Heavy quark production and large-x nuclear gluons at EIC

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1 Heavy quark production and large-x nuclear gluons at EIC C. Weiss (JLab), Santa Fe Jets and Heavy Flavor Workshop, -Jan-8 Nuclear partons e x e x B, Q c, b _ c, b _ Nuclear modifications NN interactions in QCD Nuclear gluons at large x Heavy quark production in DIS LO, NLO, sensitivity to gluons N, A G N, A (x) Charm measurements with EIC E. Chudakov, D. Higinbotham, C. Hyde, S. Furletov, Yu. Furletova, D. Nguyen N. Sato, M. Stratmann, M. Strikman, C. Weiss, JLab 6/7 LDRD Project [arxiv:6.856], [arxiv: ] Charm production rates at large x B Charm reconstruction with exclusive D s, jets Particle ID and vertex detection Impact on nuclear gluons Toward jets at EIC

2 Nuclear partons: Nucleon interactions A x i i j = Σ + Σ ij i?... Hard process, QCD factorization Nuclear matrix element A Twist- A -nucleon contribution N Twist- N nucleon PDF, Fermi motion -nucleon contribution N N Twist- N N nucleon interactions! Well-defined operator, scale dependence µ, matching with LQCD, nuclear EFT Physics questions How do interactions modify quarks/gluons with different x? What are the relevant distances in the N N interactions? What are the relevant intermediate states? Non-nucleonic DoF!

3 Nuclear partons: Nuclear modifications Nuclear gluon ratio R g (x).5.5 EPPS6 µ =.69 GeV A = shadowing enhancement? suppression? average distance interactions short distance interactions Status valence/sea quarks Talk Olness... x. < x <.8 Suppression? Interactions at short distances EMC effect cf. short-range N N correlations JLab 6/ GeV.5 < x <. Enhancement? Interactions at average distances Antishadowing x. Shadowing Coherent interactions enabled by diffraction Gribov 7s Suppression effect calculable Frankfurt, Strikman Guzey + Observed in J/ψ photoproduction on nuclei ALICE, CMS Suggests large antishadowing

4 Nuclear partons: Probing gluons 4 Determine nuclear gluon density at large x (.5)! Nuclear gluon probes ea/µa/νa Q dependence of F A,F LA + DGLAP ea/γa Heavy quark production direct probe! pa/ea/γa Jets? EIC capabilities Nuclear beams A = 8 CM energy s en 7 GeV Luminosity L 4 cm s Next-gen detectors with PID and vertex first ea collider coverage at large x B rare processes final states E. Chudakov et al., JLab 6/7 LDRD Project, see also: Aschenauer, Fazio, Lamont, Paukkunen, Zurita, PRD (7)

5 Heavy quark production: QCD description 5 e e T x x B, Q G ( x) h _ h F h (x B,Q ) = ax dx x xg(x) ˆF h g (x B/x,Q,m h,µ ) ˆF h g (...) = e h g Q /m h fun(x B/x,Q ) coefficient function a = + 4m h /Q sets limit of x integral Integrand of F (charm) [normalized] x B =., Q = GeV x B =., Q = GeV x QCD factorization γ T h h+x Inclusive heavy structure functions F h,fh L Differential cross section d 4 σ/dq dηd p T Photon-gluon fusion at LO O(e h g) Couples to gluons only Integrand localized above x ax B, probes gluons almost locally in x Witten 76; Babcock, Sivers 78; Vainshtein, Shifman, Zakharov 78; Gluck, Reya 79

6 Heavy quark production: Higher orders 6 Heavy quark production at NLO Sensitivity to light quarks at O(e h g ) LO photon-gluon fusion large at x >. gluons eg Theoretical uncertainties quantified Laenen, Riemersma, Smith Van Neerven, Harris 9+. Alekhin, Moch, Blümlein, Vogt, Kawamura et al. + quarks eg Perturbative stability LO NLO Good stability of F c with choice of effective LO scale Gluck, Reya, Stratmann 94 Rapidity, p T distributions more sensitive

7 Heavy quark production: HERA 7 cc _ σ red..5 H and ZEUS Q =.5 GeV Q =5 GeV Q =7 GeV Q = GeV Q =8 GeV Q = GeV c c, b b production in ep/γp Mostly x < Various reconstruction methods.5 Q =6 GeV Q = GeV Q = GeV Extensive tests of theory.5 Q =5 GeV Q =65 GeV HERA Q = GeV ABM9NNLO MS ABM9NLO MS Measurements of c D and b B fragmentation functions Simulation tools x HVQDIS LO/NLO cross secn + MC integration Harris, Smith 98 H + ZEUS summary. H. Abramowicz et al. EPJC 7 ()

8 EIC: Charm production rates at large x B 8 Number of events per bin Charm and DIS events in bins, 5 bins/decade in x, bin in Q Int. lumi = fb - Q > 5 GeV s en = GeV Q > GeV Total DIS Charm 4... x B Charm production rates drop rapidly at large x Charm production rates 5 at x B. (L int = fb ) Defines charm reconstruction efficiency needed for physics Charm/DIS ratio % at x. Defines charm reconstruction environment

