11. 4. 11 a. geiser, high pt qcd in ep, dis 11 1 · 4. 11 a. geiser, high pt qcd in ep, dis 11 2...
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![Page 1: 11. 4. 11 A. Geiser, high pT QCD in ep, DIS 11 1 · 4. 11 A. Geiser, high pT QCD in ep, DIS 11 2 The HERA ep collider and experiments HERA I: ~ 130 pb-1 (physics) HERA II: ~ 380 pb-1(physics)](https://reader035.vdocuments.mx/reader035/viewer/2022081615/5fd686527259580327343efd/html5/thumbnails/1.jpg)
11. 4. 11 A. Geiser, high pT QCD in ep, DIS 11 1
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11. 4. 11 A. Geiser, high pT QCD in ep, DIS 11 2
The HERA ep collider and experiments
HERA I: ~ 130 pb-1 (physics)
HERA II: ~ 380 pb-1(physics)
combined: ~ 2 x 0.5 fb-1
e (27.6 GeV)
low energy
e-
e+
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Deep Inelastic ep Scattering at HERA
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Parton density functions (PDF)
QCD evolution
valence
sea / 20
gluon / 20
x
Q2
x
x *pa
rton
dens
ity
HERALHC
Tevatron
parton densities and flavour composition measured at HERA determine cross sections at LHC
Higgs W,Z,top,jets,…
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Jets and αs
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αs
αs
Jets in ep interactions (HERA)
single (or no) jets in DIS: no QCD, measure quark densities (next talk)
dijets in DIS or photoproduction:measure both (dijets) or integrate over 2nd jet (inclusive jets)
require high ET w.r.t. photon axis
- check QCD- study performance of jet algorithms- measure αs and its running- measure gluon density (next talk)
QPM:
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Dijets in DIS see talkO. Kuprash
DESYDESY--1010--170, Eur. Phys. J. C70 (2010) 965 170, Eur. Phys. J. C70 (2010) 965
ET,B > 8 GeVMjj> 20 GeV
jet
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infrared and collinear safe jet algorithms
kT used for HERA data since decadesLHC mainly uses anti-kTstudy of anti-kT and Siscone at HERA added recently (before first LHC results)
high Q2 jet data
kT and anti-kT start to differ only from 4 partons/particles onwards -> need partial O(αs
3) QCD calculation
similar measurements also for photoproduction at HERA II
DESYDESY--1010--034, Phys. 034, Phys. LettLett. B 691 (2010) 127. B 691 (2010) 127see talkD. Lontkovskyi
see talkI. Makarenko
NLOJET++
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kt-, anti-kt and SisCone Jet production at high Q2
performance of all three jet algorithms very similar, well described by O(αs
3) QCD-> can safely be used at LHC
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Inclusive jets in DIS see talkR. Kogler
well described by NLO QCD + HERAPDF
double differential in Q2 and pT
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Multijet production + αs see talkR. Kogler
most precise (~αs2)
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H1 summary of αs measurements
optimised forminimization ofexperimentaluncertainties
good agreementwith previousmeasurementsand world average
uncertaintiesdominatedby NLO theory
see talkR. Kogler
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Inclusive jets in photoproductionfull HERA II statistics
running of αs consistent withQCD expectations
see talkI. Makarenko
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Summary of ZEUS αs measurementssee talkD. Lontkovskyi
αs running
analyses optimized forminimization of theoretical uncertainties
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Combined fit of HERAPDF + αs see talksA. Glazov,K. Nowak
good agreement with world average
uncertainty dominated by NLO theory
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Electroweak interactions/unification
electric
magnetic
gravity
weak
strong Big Bang
electromagnetic
electroweak
HERA
distance in m distance in m
even
t ra
te
LHC
If SUSY found at LHC, HERA will help to test GUT models
reminder: αs and grand unification
SUSYGrand Unification
error on αsdominates(theory!)
=> need NNLO QCD !
