1. Measurement of associated Z plus charm production in pp collisions at  s= 8 TeV Juan Alcaraz Maestre, Alberto Escalante del Valle, Juan Pablo Fernández Ramos, Isabel Josa Mutuberría(CIEMAT). SMP-VJ meeting CIEMAT Dec. 12, 2014

2. Analysis strategy Z+c: Z bosons identified in its μ and e decay channel, Z → l + l − with p T (l) > 20GeV and |η(l)| < 2.1. Leptons well reconstructed (Tight for μ's and Medium for e's)&isolated from hadron activity(details in back-up slides) In the measurement of σ(Z + c) the charm is identified through: Semileptonic channel : A lepton in a jet. Already shown in Nov. 14 Th (measure the ratio Z+c/Z+b too) D *+/- and D +/- exclusive decays. Covered here. ¾( c-quark jets with pT (jet) > 25 GeV and |η(jet)| < 2.5

3. D ± → K ∓ π ± π ± inside a Jet with a 3 tracks IVF vertex D ± channel – Selection Signal region |m(D ± ) − 1.87| < 0.05 GeV Sideband region 0.05 < |m(D ± ) − 1.87| < 0.10 GeV Distributions from now on are sideband subtracted Z ee Z μμ Signal Sideband If several candidates get the 1 st candidate in the IVF collection in the jet with higher pt

4. D *± channel - Selection Loop over all tracks in the jet (instead of using SSV or IVF col.) D0 → K - π + (+c.c.) ; Kaon: track with sign opposite to the π s Apply the following selection criteria : ◮ Lxy /σ(Lxy ) >3, D0 vertex prob.> 0.05 ◮ p t (K) > 1.75, p t (π) > 0.75, p t (π s ) > 0.5 ◮ |ΔR(D ∗, jet)| < 0.5, |ΔR(D0, π s )| < 0.1. ◮ |m(D0) − 1.865| < 0.1 GeV, |Δm − 145| < 5 MeV ◮ Signal region : 1.97 < D ∗ < 2.05 GeV ; sidebands : adyacent bands Distribution s from now on are side-band sub-tracted Z ee Z μμ Signal Sideband If several candidates get the candidate with higher pt in the jet with higher pt

5. Discriminant distribution – charm extraction Assume MC reliable obtain the fraction of Z+c & Z+b in data Z ee Z μμ D*±D*± D*±D*± D±D± D±D± MC is weighted for: Pileup PDF(MSTW) IVF SF Trigger SF e,μ rec. SF BR,FRAG JetProbability disc. MC is weighted for: Pileup PDF(MSTW) Trigger SF e,μ rec. SF BR,FRAG

6. The discrimiant distribution of the JetProbability b-tagging algorithm separates Z+c(cc) and Z+b components Z μμ D±D± Z ee D±D± Templates for Z+b, Z+c, Z+light and Dibosons from MC and ttbar from data (emu sample) f c & f b (& SF's) obtained from a fit to this JetProb. disc. distrib. Charm extraction

7. σ(Z + c) measurement Z ee Z μμ D*±D*± D*±D*± Scaling factors to apply to the fractions predicted by the simulation of Z+c D*±D*± D±D± 1.54 ± 0.31 ± 0.23 1.02 ± 0.27 ± 0.13 0.81 ± 0.13 ± 0.11 0.92 ± 0.13 ± 0.11

8. List of systematics List from Nov. (see backup-slides) plus following adaptations/changes to D hadrons Branching ratios of D hadrons and fragmentation cD (BRFRAG): reweighted the simulation to match the PDG. The error on such set of weights is considered as a source of systematic (more details on backup-slides) Tracks assigned to PV (charm): D*±D*± D±D± Reweight MC to match π s ( d 0 ) distribution in data Reweight MC to match m (2-track-IVF,prim-track ) distribution in data +20% if c D+, -4% if c D0 It increases the cut on p T of the slow pion of the D ( 2010 ) decay by 10%. Z μμ

