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D meson nuclear modification factor and vn harmonics in PbPb collisions at 5.02 TeV with CMS
Available online at www.sciencedirect.com
Nuclear Physics A 967 (2017) 608–611 www.elsevier.com/locate/nuclphysa
D meson nuclear modification factor and vn harmonics in PbPb collisions at 5.02 TeV with CMS Jian Sun on behalf of the CMS Collaboration Department of Physics and Astronomy, Purdue University, USA
Abstract The measurement of heavy flavor production is a powerful tool to study the properties of the high-density QCD medium created in heavy-ion collisions as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. In particular, the comparison between the nuclear modification factors (RAA ) of light- and heavy-flavor particles provides insights into the expected flavor dependence of in-medium parton energy loss. Furthermore, azimuthal anisotropy coefficients (vn ) of heavy-flavor particles provide insights into the degree of the thermalization of the bulk medium at low pT , and unique information about the path length dependence of heavy quark energy loss at high pT . Using the large pp and PbPb samples collected at 5.02 TeV during the 2015 LHC run, high precision open charm measurements are performed with the CMS detector in a wide transverse momentum range. This allows us to set an important milestone in our understanding of the interactions between charm quarks and the medium. In this talk, the most recent results of the RAA , v2 and v3 of prompt D0 mesons in PbPb collisions at 5.02 TeV are presented and compared to the same results for charged particles (dominated by light flavor hadrons) at the same energy. Keywords: Quark-Gluon Plasma, heavy flavor, D meson
1. Introduction Heavy quarks are produced primarily at early stages of heavy-ion collisions due to their large masses, and thus experience the full evolution of Quark-Gluon Plasma (QGP) produced in such collisions and carry important information about the medium. Therefore, the measurement of heavy flavor production is a powerful tool to study the properties of QGP medium as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. Heavy quarks are expected to lose less energy than light quarks due to the dead cone effect [1]. The comparison between the nuclear modification factors (RAA ) of light- and heavy-flavor particles provides insights into the expected flavor dependence of in-medium parton energy loss. Furthermore, detailed measurements of both production and azimuthal anisotropy in the final state for charm and bottom hadrons can supply crucial information for understanding the properties of the strongly interacting QCD matter. Azimuthal anisotropy coefficients (vn ) of heavy-flavor particles provide insights into the interaction strength between heavy quarks and the medium at low pT , and unique information about the path length dependence of heavy quark energy loss at high pT . With 2011 PbPb data at 2.76 TeV, the prompt D0 RAA has been measured with the CMS detector [2, 3]. Strong suppression of D0 production in PbPb collisions and hint of flavor dependent RAA is observed. Using http://dx.doi.org/10.1016/j.nuclphysa.2017.05.060 0375-9474/© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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the large pp and PbPb samples collected at 5.02 TeV during the 2015 LHC run, high precision open charm measurements, including the RAA [4] and vn parameters [5] of prompt D0 , are performed with CMS in a wide transverse momentum range. In this paper, the most recent results of the prompt D0 RAA and vn in PbPb at 5.02 TeV from CMS are presented. The RAA is measured up to 100 GeV/c, for the centrality classes 0–10% and 0–100%. The measurement of v2 and v3 is performed up to 40 GeV/c, for the centrality classes 0–10%, 10–30% and 30–50%. The prompt D0 RAA and vn are compared to those of charged particles at the same energy. This allows us to set an important milestone in our understanding of the interactions between charm quarks and the medium. 2. Results 25.8 pb-1 (5.02 TeV pp)
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Fig. 1. Prompt D0 cross sections in pp collisions at 5.02 TeV [4]. The calculation from FONLL [6] is plotted for comparison.
Fig. 2. Prompt D0 RAA as a function of pT for the centrality classes 0-100% (left) and 0–10% (right) in PbPb collision at 5.02 TeV [4]. The RAA of charged particles (|η| < 1.0) [7] and B+ meson (|y| < 2.4) [8] are shown for comparison.
