QCD and Hard Diffraction at the LHC

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QCD and Hard Diffraction at the LHC
Introduction QCD at the Tevatron (overview) The
High Q2 Frontier Jets, tops, W/Z, Q or X? LHC
A new arena for QCD. Detectors Very High Mass
Diffraction High Mass Central Production
(a.k.a. DPE) The FP420 Project
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Recent QCD studies at the Tevatron (CDF D0)
Every interaction is QCD!
... even that!
In May 2003 May 2005 CDF (D0) published 43 (10)
QCD papers
other topics to follow...
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QCD Topics in TeV Publications May 03 May 05
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Jets
Below 50 GeV mostly gg (at y0) Above 400 GeV
mostly q-qbar Can study g and q
fragmentation At LHC pp ? p JJ p pure gluons
Angular (or y) distributions well fit (log
scale!) ... but y 2.4 still central
Cone algorithm
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At the top of the spectrum
Run 152507 Evt 1222348
All hits/tracks
tracks pT gt 2 GeV/c
618 GeV
CDF kT algorithm
552 GeV
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Here is a beautiful 3-jet event!
Run/Event 162498/4411694
155 GeV
402 GeV
ET gt 0.5 GeV
444 GeV
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Projected Jet Cross Sections at LHC
Spectra drawn to few/100GeV bin in 100 fb-1
Let us hope these are quite wrong Peak(s),
excesses, cut-off (black hole production?) ---
the end of high pT physics!
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Coverage in (x,Q2) extended by more than an Order
of Magnitude
EVENTSHOWN
Smallest x requires very forward detectors

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Production Cross Sections Rise Strongly with
Energy
(Except at fixed x)
1 top/sec at 1033
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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 calorimeters OS
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TeV 03-05
CDF B-hadrons Run II
D0 Run II Y-production
CDF, hep-ex/0412071
Cacciari, Frixione, Mangano, Nason, Ridolfi,
hep-ph/0312132
Berger, Qiu, Wang, hep-ph/0404158
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TeV 03-05
Penguin diagram
W
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Rare Charmless B decays
CDF-7142
At LHC LHC-B ATLAS/CMS?
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TeV 03-05
pQCD !
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Probing Very Small x Gluons
High parton densities New phenomena (gluon
saturation) HERA measures q(x) to few 10-5 ?
g(x) by evolution, charm LHC measure g(x) to lt
10-5 more directly
Instrument few degree region with tracking,
calorimetry (emhad), muons, , jets,
photons ...
CASTOR, TOTEM
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TeV 03-05
MPS
CDF study charged particles transverse to
high pT jets
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Beyond Single Parton Distributions
Double and multiple parton scattering
Hint at ISR (4 jets), Seen in UA2 and CDF
Double Drell-Yan diquarks
anti-diquarks Correlations in b (impact
parameter) and x
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TeV 03-05
But before May 2003
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Categories of Diffraction at LHC
Can have a 4-unit gap with 2 TeV SD Can have
(VF)J G6 (VF)J Can have 2 x 3-unit gaps
with 700 GeV DP Can have p-G3-X-G3-X-G3-p
with M(X) 12 GeV
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QCD
Google tev4lhc Fermilab Sept 2004 BNL
Feb 2005 CERN Apr 2005 Fermilab Fall 2005
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ATLAS
A QCD machine, especially if add forward
detectors!
Very small person (?)
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(No Transcript)
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CMS at LHC
Bigger people!
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CASTOR
(MWPC TRACKING)
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Detecting Protons with xF gt 0.9
K.Eggerts talk
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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 0.2 fb at Tevatron,
  not detectable, but
• should be possible at LHC (higher L and 3
  fb?)

100 x Acc events in 30 pb-1
at Tevatron
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Central Exclusive Higgs Production
Can be inclusive (soft central hadrons) but
exclusive (nothing else) is most interesting.
Precision measurement of both p ? M(central) by
MM Possible resolutions ( 250 MeV at
Tevatron) 2 GeV at LHC. Can go for dominant
H(110-130) b-bbar decay mode Exclusive DPE ?
q-qbar dijets strongly suppressed (Jz 0
rule) Selection Rule on central Q.Nos Scalar
... p correlations confirm (need
statistics!) Non-SM H interesting!
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Acceptances vs Mx for p p ? p Mx p
In addition to 215m (TOTEM) 420m detectors
are essential for Mx lt 400 GeV ... region of H,
WW, ZZ Both ATLAS CMS want this. Join forces
FP420 project LOI for RD ? LHCC June 05
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FP420 Forward Protons at 420 m
Groups in ATLAS and CMS/TOTEM want to add very
forward proton detectors, mainly to study DPE,
central production. Central states especially
WW, ZZ, H,
TOTEM
FP420
TOTEM
FP420
Inelastic protons bent few mm out of beam 6mm x
24 mm detector (e.g. Si pixel)
10 mm
25 mm
Valentina Avati
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US
Albert De Roeck
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Diagrams for Prompt VV Pair Production in
pp/ppbar
(Prompt i.e. not from top and not from Higgs)

• Note different color flows in these
• diagrams ? can give different
• hadronic activity.
• and (b) have color 3 annihilation
• (d) has color 8 annihilation
• (c) and (e) have color singlet exchange.
• (c) high pT q forward jets (e) low pT ps
  no jets, can be exclusive

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Cross section for WW Production Energy Dependence
Tevatron cross section agrees with CTEQ NLO
Tev2 sig(ZZ) 1.39 pb sig (ZW) 3.65 pb sig WW
12.4 pb
LHC 10 x higher
If Tevatron RoT apply, At LHC SD, 1 ? 100
fb DP, 10-3 ? 10 fb
i.e. Guesstimate for DPE ? WW (ZZ) anything
10 (1) fb
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Central Exclusive WW Production at LHC
e
Nothing else on 2-lepton vertex!
White Pomeron search
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Double Pomeron ? WW- via Q6 Loop
Photon-Pomeron-Z vertex via Q6 loop Photoproducti
on at LHC? pp ? p Z p
0 in SM
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Summary
Tevatron is, and LHC will be, a cornucopia of QCD
physics
At LHC,
Jets, W, Z, b, c, production, spectroscopy,
decays and especially rapidity gaps, exclusive
production of jets, H, WW, ZZ, BSM Very Forward
Proton Detection New window on strong and
electroweak interactions