Heavy Flavour Production at HERA

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1 Journal of Physis: onferene Series OPEN AESS Heavy Flavour Prodution at HERA To ite this artile: Ringail Plaakyt and the H1 and Zeus ollaborations 014 J. Phys.: onf. Ser View the artile online for updates and enhanements. Related ontent - Note P D Thompson - Heavy flavour prodution at HERA M E Hayes and M Krämer - New parton distributions in a fixed flavour fatorization sheme from reent deepinelasti-sattering data H Khanpour, Ali N Khorramian and S Atashbar Tehrani This ontent was downloaded from IP address on 13/05/018 at 19:45

2 XI International onferene on Hyperons, harm and Beauty Hadrons (BEAH 014) IOP Publishing Journal of Physis: onferene Series 556 (014) 010 doi: / /556/1/010 Heavy Flavour Prodution at HERA Ringailė Plačakytė (on behalf of the ollaborations) Deutshes Elektronen Synhrotron, Notkestrasse 85, 603 Hamburg, Germany Abstrat. Measurements of open harm and beauty prodution at HERA provide important input for stringent tests of quantum hromodynamis and are used to onstrain the parton distribution funtions of the proton. The reent results on the heavy flavour prodution obtained by the experiments at HERA are reviewed in this ontribution. 1. Heavy Flavour Prodution at HERA The prodution of beauty and harm quarks in ep ollisions at HERA provides important tests of the theory of perturbative Quantum hromodynamis (pqd). At leading order, the dominant proess for heavy-quark prodution at HERA is boson-gluon fusion (BGF) where a virtual photon emitted by the inoming eletron (positron) interats with a gluon from the proton forming a heavy quark-antiquark pair. Besides the masses of the heavy quarks, additional sales involved in the heavy flavour prodution are the virtuality, Q, of the exhanged photon in ase of deep inelasti sattering (DIS) and the transverse momenta, p T, of the outgoing quarks. Depending on the details how the sales are treated, different approahes are available in pqd for the treatment of the heavy flavours in DIS: The zero-mass variable-flavour-number-sheme (ZM-VFNS): in this sheme only three light flavours are partiipating in the parton evolution and the harm quark is treated as a massless parton above the threshold at Q harm quark mass, m. Fixed Flavour Number Sheme (FFNS): heavy quarks are treated as massive at all sales but they are not onsidered as partons in the proton. The numbers of ative flavours are fixed to three (four) for harm (beauty). Heavy quarks are assumed to be produed only in the hard sattering proess. In the FFNS alulations [1, ] the pole mass [3] or the running mass definition [4] is used (later adopted from the reent ABM variant of the FFN sheme). General Mass Variable Flavour Number Sheme (GM-VFNS): an interpolation sheme where a low Q region with FFNS and high Q region with ZM-VFN shemes are ombined. GM-VFNS profits from the advantages of those two shemes, however, at the interpolation region some level of arbitrariness is introdued for the treatment of heavy quarks. At HERA different tehniques have been used to measure open harm prodution ross setions in DIS: the full reonstrution of D or D mesons, the long lifetime of heavy flavoured hadrons and semi-leptoni deays of heavy hadrons. The best signal-to-bakground ratio is observed using the full reonstrution of D mesons albeit having the small branhing ratios. The method using semi-leptoni deays profits from larger branhing ratios but has worse signal-to-bakground ontent from this work may be used under the terms of the reative ommons Attribution 3.0 liene. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal itation and DOI. Published under liene by IOP Publishing Ltd 1

