Sung-Won Lee 1

Study of Jets Production Association with a Z boson in pp Collision

at 7 and 8 TeV with the CMS Detector

Kittikul Kovitanggoon

Texas Tech University

2

Angular Correlation of Z and a jet

In the center-of-momentum frame (variables are marked with “ * ”), the differential cross section is

The observed cosθ* distribution can be used to indicated a new particle or improved pQCD as feed back to experts

''Z+jet'' events are predominantly produced by quark exchange processes (i.e. qq, → Z 0 g and qg → Z 0 q as shown in the previous slide)

We focus on angular variables which closely related to cosθ* Rapidity distributions of Z boson: |y

z|

Rapidity distributions of leading jet: |yjet

| Rapidity difference: y

diff = 0.5|y

z-y

jet|

Related to the scattering angle at the center of momentum frame: tanh(y

diff) = β*cosθ*

Rapidity average: ysum

= 0.5|yz+y

jet|

Rapidity boost from the center of momentum frame to the lab frame

y=12

ln ( E+pzE− pz )

3

Combined Results (Electron + Muon)

Phys. Rev. D 88, 112009 (2013)

The data for the |yZ| and |y

jet| distributions agree to better than 5% accuracy

However, MADGRAPH (LO PDF) is less consistent with the data

4

Combined Results (Electron + Muon)

Phys. Rev. D 88, 112009 (2013)

The data agree with all predictions at low region

At high region, SHERPA is the better prediction than MEADGRAPH amd MCFM

LO PDF makes MADGRAPH less consistent with the data

5

Combined Results (Electron + Muon)

Phys. Rev. D 88, 112009 (2013)

The ydif

distribution is consistent

with MCFM for ydif

< 1

The two hybrid programs differconsiderably in the prediction for y

dif

The difference in the distribution of y

dif can be attributed to the matching

algorithm, with the SHERPA CKKW scheme appearing more consistent with the data

The difference in ydiff

between the

LO and NLO matrix elements is due to the contribution from NLO diagrams with a gluon propagator that yield more forward rapidities

6

Z+jets differential Cross Section

Two of the Higgs decay modes are H → ZZ and ZH → l+l-bƀ

Z+jets can be the major background for new physics

Search of dark matter in SUSY (gluino cascades)

This analysis is the update with 2012 at 8TeV Ongoing analysis SMP-13-007

Z+jets differential cross section measurements can be used to improve high order pQCD calculation

dσd ( x )

=N signal−N bg

∫ Ldt× ε×widthbin The Z+jets production cross section as a function of the jet multiplicity : dσ/ dN

J

The Z+jets cross section as a function of the jet pT : dσ/ dpT

The Z+jets cross section as a function of the jet η : dσ/ dη

7

Results

The trend of the jet multiplicity represents the expectation of the pQCD prediction for an exponential decay with number of jets

MADGRAPH is a good description of data for jet multiplicity

Njet

8

Results (II)

MADGRAPH provides a globally satisfactory description of data,but slightly overestimating the first and second leading jet spectra at high p

T

pT

jet

1st leading jet 2nd leading jet

9

Results (II)ηjet

1st leading jet 2nd leading jet

MADGRAPH shows the slightly overestimate in the |η|<0.6 and underestimate in the |η|>1.6

10

Conclusions Jets productions in association with a Z boson in p-p collision

provides a good opportunity to test perturbative QCD and

important background for new physics

Angular distributions for the Z boson and a single jet of 5.0 fb− 1

at 7 TeV have been analyzed

Differential cross sections for the Z boson and jets of 19.8 fb− 1 at 8 TeV have been calculated

More detail studies for Differential cross sections (i.e. complete uncertainty and combine results with electron channel) will be done