9th International Workshop on Multiple Partonic Interactions at the LHC

Collectivity from interference

12 Dec 2017, 19:00

15m

Conference Hall (Hotel Peterhoff, Shimla, India)

WG5: High Multiplicities

Speaker

Boris Blok (Physics Department)

Description

In hadronic collisions, interference between different production channels af-
fects momentum distributions of multi-particle final states. As this QCD interference does
not depend on the strong coupling constant
${\alpha }_s$, it is part of the no-interaction baseline that
needs to be controlled prior to searching for other manifestations of collective dynamics,
e.g., in the analysis of azimuthal anisostropy coefficients $v_n$
at the LHC. Here, we introduce
a model that is based on the QCD theory of multi-parton interactions and that allows one
to study interference effects in the production of $m$
particles in hadronic collisions with N
parton-parton interactions (“sources”). In an expansion in powers of $1/(N_c^2-1)$ and toleading order in the number of sources
N, we calculate interference effects in the $m$-particle
spectra and we determine from them the second and fourth order cumulant momentum
anisotropies $v_n\{2\}$ and $v_n\{4\}$. Without invoking any azimuthal asymmetry and any density
dependent non-linear dynamics in the incoming state, and without invoking any interaction
in the final state, we find that QCD interference alone can give rise to values for $v_n\{2\}$ and $v_n\{4\}$
even, that persist unattenuated for increasing number of sources, that may
increase with increasing multiplicity and that agree with measurements in proton-proton
(pp) collisions in terms of the order of magnitude of the signal and the approximate shape
of the transverse momentum dependence. We further find that the non-abelian features
of QCD interference can give rise to odd harmonic anisotropies. These findings indicate
that the no-interaction baseline including QCD interference effects can make a sizeable if
not dominant contribution to the measured $v_n$
coefficients in pp collisions. Prospects for
analyzing QCD interference contributions further and their possible relevance for proton-
nucleus and nucleus-nucleus collisions are discussed shortly.

Presentation materials

shimla.pdf