gluon initial-state radiation, we extract from the latest Tevatron data of prompt J/psi hadroproduction the leading colour-octet matrix elements within the nonrelativistic-QCD (NRQCD) factorization formalism proposed by Bodwin, Braaten, and Lepage. We find that the matrix elements which describe the formation of J/psi mesons from colour-octet cc-bar pairs in the angular-momentum states ^{2S+1}L_J = ^1S_0 and ^3P_J, with J = 0,1,2, which are responsible for the excess of the predicted cross section of inelastic J/psi pho…
HERA jet data, in addition to combined HERA inclusive data, are input to the HERAPDF NLO QCD analysis in order to further constrain the gluon PDF and to allow an accurate evaluation of $α_S(M_Z)$
A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and D^*(2010) production at HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization-factorization scale is studied.
We present predictions for single inclusive distributions of charmed mesons, relevant to the HERA experiments. Our results are based upon a computation that correctly incorporates mass effects up to the next-to-leading order level, and the resummation of transverse momentum logarithms up to next-to-leading-logarithmic level. We apply the same acceptance cuts as the H1 and Zeus experiments, and compare our results to their data. We perform a study of the sensitivity of our predictions on the charm mass, $\LambdaQCD$, factorization scale, renormalization scale, and fragmentation parameters.
We calculate the cross section of charm photoproduction at HERA collider in the framework of the kt-factorization QCD approach. Our analysis cover the inclusive charm production as well as charm and associated jet production processes. Both photon-gluon and gluon-gluon fusion mechanisms are taken into account. The unintegrated gluon densities in a proton and in a photon obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription are used. Our theoretical results are compared with the recent experimental data taken by the H1 and…
We compare our theoretical results for charmed quark and J/Psi - photoproduction cross sections obtained in the semihard approach of QCD with H1 and ZEUS experimental data.
The measurement of the inelastic photoproduction of charmonium at HERA seems to have ignited a new charmonium crisis. The (already discredited) color singlet model fits the data for large charmonium energy fraction z, where the NRQCD model qualitatively fails. We here point out that by the straightforward inclusion of color singlet and octet processes in the soft color (color evaporation) scheme, the HERA data can be accommodated for all z. We anticipate that the color singlet model will fail at low z, as it does in hadroproduction.
In the framework of perturbative QCD and a model for the production of charmed hadrons the structure function $F^c_2$ is calculated and compared with the experimental data of H1 and ZEUS Collaborations. We show that the spectator mechanism of the $D^*$-meson production independent of a hadronic remnant is valid at $p_T>10$ GeV, only. We find that the evolution of $F^c_2(x,Q^2)$ versus the virtuality $Q^2$ can be neglected in the kinematic region of HERA.
A study of the $\J$-meson photoproduction at large transverse momentum at HERA energies via the charm quark excitation in the photon is presented. Based on perturbative QCD, nonrelativistic quark model and photon structure function formalism, our calculation demonstrates that the charm content of the photon may be very important for the $\J$ photoproduction at the large transverse momentum. It is shown that at HERA energies $\J$ production via the subprocess $\cg$ dominates over the resolved photon contribution via the gluon-gluon fusion at $\pt\ge 2$ GeV/c and over the leading order direct ph…
The coefficient functions for heavy-flavour production in deeply inelastic electron-hadron scattering have been calculated previously. Analytic expressions are impossible to publish due to their length. Therefore we have tabulated them as two-dimensional arrays as is often done for the scale-dependent parton densities. Using this computer program we present event rates for charm production at HERA in bins of $x$ and $Q^2$. These rates are insensitive to variations in the factorization and renormalization scale $μ$.
We apply the MC@NLO formalism to the production of heavy-quark pairs in pointlike photon-hadron collisions. By combining this result with its analogue relevant to hadron-hadron collisions, we obtain NLO predictions matched to parton showers for the photoproduction of QQ^{-} pairs. We compare MC@NLO results to the measurements of c- and b-flavoured hadron observables performed by the H1 and ZEUS collaborations at HERA.
The charm squark resonance in the $e^+ q$ channel provides one of the plausible interpretations of the reported anomaly at HERA. We show that the relevant $R$ violating coupling $λ'_{121}$ is required to be large, typically around 0.1 in a large class of supergravity based models including the minimal one with the universal boundary condition at the GUT scale. Existing constraints on this coupling are reanalysed in this light and it is argued that a large $λ'_{121}$ may be feasible but would require fine tuned cancelations.
