Inclusive production of D* mesons in deep-inelastic scattering at HERA is
studied in the range 5 < Q^2 < 100 GeV2 of the photon virtuality and 0.02 < y <
0.70 of the inelasticity of the scattering process. The visible range for the
D* meson is p_T (D*) > 1.25 GeV and |\eta(D*)| < 1.8. The data were taken with
the H1 detector in the years 2004 to 2007 and correspond to an integrated
luminosity of 347 pb^{-1}. Single and double differential cross sections are
measured. The results are compared to QCD predictions.Comment: XIX International Workshop on Deep-Inelastic Scattering and Related
  Subjects (DIS 2011, April 11-15, Newport News, USA

Jung, Andreas W.

English

arXiv

Inclusive production of D* mesons in deep-inelastic scattering at HERA is studied in the range 5 &lt; Q{sup 2} &lt; 100 GeV{sup 2} of the photon virtuality and 0.02 &lt; y &lt; 0.70 of the inelasticity of the scattering process. The visible range for the D* meson is p{sub T} (D*) &gt; 1.25 GeV and |{eta}(D*)| &lt; 1.8. The data were taken with the H1 detector in the years 2004 to 2007 and correspond to an integrated luminosity of 347 pb{sup -1}. Single and double differential cross sections are measured. The results are compared to QCD predictions

