# Presentation: 614595

## Perspectives of QCD at Fermilab

**Fermilab:** Tevatron, **CDF, D0, MIPP, BTeV**
- Comments on **QCD in Hadron Collisions**
**Run II Results**: CDF and D0 (from hard to soft)
- The **Future** of QCD at the Tevatron

**Mike Albrow, Fermilab**

## MIPP

- CDF

- BTeV

## Tevatron Run II Performance

_***Tevatron Run II Performance***_

**340 pb^-1**

- Total Run II
- ~ 440 pb^-1
- on tape per
- experiment
- so far

**As of Sep 1****st**** 2004**

## CDF Detectors

- MiniPlugs

**Possible mini-upgrades for diffractive physics:**
**Precision roman pots on both beams**
**Fully instrument very forward region (< 3 deg)**

**em + had cals, muons**

**CENTRAL OUTER TRACKER**

## D0 Detector

_***D0 Detector***_

- Possible mini-upgrade:
- Roman pots beyond dipoles
- on both beams

- For Run II added:
**Solenoidal field**
**Silicon tracking**
**Scintillating fiber tracking**
**Roman pots with fibers**

**Tracking (incl. muons)**
**+ L.A. Calorimeter**

## MIPP: Main Injector Particle Production

_***MIPP: Main Injector Particle Production***_

- 5 GeV  120 GeV
- H, Be, .. Ag targets

- Multi-particle Spectrometer:
- Drift Chambers, TPC, Magnet,
- TOF, Cerenkov, RICH
- Neutral Calorimeter

**Particle production**
**Scaling Laws**
**Non-perturbative QCD**

- ... starting now

**TPC**

## BTeV: B Physics at the Tevatron

- 2009 

- Primary motivation:
- CP-violation and mixing in
- b- and c-sectors
- But good QCD capability.
- Excellent tracking, vertexing,
- particle ID, e,

- Could add: hadron calorimeter for jets,
- veto counters for gaps,
- roman pots for diffraction ...

- Beam is at 7.5

## The REAL Strong Interaction

- point-like, weak coupling
- perturbative

- extended, strong coupling
- non-perturbative

- Many approaches, none complete:
-  Lattice Gauge Theory
-    Small volume, hadron size
-  Regge Theory: Analyticity +
-    Unitarity + Crossing Symmetry
-     + Complex angular momenta
-  String models, etc.

_**Want a complete understanding of S.I.**_
**Non-perturbative – perturbative transition**

## Bjorken: Low pT is the frontier of QCD

- As pT drops from **200 ******** 100 ******** 50  MeV** what happens?
- Larger distances: 1 f   4 fm
- How do gluon fields in protons “cut off” ?
- Multiplicity distributions of very low pT particles, correlations, ...
- Low-pT cloud in special events, new phenomena ...
- Run with reduced field, Si-only tracking, etc
- Large impact parameter, b, collisions
- RHIC AA can measure b, how can we?   Diffraction at small t, n_ass?

**b**

## QCD Event Generators (Monte Carlo) : example PYTHIA

- Collisions producing hadrons all involve non-perturbative phenomena
- and cannot be accurately calculated. Resort to “QCD-based” models
- where necessary, analytic where possible. (e+e-, e p, p p)
-  Parton distributions in beam particles with scaling violations
-  Initial and final state parton showers
-  Hard sub-processes
-  Beam remnants and “underlying event”
-  Parton fragmentation and hadron decays

- Torbjorn Sjostrand et al.    hep-ph/0308153
- http://www.thep.lu.se/~torbjorn/Pythia.html

## High E_T Jets

_***High E_T Jets***_

-         CDF event display
- em + had calorimeter   drift chamber tracks

- gg, gq and qq hard scattering

## Jet ET and Di-Jet Mass Spectra

_***Jet ET and Di-Jet Mass Spectra***_

**CDF**

**D0**

## More on Jets ...

_***More on Jets ...***_

- Angular (or y) distributions
- well fit (log scale!) ... but
- y = 2.4 still “central”

- Below 50 GeV mostly gg (at y=0)
- Above 400 GeV mostly q-qbar
- Can study g and q fragmentation

## Differences between Quark and Gluon Jets

_***Differences between Quark and Gluon Jets***_

- CDF: Integrate pT in cone, fraction out to r of max R = 0.7
- Gluon jets are wider than quark jets

- At “low” ET (~ 40 GeV)
- mostly gluon jets (PYTHIA)
- At high ET mostly quark jets

## Three-Jet Events

_***Three-Jet Events***_

- Selection (CDF) : 3 jets > 20 GeV, J1+J2+J3 > 320 GeV

**Dalitz plot**

**Density L (data) R (MC-CTEQ4M-NLO)**

**Slices, x3 for many fixed x4**

**Agreement in magnitude and shape**

## Top Quark Pair Production

_***Top Quark Pair Production***_

- (Single top (t+b) production not yet observed – background)

