# Presentation: 760285

## Upsilon production and μ-tagged jets in DØ

- Horst D. Wahl
- Florida State University
- (DØ collaboration)
- 29 April 2005
- DIS 2005
- 27 April to 1 May 2005
- Madison

## Outline:
Tevatron and DØ detector
Upsilon Υ(1S) 
High pt  jets with μ tag
Summary

Tevatron –  data taking
peak luminosity in 2005 above       1032 cm-2 s-1
DØ collected > 690 pb-1
Results shown use 150 – 300 pb-1

- Tevatron and DØ detector
- Upsilon Υ(1S)
- High pt  jets with μ tag
- Summary
- Tevatron –  data taking
- peak luminosity in 2005 above       1032 cm-2 s-1
- DØ collected > 690 pb-1
- Results shown use 150 – 300 pb-1

## The DØ Detector

## DØ muon Detector 

- 3 layers
- Drift tubes and scintillation counters
- One layer (A) inside of 1.8 T toroid
- Good coverage:
- Central  |η| < 1 PDT
- Forward  1 < |η| < 2  MDT
- Fast and efficient trigger

## Upsilon production

- Quarkonium production is window on boundary region between perturbative and non-perturbative QCD
- Factorized QCD calculations to O(α3) (currently employed by PYTHIA)
- color-singlet, color-evaporation, color-octet models
- Recent calculations by Berger et al. combining separate perturbative approaches for low and high-pt  regions
- Predict shape of pt distribution
- Absolute cross section not predicted

- Υ(1S) production at the  Tevatron:
- 50% produced promptly
- 50% from decay of higher mass states (e.g. χb →Υ(1S) )

## Analysis Overview

**Analysis Overview**

- Sample selection
- 159  10 pb-1  taken with dimuon trigger
- Opposite sign muons with hits in all three layers of the muon system, matched to a track in the central tracking system (with hit in SMT)
-  pt (μ)  > 3 GeV and |η (μ)|  < 2.2
-  At least one isolated μ
-  46k Υ(1S) events
- Analysis
- (μ+μ-) mass resolution functions obtained from J/ψ and MC studies
- Fit (μ+μ-) mass spectra for different y and pt bins, assuming 3 Υ states and background
- Get efficiencies and uncertainties

## Fitting the Signal

- Signal: 3 states (Υ(1S), Υ(2S), Υ(3S)),  described by Gaussians with masses mi,  widths (resolution) σi, weights  ci ,(i=1,2,3)
- Masses mi= m1+ m i1(PDG), widths σi = σ1 • (mi/m1), for i=2,3
- free parameters in signal fit:  m1, σ1, c1, c2, c3
- Background: 3rd order polynomial

-  All plots: 3 GeV < pt(  < 4 GeV

- m() = 9.423 ± 0.008 GeV

- m() = 9.415±  0.009 GeV

- m() = 9.403 ± 0.013 GeV

- 0 < |*y* | < 0.6

- 0.6 < |*y* | < 1.2

- 1.2 < |*y* | < 1.8

- PDG: m(Υ(1S)) = 9.46 GeV

## Efficiencies, correction factors...

- L     luminosity                     kdimu  local muon reconstruction
- y     rapidity                          ktrk      tracking
- εacc   accept.•rec.eff.             kqual   track quality cuts
- εtrig    trigger

-       0.0 < y < 0.6    0.6 < y < 1.2     1.2 < y < 1.8
- εacc    0.15 - 0.26      0.19 – 0.28        0.20 - 0.27
- εtrig             0.70               0.73                   0.82
- kdimu          0.85               0.88                   0.95
- ktrk              0.99               0.99                   0.95
- kqual        0.85               0.85                   0.93

**Efficiencies, correction factors...**

- Cross section

## Results: dσ(Υ(1S))/dy × B(Υ(1S) → μ+μ-)

- 0.0 < yΥ < 0.6          732 ± 19 (stat) ± 73 (syst) ± 48 (lum)  pb
- 0.6 < yΥ < 1.2          762 ± 20 (stat) ± 76 (syst) ± 50 (lum)  pb
- 1.2 < yΥ < 1.8          600 ± 19 (stat) ± 56 (syst) ± 39 (lum)  pb
- 0.0 < yΥ < 1.8          695 ± 14 (stat) ± 68 (syst) ± 45 (lum)  pb

- CDF Run I:
- 0.0 < yΥ < 0.4          680 ± 15 (stat) ± 18 (syst) ± 26 (lum) pb

**Results: dσ(Υ(1S))/dy × B(Υ(1S) → μ****+****μ****-****)**

- for central y bin, expect factor  1.11 increase in cross section from 1.8 TeV to 1.96 TeV (PYTHIA)

## Normalized Differential Cross Section

- shape of the pt distribution does not vary much with Υ rapidity
- Reasonable  agreement with calculation of Berger, Qiu, Wang

