Download - Lara De Nardo for the HERMES COLLABORATION
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Inclusive Measurements of inelastic electron/positron scattering on unpolarized H and D targets at
Lara De Nardo
for the
HERMES COLLABORATION
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LARA DE NARDO 2
DIS cross section and structure functions
Collider
Fixed
target
HERMES
DIS2011
,HERMES
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LARA DE NARDO 3
Why measuring inclusive DIS cross sections at
HERMES?HERMES (1996-2000) 16.4 M proton + 18.5 M deuteron
eg. Compared to NMC 3 M proton + 6 M deuteron
Gottfried Sum
Valence Quark Ratio
Explore the transition between perturbative and non-perturbative
QCD
DIS2011
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LARA DE NARDO 4DIS2011
The HERMES Spectrometer
Reconstruction: dp/p < 2%, dq < 1 mrad
Particle ID: TRD, Preshower, Calorimeter, RICH
Internal gas targets: unpol: H, D, He, N, Ne, Kr, Xe , He , H, D, H
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LARA DE NARDO 5
Kinematic plane
19 x binsUp to 6 Q2 binsTotal: 81 bins
Traditional DIS region (Q2>1GeV2) can be easily separated
DIS2011
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LARA DE NARDO 6
DIS BORN CROSS
SECTION
Extraction of cross sections
UNFOLDING
DIS YIELDS
• Particle ID efficiencies
• Trigger efficiencies
• Charge symmetric background subtraction
• Geometric acceptance
• Detector smearing
•Radiative corrections
• Tracking related effects
DIS2011
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LARA DE NARDO 7
Time interval
Luminosity
Normalization uncertainty 7.5% (proton) and 7.6%(deuteron)
Elastic reference process: interaction of beam with target shell electrons
•Electron beam: Moller scattering
•Positron beam: Bhabha scattering
annihilation
Coincidence rate Correction
for accidental
coincidence
Luminosity constant
(time dependent)
Trigger livetime
DIS2011
1032 cm-2 s-1
(unpol H)
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LARA DE NARDO 8
Particle ID efficiencies
PID
TRD
CERENKOV (RICH)
PRESHOWER
CALORIMETER
CONDITIONAL PROBABILITIES
PIDdet FOR PARTICLE
HYPOTHESIS
Leptons identified by PID>PIDcut with PIDcut=0
Hadron contamination: fractional contribution of hadrons above PIDcut
Lepton identification efficiency: fraction of leptons selected with PID>PIDcut
Correction ~1%DIS2011
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LARA DE NARDO 9
Trigger efficienciesH0
H1
PRESHOWER
CALORIMETER
DISTRIGGER
Dependence on time (voltage changes, radiation…), momentum , angle : Efficiencies are calculated separately for Top and Bottom, data production, bin
Example: H0 efficiency for 2000 data
DIS2011
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LARA DE NARDO 10
Charge symmetric background
DIS2011
meson Dalitz decay photon conversion
These e+ and e- originate from secondary processes Lower momenta (high y) concentration Correction applied by counting the number of events with charge opposite of the beam
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LARA DE NARDO 11
Experimental cross section
DIS2011
Yields are corrected for
Trigger efficiencies PID efficiencies Charge symmetric background
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Unfolding Kinematic bin Migration
Events originating in bin j and measured in bin i
Events in bin j on Born level
Background term
Smearingmatrix
4p BORN MC
Simulation of true cross sectionNo radiative effectsNo tracking
FULL DETECTOR MC
Detector material (GEANT4)Radiative effectsTracking
(Same Luminosity)
DIS2011LARA DE NARDO
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Detection efficiencies for high multiplicity radiative events
•The incoming electron can radiate a high energy photon and then scatter elastically with the nucleon.
Small scattering angle Large probability of hitting the beam pipe,
causing a shower and saturating the wire chambers •These unreconstructed events are included in the smearing matrix•Efficiencies extracted from MC
Photon:
DIS201113LARA DE NARDO
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LARA DE NARDO 14
Main source of systematics: Misalignment
TOP TOP
BOTTOM BOTTOMBOTTOM
IDEAL DETECTOR MISALIGNED BEAM + DETECTOR MISALIGNED
•IDEAL situation: Perfect alignment of beam and spectrometer•In practice:
Top and bottom parts of the detector are displaced Beam position differs from nominal position
•Simulation of misalignment done in MonteCarlo•Born cross-section rescaled by fractional changes in Born s in MC with aligned and misaligned geometry•Half the deviation in MC yields obtained with aligned and misaligned geometry are used as systematic uncertainty (< 7%, 2% on ave.) DIS2011
TOP
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15
Results: Region with no previous data
DIS2011LARA DE NARDO
arXiv:1103.5704 (hep-ex) and DESY-11-048Submitted to JHEP
GD11: update of GD07 (hep-ph/0708.3196). Normalization uncertainty: 7.5% (P), 7.6% (D)
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Results: Region with data overlap
DIS2011LARA DE NARDO
• HERMES data agree with previous data in the same kinematic range
arXiv:1103.5704 (hep-ex) and DESY-11-048Submitted to JHEP
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The Parameterization GD11-P,D
DIS2011LARA DE NARDO
•23 parameter fit using the Regge-motivated ALLM (Phys.
Lett.B269(1991)465) functional form• c2 includes point-by-point statistical and systematic uncertainties•Consistency with respect to R=sT/sL
•Experimental normalizations are fitted•Calculation of statistical error bands
With respect to GD07:• Inclusion of • combined HERA e+ and e- data instead of ZEUS and H1 data sets• JLAB: E00-115 (50pts on p,d), CLAS (272 pts on p, 1018 pts on d),
Tvaskis (5 Rosenbluth pts on p,d and model dependent 50 on p, 81 on d)
• HERMES 81 pts on p,d
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LARA DE NARDO 18
Cross section
DIS2011
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Cross section ratio
DIS2011 19LARA DE NARDO
•Determined on a year-by-year basis and then averaged•Reduction of
Normalization uncertaintymany systematic effects
(misalignment, PID…) cancel
The remaining 1.4% normalization uncertainty comes from variations of beam conditions within each data set.
Data agree with simple fit of the form
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Conclusions
DIS2011LARA DE NARDO
HERMES has measured the structure functions and Data points agree with previous data in the data-overlap region add new data in a previously unexplored region
Fits to F2p,d world data are performed including all available world
data Proton and deuteron are combined to obtain sp/sd large cancellation of syst. uncertainties on the two targets cross-section ratio world data fitted to a A(x)+B(x)ln(Q2) functional form
Results are submitted to JHEP and available at arXiv:1103.5704 (hep-ex) and DESY-11-048
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21DIS2011LARA DE NARDO
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LARA DE NARDO 22
F2 FITS
DIS2011
The fits are based on the minimization of the value of defined as:
where are the values of for data point i within the data set k, is the normalization uncertainty in data set k quoted by the experiment, is the 23-parameter ALLM functional form, is the vector of functional parameters is the vector of normalization parameters, analytically determined at each iteration:
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LARA DE NARDO 23
Normalizations from GD11
DIS2011
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24
PID efficiencies and contaminations
Dependence on momentum (eff.’s decrease at higher p), production,binEff> 94%, C<2%
DIS2011LARA DE NARDO