- Good test of pQCD at short distances
- Sensitive to new phenomena.
- Statistics still limiting – much more to come

- lepton + jets +MET + b-tag
-              163 pb-1

- CDF

## Top Backgrounds in D0 (lepton + MET + jets)

- lepton + MET + 4 jets is clean with 1 or 2 b-tagged jets

_***Top Backgrounds in D0 (lepton + MET + jets)***_

- 1 b-tagged jet                         2 b-tagged jets

- EVENTS
- Per BIN

## W are very clean at the Tevatron

_***W are very clean at the Tevatron***_

## Z are very clean at the Tevatron

_***Z are very clean at the Tevatron***_

- pT(Z) agrees with MC

- 2 “isolated” em showers > 25 GeV
- with matching tracks
- (central-central & central-plug)

## W and Z Cross Sections

_***W and Z Cross Sections***_

- s-dependence well fit by theory
- (NLO production diagrams, pdf’s and their evolution)

## W-Production and Decay

_***W-Production and Decay***_

- Angular (rapidity) distribution of (charge tagged) lepton
- is sensitive to pdf’s and u,d quark differences

- CDF now able to tag some forward
- (~12 deg) electrons using vertex,
- silicon and shower position.

- Number of jets
- with W agrees
- with MC (Alpgen)

## W,Z + high pT photon

- + inner brems

_***W,Z + high pT photon***_

## WW Production (also WZ, ZZ)

_***WW Production (also WZ, ZZ)***_

**~ 10%                          ~  90%**

## Photon-Photon Mass Spectrum

- Looser cuts to search for “bumps”

## Photon + Heavy Flavor Production

_***Photon + Heavy Flavor Production***_

- Mass of particles on 2ry vertex

- Charm      and       Beauty

- Marcello

## B-hadron Production at High pT

- Secondary vertex,
- mass of s.v. tracks

- b-jets

- Shape test only

## B-Bbar Dijet Mass Distribution

- Two secondary vertex tagged jets
- Tagging efficiency ~ 20%/jet
- 251 events in 32 pb^-1

- CP-odd h(40) ?

## J/psi and B-hadron Production

- CDF-7037

_***J/psi and B-hadron Production***_

- B-hadrons
- Run II vs I
- (trigger!)

- FO-NLL
- Cacciari et al
- hep/ph-0312132

## Rare Charmless B decays

- CDF-7142

_***Rare Charmless B decays***_

**Penguin diagram**

## Another ... 

- W

- W

- Another ...

## Charmed Hadrons

- http://www-cdf.fnal.gov/physics/new/bottom/040422.dplus/

_***Charmed Hadrons***_

- 90,000 per MeV at peak!

**QCD:**
**Charm spectroscopy**
**Production mechanisms**
**(correlations)**

## Good “laboratory” for QCD:

_***Good “laboratory” for QCD:***_

**CDF Run 1 (1998)**

**CDF Run 2 (2004)**

- Future:

- Unquenched lattice (Allison et al, 2004):

## Central Exclusive Production

- ... or, diffractive excitation of the vacuum

- “It is contrary to reason to say that there is a vacuum
- or a space in which there is absolutely nothing.”
-                                                                                                 Descartes

-  Virtual states in the vacuum can be promoted to real states
-       by the glancing passage of two particles.
- Charged lepton (or q) pairs : 2-photon exchange
- Hadronic states : 2-pomeron exchange (DPE) dominates
- Vacuum quantum number exchange.
- Central states’ quantum numbers restricted.
- Measure forward p,pbar  missing mass, Q-nos.
- Ideal for Glueball, Hybrid spectroscopy

## Hadron Spectroscopy: an example

_***Hadron Spectroscopy: an example***_

- X(3872) discovered by Belle (2003)
- Seen soon after by CDF
- Relatively narrow

- What are its quantum numbers?
- Why so narrow? What is it?

- Also, cross-section depends
- on “size/structure” of state.

- If we see in exclusive DPE:

- PRL 93, 072001 (2004)

## Gluonia and Glueballs

- Hadrons G without valence quarks
- Allowed in QCD – or, if not, why not ?
- Some can mix with         mesons
- Some have exotic quantum numbers and cannot
- Glue-glue collider ideal for production (allowed states singly,
- others in association GG’, G + mesons.)
- Forward          selects exclusive state, kinematics filters Q.Nos :
- Exclusive central states e.g.

- Other processes:

- This one 

## Use Tevatron as Tagged Glue-Glue Collider

- Glueballs and Hybrids
-              New Exotic Hadrons
-                      chi_c and chi_b states
-                                Hunting strange exotic animals (radions, ...?

