C.M.S.:

Muon Group Summer Student: Gianluca Cerminara. Division: EP Supervisor: Chiara Mariotti. Muon Group

A Study of the WW-Fusion Channel in a Model Independent way My Project A Study of the WW-Fusion Channel in a Model Independent way Purpose: The aim of my work is to verify if it’s possible to extract the signal from the background for the process ppqqWWqqℓnqq Tools: PHYTIA for the event generation ROOT for the data analysis CMSJET for the detector simulation … (with enough time a complete simulation…)

Why am I studying this channel?

Why am I studying this channel? A Model Independent Study of the WW Fusion in order to clarify the Symmetry Breaking Mechanism. The Standard Model predicts that without a Higgs the scattering amplitude of the WW fusion process violates unitarity at about 1.5 TeV… …for this reason something must happen: In the Higgs case we will observe a resonance at MHiggs = MWW otherwise the cross section will deviate from the SM prediction. We want to know with which resolution we can study the cross section as a function of the invariant mass of the two scattered W bosons! We are looking for everything that may happen in this channel!!!

What is the signal? 6 fermion final state! Topology Two quarks of the proton emit a W boson, the two bosons interact giving in the final state two other W bosons: one of them decays leptonically and the other decays into a pair of quarks. Signature We must have two jets in the forward region of the detector (from the parton hadronisation) . One muon in the barrel with high Pt and missing energy of the neutrino (from the W decay) Two jets in the central region with high Pt coming from the quarks of the W decay Cross Section s = 2.482 x 101 pb 6 fermion final state!

Quarks fwd Quarks from the W decay

What are the main backgrounds? t-tbar background Topology From the interaction of a quark and an anti-quark or of two gluons of the proton we have a t and anti-t quark pair.They immediately decay into a b and a W. Signature Since the W decays both leptonically and hadronically we have the same final state of the signal: 4 jets (2 from the b and 2 from the W) and a muon. Cross Section s = 1.262 x 102 pb W+jets background Topology A quark and a gluon/anti-quark give a W and a quark/gluon.When the W decays leptonically, the final state is similar to the one of the signal. Signature if during the hadronisation the gluon gives origin to more than one jet this background can be very “dangerous”. Cross Section s = 4.724 x 104 pb

tt-bar backgrounds

+ W+jets background

What I have done until now In order to understand the kinematics of the process I started analyzing the variables at the partonic level applying some cuts in order to evaluate the differences between signal and backgrounds. I tried to identify the most powerful cuts to reduce the background: CUT 1: Difference between the rapidity of the two quarks in the forward region > 3 |hqfwd-hqfwd|>3 CUT 2: Transverse momentum of quarks and lepton bigger than 10 GeV Pt > 10 GeV Efficiency: CUT 1: Signal e = 0.87 tt backg. e = 0.11 CUT 1+CUT 2: Signal e = 0.74 tt backg. e = 0.08 Wjet backg. e = 0.24

Signal t t-bar background W+jets background

CUT 1

CUT 2

Pt quarks forward CUT 2

What I want to do... In these days I will start the most interesting part of the study; I will analyze the reconstructed variables obtained with the CMSJET simulation of the detector.