Charmonia hadro- and photo-production are analyzed in the framework of the color-octet model taking into account higher-order effects induced by initial-state radiation of gluons. We argue that color-octet matrix elements obtained from Tevatron data might be reconciled with those extracted from HERA data on inelastic $J/ψ$ photoproduction. Finally we estimate cross sections for events with muons from prompt $J/ψ$'s as a background for the B physics programme at LHC experiments.
We analyze the capability of charm production in deep-inelastic ep scattering at HERA to constrain the gluon distribution g(y,μ^2) of the proton. The dependence of the theoretical predictions for the charm structure function F_2^c on the mass factorization scale μand the charm mass is investigated. F_2^c seems to be well suited for a rather clean and local gluon measurement at small momentum fractions y.
A QCD fit analysis to the combined HERA inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering to extract HERAPDF sets is presented. The results are used for predictions of $ p\bar{p}$ processes at Tevatron and $pp$ processes at the LHC. The QCD analysis has been extended to include the combined HERA II measurements at high $Q^2$ resulting in the HERAPDF1.5 sets, with full estimation of uncertainties. The precision of the new PDFs at high $x$ is considerably improved, particularly in the valence sector. In addition, inclusion of the HERA jet…
In the framework of semihard (k$_T$ factorization) QCD approach, we consider the differential cross sections of $D^{*\pm}$ meson production at HERA. The consideration is based on BFKL and CCFM gluon distributions. We find that in the case of BFKL LO gluon distribution the theoretical results are sensitive to the Pomeron intercept parameter $Δ$. We present a comparison of the theoretical results with available ZEUS experimental data.
We develop the pQCD description of diffraction excitation of heavy flavours in DIS and we derive the analytic formulas for the mass spectrum in leading log$m_f^{2}$. The result illustrates nicely non-factorization properties of the QCD pomeron. We predict a very steep rise of the charm content of diffraction dissociation of photons at small $x_{\Pom}$. We evaluate the contribution of open charm to scaling violations in the structure function of the pomeron.
Charged current charm and D meson production is studied in detail as a means of determining the unpolarized and polarized strange sea densities at HERA. All analyses are performed in next-to-leading order QCD, including a calculation of the so far unknown spin-dependent MSbar coefficient functions up to O(alpha_s). It is shown that a decent measurement is possible in the unpolarized case, provided a sufficient luminosity can be reached in the future, while for longitudinally polarized beams it appears to be extremely challenging due to limitations imposed on the expected statistical accuracy b…
The high precision and large kinematic coverage of the data from the HERA-I running period (1994-2000) have already allowed precise extractions of proton parton distribution functions (PDFs). The HERA-II running program is now underway and is expected to provide a substantial increase in the luminosity collected at HERA. In this paper, a study is presented which investigates the potential impact of future data from HERA on the proton PDF uncertainties, within the currently planned running scenario. In addition, the effect of a possible future measurement of the longitudinal structure function,…
The status is reviewed of recent high precision measurements of inclusive-jet, dijet and trijet production in deep-inelastic scattering and photoproduction by the HERA experiments H1 and ZEUS. The measurements are in good agreement with perturbative QCD calculations at next-to-leading order and are used for the extraction of the value of the strong coupling at the mass of the Z boson, α_s(M_Z). The methods and results of the QCD analyses are presented and a summary of the values of α_s(M_Z) from recent jet measurements at HERA is given.