Compared with the previous measurement of the prompt D0 RAA at 2.76 TeV with CMS [3], the significant improvement is that the reference of the new RAA results is measured in pp collisions at the same
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energy as PbPb collisions. Figure 1 shows the prompt D0 cross sections in pp collisions at 5.02 TeV and the calculation from FONLL [6] is plotted for comparison. The measured cross sections are consistent with the upper bound of FONLL calculations. Figure 2 shows the prompt D0 RAA as a function of pT for the centrality classes 0–100% (left) and 0– 10% (right) in PbPb collision at 5.02 TeV [4]. The RAA of charged particles (|η| < 1.0) [7] and B+ meson (|y| < 2.4) [8] are shown for comparison. The prompt D0 RAA decreases with pT for pT < 6 GeV/c and increases with pT for pT > 8 GeV/c, reaching the smallest values in the pT range around 6 to 8 GeV/c. It is found that the prompt D0 RAA is close to the charged particle RAA in a wide kinematic range. Furthermore, the RAA of prompt D0 and B+ mesons are comparable at high pT . However, the uncertainties and the different rapdity ranges should be taken into account. More accurate measurements in the same rapdity range are needed to draw conclusions on the RAA comparison of D and B mesons. CMS Preliminary PbPb sNN = 5.02 TeV 0.25 0.2
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Fig. 3. Prompt D0 v2 (top) and v3 (bottom) for the centrality 0-10% (left), 10-30% (middle) and 30-50% (right) [5]. The charged particle v2 and v3 at mid-pseudorapidity (|η| < 1.0) [9] are also plotted for comparison.
Top panel of Figure 3 shows the prompt D0 v2 for the centrality classes 0–10%, 10–30% and 30–50% [5]. The charged particle v2 at mid-pseudorapidity (|η| < 1.0) [9] is plotted for comparison. The prompt D0 v2 is found to be positive in the pT range of 1 to 40 GeV/c. The v2 increases with pT in pT range of 1 to 4 GeV/c and then decreases with pT in the higher pT range, similar to the trend observed with the charged particle v2 . Futhermore, it exhibits similar centrality dependence as in the case of the charged particle v2 . The significant v2 at low pT suggests that charm quarks pick up significant elliptic flow through the interactions with the medium constituents and thus take part in the collective motion of the system. However, it depends on the detailed microscopic interaction mechanism to evaluate how close charm quarks are to the thermalization. The positive v2 at high pT suggests path length dependence of charm quark energy
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loss. Compared with the charged particle v2 , the prompt D0 v2 is found to be lower in the pT range of 1-6 GeV/c for the non-central centrality classes 10–30% and 30–50%. It is to be further studied whether it is pure a mass ordering effect or other effects, such as hadronization and path length dependence of energy loss, are at play. In the higher pT range, the prompt D0 v2 is consistent with the charged particle v2 , which suggests that path length dependence of charm quark energy loss is similar to that of light quarks. The RAA and v2 at high pT together suggest that the energy loss of charm quarks is similar to that of light quarks. Bottom panel of Figure 3 shows the prompt D0 v3 for the centrality classes 0–10%, 10–30% and 30– 50% [5]. The prompt D0 v3 is found to be positive in the pT range of 2-8 GeV/c, which suggests that charm quarks pick up triangular flow through the interactions with the medium constituents. The v3 is consistent with 0 within uncertainties in the higher pT range. The pT dependence of the prompt D0 v3 is similar to that of the charged particle v3 , namely increasing with pT in the pT range of around 1-4 GeV/c and then decreasing as pT increases in the higher pT range. Compared with the charged particle v3 , the prompt D0 v3 is lower in pT range around 1-6 GeV/c and becomes consistent with the charged particle v3 in the higher pT range, which follows the same trend as showed in comparison of v2 of prompt D0 and charged particles. Similarly as in the case of the charged particle v3 , the prompt D0 v3 exhibits little centrality dependence. In summary, the