Uta Klein

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On the implications on HERA for the LHC physics
HERA and the LHC

• Uta Klein
• Foundation Deutsches Elektronen-Synchrotron

Picture of HERA tunnel
University of Bonn Research Seminar, November
2nd, 2006

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Outline

• Motivation
• Inclusive exploration of proton structure
• High precision QCD fits
• Gluons at low x
• Charm and beauty
• Concluding remarks
• Outlook

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ep and pp

• ep collisions (HERA)
• Ideal tool to study the
• structure of hadrons via deep inelastic
  scattering
• ? structure functions/parton densities
• Can use the photon as a point-like
• or hadronic particle through
• its virtuality
• Main contributions are in the area of QCD
  Small-x, diffraction, saturation, high
  densities, jets
• Precise understanding of QCD
• pp collisions (LHC)
• Highest energies reachable,
• can reach highest masses for new particles
  production
• Precision often limited by knowledge of
  quark/gluon
• structure of proton
• QCD effects need to be controlled to the best
  of our knowledge

xp
x1p
x2p
fb
fa
x proton momentum fraction of quark
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Tevatron and LHC
J.Stirling ICHEP04
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Physics _at_ LHC
G.Dissertori Lisbon05
The only place where success appears before work
is a dictionary..
Discovery potential relies on precise
understanding of QCD. HERA delivers partons
and understanding of production mechanism.
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Inclusive Higgs bosonproduction - SM
hep-ph/0508222v1
dominant production process
much larger compared to
bbarH coupling small in comparison to ttbarH
coupling and b-quark distribution function
smaller than gluon DF lt- input from HERA
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Inclusive Higgs bosonproduction - MSSM
hep-ph/0508222v1
beyond the SM approaches, e.g. MSSM 2 Higgs
doublets with 2 independent vacuum expectation
values -gt ratio of VEV is a free parameter -gt
couplings to t- and b-quarks are modified -gt
high values of tanß will enhance the coupling to
the b-quark -gt production cross section
measurement of Higgs is a KEY ingredient to
disentangle new physics
note similar trends for Higgs production at
Tevatron!
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Effect of PDF uncertainties onHiggs production
cross section
hep-ph/0508222v1
TEVATRON
LHC
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aS 2 -gt aS 3
NLO -gt NNLO
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PDF uncertainty NLO PDFs
Higgs mass
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Effect of PDF uncertainties contd
LHC
be aware, uncertainties for g and b are highly
correlated
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hep-ph/0508222v1
-gt important to gain better control of PDF
uncertainties and to get independent measurements
of b and gluon PDFs
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W and Z production
HERA-LHC WS procs.

• suggested to use as parton luminosity monitor

current uncertainties 8 WZ may be used as SM
benchmark measurement but 8 are large compared
to theory uncertainty of 1-2 -gt need for more
precise HERA data, in particular for gluon PDF
hep-ex/0509002v1
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Effect of excluding low x HERA data
hep-ph/0509002v4
x10.006 x20.006
total cross section
x10.12 x20.0003
x10.0003 x20.12
xmin
MRST observed instabilities of NLO QCD fits
(tension of low x HERA data and Tevatron
inclusive jet data ?) -gt not confirmed by CTEQ
studies
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Effect of excluding low x HERA data contd
hep-ph/0509002v4
- standard Qgt2 GeV
-- Qgt2.5 GeV, xgt0.001
-- Qgt3.162 GeV,xgt0.005

• All well defined if we believe in standard theory
  at low x.
• Are there measurements to further constrain
• the parton dynamics at low x?