9. Systematics Relative contribution of each systematic variation D±D±

10. Systematics D*±D*± Relative contribution of each systematic variation

11. Cross section computed as: Total cross section  MADGRAPH (Z+c, Z+b) =  (DY)  fraction of events (evaluated with MADGRAPH) passing the analysis cuts at generator level,i.e. Two opposite sign leptons from the Z with p T (lepton) > 20 GeV and |  (lepton)| < 2.1 A GenJet, classified as c-jet (b-jet) with p T (jet) >25 GeV & |  (jet)|<2.5  MADGRAPH (Z+c) = 8.02  0.09 pb (statistical error only)  MADGRAPH (Z+b) = 4.96  0.03 pb (statistical error only) D±D± D*±D*± 12.1 ± 2.5 ± 1.8 8.2 ± 2.1 ± 1.0 6.4 ± 1.0 ± 0.9 7.3 ± 1.0 ± 0.9

12. Conclusions Analysis essentially completed in three modes Working on the theoretical predictions Unfolding : only needed for σ -diff. in jets Completing the AN D±D± D*±D*± S e mi l. D±D± D*±D*± 12.1 ± 2.5 ± 1.8 8.2 ± 2.1 ± 1.0 6.4 ± 1.0 ± 0.9 7.3 ± 1.0 ± 0.9

13. Click to edit the outline text format Second Outline Level  Third Outline Level Fourth Outline Level  Fifth Outline Level  Sixth Outline Level  Seventh Outline Level  Eighth Outline Level  Ninth Outline Level Back up

14. List of systematics PU : uncertainties in the evaluation of the pileup profile (assuming an inelastic cross section of 73.5 mb instead of 68 mb) PDFs (PDFNNPDF & PDFCT10) : reweighted the Drell-Yan Monte Carlo events according to the new PDF's : NNPDF23_nnlo & PDFCT10 Jet Energy scale and Resolution (JES & JER) : JES: Change pT by its jet energy correction uncertainty JER: change pT by max[0.,pTgen+c*(pT–pTgen)], c is given in https://twiki.cern.ch/twiki/bin/view/CMS/JetResolution#JER_Scaling_factors_and_Uncertai Branching ratios of DX μ hadrons and fragmentation cD (BRFRAG): reweight the simulation to match the PDG as follows: -6% in D+ μ X, -16% in D0 μ X, -18% in Ds μ X and +20% if c D+, -4% if c D0, -20% if c Ds. The rest of channels are also changed so that the sum of all branching ratios is still 1. Missing-et : Misestimations on the Missing transverse energy: modify the missing E_t by 10% of the unclustered missing E_t. Cgluon-splitting, misestimation of the contribution to our background from gluon-splitting from charm : increase a factor 50 % the weight on events with 2c with Δ R (jet,c) < 0.5 Bgluon-splitting, increase 50% the weight on events with 2b w. Δ R(jet,b) < 0.5

15. Click to edit the outline text format Second Outline Level  Third Outline Level Fourth Outline Level  Fifth Outline Level  Sixth Outline Level  Seventh Outline Level  Eighth Outline Level  Ninth Outline Level The systematic of BRFRAG for D hadrons is evaluated by increasing the weight by the error. The weight is the ratio Gladilin/PYT or PDG/PYTHIA of the tables and the factor of increase comes from the error ( for each particle ) obtained from a combination of LEP measurements OPAL, “Measurement of f (c ! D + X), f (b ! D + X) and G ( cc¯ ) /G(had) using D ( 2010 ) mesons”, Eur. Phys. J. C1 (1998), 439–459. ALEPH Collaboration, “Study of charm production in Z decays”, Eur. Phys. J. C16 (2000), no. arXiv:hep-ex/9909032, 597–611. DELPHI Collaboration, “Determination of P(c ! D + ( 2010 ) ) and BR(c ! l + ) at LEP 1”, Eur. Phys. J. C12 (2000) 209–224.

