Heavy ion physics at LHCb

The LHCb detector, with its excellent momentum resolution and particle identification, is ideally suited for measuring heavy quark hadron and quarkonium production properties. Recent LHCb measurements of charmonium and open charm production in several configurations of proton-nucleus collisions are presented.

of nucleon interactions [76,82,89].R is negative also for x values between about 0.4 and 0.8 which corresponds to the EMC-e↵ect.This e has been first observed in DIS of muons on iron and deuteron nuclei by the European Muon Collabora and is still yet not understood [25,119].At x values close to one R is above one as a result of the Fermi motion, so the quantum mechan motion of nucleons inside their nucleus.
Between the regimes of Shadowing and EMC-e↵ect there is interval in x (x ⇡ 0.1) where R is also posit This e↵ect is called Anti-Shadowing.It is not associated to any particular dynamical e↵ect, but ra to the sum rule of the PDF [42]. Figure 9.1 also reveals to other features about nPDFs: First they very poorly constrained especially at small-x values due to the existing data.Therefore measurem on QCD processes in the forward direction as they can be done at LHCb would serve as input for nP fits at small-x values, similar to the impact of the corresponding measurements with pp data in LHC As LHCb is able to measure Z production up to a rapidity y of about 4.5 in the lab frame, there sensitivity in x down to Impact Parameter The nPDFs describe the fractional momenta xA of the di↵erent parton types inside the protons the neutrons of nuclei.Due to the nuclear e↵ects the nPDFs can have significant deviations from corresponding bare parton distribution functions (PDF) of the proton, which can be seen in   Cross-section measurements in 1.5 < y < 4.0 (forward) and −5.0 < y < −2.5 (backward) as well as p T < 15 GeV/c 27 ± 16stat ± 4syst nb < 39 nb @ 90 % C.L.

Z Production
Nuclear PDF sets so far mainly constrained by fixed target data ⇒ no constraints at very low and very high x A -values Most of the data that are used as constraints in the nPDF fits come as nuclear ratios similar to that shown in Fig. 1.What makes such ratios especially appealing is that they prove remarkably inert to the higher order pQCD corrections.Also, the dependence of the free proton baseline PDFs gets reduced.The exception here are the neutrino-nucleus DIS data, included in the dssz fit that are only available as absolute cross-sections (or as corresponding structure functions derived from those).The inclusion of these data also requires using a general-mass variable-flavor-number scheme (GM-VFNS) for treating the heavy quarks overtaking the zero-mass scheme (ZM-VFNS) employed in the older fits (eps09, hkn07).A comparison of the R Pb uV (x, Q 2 = 10 GeV 2 ) (up valence) and R Pb u (x, Q 2 = 10 GeV 2 ) (up sea) from the available parametrizations is presented in Fig. 2. The areas with yellow background obviously be required to pin down them separately in a that some neutrino data (also sensitive to the valence authors did not investigate the possible difference betwe In the case of R A u , which here generally represents th tions are in a fair agreement in the data-constrained regi are considered (Fig. 1 in Ref. [18]).Above the fications are also especially at R A g via the DGLAP evolution.The largest differences among eps09, hkn07, and ds PDFs, shown in Fig. 3.The origins of the large differen 1.5 1.5 1.5 1.5 1.5 1.5 Mass fit 1.1 4.9 13.0 1.8 19.0 90.0 Luminosity 1.9 1.9 1.9 2.1 2.1 2.1 Trigger 1.9 1.9 1.9 2.1 2.1 2.1 Binning 2.1 2.1 2.1 5.0 5.0 5.0 Reconstruction 1.5 1.5 1.5 1.5 1.5 1.5

[Figure 1 :
Figure 1: Invariant mass distribution of µ + µ pairs in the (left) forward and (right) backward samples of pPb collisions.The transverse momentum range is p T < 15 GeV/c.The rapidity range is 1.5 < y < 4.0 ( 5.0 < y < 2.5) for the forward (backward) sample.The black dots are the data points, the blue dashed curve indicates the signal component, the green dotted curve represents the combinatorial background, and the red solid curve is the sum of the signal and

Figure 1 :
Figure 1: Invariant mass distribution of µ + µ pairs in the (left) forward and (right) backward samples of pPb collisions.The transverse momentum range is p T < 15 GeV/c.The rapidity range is 1.5 < y < 4.0 ( 5.0 < y < 2.5) for the forward (backward) sample.The black dots are the data points, the blue dashed curve indicates the signal component, the green dotted curve represents the combinatorial background, and the red solid curve is the sum of the signal and Low statistics prevent differential measurement

,
Complementary measurement of cold nuclear matter effect with Υ (1S) based on R pPb and R FB R pPb , compared to other measurements and theoretical res, and blue triangles indicate the LHCb measurements s, and J/ from b-hadron decays, respectively[18].The izontal lines) show the statistical uncertainties; the outer tic uncertainties added in quadrature.In each plot data ions for ⌥ and prompt J/ mesons from di↵erent models.

Figure 3 :
Figure 3: Forward-backward production ratio, R FB , as a function of absolute rapidity.The black dots, red squares, and blue triangles indicate the LHCb measurements for ⌥ (1S) mesons, prompt J/ mesons, and J/ from b-hadron decays, respectively [18].The inner error bars (delimited by the horizontal lines) show the statistical uncertainties; the outer ones show the statistical and systematic uncertainties added in quadrature.In each plot data are compared with theoretical predictions for ⌥ and prompt J/ mesons from di↵erent models.The shaded areas indicate the |y| 0 1 2 3 4 5

Figure 2 :
Figure 2: Comparison of up valence and sea quark nuclear modification factors for the lead nucleus at Q 2 = 10 GeV 2 Blue line with errorband is eps09, green dotted line with errorbars dssz, and purple dashed hkn07.

Figure 3 :
Figure 3: Comparison of the gluon nuclear modification factors for nuclear modification for inclusive pion production in d+Au collisio