We study inclusive $J/ψ$ photoproduction at NLO at large $P_T$ at HERA and the EIC. Our computation includes NLO QCD leading-$P_T$ corrections, QED contributions via an off-shell photon as well as those from $J/ψ$+charm channels. For the latter, we employ the variable-flavour-number scheme. Our results are found to agree with the latest HERA data by H1 and provide, for the first time, a reliable estimate of the EIC reach for such a measurement. Finally, we demonstrate the observability of $J/ψ$+charm production and the sensitivy to probe the non-perturbative charm content of the proton at high…
We calculate the contribution to inclusive high tranverse momentum ($p_T$) charm production at HERA from the excitation of charm in the photon. At large values of \pt\ the results of such a calculation, in the structure function language, will be more reliable as it sums the large logs, $\log(p_T^2/m_c^2)$, as opposed to calculating the contribution of the $2 \to 3 $ subprocess in fixed order of perturbation theory. We find that this contribution is large and comparable to the contribution from $γg$ fusion production of charm. Suitable cuts on the rapidity of the `away-side' large \pt\ jet all…
Recent results of open charm and beauty production in electron proton scattering at HERA are presented. In photoproduction, the measured cross sections for charm exceed fixed order NLO QCD calculations. Experimental evidence supports the hypothesis that a significant fraction of photoproduction events with charm can be described by resolved photon processes, where the charm quark is a constituent of the resolved photon. In deep inelastic scattering the NLO calculations give in general a fairly reasonable description of the observed charm cross sections. The measurements of the structure functi…
The cross section for the photoproduction of large-p_T J/psi mesons at HERA is calculated at next-to-leading order, adopting a perturbative approach to describe the fragmentation of charm quarks and gluons into J/psi mesons. We treat the charm quark according to the massless factorization scheme, where it is assumed to be one of the active flavours inside the proton and the resolved photon. We present inclusive distributions in transverse momentum and rapidity, including the contributions due to direct and resolved photons. The importance of the colour-octet components of the J/psi wave functi…
We compute the contributions to large-$p_T$ $J/ψ$ production at HERA coming from fragmentation of gluons and charm quarks. We find that the charm quark fragmentation contribution dominates over the direct production of $J/ψ$ via photon-gluon fusion at large-$p_T$, while the gluon fragmentation is negligibly small over the whole range of $p_T$. An experimental study of $p_T$ distributions of $J/ψ$ at HERA will provide a direct probe of the charm quark fragmentation functions.
High energy factorization predictions for F2^c are derived using BFKL descriptions of the proton structure function F2 at HERA. The model parameters are fixed by a fit of F2 at small x. Two different approaches of the non perturbative proton input are shown to correspond to the factorization at the gluon or quark level, respectively. The predictions for F2^c are in agreement with the data within the present error bars. However, the photon wave-function formulation (factorization at quark level) predicts significantly higher F2^c than both gluon factorization and a next-leading order DGLAP mode…
We compare different schemes for the treatment of heavy quark production in Deep-Inelastic Scattering (DIS). For fully-integrated quantities such as $F_{2}(x,Q^{2})$, we advocate the use of the General-Massive Variable-Flavor-Number (GM-VFN) scheme; we present some results showing the progress of a Next-to-Leading Order calculation in this scheme. For differential quantities, the Fixed-Flavor-Number (FFN) scheme provides a more appropriate starting point. We present a new calculation of the azimuthal distribution of charm quark production in DIS. All results have been obtained using a Monte Ca…
A Monte Carlo simulation based on O(alpha_s) QCD matrix elements matched to parton showers shows that final-state hadrons in deep inelastic scattering (DIS) can be used to tag events with a single (anti)quark recoiled against the proton. The method is particularly suited to study the mean charge of leading particles, which is sensitive to fragmentation and sea quark contribution to the proton structure function. We also discuss methods to study the charm production in DIS using the Breit frame.
We examine the charm component F_{2,c}(x,Q^2,m^2) of the proton structure function F_2(x,Q^2) in three different schemes and compare the results with the data in the x and Q^2 region explored by the HERA experiments. Studied are (1) the three flavour number scheme (TFNS) where the production mechanisms are given by the photon-gluon fusion process and the higher order reactions with three light-flavour parton densities as input (2) the four flavour number scheme (FFNS) where F_{2,c} is expressed in four light flavour densities including one for the charm quark and (3) a variable-flavour number …
The production of Charmonium states $\etacp$ and $\hc$ at fixed-target experiment of $pN$ collisions at HERA-$B$ is considered. It is found that the HERA-$B$ at DESY is one of the best machines in further confirming and detecting these two kinds of Charmonia in the near future.
Combined HERA data on charm production in deep-inelastic scattering have previously been used to determine the charm-quark running mass $m_c(m_c)$ in the MSbar renormalisation scheme. Here, the same data are used as a function of the photon virtuality $Q^2$ to evaluate the charm-quark running mass at different scales to one-loop order, in the context of a next-to-leading order QCD analysis. The scale dependence of the mass is found to be consistent with QCD expectations.
