1

Dijet Resonances

Kazım Z. Gümüş and Nural Akchurin

Texas Tech University

Selda Esen and Robert M. Harris

Fermilab

PRS JETMET Meeting

July 6, 2005

Kazim Gumus, Texas Tech University 2

Motivation

We search for narrow resonances decaying to dijets

pp X Jet Jet (inclusive) We will use Zprime as a first model for dijet resonances, just to get started.

Theoretical motivation:

Lots of new particles decay to dijets. (See next slide)

Experimental motivation:

LHC is a parton parton collider. Resonances made from partons will decay to partons, giving jets.

3

Axigluon from Chiral Color: SU(3)L x SU(3)R qq A qq, axial-vector (JP=1+) color-octet particle with half-width /2 .05M

Coloron from extended technicolorqq C qq, vector (JP=1-) color-octet particle with half-width /2 .05M

Excited states of composite quarks qg q*qg, fermion (JP=1/2+) color triplet particle with half-width /2 .02M

Technirhos from Technicolorqq,ggqq,gg, vector (JP=1-) color octet particle with half-width /2 .01M

Diquarks in superstring inspired E6 GUT modelsud D ud, scalar (JP=0+) color triplet particle with half-width /2 .004M

Extra W bosons inspired by left-right symmetric grand unified modelsqq W ’qq, vector (JP=1-) color singlet particle with half-width /2 .01M

Extra Z bosons inspired by grand unified modelsqq Z ’qq, vector (JP=1-) color singlet particle with half-width /2 .01M

Randall Sundrum gravitons in model with large extra dimensionsqq, ggGqq,gg, tensor (JP=2-) color singlet particle with half-width /2 <.05M

Narrow Dijet Resonances(from “New Physics with Dijet” talk given by R.Harris at HCAL/JetMet Workshop, 11/12/2004)

4

Cross section

from Robert Harris

Basically, since Zprime is produced with weak force, it has low cross section.

Kazim Gumus, Texas Tech University 5

Data Sample & Software

700 GeV ZprimeData: DC04 data, 400K Zprime decaying to dijets events (Z’ mass 700GeV) We used 50K events.Software: PYTHIA, OSCAR 2_4_5 for sim., ORCA 7_6_0 for digitization. Jet Reconstruction: ORCA_8_4_0. Analysis: JetMetAnalysis/Jets in ORCA_8_4_0. All samples produced with pileup at lum = 2 x 1033 cm-2s-1. RecJetRoot trees were used to write jets on cmsuaf at Fermi lab.

5 TeV ZprimeData: 4526 Zprime decaying to dijets events (Zprime mass 5TeV)Software: CMKIN2_1_0, OSCAR 2_4_6 for sim., ORCA 7_6_0 for digitization. Jet Reconstruction: ORCA_8_7_1. RecJetRoot trees were used to write jets on cmsuaf at Fermi lab. Pileup is not included.

2 TeV ZprimeData: 19500 Zprime decaying to dijets events (Zprime mass 2TeV)Software: CMKIN4_3_1, OSCAR 3_6_5 for sim., ORCA 8_7_3 for digitization. Jet Reconstruction: ORCA_8_7_1. RecJetRoot trees were used to write jets on cmsuaf at Fermi lab. Pileup is not included.

QCD dataSee Selda Esen’s talk given at CMS Physics Week, April 14, 2005

Kazim Gumus, Texas Tech University 6

Jet Reconstruction & Correction

Iterative cone jet algorithm with R=0.5 and E scheme.Generated Jets: particles in the jet cone, excluding pileup.Reconstructed Jets: EcalPlusHcalTowers with ET>500 MeV.Corrected Jets: Reconstructed jets with jetCalibV1 applied.Correction back to particles in jet cone before pileup.

Event Selection

Find the two jets in the event with highest PT: leading jets.Require each leading jet have |eta|<1. Enhances sensitivity to new physics which is produced at low |eta|. Also, Ecal end caps may not be there, or understood, on day 1.Dijet mass: M = sqrt( (E1+E2)2 - (px1+px2

)2 – (py1+py2)2 – (pz1+pz2)2 ).