prompt D0 RAA and vn (n = 2, 3) have been measured in PbPb collisions at 5.02 TeV with CMS. The RAA is measured up to 100 GeV/c and compared with the RAA of charged particles. The RAA shows the prompt D0 production is strongly suppressed in PbPb collisions at 5.02 TeV and the suppression is pT dependent. The prompt D0 RAA is close to the charged particle RAA in a wide kinematic range, and the prompt D0 RAA is also compared with the B+ meson RAA . The measurement of the prompt D0 v2 and v3 is performed in a wide pT range up to 40 GeV/c, for the centrality classes 0–10%, 10–30% and 30–50%. The v2 is found to be positive in the studied pT range of 1 to 40 GeV/c, suggesting collective motion of charm quarks at low pT and path length dependence of charm quark energy loss at high pT . The first measurement of D0 v3 is carried out and positive value is observed at low pT . Compared with those of charged particles, the measured D0 v2 and v3 are found to be lower in the pT range of approximately 1 to 6 GeV/c. The RAA and vn results provide clear evidence that the charm quarks interact strongly with the QGP medium, and provide new constraints on the interaction between charm quarks and the QGP medium. References [1] Y. L. Dokshitzer, D. E. Kharzeev, Heavy quark colorimetry of QCD matter, Phys. Lett. B519 (2001) 199–206. arXiv:hepph/0106202, doi:10.1016/S0370-2693(01)01130-3. [2] S. Chatrchyan, et al., The CMS experiment at the CERN LHC, JINST 3 (2008) S08004. doi:10.1088/1748-0221/3/08/S08004. √ [3] Nuclear Modification Factor of prompt D0 in PbPb Collisions at sNN = 2.76 TeV (CMS-PAS-HIN-15-005). √ [4] D0 meson nuclear modification factor in PbPb collisions at sNN = 5.02 TeV (CMS-PAS-HIN-16-001). [5] D0 meson vn harmonics in PbPb collisions at 5.02 TeV (CMS-PAS-HIN-16-007). [6] M. Cacciari, M. Greco, P. Nason, The pT spectrum in heavy flavor hadroproduction, JHEP 05 (1998) 007. arXiv:hep-ph/9803400, doi:10.1088/1126-6708/1998/05/007. √ [7] V. Khachatryan, et al., Charged-particle nuclear modification factors in PbPb and pPb collisions at sNN = 5.02 TeV, submitted to JHEP. arXiv:1611.01664. √ [8] Study of B+ meson production in pp and PbPb collisions at sNN = 5.02 TeV using exclusive hadronic decays (CMS-PAS-HIN16-011). [9] A. M. Sirunyan, et al., Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV in PbPb collisions at √ sNN = 5.02 TeV, submitted to PLB. arXiv:1702.00630.
Nuclear Physics A 967 (2017) 608–611 www.elsevier.com/locate/nuclphysa
D meson nuclear modification factor and vn harmonics in PbPb collisions at 5.02 TeV with CMS Jian Sun on behalf of the CMS Collaboration Department of Physics and Astronomy, Purdue University, USA
Abstract The measurement of heavy flavor production is a powerful tool to study the properties of the high-density QCD medium created in heavy-ion collisions as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. In particular, the comparison between the nuclear modification factors (RAA ) of light- and heavy-flavor particles provides insights into the expected flavor dependence of in-medium parton energy loss. Furthermore, azimuthal anisotropy coefficients (vn ) of heavy-flavor particles provide insights into the degree of the thermalization of the bulk medium at low pT , and unique information about the path length dependence of heavy quark energy loss at high pT . Using the large pp and PbPb samples collected at 5.02 TeV during the 2015 LHC run, high precision open charm measurements are performed with the CMS detector in a wide transverse momentum range. This allows us to set an important milestone in our understanding of the interactions between charm quarks and the medium. In this talk, the most recent results of the RAA , v2 and v3 of prompt D0 mesons in PbPb collisions at 5.02 TeV are presented and compared to the same results for charged particles (dominated by light flavor hadrons) at the same energy. Keywords: Quark-Gluon Plasma, heavy flavor, D meson