The transverse momentum dependent gluon density obtained with CCFM evolution is determined from a fit to the latest combined HERA structure function measurements.
|Vcs| determination and LFU test in charm decays at BESIII
BESIII实验通过研究粲强子的纯轻与半轻衰变，精确测定|Vcs|并检验轻子味普适性LFU，发布粲物理最新研究结果。
The parameters of the electroweak theory are determined in a combined electroweak and QCD analysis using all deep-inelastic $e^+p$ and $e^-p$ neutral current and charged current scattering cross sections published by the H1 Collaboration, including data with longitudinally polarised lepton beams. Various fits to Standard Model parameters in the on-shell scheme are performed. The mass of the $W$ boson is determined as $m(W)=80.520\pm 0.115$ GeV. The axial-vector and vector couplings of the light quarks to the $Z$ boson are also determined. Both results improve the precision of previous H1 deter…
Recent \alphas determinations from jet production at HERA are presented. Three different observables lead to consistent alpha values. The result is consistent with the world average and has an error of about 0.006. This is quite a remarkable result, since it is only slightly less precise than the world average.
The latest results from the H1 and ZEUS collaborations which challenge the QCD description of high energy $ep$ collisions are presented. Data from HERA continue to provide precision measurements and are compared to the latest theoretical predictions. Measurements of new processes are also presented as well as investigation of regions where perturbative QCD fails to describe the data. Four themes are presented here. Measurements of hard QCD processes, prompt photon and jet production, are used to compare to the latest theoretical predictions and, in the case of jet production, used to make high…
In the framework of semi-hard QCD approach, we present a consistent analysis of D^* meson production at HERA energies. The consideration is based on universal unintegrated gluon densities, which have BFKL behavior in the small x region. Predictions of the CCFM evolution equation for D^* production are obtained and show a good description of D^* data at HERA.
We present a precise comparison of the results of the dipole models with the newest data from HERA on the diffractive open charm production. We found good agreement with the data on the diffractive open charm production both for the the gluon distributions from the considered dipole models and the DGLAP fits to HERA data from our earlier analysis for diffractive parton distributions with higher twist. We also show that exclusive diffractive charm production can practically be neglected
We consider the possibility of a direct determination of the polarized gluon density in the proton using charm production with polarized beams at HERA. We study total cross sections and distributions at leading order using different parametrizations of the polarized gluon density. We conclude that charm photoproduction data can be used to constrain the polarized gluon density in the proton if an integrated luminosity of 100~pb$^{-1}$ will be achieved at HERA.
We use perturbative QCD to calculate the cross sections $σ^{L,T}$ for the diffractive production of open charm $(c\overline{c})$ from longitudinally and transversely polarised photons (of virtuality $Q^2$) incident at high energy $(\sqrt{s})$ on a proton target. We study both the $Q^2$ and $M^2$ dependence of the cross sections, where $M$ is the invariant mass of the $c\overline{c}$ pair. Surprisingly, the result for $σ^T$, as well as for $σ^L$, is perturbatively stable. We estimate higher-order corrections and find a sizeable enhancement of the cross sections. The cross sections depend on the…
Processes of heavy quark photoproduction at HERA energies and beyond are investigated using the semihard ($k_{\bot}$ factorization) approach. Virtuality and longitudinal polarization of gluons in the photon - gluon subprocess as well as the saturation effects in the gluon distribution function at small $x$ have been taken into account. The total cross sections, rapidity and $p_{\bot}$ distributions of the charm and beauty quark photoproduction have been calculated. The results are compared with ZEUS experimental data for charm photoproduction cross section.
We show that the cross section for inclusive charm production exhibits geometric scaling in a large range of photon virtualities. In the HERA kinematic domain the saturation momentum $Q_{sat}^2(x)$ stays below the hard scale $μ_c^2=4m_c^2$, implying charm production probing mostly the color transparency regime and unitarization effects being almost negligible. We derive our results considering two saturation models which are able to describe the DESY ep collider HERA data for the proton structure function at small values of the Bjorken variable $x$. A striking feature is the scaling on $τ=Q_2^…
I discuss few selected topics in heavy flavour photoproduction at HERA which require large integrated luminosity in order to be experimentally investigated. I present phenomenological predictions for bottom production. As a possible application of measurements involving double-tagged charm events, I outline a method for the direct measurement of the gluon density in the proton. The possibility of using charm data in polarized electron-proton collisions to constrain the polarized gluon density in the proton is also discussed.
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