Testing Hadronisation Models with the CEPC A (small) selection of topics Peter Skands (Monash U) Nonperturbative QFT remains among the most fundamental problems in physics A day will come when someone (claims to) have a solution, or at least a systematically improvable approximation (+ LHC ⟷ further refinements of phenomenological models of NP QCD) Program of high-precision QCD measurements at CEPC/FCC-ee Ultimate trial by fire for any future treatment of confinement in high-energy processes Basic requirements: Measure effects of order Λ QCD with high precision Disentangle different “tracers”: strangeness, baryons, mass, & spin → PID Other aspects: H → gg, Colour Reconnections (in Z, WW, ttbar), and Power Corrections Interplay with other components of physics program; α s measurements; γγ collisions CEPC Workshop November 2018, IHEP, Beijing
QCD THEMES @ CEPC ๏ Measure alphaS • High-Precision Z (and W) widths • High-Precision Event Shapes, Jet Rates, … (IR safe observables sensitive to alphaS) ๏ Single-Inclusive Hadron Production and Decays • Fragmentation Functions; Hadron Spectra; (+ polarisation) • Exotic /rare hadrons, rare decays, … • + Interplay with flavour studies (+ Interplay with DM annihilation) ๏ Understanding Confinement (Multi-hadronic / Exclusive) • In high-energy processes → hadronisation • Hadron correlations, properties with respect to global (“string”) axes • Dependence on (global and local) environment (distance to jets, hadronic density, flavours) ๏ Power Corrections / Hadronisation Corrections • Interplay with high-p T physics program • Low-Q region of event shapes, jet rates, jet substructure; jet flavour tagging, … • Crucial for alphaS measurements; also for jet calibration? 2 � T ESTI N G H A DR ONISATION M O D E L S W IT H T HE CEPC P. S KAN DS - M O N ASH U.
THE FUNDAMENTAL PARAMETER OF (NON-PERTURBATIVE) QCD ๏ The “string tension” κ ~ 1 GeV/fm ~ 0.2 GeV 2 ~ (0.45 GeV) 2 • Can be extracted from hadron spectroscopy • Also: lattice quark-antiquark potential SCALING. . . POTENTIAL: 2641 46 STATIC QUARK-ANTIQUARK 0.6 • SESAM COLLABORATION “OBSERVATION OF STRING BREAKING IN QCD,” PHYS.REV. D71 (2005) 114513 Scaling plot (with string breaking) 0.4 G. BALI AND K. SCHILLING, “STATIC QUARK - ANTI-QUARK 2GeV- POTENTIAL: SCALING BEHAVIOR AND FINITE SIZE EFFECTS IN SU(3) LATTICE GAUGE THEORY,” PHYS.REV. D46 (1992) 2636 [E(r) - 2 m B ]/GeV (without string breaking) 0.2 2m B s 1 GeV— 0 2m B 2 -0.2 state |1> -0.4 state |2> B = 6. 0, L=16 'V ~ B = 6. 0, L=32 ~ ~ I ~ n f = 2 + 1 B = 6. 2, L=24 B = 6. 4, L-24 -0.6 I B = 6. 4, L=32 -2 A k, I 4 2' t 3. 0. 5 1. 2. 5 0.8 1.0 1.2 1.4 1.6 5 1 fm 5 l~ r/fm RK FIG. 4. All potential data of the five lattices have been scaled to a universal curve by subtracting Vo and measuring energies and to V(R) = R — units of &E. The dashed curve correspond ~/12R. Physical units are calculated distances in appropriate by exploit- � 1 � r − 1 ing the relation &cr =420 MeV. V ( r ) = − e + σ ( r − r c ) r c AM~a=46. 1A~ &235(2)(13) MeV . we are aware that our lattice turbative results. Although � 3 T ESTI N G H A DR ONISATION M O D E L S W IT H T HE CEPC P. S KAN DS - M O N ASH U. dare to is not yet really suScient, resolution we might apply to to say, this value does not necessarily Needless of the previe~ the continuum behavior Coulomb-like full QCD. In Fig. 6(a) [6(b)] we visualize the term from our results. behavior of the confining to the long-range In addition in the K-e plane from fits to various confidence regions it is of considerable interest to investigate its ul- lattices at P=6. 