# Presentation: 126080

## b Production

**Results from**

**Joint Experimental **
**Theoretical Seminar**
***Fermilab  ( May 12 , 2000 )***

***Arthur Maciel***
***Northern Illinois University***

## Overview of Current Results

**Hadroproduction Theory Status**

**Cross Section for b Jet Production**

**Confrontation with b  Quark Production Results**

**Comments,Plans,Run II****...**

***Contents:***

##  b Production Status at pp Colliders  

- Single Inclusive b Quark Production

-  **UA1 (540 GeV)**
** ****DØ , CDF (1.8 TeV)**
** ****UA1 , CDF , D****Ø (630 GeV)**

**All experiments are in agreement with one another, and find significant data excess over theory**** **

** ****b Production Status at pp Colliders  **

***A. Maciel***
***(NIU)***

**Tevatron, **
** ****1.8 TeV**

## ~ 2.5

- 1.8TeV

- .63TeV

**b Quark Integrated Cross Section**
**( Data / Theory )**

***A. Maciel***
***(NIU)***

**~**** 2.5**

## CDF:      B +  J/ψ K+       J/ψ  μ+μ–

- CDF:      B +  J/ψ K+       J/ψ  μ+μ–

**( both muons in SVX )**

- PT(K) > 1.25 GeV/c        PT(B) > 6.0 GeV/c

***A. Maciel***
***(NIU)***

- B Meson Production
- (same pattern)

## CDF:      B +  J/ψ K+ 

**|y (B****+****) | < 1**

**Integrated  ****σ****(B+)**** = ****3.51**** ± 0.42(stat) ± 0.53(sys) μb**
**Theory (central values μ , m****b**** , ε****P****)  is  ****1.54**** μb**

***A. Maciel***
***(NIU)***

## Slide 7

## Forward

**Forward**
**J/Ψ ******** μ****+****μ****–**

- 10 pb**–****1 ****; **dimuon trigger
**P.R.L. **_**82**_**, 35(1999)**

***A. Maciel***
***(NIU)***

## Forward Muons From

**Forward Muons From**
**Semileptonic b Decays**

- 100 nb**–****1** of low luminosity special runs
**P.R.L. **_**(in press**_**)**

**2.4 < |y****μ****| < 3.2**

***A. Maciel***
***(NIU)***

## Rapidity Dependence

**Rapidity Dependence**
**(Combining Central and Forward Muons)**

**~ 2.5    ****Ratio: Data/Theory****    ~ 4**

***A. Maciel***
***(NIU)***

## ?

**Theory Status **

- What are possible explanations for
- collider data ** ****>**  theoretical predictions

**?**

**?**

-  ***Higher orders (> ******α******s******3******)****** in the pert. expansion***
- R/F scale dependence is large
-     (and is not reduced when LO  NLO)
- Radiative corrections can be large
-    ( while < 15% for Top production @TeV)
- Large logs due to coexistence of
-    different scales;  S , PT2 , Mb2
-    (ISR, FSR; various resummation schemes)
-  ***Non perturbative fragmentation effects**** *
*   **(and contributions from higher moments of the FF)*
-  ***Other non perturbative causes**** *
-     (*e.g.* intrinsic kT of incoming partons)

**http://www-theory.fnal.gov/people/ligeti/Brun2/sept/ridolfi.ps.gz**

**See recent FNAL b-Wshop; “RunII & Beyond”**

***A. Maciel***
***(NIU)***

**also: S. Frixione *****et.al.***** hep-ph ****/**** 9702287**
**          ****M. Mangano      hep-ph ****/**** 9711337**

## ?

-       Ln(S/4Mb2) at all orders  [Collins,Ellis, NP_B360_,3(1991)]
-   b produced at high PT(hard collinear gluons),GS,
-     Ln(PT/Mb) at all orders [Cacciari,Grecco, NP_B421_,530(‘94)]
-  Exact mass dependence in VFN scheme – initial and
- final state mass singularities resummed in fragmentation approach
- [Scalise, Olness, Tung. PR_D59_,14506(1998)]

- Overall Status

- Probing Higher Orders
**(resummation schemes)**

- Individually, modest cross section improvements:
-  Enhancements inside fixed order (NLO) uncert.
-  Reduced R/F scale dependence (uncert. band)
-  Steepening of b PT spectrum  above ~20GeV
-                                  ...but...

