Double Parton Scattering in Associate Higgs Boson Production with Bottom Hi B P d ti ith B tt Quarks at Hadron Colliders M Y Hussein M Y Hussein M Y Hussein M Y Hussein Department of Physics Department of Physics University of Bahrain University of Bahrain University of Bahrain University of Bahrain SUSY 2007 The 15 th International Conference on Supersymmetry and the Unification of Fundamental Interactions and the Unification of Fundamental Interactions July July 26 July July 26 26-August 26 August August 1, August 1 2007 , 2007 2007 2007 Karlsruha, Germany Karlsruha, Germany
I. Introduction : � The discovery of the SM Higgs boson is one of the most important goals and pressing issues most important goals and pressing issues of present of present and future colliders. � An important � An important prerequisite for prerequisite for identifying the most identifying the most convenient signatures for detecting Higgs boson needs a precise knowledge of the various production cross- a precise knowledge of the various production cross sections and decay branching ratios to derive their masses, masses, their their decay width, decay width, their their couplings to other couplings to other particles. � The precision with which calculations of Higgs boson � The precision with which calculations of Higgs boson cross-sections are know for the most sub-process and improved over last years and has been widely discussed improved over last years and has been widely discussed in the literature .
In particular: In particular: � 1) Next-leading order corrections are now known for most sub-process. p 2) Knowledge of parton distribution functions has improved p as more deep p inelastic data become available. 3) ) The range g of possible p input p parameter p values decreased. � Recently, much progress has been made in the y p g detection of a Higgs boson. The dominant production of a SM Higgs boson in hadronic i t interactins is gluon-gluon fusion. ti i l l f i
� Various channels can be explored to search for Higgs boson at hadron colliders. There are only Higgs boson at hadron colliders There are only a few Higgs production mechanism which lead to to detectable detectable cross section cross-section. Each Each use use the the preference of coupling of the SM Higgs to heavy particles either massive vector bosons or massive quarks. They are: q y 1.Gluon-gluon fusion 2 WW ZZ f 2.WW, ZZ fusion i 3.Associate production with W and Z p 4.Associate production with bottom and top quarks quarks
� The associated production of a Higgs boson with a p pair of quarks has a small cross-section (due to q ( b b b b m small size of Yukawa coupling ) in the SM. b = v ≅ g 0 . 02 b b h � In some extensions of the SM such as the MSSM the � In some extensions of the SM, such as the MSSM, the Yukawa coupling of b-quarks can become strongly enhanced, the associate enhanced, the associate production of a Higgs boson production of a Higgs boson with a pair of quarks can dominate over other b b production channels and this production mechanism production channels and this production mechanism can be a significant source of Higgs bosons. � Detecting � Detecting two two bottom bottom quarks quarks in in the the final final state state identifies uniquely the Higgs coupling responsible for the enhanced cross-section and drastically reduces the the enhanced cross-section and drastically reduces the background. This corresponds to an experiment measuring the Higgs decay along two high p bottom measuring the Higgs decay along two high p t bottom quark jets
� In a four-flavor-number scheme with no b quarks in the initial state, the lowest order process are the tree , p level contributions and , gg → → b b h q q b b h illustrated in Fig. 2. g � Requiring one or two high p t bottom quarks in the final state reduces the signal cross-section, but it also final state reduces the signal cross section, but it also greatly reduces the background, moreover, it assures that the detected Higgs boson has been radiated off a that the detected Higgs boson has been radiated off a bottom or anti-bottom quark and the corresponding cross section is therefore unambiguously proportional cross section is therefore unambiguously proportional to the bottom quark Yukawa coupling. � Therefore, � Therefore a a transverse transverse momentum momentum cuts cuts on on the the bottom quark jets reduces the cross section , but also greatly reduces the background and ensure that the greatly reduces the background and ensure that the Higgs was emmitted from a bottom quark.
