Results on the proton structure from HERA Shima Shimizu (CERN) - PowerPoint PPT Presentation

Results on the proton structure from HERA Shima Shimizu (CERN) 7/Jan/2011 @ KEK

The world only e-p collider: HERA A unique collider at DESY, Hamburg electron proton Circumference: H1 ZEUS 6.3 km Operated since 1992 to 2007 2 collider experiments: H1 & ZEUS DESY, Hamburg Beam energy center of mass energy • proton : (460, 575, 820,) 920 GeV = ( 225 ~) 318 GeV • electron/positron: 27.5 GeV s 2

History of HERA HERA delivered -1 ) -1 ) -1 ) -1 ) 800 • 1992-2000: HERA-I Luminosity Integrated Luminosity (pb Integrated Luminosity (pb Integrated Luminosity (pb Integrated Luminosity (pb Low E p upgrade 700 (started with E p =820GeV, until (2000-2002) 600 1997) 500 � Make full use of large 400 820 GeV 920 GeV kinematic region. 300 1.5GeV 2 <Q 2 <30000GeV 2 200 100 0 • 2002-2007: HERA-II 0 500 1000 1500 2000 2500 days of running days of running days of running days of running HERA I HERA II – High luminosity to collect high- Q 2 data. (high-Q 2 ↔ Weak boson In total, each H1 and ZEUS exchange) gains ~0.5 fb -1 . – lepton beams are polarized. – Reduced E p runs at the end. 3

Deep Inelastic Scattering (DIS) � Kinematic variables to describe DIS Q 2 : Virtuality � probing power x : Bjorken scaling variable � momentum fraction of struck quark y : Inelasticity : center of mass energy s ⋅ 2 Q p q = = 2 = 2 x Q sxy = − = − − y 2 2 2 ' ( ) Q q k k ⋅ ⋅ p q p k • Inclusive DIS cross sections can be written with structure functions. ⎡ ⎤ ± σ πα 2 2 2 ( ) 2 d e p y Y = − − 2 2 2 m ( , ) ( , ) ( , ) ⎢ ⎥ Y F x Q F x Q xF x Q + = ± − 2 3 2 L 2 4 1 ( 1 ) Y y ⎣ ⎦ dxdQ Q Y Y ± + + Structure functions reflect momentum cross section with distribution of partons in the proton. point-like particle 4

Structure functions and PDFs = ± − 2 Measured quantity: reduced cross section 1 ( 1 ) Y y ± σ 4 2 2 Q Y d y Y ± σ = = − + − 2 2 2 m ( ) ( , ) ( , ) ( , ) e p F x Q F x Q xF x Q πα 2 3 r L 2 2 2 dxdQ Y Y + + Structure functions are used for determination of the parton distribution functions ( PDFs ), q ( x,Q 2 ) and g ( x,Q 2 ) • F 2 : [Sea + valence] quarks, (gluon) ∂ ∑ F = + ∝ ( ) 2 F A x q q xg 2 ∂ q 2 ln Q • F L : longitudinal structure function gluon (see later) sizable only at high y • xF 3 : parity violation term (Electroweak) ∑ = − high Q 2 only ( ) xF B x q q DGLAP 3 q evolution Valence quarks The Q 2 evolution can be described by perturbative QCD, using DGLAP equation. 5

DIS at HERA � Charged current DIS (CC) Pure proton target W ± � Free from target correction, nuclear effect. exchange Q 2 (GeV 2 ) 10 5 valence sea, gluon Charge selective interaction e - : u quark e + : d quark H1 10 4 ZEUS � Neutral current DIS (NC) Fixed Target Experiments: CCFR, NMC, BCDMS, at low Q 2 10 3 � Neutral current DIS (NC) E665, SLAC at high Q 2 y=1 (HERA √ s=320 GeV) γ 10 2 exchange γ ,Z 0 10 exchange ∑ 1 ∝ + γ � ( ) F x q q Fixed target 2 Sea + valence quark -1 Sea + valence quark experiments 10 ∂ Z 0 introduces parity violation. F ∝ 2 xg gluon -6 -5 -4 -3 -2 -1 ∑ 10 10 10 10 10 10 1 ∂ 2 ∝ − ln � Q ( ) xF x q q x 3 valence quark 6