- A combination of effects may hold the answer

**?**

**?**

***A. Maciel***
***(NIU)***

## 1st measurement of   γγ   bb

***1******st****** measurement of   ******γγ ************  ******bb***

- L3 note 2421
- June 1999

## Cross Section for b-Jet Production

***D******Ø Collaboration***
***( Preliminary )***

-  introduction
-  inclusive spectrum
-  tagging acceptance
-  relation with open b

-  data selection
-  b component
-   results
-  conclusion

***A. Maciel***
***(NIU)***

**Joint Experimental **
**Theoretical Seminar**
***Fermilab  ( May 12 , 2000 )***

## Introduction

***Nucl.Phys. ***_***B483***_***,  321 (1997)***

-  **QCD production of jets containing heavy quarks**
** ****LO  b Jets and  b Quarks  have identical spectra**
-  **NLO  amplitudes  have  3-parton  final  states**
-  **Loosely;  ‘MNR’(1992) + Snowmass Jet-Cone**
**      ****at partonic level;   d****σ =  dσ****(open)****  + dΔ (clustering)**

** ****Jets are more QCD-friendly** (than quarks)
-  Integrate away fragmentation details
-     (Jet Et is regardless of b-mom. fraction)
-  Jets  are  collinear-safe  objects
-     ( theory avoids resummation of large
-     logarithms from hard collinear gluons )

- (Theory)

***A. Maciel***
***(NIU)***

***Why ***_***b Jets***_*** ?***

## Introduction

- (Experiment)

**  ****A new D****Ø look into b-production**
-  **Complementary to open b-quark studies**
** ****Jet centered,  muons as taggers only**
-   **Jets are directly observable**
-  **Less model dependence in connecting**
**            ****observation with theory**
** ****Access to differential cross sections**
**  ****Jet counting  (muon tagged jets);**
-  **theory counts jets with b ( b-integrated)**
** ****D****Ø counts tagging muons (in jets)**
- 	         μ+ + μ–             b + b
- 	          2 B.R.            2

- =

- Δσ**bJet**  A**TAG**(ET)       FB(ET)         ΔN**μJet**
- ΔET      2(B.R.)    L ε(PT**μ**,ET**Jet**)  ΔET

- =

***A. Maciel***
***(NIU)***

**| ****η**** | < 1**

## Data Sample

- Run-1B (5.2±0.3) pb**–1  **muon **& **jet trigger
**L1: **muon PT > 4GeV  Jet Tower > 3GeV

| Jets  | Muons |
| --- | --- |
| ET > 25 GeV | PT > 6 GeV |
| | η | < 0.6 | | η | < 0.8 |
| ΔR = 0.7 | ΔR < 0.7 |

*Offline Selection*

-  PT**μ**>6GeV  b’s emerge from light bckgnd
-  muon exclusion (φ = ± 20°) around M.R.
-  “out of time” muon contamination < 1%

***A. Maciel***
***(NIU)***

**30K events**

## Detection Efficiencies

|  | Jet | Muon |
| --- | --- | --- |
| Trigger | ET (85 - 100%) | PT (50 - 60%)* |
| Reco | 100% | PT (90 - 95%) |
| Offline | (97±1)% | (83±3)% |

**(*) Includes geom. acceptance**

- Combined

***A. Maciel***
***(NIU)***

## Inclusive Spectrum

**Muon-Tagged Jets**

***A. Maciel***
***(NIU)***

## Extraction of the b Component

-  PTRel templates from **ISAJET** (b and non-b)
-  Fits to data using  Cernlib’s  “**HMCMLL”**
-  Individual b-fraction measurements at four
-     separate ET ranges; 20-25-35-50-100 GeV
-  Closure tests with Monte Carlo samples
-  Model dependence tests (and **HERWIG**)
-  PTRel discrimination power limits b-Jet
-      sample to ET < 100GeV
-  This is the dominant source of uncertainty

***A. Maciel***
***(NIU)***

## b Component

**P****T****Rel**

**P****T****μ**

**Jet**

- P**T****Rel** template
- (b and non-b)
-  fits to data at
- four E**T **ranges

***A. Maciel***
***(NIU)***

## x E-3

**χ****2**** **=** 0.96**

| 2.65 | 1.35 | 0.48 | -0.01 |
| --- | --- | --- | --- |
|  | 1.45 | 1.52 | 1.56 |
|  |  | 2.22 | 2.67 |
|  |  |  | 3.39 |

***Covariance Matrix***

**x** E-3

***b Component of Jets***

***A. Maciel***
***(NIU)***

***Relative Uncertainty***

## b Jet Spectrum

**b-Tagged Jets**

***A. Maciel***
***(NIU)***

## Tagging Acceptance

_*Corrections due to*__;_
-  **Muon  ****η-range , p****T****-threshold**
** ****Muon-Jet association; ****ΔR<0.7**
** ****Unseen Jet-E****T****;  ( μ + ν )**
** ****B. R.   b ******** μ X**
** ****Jet η-range **

- A(ET)–1 =

**Correct observed spectrum**
**with Monte Carlo ratio;**
- MC(bμ) parton jets, |η|<1
- MC(bμ)  analysis  image

***A. Maciel***
***(NIU)***

## Tagging Acceptance

-  **Correction factor does not depend on MC production rates**
** ****Fragmentation is the most relevant issue (fully correlated)**
** ****Lepton E****T ****correction sensitivity is minimized by kinematic**
**     ****constraints over fragmentation  (hadrons + leptons = const.)**
** ****Impact of fragmentation is an edge effect associated with the**
**     ****Influx (outflux) of tagging muons across p****T**** threshold **
** ****Overall acceptances cross checked with HERWIG v5.9**

