The LHC experiment will be sensitive to the low x values, so we need to know precisely
the partons (quarks, gluons) momentum distribution in the proton. More recent results about this topic
can be obtained at
HEPDATA.
There are some groups work on this field. They do a slightly different parametrisation of those PDF's functions.
Most popular are
MRST and
CTEQ.
One may plot these functions and see the differense
here.
Evolution of the PDF's at low x is also an impotant issue. See BFKL theory for example.
See also:
Structure functions on PDG
The idea is to study the physical distributions dependaning on different PDF sets.
So it is possible now to generate Pythia samples with different PDF's. The package for that is called
LHAPDF.
In the CMS experiment, very forward jets can be identified using the two HF calorimeters (3<|η|<5). The HF, located 11.2 meters away
on both sides of the interaction point (IP), is a steel plus quartz-fiber Cherenkov calorimeter segmented into 1200 towers of
Δη×Δφ∼0.175×0.175. It has an interaction length of 10.3λ and is sensitive to deposited
electromagnetic (EM) and hadronic (HAD) energy. The two HFs have been specifically designed for forward jet and missing-energy
measurements. In particular, the HF plays a prominent role in forward jet tagging for the vector-boson-fusion (VBF, qq→ qqH) Higgs
production channel. The HFs have an energy (position) resolution of ∼20%(∼10%) for typical jets with ET ∼ 40 GeV
(i.e. E = ETcoshη ≈ 1 TeV at η=4).
Events for this analysis can be selected online with a L1 trigger requirement of a jet candidate
with a transverse energy threshold of ET≈10 GeV since the default CMS jet L1 algorithm includes
as primitives the 2×72 trigger towers in HF+/- (each tower has an η−φ segmentation
of about 0.5×0.35). In addition, an HLT trigger currently exists (although with a higher ET =
30 GeV threshold) for the fast jet reconstruction and tagging of forward-backward jets in HF
emitted in the Higgs VBF channel.
-- new regions in Q-x plot
-- test resolution of HF calorimeter
Material about "Low-x QCD physics" can be found in
CMS Note-2007/002
and article
Forward Physics at the LHC
See
HF Layout and Design and
CMS NOTE
2006/044: "Design, Performance, and Calibration of CMS Forward Calorimeter Wedges".