## Comparison with previous results

- σ(1.2 < yΥ < 1.8)/σ(0.0 < yΥ < 0.6)

- PYTHIA

**Comparison with ****previous results**

- band = uncertainties  of relative normalization

- only statistical uncertainties shown

## μ-tagged jet cross section

- Data sample:
- 294  18 pb-1
- Standard jet triggers
- Standard (y,φ) (R = 0.5)  cone jets in |yjet| < 0.5
- Standard jet quality cuts,  standard jet energy scale correction
- Jet tagged with medium quality muon: ΔR(μ, jet) < 0.5
- Additional quality cuts to reduce fake muons from punch-through
- 4660 μ-tagged jets
- Analysis:
- Establish jet energy scale correction for μ-tagged jets
- Determine resolution for μ-tagged jets
- “Unsmear” resolution
- Determine efficiencies
- Extract heavy flavor component

## Efficiencies....

| efficiency | detail | value |
| --- | --- | --- |
| T | Trigger Eff | 1.000 |
| PV | Primary Vertex: |z| < 50cm, ≥ 5tracks | 0.84 ± 0.005 |
|  |  Eff (geom, μ det., tracking, match) | 0.37 ± 0.05 |
| j | Jet Eff (jet quality cuts) | 0.99 ± 0.01 |
| fbg
 | Frac background   (Pt > 4 GeV) | pt dependent |
| fHF | Frac heavy flavor   (Pt > 4 GeV) | pt dependent |

**Efficiencies....**

- Overall efficiency = 0.31 ± 0.05

## Jet energy scale  for μ-tagged jets

**Jet energy scale  for ****μ****-****tagged jets**

- Pt imbalance in events with 2 jets (one with, one without μ)
- find 3.8% offset,                       not strongly pt dependent          for pt in (75, 250 GeV)
- Scale energies of μ-tagged jets
- Order-randomized imbalance used to get resolution

- STD JES 5.3 gives a 3.8% offset for -tagged jets.
- It is independent of Pt      (75-250 GeV).  Maybe higher above that.  Need to rebin and revisit the idea that the muon Pt may be mis-measured.
- Same plot when scaling the -tagged jet energies by 3.8%.

## Resolution

- Neutrinos in μ-tagged jet  resolution worse than for jets  without μ
- Take rms of order-randomized  imbalance
- Parameterize, Fit  (fig. (a))
- Subtract  (in quadrature)     resolution for jets without μ  ****	              obtain resolution for μ-tagged jets (fig. (b))
- Fit:
- N = 7.7  4.1
- S = 1.9  0.1
- C = 0.0  0.1
- Resolution parameterization used in “unsmearing”

- pt of jet

- pt of jet

## Unsmearing correction

- Fit data to convolution of    “ansatz function” with resolution
- Obtain unsmearing correction factors for pt bins (ratio of unsmeared to smeared ansatz)
- 0.65 to 0.77,                  smooth variation with pt
- Used two different ansatz functions
- estimate of systematic error: <5% for pt > 100 GeV

## HF fraction of μ-tagged jet sample

- Sample of jets with μ-tagged jets contains jets with μ from non-HF sources (e.g. π**, **K decays...)
- Use PYTHIA with standard DØ  detector simulation to find HF fraction of jets tagged with muons vs (true) pt
- Fit with *O + N e****-Pt/k***
- O = 0.44  0.06
- N = 0.42  0.12
- k = 114  68

## Data vs theory

- Use PYTHIA (with standard DØ MC) to find μ-tag fraction of jets and HF fraction of jets tagged with muons .
- NLO:  NLOJET++  (with CTEQ6M) multiplied  by    PYTHIA μ-tagged HF fraction
- Uncertainties:
- Multiplicative factors
- “JES”: jet energy scale
- “NO HF”: HF fraction uncertainty set to 0

**Data vs theory**

## Summary

- Υ(1S) cross-section
- Presented measurement of Υ(1S) cross section • BR(→μμ) for 3 different rapidity bins out to  y(Υ) = 1.8, as a function of pt(Υ)
- First measurement of  Υ(1S) cross section at  √s = 1.96 TeV.
- Cross section values and shapes of  dσ/dpt show only weak  dependence on rapidity.
- dσ/dpt is in good agreement with published results (CDF at 1.8 TeV)
- Normalized dσ/dpt in good agreement with recent QCD calculations (Berger at al.)
- μ-tagged jet cross section:
- Measured dσ/dpt in central rapidity region |y|<0.5 for μ-tagged jets   originating from heavy flavor (estimating HF contribution by MC)
- Resulting HF-jet cross section values lie between PYTHIA and simple NLO calculation
- Future:
- Reduce systematic uncertainties
- Find data driven method of estimating HF fraction (ptrel ,imp. par...?)
- Try other jet-tagging methods (sec. vertex, impact par., ..)