1. Introduction Heavy quarks are produced primarily at early stages of heavy-ion collisions due to their large masses, and thus experience the full evolution of Quark-Gluon Plasma (QGP) produced in such collisions and carry important information about the medium. Therefore, the measurement of heavy flavor production is a powerful tool to study the properties of QGP medium as heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. Heavy quarks are expected to lose less energy than light quarks due to the dead cone effect [1]. The comparison between the nuclear modification factors (RAA ) of light- and heavy-flavor particles provides insights into the expected flavor dependence of in-medium parton energy loss. Furthermore, detailed measurements of both production and azimuthal anisotropy in the final state for charm and bottom hadrons can supply crucial information for understanding the properties of the strongly interacting QCD matter. Azimuthal anisotropy coefficients (vn ) of heavy-flavor particles provide insights into the interaction strength between heavy quarks and the medium at low pT , and unique information about the path length dependence of heavy quark energy loss at high pT . With 2011 PbPb data at 2.76 TeV, the prompt D0 RAA has been measured with the CMS detector [2, 3]. Strong suppression of D0 production in PbPb collisions and hint of flavor dependent RAA is observed. Using http://dx.doi.org/10.1016/j.nuclphysa.2017.05.060 0375-9474/© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
J. Sun / Nuclear Physics A 967 (2017) 608–611
609
the large pp and PbPb samples collected at 5.02 TeV during the 2015 LHC run, high precision open charm measurements, including the RAA [4] and vn parameters [5] of prompt D0 , are performed with CMS in a wide transverse momentum range. In this paper, the most recent results of the prompt D0 RAA and vn in PbPb at 5.02 TeV from CMS are presented. The RAA is measured up to 100 GeV/c, for the centrality classes 0–10% and 0–100%. The measurement of v2 and v3 is performed up to 40 GeV/c, for the centrality classes 0–10%, 10–30% and 30–50%. The prompt D0 RAA and vn are compared to those of charged particles at the same energy. This allows us to set an important milestone in our understanding of the interactions between charm quarks and the medium. 2. Results 25.8 pb-1 (5.02 TeV pp)
1010 109
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Global uncert. 12.1%
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Fig. 1. Prompt D0 cross sections in pp collisions at 5.02 TeV [4]. The calculation from FONLL [6] is plotted for comparison.
Fig. 2. Prompt D0 RAA as a function of pT for the centrality classes 0-100% (left) and 0–10% (right) in PbPb collision at 5.02 TeV [4]. The RAA of charged particles (|η| < 1.0) [7] and B+ meson (|y| < 2.4) [8] are shown for comparison.
Compared with the previous measurement of the prompt D0 RAA at 2.76 TeV with CMS [3], the significant improvement is that the reference of the new RAA results is measured in pp collisions at the same
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energy as PbPb collisions. Figure 1 shows the prompt D0 cross sections in pp collisions at 5.02 TeV and the calculation from FONLL [6] is plotted for comparison. The measured cross sections are consistent with the upper bound of FONLL calculations. Figure 2 shows the prompt D0 RAA as a function of pT for the centrality classes 0–100% (left) and 0– 10% (right) in PbPb collision at 5.02 TeV [4]. The RAA of charged particles (|η| < 1.0) [7] and B+ meson (|y| < 2.4) [8] are shown for comparison. The prompt D0 RAA decreases with pT for pT < 6 GeV/c and increases with pT for pT > 8 GeV/c, reaching the smallest values in the pT range around 6 to 8 GeV/c. It is found that the prompt D0 RAA is close to the charged particle RAA in a wide kinematic range. Furthermore, the RAA of prompt D0 and B+ mesons are comparable at high pT . However, the uncertainties and the different rapdity ranges should be taken into account. More accurate measurements in the same rapdity range are needed to draw conclusions on the RAA comparison of D and B mesons. CMS Preliminary PbPb sNN = 5.02 TeV 0.25 0.2
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Fig. 3. Prompt D0 v2 (top) and v3 (bottom) for the centrality 0-10% (left), 10-30% (middle) and 30-50% (right) [5]. The charged particle v2 and v3 at mid-pseudorapidity (|η| < 1.0) [9] are also plotted for comparison.