0 potential on- and off-axis potentials on the 32 into the weak cou- structure. As we proceed traviolet [6. 4]. We observe that the impact of lattice discretization on e decreases by a factor 2, as we step up from P = 6. 0 to are expected to meet per- pling regime lattice simulations 150 Barkai '84 o '90 MTC Our results:--- 140 130- 120- 110- 100- 80— 5. 6 5. 8 6. 2 6. 4 c = &E /(a AL ) ] as a function of P. Our results are combined FIG. 5. The on-axis string tension [in units of the quantity with pre- and Rebbi [11]. vious values obtained by the MTc collaboration [10] and Barkai, Moriarty,
I CAN’T — SCHWINGER COULD J. S. SCHWINGER, “ON GAUGE INVARIANCE AND VACUUM POLARIZATION,” PHYS. REV. 82 (1951) 664–679. ๏ Schwinger (1951) • Non-perturbative pair creation of e + e - pairs in a strong external electric field Schwinger Effect ÷ Non-perturbative creation of e + e - pairs in a strong external Electric field ~ E Probability from e + Tunneling Factor ✓ − m 2 − p 2 e - ◆ ⊥ P ∝ exp κ / π + ( κ is the string tension equivalent) (Not observed experimentally yet, but may happen soon) G. V. DUNNE, “NEW STRONG-FIELD QED EFFECTS AT ELI: NONPERTURBATIVE VACUUM PAIR PRODUCTION,” EUR. PHYS. J. D55 (2009) 327–340, 0812.3163. 4 � T ESTI N G H A DR ONISATION M O D E L S W IT H T HE CEPC P. S KAN DS - M O N ASH U.
<latexit sha1_base64="HqaEV6u+WmjbKkU8tA6AW46qFGc=">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</latexit> <latexit sha1_base64="HqaEV6u+WmjbKkU8tA6AW46qFGc=">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</latexit> <latexit sha1_base64="HqaEV6u+WmjbKkU8tA6AW46qFGc=">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</latexit> <latexit sha1_base64="HqaEV6u+WmjbKkU8tA6AW46qFGc=">ACdHichVFNbxMxEPVuC7ThKy0HDvRgiCqVS7QbQOVQoQoOcCwSvF6crzCZWbK+xZ5Gi1f6C/jtu/AwunOukW6m0SIxk6em9N/LMm9wq6TFJfkXxua9+w+2tjsPHz1+8rS7szvyZeUEDEWpSneWcw9KGhiRAVn1gHXuYLTfPFpZ/+AOdlab7h0sJE85mRhRQcA5V1L5iCAo+ozZgFZ8HlDk5m+OHjGmOc6drDb40DWVeahrU/9m/V9wtWjsrHBf1gC24tbypmZWtcJD037xj9LrnM4ya1+eDrNtL+sm6F2QtqBH2jrJuj/ZtBSVBoNCce/HaWJxUnOHUihoOqzyYLlY8BmMAzQ87DKp16E1dD8wU1qULjyDdM3e7Ki59n6p8+BcjelvayvyX9q4wuL9pJbGVghGXH1UVIpiSVcXoFPpQKBaBsCFk2FWKuY8JIXhTp0Qnp75btgNOinAX92zv+2MaxRV6QV+SApOSQHJMv5IQMiSC/o+cRjV5Gf+K9uBfvX1njqO15Rv6quH8J6C298w=</latexit> I CAN’T — SCHWINGER COULD J. S. SCHWINGER, “ON GAUGE INVARIANCE AND VACUUM POLARIZATION,” PHYS. REV. 82 (1951) 664–679. ๏ Schwinger (1951) • Non-perturbative pair creation of e + e - pairs in a strong external electric field Several groups found same form for QCD at successive levels of Schwinger Effect modeling/approximation ÷ Non-perturbative creation Generic prediction: of e + e - pairs in a strong external Electric field Neglecting perturbative effects, ~ hadrons produced from a QCD string E Probability from e + stretched between a quark and Tunneling Factor antiquark should have a universal ✓ − m 2 − p 2 e - ◆ (flavour-independent) p T spectrum, with ⊥ P ∝ exp κ / π quark ∼ 2 κ p 2 p 2 π ∼ (0 . 35 GeV) 2 + ⌦ ↵ ⌦ ↵ meson ∼ 2 ( κ is the string tension equivalent) ⊥ ⊥ (Not observed experimentally So this is an interesting scale! yet, but may happen soon) (modified by perturbative effects + hadron decays) 5 � T ESTI N G H A DR ONISATION M O D E L S W IT H T HE CEPC P. S KAN DS - M O N ASH U.
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