The final state swing Leif Lnnblad Department of Astronomy and - PowerPoint PPT Presentation

Introduction Parton and dipole showers Colour reconnectionsˇ The final state swing Leif Lönnblad Department of Astronomy and Theoretical Physics Lund University Lund 2019-02-27 Swing 1 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Outline ◮ Parton showers,“Pre-confinement” and the size of N C ◮ Colour reconnections ◮ The dipole swing in the shower ◮ Outlook ( p A & AA ) Swing 2 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ The importance of colour connections ◮ All hadrons are colour singlets. ◮ Any realistic hadronisation model must ensure this. ◮ Exact treatment of colour structures in LHC events is impossible(?) ◮ All partons shower approaches use the N C → ∞ approximation which gives a unique colour strucure. Swing 3 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Introduction Parton and dipole showers Colour reconnectionsˇ Parton and dipole showers ◮ Parton splitting ¯ q ◮ Dipole splitting ◮ Pre-confinement: partons close in phase space are likely to be γ ⋆ colour-connected. Nature likes short strings. ◮ N C → ∞ gives a unique colour flow. q ◮ But N C = 3. Swing 4 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Colour reconnections Colour reconnections is a way to include effects of N C < ∞ . The guiding principles are: ◮ Probability to reconnect ∼ 1 / N 2 C ◮ Nature likes short strings ◮ There are no colour-singlet gluons. [Sjöstrand, Khoze, Gustafson, Zerwas, Lönnblad, Edin, Ingelman, Rathsman, Gieseke, Kirchgaeßer, . . . ] Swing 5 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Short strings? We typically measure the string lengths in terms of the λ -measure For a string consisting of n dipoles between a quark and an anti-quark connected with n − 1 gluons: ( q 0 − g 1 − g 2 − · · · − g n − 1 − ¯ q n ) n − 1 � m 2 � i , i + 1 � λ = log 1 + m 2 0 i = 0 Swing 6 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Short strings? We typically measure the string lengths in terms of the λ -measure For a string consisting of n dipoles between a quark and an anti-quark connected with n − 1 gluons: ( q 0 − g 1 − g 2 − · · · − g n − 1 − ¯ q n ) n − 1 � m 2 � n − 1 � m 2 � i , i + 1 i , i + 1 � � λ = log 1 + ∼ log m 2 m 2 0 0 i = 0 i = 0 Swing 6 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Simple reconnections ¯ q 3 q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N 2 C ◮ only if m 14 m 23 < m 12 m 34 Swing 7 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Simple reconnections ¯ q 3 q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N 2 C ◮ only if m 14 m 23 < m 12 m 34 Swing 7 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Simple reconnections ¯ q 3 q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N 2 C ◮ only if m 14 m 23 < m 12 m 34 Swing 7 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Junctions q 3 ¯ q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N C ◮ only if λ -measure is reduced Swing 8 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Junctions q 3 ¯ q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N C ◮ only if λ -measure is reduced Swing 8 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Junctions q 3 ¯ q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N C ◮ only if λ -measure is reduced Swing 8 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ Junctions q 3 ¯ q 4 ¯ q 1 q 2 Reconnect? ◮ with probability 1 / N C ◮ only if λ -measure is reduced Swing 8 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ More Junctions q 5 ¯ q 6 q 3 ¯ q 4 q 1 ¯ q 2 Reconnect? ◮ with probability 1 / N 3 C ◮ only if λ -measure is reduced ◮ (acessible with two subsequent reconnections) Swing 9 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ More Junctions q 5 ¯ q 6 q 3 ¯ q 4 q 1 ¯ q 2 Reconnect? ◮ with probability 1 / N 3 C ◮ only if λ -measure is reduced ◮ (acessible with two subsequent reconnections) Swing 9 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ More Junctions q 5 ¯ q 6 q 3 ¯ q 4 q 1 ¯ q 2 Reconnect? ◮ with probability 1 / N 3 C ◮ only if λ -measure is reduced ◮ (acessible with two subsequent reconnections) Swing 9 Leif Lönnblad Lund University

Parton and dipole showersˆ Colour reconnections The dipole swingˇ More Junctions q 5 ¯ q 6 q 3 ¯ q 4 q 1 ¯ q 2 Reconnect? ◮ with probability 1 / N 3 C ◮ only if λ -measure is reduced ◮ (acessible with two subsequent reconnections) Swing 9 Leif Lönnblad Lund University