Top panel of Figure 3 shows the prompt D0 v2 for the centrality classes 0–10%, 10–30% and 30–50% [5]. The charged particle v2 at mid-pseudorapidity (|η| < 1.0) [9] is plotted for comparison. The prompt D0 v2 is found to be positive in the pT range of 1 to 40 GeV/c. The v2 increases with pT in pT range of 1 to 4 GeV/c and then decreases with pT in the higher pT range, similar to the trend observed with the charged particle v2 . Futhermore, it exhibits similar centrality dependence as in the case of the charged particle v2 . The significant v2 at low pT suggests that charm quarks pick up significant elliptic flow through the interactions with the medium constituents and thus take part in the collective motion of the system. However, it depends on the detailed microscopic interaction mechanism to evaluate how close charm quarks are to the thermalization. The positive v2 at high pT suggests path length dependence of charm quark energy
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loss. Compared with the charged particle v2 , the prompt D0 v2 is found to be lower in the pT range of 1-6 GeV/c for the non-central centrality classes 10–30% and 30–50%. It is to be further studied whether it is pure a mass ordering effect or other effects, such as hadronization and path length dependence of energy loss, are at play. In the higher pT range, the prompt D0 v2 is consistent with the charged particle v2 , which suggests that path length dependence of charm quark energy loss is similar to that of light quarks. The RAA and v2 at high pT together suggest that the energy loss of charm quarks is similar to that of light quarks. Bottom panel of Figure 3 shows the prompt D0 v3 for the centrality classes 0–10%, 10–30% and 30– 50% [5]. The prompt D0 v3 is found to be positive in the pT range of 2-8 GeV/c, which suggests that charm quarks pick up triangular flow through the interactions with the medium constituents. The v3 is consistent with 0 within uncertainties in the higher pT range. The pT dependence of the prompt D0 v3 is similar to that of the charged particle v3 , namely increasing with pT in the pT range of around 1-4 GeV/c and then decreasing as pT increases in the higher pT range. Compared with the charged particle v3 , the prompt D0 v3 is lower in pT range around 1-6 GeV/c and becomes consistent with the charged particle v3 in the higher pT range, which follows the same trend as showed in comparison of v2 of prompt D0 and charged particles. Similarly as in the case of the charged particle v3 , the prompt D0 v3 exhibits little centrality dependence. In summary, the prompt D0 RAA and vn (n = 2, 3) have been measured in PbPb collisions at 5.02 TeV with CMS. The RAA is measured up to 100 GeV/c and compared with the RAA of charged particles. The RAA shows the prompt D0 production is strongly suppressed in PbPb collisions at 5.02 TeV and the suppression is pT dependent. The prompt D0 RAA is close to the charged particle RAA in a wide kinematic range, and the prompt D0 RAA is also compared with the B+ meson RAA . The measurement of the prompt D0 v2 and v3 is performed in a wide pT range up to 40 GeV/c, for the centrality classes 0–10%, 10–30% and 30–50%. The v2 is found to be positive in the studied pT range of 1 to 40 GeV/c, suggesting collective motion of charm quarks at low pT and path length dependence of charm quark energy loss at high pT . The first measurement of D0 v3 is carried out and positive value is observed at low pT . Compared with those of charged particles, the measured D0 v2 and v3 are found to be lower in the pT range of approximately 1 to 6 GeV/c. The RAA and vn results provide clear evidence that the charm quarks interact strongly with the QGP medium, and provide new constraints on the interaction between charm quarks and the QGP medium. References [1] Y. L. Dokshitzer, D. E. Kharzeev, Heavy quark colorimetry of QCD matter, Phys. Lett. B519 (2001) 199–206. arXiv:hepph/0106202, doi:10.1016/S0370-2693(01)01130-3. [2] S. Chatrchyan, et al., The CMS experiment at the CERN LHC, JINST 3 (2008) S08004. doi:10.1088/1748-0221/3/08/S08004. √ [3] Nuclear Modification Factor of prompt D0 in PbPb Collisions at sNN = 2.76 TeV (CMS-PAS-HIN-15-005). √ [4] D0 meson nuclear modification factor in PbPb collisions at sNN = 5.02 TeV (CMS-PAS-HIN-16-001). [5] D0 meson vn harmonics in PbPb collisions at 5.02 TeV (CMS-PAS-HIN-16-007). [6] M. Cacciari, M. Greco, P. Nason, The pT spectrum in heavy flavor hadroproduction, JHEP 05 (1998) 007. arXiv:hep-ph/9803400, doi:10.1088/1126-6708/1998/05/007. √ [7] V. Khachatryan, et al., Charged-particle nuclear modification factors in PbPb and pPb collisions at sNN = 5.02 TeV, submitted to JHEP. arXiv:1611.01664. √ [8] Study of B+ meson production in pp and PbPb collisions at sNN = 5.02 TeV using exclusive hadronic decays (CMS-PAS-HIN16-011). [9] A. M. Sirunyan, et al., Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV in PbPb collisions at √ sNN = 5.02 TeV, submitted to PLB. arXiv:1702.00630.