Phenomenological Analysis of DPS process · Phenomenological Analysis of DPS process Edgar Y....
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Phenomenological Analysis of DPS process Edgar 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 sections can be estimated assuming that the dominant interaction occurs between 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 the initial state of the collision. In this work we will present some of the results obtained from a phenomenological analysis using the simplified 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 the final state of a pp collision incorporates two elements. The first is the hard scattering, which involves a large transfer of transverse momentum and is calculable in pQCD. The second contains non perturbative effects, taking into account low-p t interactions and hadronization. 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 hadron collision. However, experiments at CERN, conducted back in the 80’s by the AFS collaboration, allowed us to observe contributions 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 parton interactions 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, Q 2 ∼ q i , while the hadronic scale (around the order of the hadronic mass M ), which characterizes non-perturbative interactions, 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 Λ 2 . We define DPS cross section: Hypotheses considered 1 Independence of terms longitudinal and transverse momentum. 2 The partons do not have longitudinal correlation. 3 We define σ eff , which has all the transverse information. Define: DPS cross section σ DPS p 1 p 2 = m 2 σ SPS A σ SPS B σ eff . DPS interaction Measurements of σ eff to diferents collaboration. Single Parton Scattering (SPS) Factorisation implies that perturbation theory can be used to calculate the hard scattering cross section, while universal functions such as the PDFs can be included a posteriori to obtain the full theoretical predic- tion. It has been shown experimentally that due to factorisation, PDFs are universal; that is, they can be derived from different physics processes and then used to provide full theoretical predictions, independently from the calculation of the hard scattering cross section. 10 -3 10 -2 10 -1 10 0 x 0 0,2 0,4 0,6 0,8 1 x f i (x,Q 2 ) u u d d s s c c b b g/10 PDFs CTeQ Q 2 = 10GeV 2 Results and Conclusions -8 -6 -4 -2 0 2 4 6 8 Y 10 -4 10 -2 10 0 10 2 10 4 10 6 10 8 d 2 σ/dYdM (pb/GeV) SPS_c c SPS_l l M = 10 GeV s 1/2 = 14 TeV Distribution of rapidity SPS 10 3 10 4 10 5 s 1/2 (GeV) 10 -4 10 -2 10 0 10 2 10 4 10 6 σ (μb) ( c c ) SPS ( l l ) SPS ( c c l l ) DPS LHC Mixed production of bosons with heavy quark -8 -6 -4 -2 0 2 4 6 8 Y 2 10 -3 10 -2 10 -1 10 0 dσ c c /dY 1 dM 1 * dσ l l /dY 2 dM 2 (Pb/GeV 2 ) Y 1 =0 Y 1 =2 Y 1 =4 Y 1 =6 M 1 = M 2 = 10 GeV s 1/2 = 14TeV Distribution of rapidity DPS Conclusions Exploring in the kinematic regime of LHC specifi- cally to SPS and DPS process, when final states are c ¯ c, l ¯ l and c ¯ cl ¯ l , we can map the phase space of these processes observing contribution important to DPS process in 14 TeV with respect to SPS process, and that production charm with rapidez Y=0 makes this possible, and so it goes decreases when the rapidity increases. 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.
Transcript of 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.