=> HERA would yield most precise αs value ( O(1-2%) )
GUT
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encouragement
would like to express strongencouragement to the brave theorycollegues who are engaged in such difficultNNLO calculations for HERA
for (some) recent progress, see e.g. HERA-LHC and PDF4LHC workshops, and theory talks at thismeeting
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Heavy Flavours
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Why are heavy flavours important?
charm contribution to HERA data up to 30%! (beauty ~1-3%)
kinematic effect of masscompeting scales for perturbative expansione.g. m, Q2, pT -> terms log Q2/m2
log pT2/m2 etc.
=> “massless” treatment (ZM-VFNS) allows resummation, but fails near “mass threshold” -> avoid !
=> “massive” treatment gets kinematics right,but does not allow resummation (fixed flavour number schemes, FFNS) or induces ambiguities in QCD corrections near flavour threshold (variable flavour number schemes, GM-VFNS)
check different schemes against HERA data
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Charm in DIS from D* production
NLO: massive FFNS (HVQDIS) OK, massless ZM-VFNS fails
large phase space coverage: pT(D*) > 1.25 GeV, |η(D*)|<1.8
see talkA. Jung
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Beauty and Charm jets in DIS
data well described by FFNS NLO QCD prediction
from secondary verticessee talkP. Thompson
DESYDESY--1010--083, 083, Eur.Phys.JEur.Phys.J. C71 (2011) 150. C71 (2011) 150
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Beauty jets in DIS
most precisemeasurement so far
almost fullphase space coverage
NLO QCD:massive FFNS(HVQDIS)a bit low but OK
see talkV. Libov
from secondary vertices
Q2>4 GeV2
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Beauty in DIS from b->e decaysDESYDESY--1111--005, arXiv:1101.3692005, arXiv:1101.3692
see talkR. Shehzadi
also double differential in Q2 and x
0.9<pTe<8 GeV|ηe|<1.5
NLO
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Heavy flavour contributions to F2
cor c
flavourtagging
-> F2bb, F2
cc
c
cQCD
,
,
~detect
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NLO and partial NNLO QCDin agreement with data, NNLO slightly better
beauty contribution to F2
HERA LHC, e.g. H,Z
Q2 >> mb2
newnew
see talkV. Libov
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charm contribution to F2
combined HERA (H1 and ZEUS) charm data:
sensitive to mcand to differences in Heavy Flavour schemes
fit to these data reduces uncertainties on W/Z cross sectionsat LHC (next talk)
here: massive VFNS schemes
see talksA. Glazov,R. Placakyte
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beauty and charm jets in photoprod.
see talkI. Brock
reasonably described byNLO QCD up to high pT
from secondary vertices
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beauty in photoproduction
reasonably described by NLO QCD down tothreshold
see talkM. Sauterfrom bb -> ee
new
new
agreement with prev. measurements
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Jets in Diffraction
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Forward Jets in Diffraction proton tagged by forward proton spectrometer see talk
R. Polifka
central
forward
good agreement withDGLAP NLO prediction
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Diffractive dijets in DIS proton tagged by very forward proton spectrometer see talk
J. Delvax
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Summary and conclusionsHERA still one of the best QCD laboratories
in general, agreement with NLO QCD, success of the Standard Model !(-> limits on new physics, see talks G. Brandt, E. Gallo, H. Pirumov, D. South)
HERA jet measurements successfully test and constrain QCD parameters -> potential to yield world best measurements of αs(need NNLO calculations ! partially in progress).
Heavy Flavour measurements at HERA successfully described by QCD,contribute to improve cross section predictions for LHC
new results on diffractive jet production with tagged forward protonsin agreement with DGLAP QCD expectations
for QCD only fraction of statistics has been analyzed so far in many cases. combination of H1/ZEUS results ongoing-> towards full 1 fb-1 results (H1+ZEUS, HERA1+2).-> expect significant further improvements over next few years