A Simulation Study Of The Coupling Between Higgs Particles And Bottom Quark Yukawa On The Large Hadron Collider

Since the Higgs boson were discovered at LHC in 2012,all the parti-cles predicted by the Standard Model(SM)were all found in experiments.So far,all experiment results agree with the SM very well,but there are some unsolved problems,so the new physics beyond the SM is expected to be found to solve these problems.There are some parameters that can be measured in SM,such as Hbb Yukawa coupling.If these parameters agree with the SM,it means that the SM is verified,otherwise there may be the hints of new physics beyond the SM.In the SM,the Higgs boson is different from other particles.The boson and fermion get mass through the Higgs mechanism.So one of the major task of the LHC is to study the properties of Higgs.The coupling between the Higgs and heavy quarks(bottom and top quark)is one of the properties.Compared to the top quark,the coupling between bottom quark and Higgs has the following advantages,Firstly,the Higgs can directly decay to bottom and anti-bottom quarks.Secondly,the Hbb can be enhanced in large tan ? region in the MSSM model.In LHC experiment,the Hbb coupling has been measured in the pro-cess pp ? VH,H? bb.In this channel,the bottom quark showers to b-jet,so the bottom quark is reconstructed from b-jet tagging.In LHC a great many processes may contain two jets,so we choose the process of the Higgs decay to four leptons to study to avoid analyzing two-jets final states backgrounds.The parton distribution functions(PDFs)containing bottom quark PDF is 5 flavor PDF schemes(5FPDFS),while the 4 flavor PDF schemes(4FPDFS)don't contain bottom quark PDF.In 4FPDFS,the bottom quark is sea quark,and in 5FPDFS the bottom quark is valence quark.When calculating the cross section of VH process with four flavor scheme PDF and five flavor scheme PDF respectively,the difference between the two PDF schemes is as much as an order of magnitude.It should be coincident that the cross sec-tions calculated with 4FPDFs and 5FPDFs for the same process.To solve this problem,the Higgs cross section workgroup at LHC have matched the 5FS and 4FS with Santander Matching prescription.In 4FPDFs,there will not be gb ? Hb process in tree level in the SM,and in 5FPDFS there will be the collinear singularity derived from the gluon splitting to bottom and anti-bottom quarks.How to absorb this collinear singularity corresponds to different flavor PDF schemes.The Monte Carlo simulation contains the steps as followings.Firstly,we generate 105 pp ? Hb,H?4l events as signal,105 pp ? b4l events as irreducible background,and 105 pp?Hj,H ? 41 events as reducible background respectively with Madgraph@NLO package,and then calcu-late the probabilities of the final state leptons that can be probed with the kinematic informations after Delphes simulation.The Higgs can decay to four electrons,four muons and two electrons associated with two muons seperately via a on-shell Z boson and a off-shell Z boson.We can calculate the cross section of the three different combinations of final state leptons,and calculate the number of four leptons.Becacuse the detection efficien-cies for each kind of leptons is independent,so we can calculate event de-tection efficiency with the lepton detection efficiencies.Secondly,we can get the b-tagging efficiency after detector simulation with Delphes and cal-culate the event detection efficiency.The results can be compared with the events detection efficiency calcuted with lepton detection efficiency.Finally,we combine the signal and backgrounds in the same histogram,and calculate the signal significance after normanize the events number to 3000fb-1 and the corresponding cross sections,which is 1.7.The result can provide reference for future LHC experiment.