phenomenological analysis of dps process · phenomenological analysis of dps process edgar y....

Phenomenological Analysis of DPS processEdgar Y. Huayra Paitán e Emmanuel Gräve de Oliveira

Federal University of Santa Catarina

Introduction

Our understanding about the matter and its interactions is be-ing tested in proton-proton collisions at the Large Hadron Collider(LHC). Differently from previous colliders, where the cross sectionscan be estimated assuming that the dominant interaction occursbetween one parton of the projectile and one parton of the target,named Single Parton Scattering processes (SPS).

In the LHC the contribution of Double Parton Scattering (DPS)processes is not negligible due to the high parton luminosity in theinitial state of the collision. In this work we will present some ofthe results obtained from a phenomenological analysis using thesimplified form of the DPS cross section, where the initial state in-volves gluons. Next we will discuss in which regime DPS is relevant,and its possible explanations and contributions to phenomenologi-cal analysis.

Hadronic Processes

A full description of thefinal state of a ppcollision incorporatestwo elements. The firstis the hard scattering,which involves a largetransfer of transversemomentum and iscalculable in pQCD.The second containsnon perturbative effects,taking into accountlow-pt interactions andhadronization.

Particle interaction within LHC

Drell-Yan processes

Double Parton Scattering (DPS)

The standard approach to hard processes usually assumes that only single parton scattering (SPS) occurs in the hadroncollision. However, experiments at CERN, conducted back in the 80’s by the AFS collaboration, allowed us to observecontributions due to double parton scattering. This type of scattering is one of the processes of multi parton interactions(MPI) and occurs when, in one hadron-hadron collision, two independent hard interactions take place. The multi partoninteractions allow us to gain new data on the hadron structure and correlations between the partons within them.

We assume the following:1 The largest scale in the process is a hard scale Q, taken to be aproximately equal to

the masses of the final state particles, Q2 ∼ qi, while the hadronic scale (aroundthe order of the hadronic mass M), which characterizes non-perturbativeinteractions, is much smaller than the hard scale, Λ � Q.

2 All transverse momenta are of the order of the hadronic scale.3 The scattering partons have small virtualities of the order of Λ2.

We define DPS cross section:

Hypotheses considered1 Independence of terms longitudinal and transverse momentum.2 The partons do not have longitudinal correlation.3 We define σeff , which has all the transverse information.

Define:

DPS cross section

σDPSp1p2 = m

2σSPSA σSPSB

σeff.

DPS interaction

Measurements of σeff to diferents collaboration.

Single Parton Scattering (SPS)Factorisation implies that perturbation theory can be used to calculatethe hard scattering cross section, while universal functions such as thePDFs can be included a posteriori to obtain the full theoretical predic-tion.

It has been shown experimentally that due to factorisation, PDFs areuniversal; that is, they can be derived from different physics processesand then used to provide full theoretical predictions, independently fromthe calculation of the hard scattering cross section.

10-3

10-2

10-1

100

x

0

0,2

0,4

0,6

0,8

1

x f

i (x,Q

2)

uuddssccbbg/10

PDFs CTeQ

Q2 = 10GeV

2

Results and Conclusions

-8 -6 -4 -2 0 2 4 6 8

Y

10-4

10-2

100

102

104

106

108

d2σ

/dY

dM

(

pb

/GeV

) SPS_cc

SPS_llM = 10 GeV

s1/2

= 14 TeV

Distribution of rapidity SPS

103

104

105

s1/2

(GeV)

10-4

10-2

100

102

104

106

σ

(µb

)

( cc ) SPS

( l l ) SPS

( cc ll ) DPS

LHC

Mixed production of bosons with heavy quark

-8 -6 -4 -2 0 2 4 6 8

Y2

10-3

10-2

10-1

100

dσ

cc/d

Y1dM

1 *

dσ

ll/d

Y2dM

2 (P

b/G

eV

2)

Y1=0

Y1=2

Y1=4

Y1=6

M1 = M

2 = 10 GeV

s1/2

= 14TeV

Distribution of rapidity DPS

Conclusions

Exploring in the kinematic regime of LHC specifi-cally to SPS and DPS process, when final states arecc̄, ll̄ and cc̄ll̄, we can map the phase space of theseprocesses observing contribution important to DPSprocess in 14 TeV with respect to SPS process, andthat production charm with rapidez Y=0 makes thispossible, and so it goes decreases when the rapidityincreases.

Bibliography

[1] THOMSON, M. particle physics. New York: Cambridge University Press, 2013.

[2] GAUNT, J. R.; KOM, C.-H.; KULESZA, A.; STIRLING, W. J. Same-sign W pair production as a probe of double-parton scattering at the LHC.The European Physical Journal C, Springer, v.69, n. 1-2, p. 53–65, 2010.

[3] KULESZA, A.; STIRLING, W. J. Like-sign W boson production at the LHC as a probe of double parton scattering. Physics Letters B, Elsevier, v. 475, n. 1, p. 168–175, 2000.

[4] DIEHL, M.; OSTERMEIER, D.; SCHÄFER, A. Theoretical considerations on the double Drell-Yan process as a prototype for multiparton interactions. MPI@ LHC 2011, p. 235.