3 XI International onferene on Hyperons, harm and Beauty Hadrons (BEAH 014) IOP Publishing Journal of Physis: onferene Series 556 (014) 010 doi: / /556/1/010 ratio. Finally, inlusive analyses using lifetime information have no limitation on branhing ratios but yield the worst signal-to-bakground ratio. In the following, the reent HERA heavy flavour measurements are reviewed.. ombination of harm Prodution Measurements and QD Analysis Nine different harm data sets measured with different harm tagging tehniques are ombined into one onsistent set taking into aount orrelated systemati unertainties and the normalisation [5]. The effet of inluding the ombined HERA harm data in the QD analysis of the parton distribution funtions (PDFs) of the proton was also studied in [5]. In this study, the harm and the inlusive data are used with different implementations of the GM-VFN shemes, whih an have different impats on the harm ontribution to the sea quark distribution and thus affet the flavour omposition of the quark PDFs. Therefore the auray of the harm data influenes the unertainties on the W ± and Z prodution ross setion preditions at LH. Figure 1 (left) summarises the study by showing the harm quark mass M (whih, due to freedom introdued by an interpolation approah in GM-VFN shemes, an be treated as a parameter in the fit) for all shemes used in the fits. It is interesting to observe that firstly, different shemes have different optimal harm quark mass parameter M opt, and seondly, the χ minimum values are omparable for all shemes despite different optimal values of M. The PDFs with M opt were then propagated to the alulation of W ± and Z boson prodution ross setion preditions for the LH. As an example, the W + prodution ross setion as a funtion of M for the different shemes is shown in figure 1 (right). Good agreement between these preditions is observed at M opt whih results in a redution of the unertainties due to the heavy flavour treatment to below 1.5%. In addition, the running mass of the harm quark m (m ) is determined using the FFN sheme where, unlike in GM-VFNS, the harm quark mass orresponds diretly to a physial mass (figure, left). ) (M χ harm + HERA I inlusive RT standard RT optimised AOT full S AOT χ ZM VFNS opt M [nb] + W σ harm + HERA I inlusive RT standard RT optimised AOT full S AOT χ ZM VFNS opt M s = 7 TeV M [GeV] [GeV] M Figure 1. Left: The values of χ (M ) for the PDF fit to the ombined HERA inlusive DIS and harm measurements. Right: W + prodution ross setion σ W + at the LH for s = 7 TeV obtained from the resulting PDF fits as a funtion of M. The lines represent different heavy flavour shemes and the stars indiate the values of M opt for eah sheme. 3. Measurement of the harm Mass Running Similarly to running of α s, the sale dependene of the masses of heavy quarks an be alulated perturbatively. For example, the running of the M S beauty quark mass has been established

4 XI International onferene on Hyperons, harm and Beauty Hadrons (BEAH 014) IOP Publishing Journal of Physis: onferene Series 556 (014) 010 doi: / /556/1/010 χ harm + HERA I inlusive FF (ABM) m (m )=1.6 ± 0.05 GeV m (µ) [GeV] preliminary HERA (prel.) PDG with evolved unertainty m (m ) [GeV] µ [GeV] Figure. Left: The values of χ for the PDF fit to the ombined HERA DIS and harm data as a funtion of the running harm quark mass m (m ). Right: The running of the harm mass m (µ) obtained in the MS mass sheme as a funtion of the sale µ. The PDG world average [6] and the band of its expeted running [7] are also shown. from measurements at the LEP ollider [8] but no similar measurement has been performed for harm quark so far. The ombined HERA harm data [5] have been used to show the running of the harm quark mass for the first time. The basi idea is the following: the value of the harm quark mass m (m ) is extrated from the χ distribution of data to theory omparison using PDFs obtained from inlusive DIS HERA data and the same setup as in [5] but varying the harm mass. The extration is performed from harm data subdivided into several kinemati intervals aording to Q and assuming the running of α s and m as predited by QD. The measured m (m ) are reinterpreted in terms of a value of m (µ) at the typial harm measurement sale µ = Q + 4m. In this way, the effet of the initial assumption of QD running on the interpretation of the measurement is minimised. The omparison of m (µ) at different sales with the expeted running behavior is illustrated in figure (right). More details about the extration of the harm mass running at HERA an be found in [9]. 4. Latest Heavy Flavour Measurements at HERA After the ombined analysis of the harm data [5] was performed, new measurements of harm prodution in DIS have been reported at HERA, the most reent of whih are disussed below. The harm prodution has been measured with the detetor using an integrated luminosity of 354 pb 1 by reonstruting D ± mesons in the D ± K ± π ± π ± deay hannel [10]. These new preise data have the potential to onstrain further the parton densities in the proton. In another reent measurement, the ross setions for the photoprodution of D mesons have been measured at three different ep entre-of-mass energies, s = 318, 51 and 5 GeV [11], see figure 3 (left). The dependene on s in this study is presented as normalised to the high-statistis measurement at s = 318 GeV leading to the anellation of a number of systemati effets. Preditions from the next-to-leading order QD desribe the s dependene of the data well demonstrating onsisteny of the gluon distribution probed here with that extrated in PDF fits to inlusive DIS data. These results enhane the onfidene in the QD preditions of harm prodution rates and QD proesses for a future TeV-sale ep ollider. The new, most preise D data measured with integrated luminosity of 363 pb 1 with the detetor have been used to extrat the harm ontribution to the proton struture funtions [1]. These data together with the measurements from H1 [13, 14] were used in the D ombination at the visible ross setion level [15]. The ross setions were ombined 3

