# Presentation: 179639

## Preons and Fibers Tales from the Front

- Preons and Fibers Tales from the Front

- Don Lincoln
- Fermilab

## Overview

- Lots of neat stuff going on at DØ
- What to talk about?
- Two mini-talks
- Interesting hardware (Scintillator/VLPC detectors)
- Central Fiber Tracker
- Two preshower detectors
- Run II physics prospects
- Search for compositeness

**Generic **
**Travelogue**

## Scintillating Fiber Tracker

- Provides:
- 1. With Silicon system
- Track Reconstruction
- Momentum measurement over 
- Charge determination
- Tagging of b-quarks
- 2. Fast Level 1 Triggering
- Combining info. from muon and preshower systems
- Single e,  Triggers

**Z******************** + 1 min bias**

- 1 ft

## System Layout

- 8 nested cylinders
- r  = 20 ****51 cm
- Each layer
- 1 axial doublet
- 1 stereo (u or v)
- xu - xv - xu - xv - ....
- Constant pitch ********
- Layers
- 1,2 - 1.8 m long
- 2,8 - 2.6 m long
- Total channel count ****
- Clear fiber brings signal to VLPCs -
-      7 - 11m

## Overview of VLPC Detectors

- The 3 VLPC detectors use Analog Front End (AFE) boards: the Central Fiber Tracker, the Central Preshower, and the Forward Preshower.

**Scintillating or wavelength shifting fiber**

**Optical connector**

**Waveguide**

**VLPC cassette**

**Electronics**

**Cryostat**

**Mirror**

## Scintillating Fiber Ribbons 

- Interlocking doublet
- 835 m fiber diameter
- Pitch between 915 and 990 m
- Grooved substrate - machined Delrin
- Substrate put into curved backbone
- Fibers glued together with polyurethane adhesive
- Edge control good to 5 mil inter-ribbon gap specification
- Curved Torlon connectors then attached
- 95% coupling efficiency

- 

## Scintillating and Clear Fiber

- Fiber:
- High Yield (excellent attenuation properties)
- Precise : Diameter ****835m1%
- Robust
- > 1,000,000 m of clear fiber
- >200,000 m of 3HF (scintillating) fiber

## VLPCs for DØ

- VLPC: Visible Light Photon Counter
- Solid state photon detectors
- Detects single photons
- Operate at a few degrees Kelvin
- Can work in a high rate environment
- Quantum efficiency ~80%
- High gain ~40 000 electrons per                                         converted photon
- Low gain dispersion

- Visible

- 99.5%

- Pedestal

- LED

## Gain

- Gains range from
- 20 000 to 60 000
- Gain dispersion of the pixels within one chip
- About 1.5 %    (Note: includes amplifier gain variations)

- 

- 

- 

## Gain Behavior

- Gain poorly correlated with voltage, but relative gain extremely correlated.
- Operating voltage range ~5.8 - 8.0 V.

- 2% !!!!

## Qualitative Threshold

- Noise grows very quickly, once a voltage threshold is exceeded.

## Temperature Behavior

- Temperature affects response.
- All plots normalized to signal at 9 K (nominal operating temperature).

## Linearity at 0 MHz Background

- VLPC’s are linear to <10% for Equivalent PE ~600 (~750 photons)
- Slight gain dependence, although gain is only tangentially related.

- Gain ~50 000

- Gain ~30 000

- Normalization Point

- Measurement
- Artifact

## Infrastructure

- Associated electronics
- 100% functional   (some uncertainty)
- Instrumented with AFEs: [Now]
- CFT Axial   	100%
- CFT Stereo	  40%
- CPS Axial      100%
- CPS Stereo       30%
- FPS 		     0%
- Slightly less due to ongoing upgrades

- VLPCs

- To Trigger

## AFE Boards

- Two per VLPC cassette (boards are handed)
- 512 channels each
- 8 MultiChipModules
- 1 SVX (64/128) channels
- 4 SIFT (ScIntillating Fiber Trigger) chips (14/18/18/14)

- MCM

- ~50 cm

## Discriminator Turn-On

- Discriminator (SIFT)
- 1 pe ~ 7 DAC settings
- 2 is 0.5 pe
- SIFT noise feeds SVX
- VLPC thresholds
- ~1.2-1.6 pe
- Bottom line:
- Should see photopeaks

- SIFT

- SVX

- Signal

- Discriminator

## LED Spectra: DØ in-situ Testing

## Base Performance 10 AFE boards

- Gain variation 25%
- Within expectations for these cassettes
- Can be reduced to 2-5%

- Pedestal RMS 0.5 pe
- ~3% noise occupancy  1 pe     ( + 2 )
- ~1% noise occupancy 1.5 pe    ( + 3 )

## Event Displays

- Projected

- Silicon detector shows some
- tracks correlated with CFT

- Projected Tracking Resolution
- (CFT and SMT)

## CFT and Calorimeter

- Calorimeter
- Energy Deposition

- Calorimeter energy deposition
- clearly correlated with CFT

- The number of
- physics topics that DØ
- can do is extensive.
- I present one such analysis here.