� At high energies and due to large flux � At high energies and due to large flux in particular at the LHC, another type of scattering mechanism contributes to of scattering mechanism contributes to the cross section besides to single scattering.Thus,for tt i Th f production d ti b b h there would be two computing mechanisms: � � single parton scattering and double single parton scattering and double parton scattering featuring two Drell- Yan Y processes h happening i simultaneously. ( P. Landshof and J. Polkinghone; F. Halzen, D. Hoyer and W. stirling; CDF Collaboration; …… )
� The purpose of the present work is to point out that the same final state can be produced p b b h also by double parton scattering collision process. process. � The large rate of production of pairs b b expected at the LHC gives rise to a relatively expected at the LHC gives rise to a relatively large probability of production of a in the b b h process underling the H production process underling the H production. � In fact as a result of the present analysis it is found f d that th t d double bl parton t scattering tt i may represent a rather sizable source of b background. k d
I I . DOUBLE SCATTERI NG MECHANI SM � M ltiple � Multiple pa ton parton inte action interaction p ocesses processes, where different pairs of partons have hard p p scattering in the same hadronic collision, become experimentally important at high become experimentally important at high energies because of the growing flux of partons. Recently, the importance of double double parton parton scattering scattering at at the the Large Large Hadron Collider (LHC) has been redressed. ( D. Treleani, N Paver and A. Del Fabbro …… .)
� The multiple parton scattering occurs when two or or more more different different pairs pairs of of parton parton scatter scatter independently in the same hadronic collision. Fig (1) Double parton scattering Fig.(1) Double parton scattering mechanism
� With the only assumption of factorization of the two hard parton processes A and B, the inclusive cross section of a parton processes A and B the inclusive cross section of a double parton-scattering in a hadronic collision is expressed by: m ∑ ∑ D A B 2 b ′ ′ ′ ′ ′ ′ σ σ = = Γ Γ σ σ σ σ Γ Γ ˆ ˆ ( ( x x , x x ; ; b b ) ) ( ( x x , x x ) ) ( ( x x , x x ) ) ( ( x x , x x ; ; b b ) ) dx dx d d x x dx dx d d x x d d b , ( A , B ) i , j 1 2 ik 1 1 jl 2 2 kl 1 2 1 1 2 2 2 i , j , k , l Γ � Where ( , ; ) x x b are the double parton distribution function, ij 1 2 depending on the fractional momenta x 1 , x 2 and the relative transverse distance b of the two parton undergoing the hard processes A and B, the indices i and j refer to the different processes A and B, the indices i and j refer to the different B σ ˆ A parton species and and are the partonic cross section. σ ˆ jl ik The factor m/2 is for symmetry, specifically m= 1 for indistinguishable parton processes and m= 2 for distinguishable processes. Γ Γ ( ( x x , x x ; ; b b ) ) The double distribution The double distribution are the main reason of interest are the main reason of interest ij 1 2 in multiparton collisions. This distributions contain in fact all the information of probing the hadron in two different points contemporarily through the hard processes A and B.
� The cross section for multiparton process is sizable when the flux of partons is large, namely at small x. p g , y Given the large flux one may hence expect that correlations in momentum fraction will not be a major effect and partons to be rather correlated in transverse space. Neglecting the effect of parton p g g p correlations in x one writes: i Γ = Γ Γ ( x , x ; b ) ( x ) ( x ) F ( b ) ij ij 1 1 2 2 i i 1 1 2 2 2 2 j j � Where Γ ( x ) are the usual one boday parton i distribution distribution function function and and F i is a function is a function F j ( b ( b ) ) normalized to one and representing the pair density in in transverse transverse space space. The The inclusive inclusive cross section cross section hence simplifies to: m m � � ∑ Θ ∑ D D ij ij σ = σ ˆ ˆ σ ˆ ˆ ( A ) ( B ), ( A , B ) kl ij kl 2 ijkl
Recommend
More recommend