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The H1 Detector
320 authors, 42 institutes
Fast Track Trigger
Forward Proton and Neutron Spectro- meters
Luminosity spectrometer
p
e
27.5 GeV
920 GeV
Forward tracking Si DC
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The ZEUS Detector
Luminosity spectrometer
Beam Pipe Magnets
350 authors 35 institutes
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Luminosity development at HERA I 92-00
(unpolarized e) II 03-07 (polarized e)

• HERAI H1 and ZEUS took
• about 130pb-1 with HV on
• including 16 pb-1 e- data
• HERAII luminosity upgrade
• lumi on tape
• 2003/2004 positrons 50 pb-1
• 2004-06 electrons 213 pb-1
• 2006 positrons so far 60 pb-1
• 2007 scheduled end of HERA

status 1.11.2006
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Deep inelastic scattering kinematics
Neutral Current (NC) interactions

• Q2 -q2 resolving power of the
• exchanged boson 1/vQ2
• DIS Q2 gtgt M2proton
• snapshot of proton structure
• x Q2/2Pq fraction of proton
• momentum carried by struck quark (Bjorken
  68)
• y Pq/Pk fraction of lepton momentum carried
  by the exchange (inelasticity, please
• do not mix with the rapidity y!)

hadronisation
At HERA NC kinematics over-constrained
(Ee,?e and/or Ejet,?jet) CC ? escapes
detection kinematics from Ejet,?jet
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kinematic limit
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NC and CC cross sections
Neutral Current
e ?
? p
Charged current
Charged Current
e ?
? p
?
ZEUS (H1) r 0.85 (1.0) 10-18 m ? quarks are
point-like down to proton radius/1000
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DIS structure functions
PDFs
below bottom threshold
valence quarks
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What HERA DIS data taught us on F2em
e.m. structure of the proton known to few in a
large area of x and Q2
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PDFs
at low x
x dependence of q(x,Q2) determined by fit to eN
data, Q2 dependence determined by DGLAP equations
at high x
HERA-I ?F2/F230
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Reduced charged current cross sections

_ _ --- s (e-p) x (uc) (1-y2) x (ds)
_ _ --- s (ep) x
(uc) (1-y2) x (ds)
HERA can disentangle parton distributions at
large Q2 and large x gt 0.01 within single
experiments, independently of nuclear
corrections and free of higher twists and
isospin assumptions (measure d of the proton
directly)
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Unfolding PDFs using CC and NC cross sections
E.g. ZEUS NLO QCD fit EPJC42(2005)1
Q210 GeV2
Parameterisation

• Constraints
• ? momentum and quark number sum rules
• ? low-x behaviour of uv and dv set equal
• ? ? set consistent with Gottfried sum and DY
• 11 free parameters in total
• heavy quarks treated in variable flavour
• number scheme of Thorne and Roberts
• ? uncertainties evaluated using Offset Method

EPJ C30(2003)1
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Sea quarks and gluon
ZEUS inclusive NCCC jets ? improved
precision for gluon
at medium x

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The strong coupling aS from NLO QCD fits
ZEUS
H1
EPJC42(2005)1
EPJ C21(2001)33

• strong improvement observed from using ep jet
  data
• experimental uncertainties in the range of 2
• both aS values have an additional scale
  uncertainty of 0.005 (4.3) which
• reflects an ad hoc approach to cover beyond
  NLO effects
• ? precision of HERA data call for NNL0 QCD
  analyses
• NNLO calculation now available, thanks
  S.Moch,J.A.M. Vermaseren,A.Vogt hep-ph/0403192
  0404111
• deuterons at HERA would disentangle nonsinglet
  singlet evolution and further reduce aS error
  significantly

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Side remark
B.Reisert, DIS03-WS hep-ph/0601012 (p101)
this chance is now gone for HERA
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Alfas results
- 2006 a _at_ 10-9 - 2006 GF _at_ 10-5 - 2006 G _at_
0.02 - 2006 a S _at_ 1-2
C. Glasman, hep-ex/0506035
Improved accuracy with more and more accurate
data (statistics and systematics), inclusive and
jets Theory uncertainty NNLO, ?/2?
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Gluons at low x
Derivative and F2 determine gluon distribution
but only within DGLAP and not very accurately. FL
is necessary to test QCD at h.o.
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FL from reduced inclusive DIS cross section

F2

• extrapolated to low
• Q2 lt 3.5 GeV2

• But H1 determination of FL has two limitations
• small x FL extraction needs assumptions on F2
• x-dependence of FL can not be determined
• ? Precision FL measurement requires low-Ep
  running!