- Segue

- The DØ CFT detector is installed and in working
- order
- Efforts are ongoing to optimize detector
- performance

## Slide 22

## Quark/Lepton Sub-structure

- The idea:
- The repeating patterns seen in quark and lepton generations signal the existence of sub-structure
- The problem:
- No experimental and very little theoretical guidance as to what that composite nature could be.
- Quark and lepton substructure scales not necessarily the same.

## General ‘Theory’

- Theory consists of all terms of any chiral combinations

- Drell-Yan Only

## CDF Results

- In Drell-Yan, invariant
- mass distributions are the
- measure of choice.
- Note differences in positive
- and negative coupling constants.
- -  Positive interference
- +  Negative interference

- Limit summary given at
- end of this section of talk.

- LL

- Quark helicity
- state

- Lepton helicity
- state

## DØ results

- Superior ee limits, no
-  limits.

- Note:
-   VV = LL + RR + LR + RL
-   AA = LL + RR - LR - RL

## Also can explore qq final states

- Also can explore *qq* final states

- In jet final states, several variables used

- Direct Comparison to
- Drell-Yan

- Nearly PDF independent

- Most ‘Rutherford-like’

- Note:  Lagrangian similar, but different

## Inclusive Jet Cross Section

- CDF: 0.1 < || < 0.7

- Good Agreement with NLO QCD

- DØ: _[PRL:82 2451 (1999) ](http://www-spires.dur.ac.uk/spires/find/hep/www?j=PRLTA,82,2451)_        _PRD:64 032003 (2001)_

- CDF: _[hep-ph/0102074 ](http://arxiv.org/abs/hep-ph/0102074)_(acc PRD)

- Big Hoopla

## Comparisons with CDF

- DØ analyzed 0.1 < || < 0.7 to compare with CDF
_**Good Agreement**_
- If we calculate 2 between DØ data and fit to CDF and its uncertainties
- CDF’s excess can be explained via small change in gluon PDF at high *x *(CTEQ-4HJ)

-  = 1.6 TeV

## DØ Dijet Mass Analysis

- Central and more
- inclusive data sets
- (more later).

- Dijet mass looks for
- both resonances and
- is sensitive to high-
- mass excesses
- (indicating onset of
- compositeness or
- other new physics

## Dijet Mass Spectrum

- Experiments in excellent agreement.
- Different rapidity ranges and very different analysis techniques.
- Reasonable agreement with predictions.

**       ****N****events**
**L ********M ******************

## Dijet Mass Cross Section Ratio 

- Dijet Mass Cross Section Ratio

****** ******** ****2.4 TeV ****(95% confidence level)**

**Systematic**
**Uncertainty**** ~ 8%**

**  ****Theory uncertainty ~ **
**   ****6% (m) , 3% (PDF)**

**NLO QCD in good agreement with data**

-  < 0.5 ) / 0.5 <  1 )  (s=1800 GeV ) PRL 82, 2457-2462, 1999

## Dijet Angular Distribution

- Verifying QCD and searching for compositeness.
- Predominantly *t*-channel (distinct from Drell-Yan)

- Expect compositeness signal to background to be largest for high masses.

- cos

- *

- Note: CM frame

## Dijet Angular Distribution

- We integrate over *M* and boost and actually measure

- Transformation flattens
- out angular distribution

- 25°

- 35°

- 48°

## Dijet Angular Distribution

- The angular distribution of the major QCD processes (gggg,qg qg,qq qq) have similar angular distributions.
- Hence choice of pdf  has little effect on the angular distribution.
- Angular distribution is a very effective probe of the QCD matrix elements

## Compositeness

- dN/d is sensitive to contact interactions introduced by compositeness
- at high *M*.

- Lower mass  no sensitivity

## Dijet Angular Distribution: PRL 80 666 (98)

- Good agreement
- with NLO QCD
- predictions

## Compositeness Search

## Limits on Quark Compositeness

- Need to handle correlations
- Define:

- Optimize for compositeness (=4) using LO calculation

- Note:
-     < 4
-    cos * < 0.6
-    53° < * < 127°
-    |*| < 0.7

## Tevatron Run I Limits

- Drell-Yan

- QCD

- Units:
- TeV

## Tevatron Run II

- Run II heralds an era where new opportunities present themselves.
- Advantages over Run I
- 20-300 luminosity

- Not so small!!

## Case Study: Dijet Mass Spectrum

**Dramatic increase in high p****T**** cross sections**
**Large gains in statistics**

## Run II: Drell-Yan

- Constructive
- Interference

- Destructive
- Interference

- Projected Limits (Bayesian)

- PRL 82 4769 (1999)

## Compositeness Example

- cos(*)

-  

- No Helicity Flip

- Helicity Flip

- Can exploit
- shape!!

- Compositeness
- Drell-Yan

## Summary

- DØ’s new tracker, using entirely new technology, works.
- Performance determination ongoing
- Many cool new physics topics accessible to DØ
- Run II will double and then re-double compositeness limits.
- Dress rehearsal for LHC...