5 XI International onferene on Hyperons, harm and Beauty Hadrons (BEAH 014) IOP Publishing Journal of Physis: onferene Series 556 (014) 010 doi: / /556/1/010 R σ W = 136 GeV 15 GeV 19 GeV m b (µ) [GeV] (prel.) ep D* X NLO QD Q < 1 GeV η D* < 1.6 D* 1.9 <p < 0 GeV T <y< s (GeV) PDG with evolved unertainty DELPHI 3-jets DELPHI 4-jets NLO ALEPH OPAL SLD µ [GeV] Figure 3. Left: Normalised D visible photoprodution ross setions as a funtion of the ep entre-of-mass energy. The data points are shown with statistial unertainties (inner error bars) and statistial and systemati unertainties added in quadrature (outer error bars). The preditions from NLO QD are shown as a line with the band representing its unertainty. Right: The running of the beauty mass m b (µ) obtained in the MS mass sheme as a funtion of the sale µ and ompared with the PDG world average [6]. taking into aount all relevant orrelations and thus signifiantly reduing the unertainties. The ombined ross setions an be ompared diretly to differential NLO preditions without the need for extrapolation, however NNLO alulations are desired to math the data preision. Finally, the inlusive jet ross setions in beauty and harm events were used to extrat the heavy-quark ontribution to the proton struture funtion F in the ollaboration [16]. In this analysis the long lifetimes of the weakly deaying b and hadrons and their large masses were exploited. The running beauty-quark mass in the M S sheme was determined (figure 3, right) from an NLO QD fit in the fixed-flavour-number sheme following a proedure similar to that used for extration of the harm-quark mass [5]. This represents the first measurement of the b-quark mass using HERA or any other hadron ollider data. Referenes [1] E. Laenen et al., Phys. Lett. B91, (199) 35; E. Laenen et al., Nul. Phys. B39, (1993) 16; E. Laenen et al., Nul. Phys. B39, (1993) 9; S. Riemersma, J. Smith and W. L. van Neerven, Phys. Lett. B347, (1995) 143 [hep-ph/ ]. [] B. W. Harris and J. Smith, Phys. Rev. D57, (1998) 806 [hep-ph/ ]. [3] K. Nakamura et al., [Partile Data Group], J. Phys. G37, (010) [4] S. Alekhin and S. Moh, Phys. Lett. B699, (011) 345 [arxiv: ]. [5] [ ollaborations], H. Abramowiz et al., Eur.Phys.J. 73 (013) 311 [arxiv: ]. [6] [Partile Data Group], J. Beringer et al., Phys. Rev. D86 (01) 1. [7] B. Shmidt, M. Steinhauser, RunDe: ++ pakage for running and deoupling of the strong oupling and quark masses [arxiv: ]; K.G. hetyrkin, J.H. Kuhn, M. Steinhauser, RunDe: Mathematia pakage for running and deoupling of the strong oupling and quark masses, omp. Phys. omm. 133 (000) 43. [8] [DELPHI ollaborations], J. Abdallah et al., Eur.Phys.J. 55 (008) 55. [9] [ ollaborations], H1-prelim , -prel [10] [ ollaboration], I. Abt et al., JHEP 1305, [11] [ ollaboration], H. Abramowiz et al., DESY-14-08, [arxiv: ]. [1] [ ollaboration], H. Abramowiz et al., JHEP [13] [H1 ollaboration], F.D. Aaron et al., Phys. Lett. B686 (010) 91. [14] [H1 ollaboration], F.D. Aaron et al., Eur. Phys. J. 71 (011) [15] [ ollaborations], H1-prelim , -prel [16] [ ollaboration], DESY , to be published in JHEP [arxiv: ]. 4