# Presentation: 226801

## Jet Production with Two Rapidity Gaps

**Gilvan Alves**
**Lafex/CBPF**
**for the **
**D-Zero Collaboration**

-  Introduction
-  Data Selection
-  Event Characteristics for 1800/630 Data
-  Monte Carlo
-  Summary

## Introduction

**Motivations for Study Double Pomeron Exchange**
**p p **=>** p p + X**

**Pomeron-Pomeron collisions provide an extra process**
**to gain insight into the nature of the pomeron.**
**Clean signature for new particle searches**

**In this analysis we  use a trigger that demands central jet **
**production with a rapidity gap on one side (SD **
**candidates) and study the multiplicity on the opposite**
**side.**

## HDPE Models

**Factorizable Approach**

**Non-Factorizable Approach**

## D0 Calorimeter

- p beam direction

- z

- x

-  = - ln(tan /2)

## Gap Definition

**Detector coverage for gap definition**

**Thresholds:**
**EM:   125 MeV**
**HAD: 500 MeV**
**HAD**
**END:   50 MeV**

**Gap definitions:**
**1) Ncal=0  in ********(2.0,5.2)**
**2) Ncal=0  in ********(2.5,5.2)**

** ****Calorimeter Coverage        EM     HAD**

**Level 0 coverage**
**(scintillator array) **

## Data Selection

**To search for double gap events we use our enhanced**
**sample of single gap events from the SV trigger.**
**We re-enforce the gap at trigger level w/ calorimeter**
**tag and plot L0/CAL multiplicities on opposing side...**

- _Data sample _
-  Three Triggers for Different Gap Requirements
- 	- Inclusive Trigger (2 jets > 15 GeV)
- 	- Single Veto Trg.  (Add 1 Gap at L0)
- 	- Double Veto Trg. (Add 2 Gaps at L0)
-  Event and jet quality cuts
- - single interaction cut
- - 1 central vertex
- - low missing ET < 25 GeV
- - remove events w/ spurious jets

- Require 2 leading jets > 15 GeV , |jet| < 1.0
- Restrict to low lum runs < 6x1030 cm-2 s-1

## 1800 GeV Multiplicities I

**Require 1 gap w/ 2.5< |********|< 5.2; ****2 jets ET> 15 GeV, |********_jet| < 1.0**
**Plot detector multiplicity in same region on opposite side**

**D0 Preliminary**

## 1800 GeV Multiplicities II

**Require 1 gap w/ 2.0< |********|< 5.2; ****2 jets ET> 15 GeV, |********_jet| < 1.0**
**Plot detector multiplicity in same region on opposite side**

**D0 Preliminary**

**Little change w/ addition of 1/2 unit of rapidity in **
**gap definition**

## 1800 Gev Event Characteristics I 

**D0 Preliminary**

**Select ‘low background’ double gap events**
**N_L0 + N_CAL = 0 on both sides (Use DV trig)**

**Double gap events vs. inclusive events**
**w/ 2 leading jets > 15 GeV, |********_jet| < 1.0**

## 1800 Gev Event Characteristics II 

**D0 Preliminary**

**DG events more quiet, thinner jets**

**Select ‘low background’ double gap events**
**N_L0 + N_CAL = 0 on both sides**

**Double gap events vs. inclusive events**
**w/ 2 leading jets > 15 GeV, |********_jet| < 1.0**

## 1800 Gev ET Distributions

**D0 Preliminary**

**Double gap events vs. single gap and **
**                                                    ****inclusive events**
**w/ 2 leading jets > 15 GeV, |********_jet| < 1.0**

**Similar ET spectra in each sample**

## 630 GeV Data

**We have performed a parallel analysis with a**
**sample of data taken during a 630 GeV running**
**period. **

**Event cuts and gap definitions were similar to the **
**1800 GeV analysis**
**Except lower trigger thresholds were used and in **
**this analysis we require 2 leading jets with ET > 12 GeV**

## 630 GeV Data

- Event Display

## 630 GeV Multiplicities 

**D0 Preliminary**

**Require 1 gap w/ 2.5 < |********| < 5.2**
**Plot detector multiplicity in same region on opposite side**

## 630 GeV Event Characteristics I

**D0 Preliminary**

**Select ‘low background’ double gap events**
**N_L0 + N_CAL = 0 on both sides**

**Double gap events vs. inclusive events**
**w/ 2 leading jets > 12 GeV, |********_jet| < 1.0**

## 630 GeV Event Characteristics II

**D0 Preliminary**

**Select ‘low background’ double gap events**
**N_L0 + N_CAL = 0 on both sides**

**Double gap events vs. inclusive events**
**w/ 2 leading jets > 12 GeV, |********_jet| < 1.0**

## 630 GeV ET Distributions

**D0 Preliminary**

**Double gap events vs. single gap and **
**                                                    ****inclusive events**
**w/ 2 leading jets > 12 GeV, |********_jet| < 1.0**

## DPE Monte Carlo

**Modified Version of POMPYT **
**Allowing 2 pomerons as beam particles**
** ****in PYTHIA**

**p**

**p**

**P**

**P**

-  Each pomeron has a probability for
-   carrying a fraction  of the parent’s
-   momentum

## DPE Monte Carlo

**DPE Monte Carlo**
**Distributions**

- 1800 GeV

- 630 GeV

- SD

- DP

- 

- Arb. units

- SD

- DP

## DPE Monte Carlo

**Distributions**

-  between leading jets

- 1800 GeV

- 630 GeV

- SD

- DP

- Arb. units

## DPE Monte Carlo

**Distributions**

- 1800 GeV

- 630 GeV

- ET Distribution of leading 2 jets

- Arb. units

-  SD

-  DP

-  SD

-  DP

## DPE Monte Carlo

**Distributions**

- 1800 GeV

- 630 GeV

- Arb. units

-  distribution leading 2 jets

## DPE Monte Carlo

**Distributions**

- 1800 GeV

- 630 GeV

- Arb. units

- Particle Multiplicity  2.5 < <5.2

## Summary

**Qualitative Observations:**
**- We observe Double Gap signals at 1800 and 630 GeV CM energies in excess of  a smooth background assumption**
**- Double Gap Signal has weak dependence on gap size ****(though gap range shown is quite limited)**
**- ET Spectrum of jets in Double Gap events looks a lot like inclusive p p scattering**
**	****(though events are quieter and jets tend ****	****to be narrower) ****	**

**MC Distributions for factorizable DPE model allow for**
**Similar**** ET spectrum ****at BOTH CM energies.   Rates**
**630/1800 should be the key to see if this picture holds.**

- - First look at Monte Carlo Distributions at Generator
-   Level.
- - Fully Simulated Events will allow better understanding
-    of data