Cross Section

Bin the dijet mass in ~10% wide bins: bin size increases with mass.Divide rate by the luminosity and bin width: differential cross section

Analysis

(from “New Physics with Dijet” talk given by R.Harris at HCAL/JetMet Workshop, 11/12/2004)

Kazim Gumus, Texas Tech University 7

700 GeV Dijet Mass Distribution

Reconstructed and corrected dijet mass distribution for 700GeV dijets.

Long tail to the low mass is due to final state radiation.

We fit the peak and high mass tail (core) to a gaussian and get mean and .

Kazim Gumus, Texas Tech University 8

2 TeV Dijet Mass Distribution

Reconstructed and corrected dijet mass distribution for 2 TeV dijets.

Kazim Gumus, Texas Tech University 9

5 TeV Dijet Mass Distribution

Reconstructed and corrected dijet mass distribution for 5 TeV dijets.

Rise in the long tail at low mass is due to parton distributions enhancing the tail of the Breit-Wigner resonance at low mass.

Kazim Gumus, Texas Tech University 10

Dijet Resolution (core)

Dijet mass resolution varies from 9.5% at 700 GeV to about 6% at 5 TeV.

Mass bins now roughly 10%, a little larger than resolution. Will reduce them.

Kazim Gumus, Texas Tech University 11

QCD cross section

from Selda Esen

(|eta|<1 )

(Lum=1 fb-1)

There was a bug inthe previously

shown dijet mass cross sections.

They were about a factor of 20 too

small.

This plot is an update, in which the bug has been

removed. The cross section

agrees with a LO QCD calculation.

Kazim Gumus, Texas Tech University 12

700 GeV Dijet Cross section

(|eta|<1, Lum=1fb-1)

Kazim Gumus, Texas Tech University 13

2 TeV Dijet Cross section

(|eta|<1, Lum=1fb-1)

Kazim Gumus, Texas Tech University 14

5 TeV Dijet Cross section

(|eta|<1, Lum=1fb-1)

Kazim Gumus, Texas Tech University 15

Cross section (all)

(|eta|<1 )

(Lum=1fb-1)

Kazim Gumus, Texas Tech University 16

QCD sensitivity

From Selda Esen

600 30 1Trigger Prescales

( Lum = 1 fb-1 )

Kazim Gumus, Texas Tech University 17

Signal sensitivity

(|eta|<1 )

(Lum = 1fb-1)This plot is an update to the one shown in

the SUSY/BSMMeeting on

June 9.

The plot shown on June 9 was affected by the

QCD cross section bug,

and showed too much sensitivity

to a Z’

Kazim Gumus, Texas Tech University 18

Excited quarks are produced with strong interaction. It has significantly higher cross section than Zprime.

We scaled the Zprime events with the ratio of excited quark cross section to the Zprime cross section to see the excited quark sensitivity.

The E6 diquarks have "electromagnetic strength" coupling. However they have competitive cross section compared to excited quarks at high mass, because they are produced from the valence quarks in the proton, which have higher momentum.

Same as excited quarks, we plotted E6 diquark cross section histogram and used it to see its sensitivity.

See next page for results.

Excited quark and E6 diquark

'

*'* )()(

Z

qZq histhist

'' )()(

Z

DZD histhist

Kazim Gumus, Texas Tech University 19

Excited quarks and E6 diquarks

( Lum = 1 fb-1 )

Kazim Gumus, Texas Tech University 20

Conclusions and Future Plans

• Our first look at search for dijet resonances.

• Hard to see a Z’ with 1 fb-1 due to limited statistics for both signal and background: Z’ has a small cross section compared to QCD.– Around 2 TeV, where the unprescaled trigger begins, there is some

sensitivity to a Z’ which may allow observation with larger luminosities (10 – 100 fb-1)

• Sensitivity to excited quarks (strongly produced) and E6 diquarks (produced from valence quarks) are much better than Z’. – We should be able to see these up to a few TeV (3-5) for 1 fb-1. – Our sensitivity to Axigluons or Colorons is similar to excited quarks.

• Working on producing likelihoods to estimate 5 discovery mass reach and 95% CL mass limits for all models (Z’, q*, diquarks, etc.)– Working on the cross section for new models, like technirhos (R. Harris)

• Plan to redo mass binning to correspond to mass resolution.

Kazim Gumus, Texas Tech University 21

Back up Slide

5TeV Zprime (generator particle) mass dist. (CMKIN level)