1. W and Z production: cross section and asymmetries at the LHC
Monika Wielers
RAL
On behalf of ATLAS and CMS

2. W and Z production LHC is W/Z factory Foreseen measurements
(Wl) ~ 15nb  107 events in L dt = 1 fb-1
(Zll) ~ 1.5nb  106 events in L dt = 1 fb-1
Foreseen measurements
Measurement of W/Z inclusive cross section as well as W/Z+jet
Constraining PDF’s
Measurement of sin2W
Measurement of W mass and width (see talk by M. Malberti later this morning)
Measurement of gauge boson pair production (see talk by Z. Zhao tomorrow afternoon)
Measurement of triple gauge couplings
Understanding detector and performance
In situ calibration of EM calorimeter using Zee
Alignment via Z
Extraction of trigger and offline lepton identification efficiencies
Measurement of luminosity
ICHEP, July 2006
M. Wielers (RAL)

3. ATLAS Detector Magnetic Field Inner Detector Calorimetry
2T solenoid plus air core
toroid
Inner Detector
s/pT ~ 0.05% pT(GeV)0.1%
in |h| < 2.5
Calorimetry
Covers |h| < 5.0
EM Calorimetry
s/E ~ 10%/√E(GeV)1%
|h| < 3.2 with fine granularity
Hadronic Calorimetry
s/E ~ 50%/√E(GeV)3% in
||<3
Muon Spectrometer
s/pT ~ 2-7 % in |h| < 2.7
Precision physics in |h|<2.5
ICHEP, July 2006
M. Wielers (RAL)

4. The CMS Detector Magnetic Field Inner Detector Calorimetry
4T solenoid
Inner Detector
s/pT ~ 0.015% ·pT(GeV) in
|h| < 2.5
Calorimetry
Covers |h| < 5.0
EM Calorimetry
s/E ~ 5%/√E(GeV)2% in
|h| < 3.2
Hadronic Calorimetry
s/E ~ 65%/√E(GeV)5% in
||<3
Muon Spectrometer
s/pT ~ 0.05 ·pT(TeV)
(tracking+muon)
Covers |h| < 3.0
ICHEP, July 2006
M. Wielers (RAL)

5. Status of ATLAS/CMS
ICHEP, July 2006
M. Wielers (RAL)

6. New LHC machine schedule
Machine milestones
Initial operation will be with 450 GeV beam energy with a static machine (no ramp, no squeeze) to debug machine and detectors
Afterwards shut-down (~3 months) during which the remaining machine sectors will be commissioned without beam to full energy (7 TeV)
In spring 2008 LHC will be brought into operation for the first physics run at 7+7 TeV, with the aim to integrate substantial luminosity by the end of 2008
SPC stressed that the goal should be several fb-1 integrated luminosity at the end of 2008
Last magnet delivered
October 2006
Last magnet tested
December 2006
Last magnet installed
March 2007
Machine closed
August 2007
First collisions
November 2007
ICHEP, July 2006
M. Wielers (RAL)

7. W and Z production at the LHCx
xf(x,Q2)
Large W/Z cross section at LHC
(Wl) ~ 15nb
(Zll) ~ 1.5nb
Main (LO) contribution
Sea-sea parton interactions at low-x will dominate
At Q2~M2W/Z sea driven by the g  qq contribution
gluon far less precisely determined for all x values x
Q2 (GeV)
ICHEP, July 2006
M. Wielers (RAL)

8. Measurement of W / Z cross-sections
Cross section measurement accuracies for CMS for L =1fb-1
s(Zmm + X) = 1160 ± 1.5 (stat) ± 27 (syst)  116 (lumi) pb
s(Wmn + X) = ± 6 (stat) ± 485 (syst)  1470 (lumi) pb
Systematics theory dominated (acceptance).
At a later stage these processes can be used as luminosity monitor (Error on luminosity: ~5%)
W
CMS
pT effects in LO/NLO
1.83 %
Tracker efficiency
1 %
PDF uncertainty
0.7 %
pT effects in LO/NLO
2.29 %
Missing ET
1.33 %
Trigger efficiency
1 %
Muon efficiency
We
ATLAS
ICHEP, July 2006
M. Wielers (RAL)

9. We rapidity distributions
At LHC experimental uncertainty dominated by systematics
Theoretical uncertainties, dominated by PDFs
Exp. uncertainty sufficiently small to distinguish between different PDF sets
PDF error sensitive to W→e rapidity distribution
PDF uncertainties only slightly degraded after detector simulation and selection cuts
CTEQ61
MRST02
ZEUS02
e- rapidity
e+ rapidity
Generated y
ds(We)/dy
Reconstructed
ICHEP, July 2006
M. Wielers (RAL)

10. PDF constraining potential of ATLAS
Include ATLAS W Rapidity “pseudo-data” in global PDF Fits
Simulate real experimental conditions:
Generate 1M “data” sample with CTEQ6.1 PDF through ATLFAST detector simulation and then include this pseudo-data (with imposed 4% error) in the global ZEUS PDF fit (with Det.Gen. level correction).
ZEUS-PDF AFTER including W data
ZEUS-PDF BEFORE including W data
e+ CTEQ6.1
pseudo-data
ds/d (nb)
e+ CTEQ6.1
pseudo-data
|h|
|h|
low-x gluon shape parameter λ, xg(x) ~ x –λ :
BEFORE λ = ± 0.046
AFTER λ = ± 0.027
41% error reduction
(after few days of LHC
Running at L=1033cm-2s-1)
Normalisation free  independent of luminosity
ICHEP, July 2006
M. Wielers (RAL)

11. High-Mass Lepton pair Production
Important benchmark process
Deviations from SM cross section indicate new physics
ds/dm() (fb/GeV)
Di-lepton mass spectrum
m() GeV
m(ll) GeV
# events
Systematic error
CMS
Size of uncertainty
m(ll) GeV
ICHEP, July 2006
M. Wielers (RAL)

12. Determination of sin2θW(MZ2 )
Measure AFB = b { a - sin2θW( MZ2 ) }, a, b calculated to NLO QED and QCD
Measure AFB with leptons in Z0 DY events. Can fit with Mt to constrain MH
Require pTe > 20 GeV, 85.2 < Mee < 97.2 GeV
For L = 100 fb-1 (ATLAS)
Current error on world average 1.6x10-4
need small systematic error:
PDF uncertainty,
precise knowledge of lepton acceptance and efficiency
effects of higher order QCD
At LHC no asymmetry wrt beam, assume Qq collision
quark Q direction from y(ll)
measurement at high y(ll) Q q
y cuts – e+e-
(|y(Z)| > 1)
∆AFB
(Stat)
∆sin2θW
|y( l1,2 )| < 2.5
3.0 x 10-4
4.0 x 10-4
|y( l1 )| < |y( l2 )| < 4.9
2.3 x 10-4
1.4 x 10-4
[%]
ATLAS
y(ee)
ICHEP, July 2006
M. Wielers (RAL)

13. Conclusions W and Z cross sections important early measurements at LHC
Instrumental systematics on W+Z cross-sections with Ds/s~few % for 1fb-1
W and Z production will help to understand
Detectors and physics performance
Calibration, alignment, efficiency extraction, optimisation of e/ isolation cuts, etc.
Reduce theoretical errors
Gluon pdf’s measured via W rapidity distributions will reduce significantly the error on gluon shape parameter
Measure sin2qW from Zee decays
Potential for measurement comparable with current limits, requires extending electron coverage at large h
ICHEP, July 2006
M. Wielers (RAL)