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FERMILAB-CONF-11-344-ED∗ production in deep-inelastic Scatteringat low Q2Andreas W. Jung (for the H1 collaboration)Fermi National Accelerator Laboratory (Fermilab)E-mail: ajung@fnal.govAbstract. Inclusive production ofD∗ mesons in deep-inelastic scattering at HERA is studied in therange 5< Q2 < 100 GeV2 of the photon virtuality and 0. 2< y < 0.70 of the inelasticity of thescattering process. The visible range for theD∗ meson ispT (D∗) > 1.25 GeV and|η(D∗)| < 1.8.The data were taken with the H1 detector in the years 2004 to 2007 and correspond to an integratedluminosity of 347 pb−1. Single and double differential cross sections are measured. The results arecompared to QCD predictions.Keywords: HERA, H1, DIS, charm,D∗, differential cross sectionPACS: 13,14INTRODUCTIONHERA was the unique electron-proton (ep) accelerator colliding 27.6 GeV electrons(positrons) with 920 GeV protons providing a center-of-mass energy of√s = 318 GeV.The charm quark production inep scattering is dominated by the boson-gluon-fusion(BGF) process(γ p → cc̄). This production process is directly sensitive to the gluondensity in the proton and allows its universality to be tested. The kinematic region ofdeep-inelastic scattering (DIS) is defined by the four-momentum transfer squared (Q2)of the exchanged photon:Q2 & 5 GeV2. Due to the presence of a hard scale (mc,Q2 orpT ) perturbative Quantum Chromodynamics (pQCD) can be applied. If one of the otherscales is much bigger than the mass, charm quarks can be treatd as massless ("masslessscheme"), otherwise the mass needs to be taken into account ("massive scheme"). Thelatter assumes no charm quark content of the proton.D∗± CROSS SECTION MEASUREMENTS IN DISEvents containing charm quarks are efficiently identified reconstructingD∗ mesons bythe mass difference method.D∗ production in DIS has been measured for photon virtual-ities of: 5< Q2 < 100 GeV2 and inelasticities of: 0. 2< y < 0.70. The full HERAII dataset corresponding to an integrated luminosity of 347 pb−1 has been analyzed. The visi-ble phase space of theD∗ meson is restricted topT (D∗) > 1.25 GeV and|η(D∗)| < 1.8[2]. This measurement yields currently the largest phase space coverage at HERA for aninclusiveD∗ cross section measurement.TheD∗ cross section as a function ofQ2 andx is depicted in Figure 1(left) and (right).6 7 8 910 20 30 40 50 210]2 [nb/GeV2 / dQσd -210-110110]2 [nb/GeV2 / dQσdH1 data (prel.)HVQDIS (MSTW2008f3)HVQDIS (CT10f3)H1 Preliminary]2 [nb/GeV2 / dQσdD* in DIS]2 [GeV2QnormR0.811.2normR5 10 20 50 100-410 -310 -210 / dx [nb]σd10210310410510 / dx [nb]σdH1 data (prel.)HVQDIS (MSTW2008f3)HVQDIS (CT10f3)H1 Preliminary / dx [nb]σdD* in DISx-410 -310 -210normR0.60.811.21.4normRFIGURE 1. D∗ cross section as a function ofQ2 (left) andx (right) compared to the massive NLO QCDcalculation (HVQDIS) using two different proton PDFs: MRST2008f3 [4] or CT10f3 [5].The data are compared to the massive NLO QCD calculation (HVQDIS) using two dif-ferent proton parton density functions (PDFs): MRST2008f3[4] or CT10f3 [5]. TheQ2dependence of the data is well described, while the slope inx is not very well repro-duced. Figure 2 shows theD∗ cross section as a function ofpT (D∗) (left) andη(D∗)2 3 4 5 6 7 8 910 20(D*) [nb/GeV]T / dpσd -310-210-110110210(D*) [nb/GeV]T / dpσdH1 data (prel.)HVQDIS (MSTW2008f3)HVQDIS (CT10f3)H1 Preliminary(D*) [nb/GeV]T / dpσdD* in DIS(D*) [GeV]TpnormR0.511.5normR1.25 2 3 4 5 10 20-1.5 -1 -0.5 0 0.5 1 1.5(D*) [nb]η / dσd01234(D*) [nb]η / dσdH1 data (prel.)HVQDIS (MSTW2008f3)HVQDIS (CT10f3)H1 Preliminary(D*) [nb]η / dσdD* in DIS(D*) [nb]η / dσd(D*)ηnormR0.811.2normR-1.8 -1 -0.5 0 0.5 1 1.8FIGURE 2. D∗ cross section as a function ofpT (D∗) (left) andη(D∗) (right) compared to the massiveNLO QCD calculation (HVQDIS) using two different proton PDFs: MRST2008f3 or CT10f3.