DIS in the detectors Charged current (CC) process Neutral current (NC) process W +- exchange γ /Z 0 exchange ep � ν X ep � e’X ν e’ p p e +/- e +/- jet jet • Kinematic variables are reconstructed by two of measured variables; energy scattered electron of angle jet (~ struck quark) 7

HERA I inclusive DIS cross sections and HERA PDF1.0 published: JHEP01 (2010) 109

Combining H1 and ZEUS cross sections Combining all the HERA-I inclusive DIS cross sections from H1 and ZEUS: � HERA I: e + p ~100pb -1 , e - p ~16pb -1 � NC: 0.045 < Q 2 < 30000 GeV 2 , CC: 280 < Q 2 < 30000 GeV 2 � 1402 points (14 papers) � After combination: 741 points Combination is done by averaging each data point by simultaneous χ 2 fit. � Assumption: H1 and ZEUS measure the same cross sections. � Taking account of correlated systematics within/between experiments. Different detectors and analysis techniques bring different sensitivities to similar sorce of correlated systematic uncertainties. � Cross calibration of experiments Reduction of systematic uncertainties. JHEP01 (2010) 109 9

Combining H1 and ZEUS cross sections H1 and ZEUS 1.6 σ r,NC (x,Q 2 ) x=0.002 HERA I NC e + p x=0.0002 1.4 + ZEUS H1 1.2 x=0.008 1 0.8 Uncertainty gets improved by more than sqrt(2). x=0.032 0.6 � Main reduction in x=0.08 0.4 systematic uncertainties. x=0.25 0.2 0 2 3 4 1 10 10 10 10 Q 2 / GeV 2 JHEP01 (2010) 109 10

Combined inclusive DIS cross sections H1 and ZEUS σ r,NC (x,Q 2 ) x 2 i 10 7 HERA I NC e + p x = 0.00005, i=21 � Precision of 1-2% for Fixed Target 10 6 x = 0.00008, i=20 Low x x = 0.00013, i=19 HERAPDF1.0 3 < Q 2 < 500 GeV 2 . x = 0.00020, i=18 x = 0.00032, i=17 10 5 x = 0.0005, i=16 + x = 0.0008, i=15 x = 0.0013, i=14 10 4 x = 0.0020, i=13 � Scaling violation is x = 0.0032, i=12 x = 0.005, i=11 10 3 x = 0.008, i=10 clearly seen. x = 0.013, i=9 x = 0.02, i=8 10 2 ∂ x = 0.032, i=7 F ∝ 2 x = 0.05, i=6 xg ∂ 2 ln x = 0.08, i=5 Q 10 x = 0.13, i=4 x = 0.18, i=3 1 High x x = 0.25, i=2 -1 x = 0.40, i=1 10 -2 x = 0.65, i=0 10 -3 10 2 3 4 5 1 10 10 10 10 10 Q 2 / GeV 2 JHEP01 (2010) 109 11

HERA PDF 1.0 Data sets � Combined HERA I inclusive DIS cross sections e - p CC, e+p CC, e - p NC (Q 2 >100GeV 2 ), e + p NC (Q 2 > Q 2 min ) Settings � PDF parameterized at the starting scale Q 0 2 α S (M Z ) 0.1176 = + U u c 0.31 = + + fs=s/D D d s b Central fit has 10 free parameters: m c (GeV) 1.4 � chosen by saturation of χ 2 m b (GeV) 4.75 � RT-VFN scheme min (GeV 2 ) Q 2 3.5 � NLO DGLAP evolution using QCDNUM17.02 2 (GeV 2 ) 1.9 Q 0 � Scales: μ R = μ F = Q 2 12

HERA PDF 1.0 Uncertainties H1 and ZEUS 1 1 1 xf • experimental: 2 2 Q = 10 GeV Δχ 2 =1 HERAPDF1.0 • model: 0.8 0.8 0.8 exp. uncert. Different set of model uncert. values of xu parametrization uncert. v 0.6 0.6 0.6 f s , m c , m b , Q 2 2 min , Q 0 × xg ( 0.05) • parameterization: 0.4 0.4 0.4 envelope of xd v parameter variation × xS ( 0.05) 2 , negative e.g. Q 0 0.2 0.2 0.2 gluon, relax B u =B d , additional parameter. -3 -4 -2 -1 10 10 10 10 1 x 13