FLgt0
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Low energy running proposal
M Klein DIS06 summary
Rochester Conference 1955
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M Klein DIS06
Rosenbluth representation of cross section
920 575 460 GeV
F2
F2-FL
f(y)
L Ep2
10 5 2 pb-1

Binning crucial used Q2, ?sy/2M Choice of 3rd
energy value to divide f(y) linearly 575 GeV if
460 GeV is the lowest energy. At larger x all
measurements are at low y (f(y)) and thus the
sensitivity to FL decreases rapidly. For full y
range a new precise measurement of F2 results.
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M Klein DIS06
H1 FL simulation of two energies
920 GeV 30 pb-1 460 GeV 10 pb-1
Error between 0.05 and 0.1, statistical and
systematics about matched, At high y efficiency
and yp background sources of uncertainty similar.
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D Kollar DIS06
ZEUS Detailed FL simulation of two energies
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J Feltesse Lowx2006
A direct measurement of FL at x from 10-4 to
10-3 is difficult but feasible by running HERA
for a few weeks at low proton beam energy.
Agreed by both H1 and ZEUS and supported by the
PRC. The measurement of FL provides a very
attractive added value to the legacy of HERA.
It could also provide the first measurement of
FLD at the 3-4 sigmas level. Lets do it.
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Charm and Bottom
M.Klein, BINN-LHC-04 B.Reisert, priv.comm
hep-ph/0601012 (p100)

• at x0.001
• dominated by sea
• quarks
• but valence quark
• PDFs although small
• also not well known
• ?xG3 from HERA II
• dramatic increase
• of sea PDFs towards
• high Q2 c,b sizeable
• how to improve
• knowledge on HQ
• PDFs?
• how well does
• evolution work?

UV
dV
c
b
s
HERA ? LHC
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Charm and beauty in DIS
dominated by boson-gluon fusion
D production in DIS
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H1 hep-ex/0507081
F2cc
F2bb
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• Impact parameter tagged
• with Si-vertex detector
• -gt very promising measurements
• a challenge for HERA II

HERA
LHC, e.g.
H,Z
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Polarized charged current DIS
A.Tapper ICHEP06
text book measurement
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Dependence on Pe
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Limits for MWR
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HERA combined NC measurements
NEW ICHEP06
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QCD EW SM analysis
New ICHEP06
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Concluding remarks

• HERA data have been delivering a deeper
  understanding of p structure as encoded in PDFs
  and their uncertainties. Those are widely used in
  the HE community.
• First round of measurements and QCD analyses of
  NC and CC DIS HERA I data is essentially
  finished.
• Further results to come with increasing
  luminosity, time and precision and employing new
  techniques and theoretical developments
• inclusion of ep jet data
• inclusion of new polarized HERA II data
• combined EW and QCD analysis
• Dedicated run at lower proton energy would allow
  a first measurement of FL and a direct
  determination of gluons at low x scheduled for
  last 3 months of HERA running
• HERA data have a great potential but to reach a
  next level of precision in PDFs and aS is a
  serious challenge (systematic 1, NNLO).
• These analyses require a few more years of
  dedicated analyses (also combining H1ZEUS.
• Workshops next year HERA-LHC CERN, DIS07MPI,
  DIS_at_TeVCERN

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now then
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Kinematics of the Large Hadron electron Collider
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hep ex
ep collider in the LHC tunnel 70 7000
GeV2 further studies at forthcoming
workshop cost estimate and design study ready by
about 2010 an attractive option for upgrading
the LHC physics Search for
and spectroscopy of new particles (eq
states), new strong i.a. at TeV
scale? Exploration of high density QCD High
precision ep in LHC range
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LHeC parameters
Compare with HERA maximum reached was 0.05 1033
cm-2s-1 Estimated luminosities of linac-ring ep
colliders below HERA
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Back Ups
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