(right) compared to the massive NLO QCD predictions by HVQDIS. With either protonPDFs the massive NLO calculation describes the data nicely,except for the highη(D∗)region (forward direction) where it slightly undershoots the data. The two-dimensionalcross section reveals this to be located at lowpT of theD∗ (see Figure 3). Otherwise thedata are reasonable described by the NLO calculation. In order to allow comparisonswith the massless NLO calculation (ZM-VFNS) [7] an additional transverse momen-tum cut in the photon-proton rest frame ofp∗T(D∗) > 2 GeV is applied. The ZM-VFNScalculation uses the CTEQ6.6 proton PDF [1] together with the fragmentation function(D*)η-1.5 -1 -0.5 0 0.5 1 1.500.511.52 (D*) < 2.00 GeVT1.25 < p [nb/GeV]T dpη / dσ2dH1 Preliminary(D*)η-1.5 -1 -0.5 0 0.5 1 1.500.51(D*) < 2.75 GeVT2.00 < p(D*)η-1.5 -1 -0.5 0 0.5 1 1.500.20.40.6 (D*) < 4.00 GeVT2.75 < p(D*)η-1.5 -1 -0.5 0 0.5 1 1.500.050.10.150.2(D*) < 6.00 GeVT4.00 < p(D*)η-1.5 -1 -0.5 0 0.5 1 1.500.0050.01(D*) < 20.00 GeVT6.00 < pH1 data (prel.)HVQDIS (MSTW2008f3)HVQDIS (CT10f3)D* in DISFIGURE 3. Two dimensionalD∗ cross section as a function ofη(D∗) and pT (D∗) compared to themassive NLO QCD calculation (HVQDIS) using two different proton PDFs: MRST2008f3 or CT10f3.KKKS08 [6]. The massless calculation fails completely to describe the data as a func-tion of x (see Fig. 4(left)), whereas the data are reasonably well describ d by the massiveNLO QCD calculation provided by HVQDIS. Figure 4(right) shows theD∗ cross sec-tion as a function ofy which also shows the bad description of the data by the masslessNLO calculation at low values ofy. Differential D∗ cross sections have also been mea-sured for a restrictedD∗ phase space region:|η(D∗)| < 1.5 andpT (D∗) > 1.5 GeV [2].Figure 5 shows these restricted cross section data as a function of Q2 together with thedata from the measurement ofD∗ cross sections at highQ2: 100< Q2 < 1000 GeV2 [8].Data are compared to the massive NLO QCD calculation which describes the data wellwith either proton PDFs, also theQ2 slope is nicely described.-410 -310 -210 / dx [nb]σd10210310410510 / dx [nb]σdH1 data (prel.)ZM-VFNS (CTEQ6.6M)HVQDIS (CT10f3) / dx [nb]σdH1 PreliminaryD* in DISx-410 -310 -210normR0123normR0.1 0.2 0.3 0.4 0.5 0.6 0.7 / dy [nb]σd05101520 / dy [nb]σdH1 data (prel.)ZM-VFNS (CTEQ6.6M)HVQDIS (CT10f3)H1 Preliminary / dy [nb]σdD* in DISy0.1 0.2 0.3 0.4 0.5 0.6 0.7normR0123normRFIGURE 4. D∗ cross section as a function ofx (left) andy (right) for p∗T> 2 GeV compared to themassive NLO QCD calculation (HVQDIS) using the proton PDF: CT10f3 and to the massless (ZM-VFNS) NLO QCD calculation using CTEQ6.6M [1].2 2 3]2 [nb/GeV2 / dQσd-410-310-210-110110]2 [nb/GeV2 / dQσdH1 data)2H1 D* (high QHVQDIS (MSTW2008f3)HVQDIS (CT10f3)]2 [nb/GeV2 / dQσdD* in DISH1]2 [GeV2QnormR0.511.522.55 10 20 50 100 1000FIGURE 5. D∗ cross section as a function ofQ2 with the additional cuts:|η(D∗)| < 1.5 andpT (D∗) >1.5 GeV are shown together with the results from the highQ2 D∗ publication [2]. Data are compared to themassive NLO QCD calculation (HVQDIS) using two different proton PDFs: MRST2008f3 or CT10f3.CONCLUSIONNew measurements using the full H1 HERAII data sample have been analyzed forD∗production inep scattering. The measurement in the DIS regime at mediumQ2 hasbeen carried out in the largest phase space at HERA for inclusive D∗ cross sectionmeasurements. The data are reasonable described by the massive NLO QCD calculation.However, the NLO calculation undershoots the data slightlya high η(D∗) and lowpT (D∗) for either PDFs. The slope inx is not very well reproduced for the massiveNLO QCD calculation, whereas the massless one fails completely to describe thexand y slopes. A restrictedD∗ phase space region allows to compare the data from5 < Q2 < 1000 GeV2 - this includes the highQ2 D∗ data - to the massive NLO QCDpredictions which describes the data nicely in slope and normalization.REFERENCES1. P. M. Nadolskyet al., Phys. Rev. D78 2008 [hep-ph/0802.0007]2. H1 Collaboration, Measurement ofD∗± Meson Production and Determination ofFcc̄2 at low Q2 inDeep-Inelastic Scattering at HERA, 2011 [hep-ph/1106.1028].3. B. W. Harris and J. Smith, Nucl. Phys. B452 (109) 1995.Laenen, E. and Riemersma, S. and Smith, J. and van Neerven, W.L. Nucl. Phys. B392 (162 & 229)1993.4. A.D. Martin, W.J. Stirling, R.S. Thorne and G.Watt Eur. Phys. J. C70 (51) 2010[arXiv:1007.2624]5. H. L. Lai et al., Phys. Rev.D82 2010 074024 [arXiv:1007.2241].6. T. Kneesch, B. A. Kniehl, G. Kramer and I. Schienbein, Nucl. Phys. B799 2008[hep-ph/0712.0481].7. G. Heinrich, B. A. Kniehl, Phys. Rev.D70 2004 [hep-ph/0409303];C. Sandoval, Proc. of XVII International Workshop on Deep-Inelastic Scattering (DIS 2009), Madrid,2009, [hep-ph/0908.0824];C. Sandoval, Inclusive Production of Hadrons in Neutral andCharged Current Deep Inelastic Scatter-ing, Ph.D. Thesis, Univ. Hamburg (2009), DESY-THESIS-2009- 44.8. F.D. Aaronet al. [H1 Collaboration], Phys. Lett.B686 (2010) 91 [arXiv:0911.3989].

D^* production in deep-inelastic scattering at low Q^2

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D* production in deep-inelastic Scattering at low Q2

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