# Presentation: 366057

## Using HF for Luminosity

**Jim Freeman**
**FNAL **
**June 14, 2001**

## Overview

**HF is finely segmented and very fast. Sensitive to single crossings.**
**Monte Carlo studies show HF has low occupancy even at 10****34**** luminosity.**
**	******** ****can count “empty” towers as measure of            luminosity. **
**	******** ****Use “muon feature bit” in HF to flag empty tower.**
**	******** ****Would like to monitor luminosity for each bucket**
**Ideally, count towers with < single pe. This measurement is stable against energy scale shifts, ...**
**	******** ****need single pe well separated from pedestal in normal data-taking mode**
**	********Do monte carlo study to see if possible**

## Lego of crossing, <MB>=17

## Lego of crossing, <MB>=17

## Some numbers

**PMT Gain = 4X10**4**
**Front end input noise = 6000e- **
**QIE bin = 17,000 e- (non-inverting input)**
**Lightyield = 0.25 pe/GeV **
**PMT pe resolution = 50%/sqrt(Npe)**

## Toy Monte Carlo

**Model:**
**Inject energy into tower (multiple MB events, using Sarah’s histograms as MB Et model)**
**HF light yield GeV to pe’s (quantize nr pe’s)**
**Pmt gain**
**Pmt resolution for photoelectron**
**Front end noise (rms=6000e-)**
**QIE quantization (17000 e- / bin)**
**Then study results**

## Eta=4, <MB>=1, 1 physical tower

**Quantization on X axis is ADC binning converted back into GEV. Recall 4 GeV = ADC bin 3.35**
**Note that single pe should also appear as 4 GeV. (0.25 pe/GeV)**

## Eta=4, <MB> = 10, physical tower

## Eta=4, <MB> = 20, physical tower

**Single PE peak**

**An empty tower (zero tower) means ADC count = 0**

## Fraction zeros vs <mb> for physical tower

**Very linear relationship between <MB> and zero fraction. **
****** ****good for luminosity measurement**

## Higher PMT gain doesn’t hurt

**Better separation at pmt gain = 10**5**

**Things get easier at higher pmt gain. Perhaps can run lower eta pmts at higher gain?**

## HF Trigger Segmentation

**HF trigger tower is 6 physical towers**

## Eta=4, <MB> = 20, trigger tower=1 physical tower

**Simulate trigger tower by summing ADC values of physical towers inside of trigger tower, making cut on sum.  X axis of histogram is ADC sum for trigger tower.**

## Eta=4, <MB> = 20, trigger tower=2 physical towers

## Eta=4, <MB> = 20, trigger tower=6 physical towers

## Fraction zeros vs trigger tower size, <MB> = 20

## Fraction zeros vs <MB>, trigger tower = 6 physical towers

## Problem with Large trigger towers

**6-to-1 physical-to-trigger towers looks like a problem. There is substantial saturation of occupancy.**
**A possible solution:**
**Associate muon feature bit with one of the six towers (arbritrary). Then lose 6X statistics but...**
**One orbit is 88 ********s. So 1000 measurements of each crossing bucket in 88 ms. **
**144 trigger towers. So 144 independent measurements per crossing. **
**We have seen that average physical tower zero occupancy is ~30% at 10**34.  So measurement is Sqrt(40,000)/40000 = 0.005**
** ******** ****in 88 ms, can measure each crossing bucket luminosity to ~0.5% accuracy**

## Conclusions (tentative)

**HF occupancy .ge. single photoelectron seems to be low, even at full luminosity**
**Counting zeros on a physical tower basis should work well. Even better at pmt gain = 10**5.**
**Losing a factor of 6 due to trigger tower granularity not a problem.**
**Counting zeros looks like a promising way to measure instantaneous luminosities of each bucket. (Accurate measurements each 88ms).**
**Should investigate feasibility of doing counting, histogramming in Level 1 Global Trigger. Can use otherwise unused HF muon feature bit to transmit information.**