- tag

- tag

- Everywhere: **Gluodynamics**, perturbative and non-perturbative issues

- (Stretch Goal)

## Very Forward: Roman Pots

_***Very Forward: Roman Pots***_

- D0 has 8+8 quadrupole spectrometer pots + 2 dipole spectrometer pots
- Scintillating fiber hodoscopes

- CDF has 3 dipole spectrometer pots
- 0.8 mm x-y fibers

- Possible: Quads + near + far dipoles
- Silicon ustrips, pixels, trig scint
- Quartz Cerenkov for ~ 30 ps TOF

## Central Exclusive Production

_***Central Exclusive Production***_

- gg fusion: main channel for H production.
- Another g-exchange can cancel color, even leave p intact.
-                        p p  p    +    H     +      p
- Theoretical uncertainties in cross section, involving skewed
- gluon distributions, gluon k_T, gluon radiation, Sudakov ff etc.
- Probably                 ~ 0.3 fb at Tevatron, not detectable, but
- may be possible at LHC (higher L and                ~ 3 fb ?)

## {Measuring forward p  central quantum numbers

- {Measuring forward p  central quantum numbers
-                         2+ forbidden at t=0 for         state}

- Predictions for Tevatron ~ 600 nb (~ 20 Hz!)

## Exclusive Dijets?

**Meaning ****p p  ********  p          JJ          p**** and practically nothing else**
**See antiproton in roman pots, see rap gap on other side.**
**CDF Run I discovery {pGJJXG} (130/~10 bg) ... Run II trigger:**

**So far: upper limit ~ theoretical expectations**
**Expect enhancement rather than peak**
**They should all be gluon jets ! Unique sample**

## Central Exclusive Production at LHC

**Nothing else on 2-lepton vertex!**

- e

**+ White Pomeron search**

## The “White Pomeron”

- Alan White: **Pomeron = reggeized gluon + cloud of wee gluons.**

- Asymptotic freedom  16 color triplet q’s  ... Only 6 known
***AHA!***            1 color sextet Q counts 5 x 1 color triplet q
- {ud}+{cs}+{tb}         +       {UD}       AF

- e.g.   A.R.White hep-ph/0412062
- The Physics of a Sextet Quark Sector

## Two interesting Run II events

**Probable ZZ**
**4e > 20 GeV**.
**~ 70 tracks****   &  **y < 1 :  _**34**_

-    **ee MET (WW or ZZ)**
**2 tracks with  y < 1 **
**  ****& ****very low forward activity**

_***Two interesting Run II events***_

- pT  >  0.4 GeV/c

**Fluctuation? High-b? Diffractive?**
**MC + more data**

**(2 / 20)**

## BFKL and Mueller-Navelet Jets

- Color singlet (IP) exchange between quarks
- Enhancement over 1g exchange – multiRegge gluon ladder
- Jets with large y separation
- n minijets in between (inelastic case)
- large gap in between (elastic case)

- Fundamental empirical probe of new regime:
- non-perturbative QCD at short distances.

**Very forward OS calorimeters**

## Probing Very Small x Gluons

- High parton densities
- New phenomena (gluon saturation)
- HERA measures q(x) to ~ 10^-5
- g(x) by evolution, charm
- Could measure g(x) to ~ 10^-4
- (also x >~ 0.5) more directly

- Instrument                   region with tracking,
- calorimetry (em+had), muons,
- jets, photons ...

**Very forward SS calorimeters**

## Colliders study (mostly) Central Region

_***Colliders study (mostly) Central Region***_

- Jim Pinfold

## Forward “Cone” Spectrometer for CDF?

_***Forward “Cone” Spectrometer for CDF?***_

- Now: luminosity counters + 1.1 interaction length calorimeter

- Possible upgrade:
-  Tracking (in mag field)
-  electrons & photons
-  hadron calorimetry – jets
-  muons

- Could be done if sufficiently motivated (and funded!)

## What do we need to do?

**Gain slow, LHC take-over**

**Low B runs, roman pots at small t**

- b

- c

**LHC take-over**

## The Future of QCD at the Tevatron

- Workshop May 2004:

**http://conferences.fnal.gov/qcdws/**

**Very active program** will continue  > **10 x statistics**
**CDF** and **D0** detectors stop detecting in 2009 (probably)
- Before:
- Could add **precision (Si) roman pots** on both sides
- Could upgrade CDF very forward (**cone spectrometers**)
- Special running: root **s-scan** (630 – 1960), low **B-field** run
**BTeV:** Supplement B-physics program with more QCD studies:
- + roman pots, hadron calorimeter, veto (rap-gap) counters, + ?
- QCD Studies in **TeV4LHC Workshops** Fall 2004-2005