9 EIC: Charm angle and momentum distributions 9 x ~. c e A e 5 GeV/N GeV 5 GeV/N GeV A c e Large-x c c pairs produced almost at rest in low-ratio collider Example: Gluon with x =. and 5 GeV/N Contrast with high-ratio collider! π/k produced at large angles, with typical momenta 5 GeV Favorable situation! Good PID and momentum resolution available in central detector Enables new methods of charm reconstruction

10 EIC: Charm reconstruction methods Exclusive D-meson decays Inclusive decays with displaced vertex Questions How well do the methods work at large x? What are the overall efficiencies and uncertainties? What detector performance is required? Simulations at different levels ) Theoretical estimates of reconstruction efficiency ) Model acceptance and PID performance, describe resolution effects through smearing of vertex and momentum distributions ) Tracking and vertexing based on schematic JLEIC detector model

11 EIC: Charm with exclusive D s π + D K π + π + π + π+ K K π + K + φ K D + D D + D s + Simple exclusive channel D + π + (slow)+(k π + ) D Used at HERA without PID. Efficiency < % EIC PID + vertex detection allow use of other exclusive channels D,D +,D + s Theoretical efficiency % summed over channels Fragmentation ratio f Branching ratio BR

12 EIC: Charm reconstruction with exclusive D s 8 6! no vertex no PID 5! no vertex 8% PID 9 8! no vertex % PID M K m K [GeV/c ] "##$ vertex no PID m K [GeV/c ] %&$ vertex no PID m K [GeV/c ] %&$ vertex 8% PID D Invariant mass spectrum of two charged tracks/mesons in sample of charm events with Q > GeV and x B >.5. PYTHIA 6 simulation, arbitrary normalization of event sample, no DIS background, vertex cut µm m K [GeV/c ] m K [GeV/c ] m K [GeV/c ] Example: D meson reconstruction using exclusive decay D K π + Level- simulation with mass/momentum and vertex smearing Also other channels Impact of PID and vertex detection

13 EIC: Charm reconstruction with inclusive modes )#%/)&,&-*)"5"$* 4)#%/).(-%!"#$ %&'($)*+,$%-.$&/ ).(-%)*&'- :;<)=>6 Projection on K axis (pos/neg) K momentum axis Primary vertex Secondary vertex Decay length 6".-7)"'$()8%/9".$&/ 4 5 vertex [µm] 4 5 vertex [µm] Decay length significance distribution Establish secondary vertex Project decay length on jet axis, positive/negative Identify D-meson decays through positive projection Used at HERA with vertex detector Use for charm at EIC Identified K from PID Efficiency up to %

14 EIC: Charm reconstruction efficiency 4 ) log(q Kin plot X, Q hxq Entries 689 Mean x.78 Mean y.59 5 Std Dev x.77 Std Dev y.66 log Q hxq_true Charm produced hxq_true Entries 465 Mean x.78 Mean y.59 5 Std Dev x.76 Std Dev y hxq_dall Reconstructed exclusive (sum) hxq_dall Entries 999 Mean x.77 Mean y.5 Std Dev x.76 Std Dev y log x log (X) hxq_ceff hxq_reck hxq_kceff Efficiency exclusive hxq_ceff Entries 9 Mean x.86 Mean y.99 Std Dev x.59 Std Dev y Kaons selected inclusive hxq_reck Entries 8966 Mean x.75 Mean y.5 Std Dev x.744 Std Dev y Efficiency inclusive (*) hxq_kceff Entries 58 Mean x.7877 Mean y.965 Std Dev x.44 Std Dev y Total efficiency estimated 5-7% exclusive, % inclusive Little kinematic variation in (x,q ) region of interest Systematic uncertainties? HERA % Both vertex detection and PID are essential for charm reconstruction

15 Charm impact: PDF reweighting 5 Ensemble χ { a} { a} PDF reweighting Method for quantifying impact of new (pseudo-) data on existing global fit Giele, Keller 98; NNPDF Collab Ball et al ; Paukkunen, Zurita 4; Sato et al 6 Represents existing fit as statistical ensemble, uses Bayes theorem Avoids costly re-fitting Widely used in PDF analysis, HEP Implemented for charm pseudodata from EIC Presently F c, can be extended to other observables Python code package, on github:

16 Charm impact: Large-x gluons 6 F A (charm) Pseudodata error Hessian error Q = x B 6 7 Nuclear gluon ratio g A (x) / [A g N (x)].5.5 present uncertainty EPS9 with EIC F (charm) µ = GeV A = 56.. x Charm pdeudodata F c (x,q ), assumed % total uncertainty, dominated by systematics, point-to-point Here EPS9, LO approximation. To be updated/refined Substantial impact on large x nuclear gluons See also: Aschenauer et al, PRD (7) Theoretical uncertainties to be estimated Nuclear final-state interactions vs. initial-state modifications Uncertainties of nuclear ratios

17 Summary 7 Nuclear PDFs as window on nucleon interactions in QCD New physics topic next step after nucleon structure Twist- operators clear connections with EFT, LQCD, phenomenology Open charm production at EIC can constrain large x nuclear gluons Natural measurement for medium-energy collider Particle ID and vertex detection essential for charm reconstruction Simulation tools available, can start detailed studies JLab LDRD Project LD7/6, Toward jet measurements at EIC New applications: G in ep, medium properties in ea Talk Petriello Theoretical questions: Jet definition at moderate momenta p few GeV Available tools can be used to simulate jet measurements at EIC Open for collaboration!