**Acceptance extracted from**
**ISAJET v7.37 with CLEO decay modes**
**Frag (Peterson) ****ε**** = 0.006 ****±**** 0.003**
**Error = (+8% ; ****–****9%) E****T**** independent**

***A. Maciel***
***(NIU)***

## Systematic Uncertainties Summary

***( relative , percentual , mostly correlated )***

***A. Maciel***
***(NIU)***

## b Jets Cross Section

**(*)** **2 ****μ****O**** ...**** ****μ****O****/2  ,  ****μ****O**** = (E****T****2**** + M****b****2****)****1/2**

***A. Maciel***
***(NIU)***

## (Data-Theory) / Theory

***A. Maciel***
***(NIU)***

## Comments

-  **Repeats general pattern “data above theory” , but...**
** ****Converging to upper band of theory uncertainty**
** ****Scale dependence is the same as with p****T**** spectrum**
**     ****for open b quarks.  ( ****~ ****50% )**
** ****b Jets favor        ****μo/2  **
**    ****b Quarks favor  ****μo/4  **
** ****Scale choices for HQ(jet) and HQ(open) are not  **
**                                     ****independent**
** ****Inconsistency among two quantities derived from**
**                          ****the same underlying physics**

**as choice for R/F (QCD) scale**

***A. Maciel***
***(NIU)***

**?**

**?**

**?**

**?**

**Revisit previous (open b) analysis **
**(daughter muons  ******** parent b quarks)**
**using present data sample**

**μ****o**** = (M****B****2**** + E****T****2****)****1/2**

## Cross Section for

-  b Quark Production

-  **Straightforward repetition of  (integrated)  ****σ****b****ptmin**
**     ****extracted from inclusive muons**
** ****A cross check against all previous ****σ****b****ptmin**** measurements**
** ****b fraction ( ****p****t****rel**** ) exercise simpler than with b jets --**
**     ****b signal increases with muon pt**
** ****Errors are now dominated by kinematic relationship**
**     ****between parent b and daughter muon spectra**

***A. Maciel***
***(NIU)***

| Jets  | Muons |
| --- | --- |
| ET > 20 GeV | PT > 6 GeV |
| | η | < 0.6 | | η | < 0.8 |
| ΔR = 0.7 | ΔR < 0.7 |

*Offline Selection*

**40K events**

## b Muon Spectrum

***A. Maciel***
***(NIU)***

**b-Tagged Muons**

## Systematic Uncertainties 

**Systematic Uncertainties **
**(Muon Spectrum)**

***A. Maciel***
***(NIU)***

**Vertical marks indicate p****T****μ**** integration bins**

## b-Quark Integrated Cross Section

**b-Quark Integrated Cross Section**

**(*)** **2 ****μ****O**** ...**** ****μ****O****/2  ,  ****μ****O**** = (P****b****T****2**** + M****b****2****)****1/2**

**(*)**

***A. Maciel***
***(NIU)***

## Conclusion

***A. Maciel***
***(NIU)***

- b production stuck between two
-  spectacular QCD successes

- m
- a
- s
- s
- s
- c
- a
- l
- e

- proves
- hard QCD

- proves jet
- mechanism

## Clearly  b production

- holds an important
- QCD lesson

***A. Maciel***
***(NIU)***

- How should we proceed ?

-  Devise production measurements under conditions such as to jointly minimize uncertainties at both ends, theory** **and experiment.

-  Identify observables for which NLO QCD calculation is stable under scale variations

-  Verify this high P**T** convergence trend
- (does it continue ?)

- examples...

## Di-bJets:  exploit

- _b Jets_    reduce fragmentation uncertainties
-              (+) afford very wide ET coverage
-              (++) multiple b tagging handles

- Restricted kinematic ranges:
-  minimize higher order contributions
-  optimize triggering and tagging

***Di-bJets*****:**  exploit
-  double tagging
-  bb correlations

- b Jets
- c Jets

-  b Jets
- all Jets

- scale dependence (*)

- ET dependence (*)

***(*) See SF & MM*****,**  ***Nucl.Phys. ***_***B483***_***,  321 (1997)***

***Ratios:***

- How should we proceed ?

***A. Maciel***
***(NIU)***

## Summary

- data-theory convergence at
- higher transverse momenta

***A. Maciel***
***(NIU)***

- Different experiments, and also
- different measurements within
- each experiment, all confirm a
- pattern for b production where
- data shows normalization excess
- over theory  (NLO - pQCD)

-  Thanks !

- Tevatron Run-II (March 2001)
- should revisit /confirm this trend