Relative Uncertainties at High Q 2 H1 and ZEUS 1 1 1 1 1 1 v v xu xd 2 2 2 2 Q =10000 GeV Q =10000 GeV 0.8 0.8 0.8 0.8 0.8 0.8 HERAPDF1.0 exp. uncert. 0.6 0.6 0.6 0.6 0.6 0.6 model uncert. param uncert. 0.4 0.4 0.4 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.2 0.2 At Q 2 = 10000GeV 2 , 0 0 0 0 0 0 0.2 0.2 0.2 0.2 0.2 0.2 2% uncertainty on 0 0 0 0 0 0 gluon for x<0.01. -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -4 -3 -2 -1 -4 -3 -2 -1 10 10 10 10 10 10 10 10 1 1 x x 50 50 50 100 100 100 xS xg 2 2 2 2 Q =10000 GeV Q =10000 GeV 40 40 40 80 80 80 xu sea xd 30 30 30 60 60 60 sea xs sea xc sea 20 20 20 40 40 40 xb sea 10 10 10 20 20 20 0 0 0 0 0 0 0.2 0.2 0.2 0.2 0.2 0.2 0 0 0 0 0 0 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -3 -3 -4 -2 -1 -4 -2 -1 10 10 10 10 10 10 10 10 1 1 x x 14

HERA PDF and Tevatron Data 0.9 0.9 0.9 0.9 0.9 0.9 Tevatron Jet Cross Sections CDF data 0.8 0.8 0.8 0.8 0.8 0.8 d 2 σ /dy jet dp T jet [ nb/(Gev/c) ] 10 8 HERAPDF1.0 D0 RunII 0.7 0.7 0.7 0.7 0.7 0.7 total uncert. 10 6 HERAPDF1.0 0.6 0.6 0.6 0.6 0.6 0.6 MSTW08 Cone R=0.7 - fastNLO A(W) (+ non-perturbative corr.) 0.5 0.5 0.5 0.5 0.5 0.5 10 3 0.4 0.4 0.4 0.4 0.4 0.4 0.3 0.3 0.3 0.3 0.3 0.3 1 0.2 0.2 0.2 0.2 0.2 0.2 |y jet | < 0.4 (x 10 6 ) -3 10 0.1 0.1 0.1 0.1 0.1 0.1 0.4 < |y jet | < 0.8 (x 10 3 ) 0 0 0 0 0 0 -6 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 10 y 0.8 < |y jet | < 1.2 -9 10 1.2 < |y jet | < 1.6 (x 10 -3 ) Good description of Tevatron -12 10 1.6 < |y jet | < 2.0 (x 10 -6 ) data by HERA PDF. -15 10 2.0 < |y jet | < 2.4 (x 10 -9 ) 0 100 200 300 400 500 600 700 P T jet [ Gev/c ] 15

HERA PDFs for LHC Several predictions are calculated with reasonable uncertainties. = 7 TeV HERA PDF1.0 s G. Watt, PDF4LHC, 2010 0.5 0.5 0.5 0.5 Asymmetry Asymmetry Asymmetry Asymmetry Data 2010 ( s =7 TeV) Data 2010 ( s =7 TeV) MC NLO, CTEQ 6.6 MC NLO, CTEQ 6.6 MC NLO, HERAPDF 1.0 0.4 0.4 MC NLO, HERAPDF 1.0 0.4 0.4 Comparison with DYNNLO, MSTW 08 DYNNLO, MSTW 08 → ν → µ ν W e W 0.3 0.3 data has started. 0.3 0.3 0.2 0.2 0.2 0.2 ATLAS 0.1 0.1 ATLAS 0.1 0.1 CERN-PH-EP-2010-037 ∫ ∫ -1 L dt = 315 nb -1 L dt = 310 nb arXiv:hep-ex 1010.2130 0 0 0 0 0 0 0.5 0.5 1 1 1.5 1.5 2 2 0 0 0.5 0.5 1 1 1.5 1.5 2 2 ⏐ ⏐ η η ⏐ ⏐ lepton ⏐ ⏐ η η ⏐ ⏐ 16

Further measurements at HERA