Transcript intro-crystal-channeling-mar07 - Indico

Diffraction at the LHC
Michele Arneodo, Università del Piemonte Orientale, Novara, Italy
Mario Macrì, INFN, Genova, Italy
Crystal Channeling for Large Colliders :
Machine and Physics Applications, CERN 23 March 2007
1) Diffraction
2) Experimental tools at the LHC
1
Diffraction ?!
p
p
p
p
2
Diffraction in hadron scattering
Double Pomeron Exchange (DPE):
Single diffraction (SD):
p
X
central Atlas/CMS
apparatus
p
IP
IP
Large Rapidity Gap
IP
p
vacuum
quantum
numbers
Near-beam
detectors
Near-beam
detectors
p
vacuum
quantum
numbers
X
central
Atlas/CMS
apparatus
Near-beam
detectors
SIGNATURE:
(i) Scattered proton with energy close to beam energy (within a few %);
(ii) Large Rapidity Gap (LRG)
o) If X = anything:
Measure fundamental quantities of soft QCD
o) If X includes jets, Ws, Zs, Higgs (!):
Hard processes, calculable in perturbative QCD
Measure proton structure, QCD at high parton densities, discovery physics
3
Pomeron ?!
• Pomeron goes back to the ‘60s: Regge trajectory, ie a moving pole
in complex angular momentum plane (?!)
• Now understand in terms of QCD
• In diffractive events look at the proton constituents through a lens
that filters out all parton combinations except those with the
vacuum quantum numbers
IP
p
p
p
p
2-gluon exchange:
LO realisation of vacuum
quantum numbers in QCD
4
Central exclusive production of the Higgs
• Khoze, Martin, Ryskin hep-ph 0111078
• Central system is (to a good approx) 0++
H
b, W
b, W
• If you see a new particle produced
exclusively with proton tags you know its
quantum numbers
• Proton tagging may be the discovery
channel in certain regions of the MSSM
• Measuring the protons means excellent
mass resolution (~ GeV) irrespective of the
decay products of the central system
• Attractive for MH=120-250 GeV
ξ: fractional momentum loss of proton – for 120 GeV Higgs, x~ 1%
t: 4-momentum transfer squared at proton vertex
5
Experimental tools at LHC
6
Diffraction: how to measure the protons
•
At I.P. 5 (CMS): TOTEM, Roman Pots at 150 and 220m from I.P.
Excellent coverage in x and t at low luminosity optics (b*=90, 1540m)
Coverage 0.02<x<0.2 at high luminosity optics (b*=0.5m)
[F. Ferro, M. Oriunno]
•
At I.P. 1 (ATLAS): FP220
Roman Pots at 220 m
Coverage similar to TOTEM at high luminosity optics
•
At I.P. 1 and 5 (ATLAS and CMS): FP420
R&D project, aim to instrument region at 420m from I.P.
0.002<x<0.02 (high luminosity optics only) [F. Roncarolo]
Logx
b*=0.5m
detectors@420m
Logt
TOTEM
FP220
xL=P’/Pbeam= 1-x
FP420
7
How to measure the protons
FP420
TOTEM
(or FP220 at ATLAS)
• Cold region
of LHC
• Too far for
L1 trigger
8
sEL, sTOT
p
• Elastic scattering:
p
IP
p
p
• Elastic part drives stot via optical theorem: dsel/dt|t=0 (stot)2
b*=1540m
b*=90m (proposed)
See talks by
M. Oriunno, F. Ferro
Also:
Recent proposal by ATLAS,
b*=2500m
9
CMS+TOTEM:
unprecedented coverage in 
CMS IP
T1/T2, Castor
ZDC
RPs@150m
RPs@220m
possibly detectors@420m
T1 (CSC) 3.1 ≤ || ≤ 4.7
HF 3 ≤|| ≤ 5
T2 (GEM): 5.3 ≤ || ≤ 6.6
Castor 5.3 ≤ || ≤ 6.6
Carry out a program of diffractive
and forward physics as integral part
of the routine data taking at the LHC,
i.e. at nominal beam optics and
up to
10
the highest available luminosities.
CMS+TOTEM: physics map
Low lumi
Rapidity gap selection possible
HF, Castor, BSCs, T1, T2
Proton tag selection optional
RPs at 220m and 420 m
Diffraction is about 1/4 of stot
High cross section processes
“Soft” diffraction
Interesting for start-up running
Important for understanding pile-up
High lumi
No Rapidity gap selection possible
Proton tag selection indispensable
RPs at 220m and 420 m
Central exclusive production
Discovery physics:
Light SM Higgs
MSSM Higgs
Extra dimensions
Gamma-gamma and gamma-proton interactions (QED)
Forward energy flow - input to cosmics shower simulation
QCD: Diffraction in presence of hard scale
Low-x structure of the proton
High-density regime (Color glass condensate)
Diff PDFs and generalized PDFs
Diffractive Drell-Yan
“Prospects for diffractive and forward physics at the LHC”
11
CERN/LHCC 2006-039/G-124, CMS Note 2007/002, TOTEM Note 06-5, Dec 2006
Summary
• A lively experimental program addressing elastic and diffractive
scattering at LHC
• Different experiments joining forces: CMS+TOTEM, ATLAS and CMS
in FP420
• Can the scope of this program be widened by using crystals ?
12