16. Syst. Uncert. due to the limited statistics of the Monte Carlo (MC). Procedure: A new template of each kind is formed by varying each bin on each template independently (done for each bin independently, for each template independently and in the end for all bins of all templates). Each time that all bins are varied, new templates are formed and used to compute the new fractions of Z+c and Z+b. We repeat the first two steps N-times. The new values for each bin should follow a Poisson distribution around the nominal value for that bin. The N new correction factors for Z+c (i.e. fractions of Z+c) are fitted to a gaussian (same for Z+b) The sigma_G of that gaussian is taken as the contribution to the systematics comming from MC (the relative contribution is σ_ G / Mean_G). Z+c with Z μμ Z+b with Z μμ

17. A method has been presented to measure the c-jet tagging efficiencies in CMS-AN-2014/225.This measurement studies a very high purity sample of charm jets associated with a W. In order to account for the possible misestimation of the the c-tagging scale factor, we increase its value by its statistical error ( between 3 % and 4 % depending on the pT(jet) ). c-tagging efficiencies (btag): In addition, and following the strategy of CMS-AN-2013/154 we evaluate the efficiency of finding a b-jet with a reconstructed secondary vertex, either SV or IVF as a function of pT(jet). An systematic uncertainty is computed by correcting by 1 plus the error on the estimation of the SF.

18. Luminosity : 2.6% Correction factors for electrons and muons (zid): Lepton trigger, identification and reconstruction efficiencies are evaluated with the samples of simulated events. In order to account for possible misestimation of the correction factors we increase the correction by the recomended ammount of a 2 % for muons and a 4 % for electrons. mu reco. in jet: We add a 3 % for the misestimation on the reconstruction of a muon within a jet

19. Click to edit the outline text format Second Outline Level  Third Outline Level Fourth Outline Level  Fifth Outline Level  Sixth Outline Level  Seventh Outline Level  Eighth Outline Level  Ninth Outline Level Preselection Standard preselection of Z  ee and Z   plus jets Jets: – PFJets anti-kT, R=0.5 – JEC corrected, both in data and MC – pT(jet) > 25 GeV, |  (jet)| < 2.5 Z  ee: – HLT_Ele17_*_Ele8_* – Electron Id Medium WP – pT(e)> 20 GeV, |  (e)| < 2.1 – Isolated: Icomb/pT <0.15 – Energy corrected – MC corrected for differences in Electron Id and Iso (POG) Z  μμ : – HLT_Mu17_*_Mu8_* – Tight Id WP – pT(e)> 20 GeV, |  (e)| < 2.1 – Isolated: Icomb/pT <0.2 – Momentum scale and resolution corrected (Rochester correction) – MC corrected for differences in Muon Trigger, Id and Iso (POG)

20. Fitting nid = Number of events in data in the ith bin of the vertex mass distribution NiZ+c, NiZ+b, NiZ+light = Number of Z+c, Z+b, Z+light events expected in the ith bin Nittbar, NiVV= Number of ttbar, Dibosons events expected in the ith bin Parameters to fit: scaling factors wrt the MC predictions – SFZ+c, SFZ+b left free in the fit – SFZ+light, SFttbar, SFVV constrained within 30%, 10%, 30%

21. Z ee

22. Click to edit the outline text format Second Outline Level  Third Outline Level Fourth Outline Level  Fifth Outline Level  Sixth Outline Level  Seventh Outline Level  Eighth Outline Level  Ninth Outline Level Signal definition: Z+c event if there is a GenJet with pT> 15 GeV, and a c-hadron AND no b-hadron, in a  R<0.5 aound the GenJet axis. the branching fraction of the decay chain Br(D + ! Kp + p + )(+c.c.) in the 164 PYTHIA simulation (7.9630.025) is lower than the PDG (9.130.19) and we also note that 165 the fragmentation from c to D in the PYTHIA simulation (19.440.02) is lower than the value 166 at [27] (22.70.90.5) obtained from a combination of published measurements performed at 167 LEP[28–30]. The fragmentation from b to D in the PYTHIA simulation (20.780.23) is also 168 lower (22.31.00.5). In all plots comparing data andMC theMC predicted rate for this decay 169 chain is reweighted in order to match the experimental value The product of the branching fractions Br(c ! D + ( 2010 ) )Br(D + ( 2010 ) ! D 0 p + )(+c.c.) in 201 the PYTHIA simulation is 0.743 0.005%, which is about 20% larger than the estimation of 202 the experimental value, (0.622 0.020)%.