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Inclusive Proton Structure Functions at HERA

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Inclusive Proton Structure Functions at HERA Photoproduction-DIS transition 2 (F2 at very low Q ) AlexeyAlexey Petrukhin,Petrukhin, ITEP/DESYITEP/DESY (on(on behalfbehalf ofof H1H1 andand ZEUSZEUS collaborations)collaborations) DIFFRACTION 2008 La Londe-les-Maures, France Content • Introduction to HERA • Deep Inelastic Scattering • Structure function F2 • Rise of F2 at low x • Conclusions 2 H1 and ZEUS at HERA • HERA collider at DESY, Hamburg • ep accelerator ring, 27.6 x 920 GeV,s ep = 319 GeV • Circumference: 6.3km • 4 experimantal halls, 2 collider experiments (collected data: 1992-2007) H1 ZEUS 3 HERA luminosity •Luminosity upgrade: mid 2000 – end 2001 •Improvement in machine performance •Low energy running: March – June 2007 HERA delivered )))) 600 -1-1-1-1 End of HERA 500 operation: June 30, 2007 400 300 Integrated Luminosity (pbIntegrated Luminosity (pbIntegrated Luminosity (pbIntegrated Luminosity (pb 200 100 0 0 200 400 600 800 1000 1200 1400 days of running 4 Inclusive Deep Inelastic Scattering at HERA Neutral current e(k) e(k‘) γ/Z°(Q2 ) p(P) X Q2 = (') k k2 - four momentum transfer squared n thei eactionr Q2 x = - fraction of the rotonp momentum carried by the parton 2P ( k- 'k ) y= Q2 sx- inelasticity 5 s= 4 Ee pE - center-of-mass energy squared Cross section and structure functions NC Cross Section: ~ 2 NC Reduced cross section: σ NC(,)x Q 2 ± 2 2 dσ NC( ep )π 2α y ~- ~ 2 = 4 Y[]+ F 2 F L dxd Q xQ Y + 2 Y+=1 ( + 1y ) Dominant contribution Sizeable only at high y (y>~0.6) •The proton structure function in QPM: 2 - sum of the (anti)quarks density F2 = e∑[ xi ( q i )+ xi ( q )] x i h their ibutions weighted witrdist electric charge squared •Structure function F L ~ gluon density g(x) in NLO QCD and 0 in QPM 6 Low Q2 event in H1 detector LAr elmg. Central Tracker LAr hadr. H1 NVX BSTϑ e' = : ° 176 . 5 max BST (ardBackw e' H1 SVX BSTϑmax= : ° 177 . 8 acker)rSilicon T e' ZEUS BPTϑmax= : ° 179 . 0 e p SpaCal 7 Kinematic plane coverage 2 • HERA extends kinematic plane 2 coverage to lower x and higher Q / GeV 2 ZEUS 4 by 2 orders of magnitude Q 10 ZEUS BPT H1 • H1 and ZEUS overlap H1 SVX, NVX prel. 10 3 with fixed target results NMC in wide range of x BCDMS and Q2 E665 10 2 SLAC • H1 SVX, NVX: special runs with open triggers for inclusive DIS 10 events • Nominal vertex data access high y region 1 • Shifted vertex data access y = 1 2 -1 lowerst Q 10 y = 0.6 y = 0.004 -6 -5 -4 -3 -2 -1 10 10 10 10 10 10 8 1 x Reconstruction of event kinematics • ‘Electron method’- ed for measurements at 0.1<y<0.8:su γ ' 2EEe− ( 1 e − cosθe 2Ee− ) Σ e e e‘ ye = ≡ where Σe (E= − z p el ) 2Ee 2Ee ' 2 2 2 2 Ee sin θe Qe Qe = and xe = 1− ye E4 E y p e e ISR: p X ’ d o h t e m a m- sed g for i 0.002<y<0.1 S •‘ and also for low Qu2 by accepting events with Initial State Radiation (ISR): y= 1 y= 0.1 y= 0.01 y= 1 y= 0.1 y= 0.01 2 2 /GeV Σ /GeV 2 h 2 Q y = Q 10 Σ ' SVX y= 0.001 NVX Σh( + 1E e −cosθe ) e meth e-meth Σ meth Σ-meth y= 0.001 θ = 176.5° Σh=(Ez − p had ) e θ = 177.8° 1 e ' 2 2 1 2 Eesinθ (e ) QΣ = 1− yΣ 2 QΣ 1 xΣ = ⋅ E2 yp Σ E− z p -1 -1 10 -6 -5 -4 -3 -2 10 -6 -5 -4 -3 -2 10 10 10 10 10 10 10 10 10 10 x 9 x Extended by ISR Electron energy scale calibration 3 8 Kin. peak H1 data prel. ) / % 2 MC events MC 3 /E 10 6 data 1 (1-E 4 0 π0 kin. peak -1 ψ 2 J/ QED Compton -2 0 -3 21 22 23 24 25 26 27 28 29 30 0 5 10 15 20 25 30 E/ GeV E/ GeV •Use multi-step calibration. •Use π0 events to calibrate low Correct for the gain difference energy, correct for non-linearity of PMTs and for non-uniformities and check intermediate range with of SpaCal J/ψ and QED Compton events •The precision of energy calibration: 0.2% at 27.6 GeV to 1% at 2 GeV 10 Control distributions 15 15 40 a) b) H1 data prel. MC DIS+γp γ events events events events MC p 3 3 3 30 3 20 10 10 10 10 10 10 H1 data prel. MC DIS+γp 20 MC γp 10 5 5 10 0 0 0 0 -5 -4 -3 -2 0 3 6 9 12 15 5 1015202530 166 169 172 175 178 10 10 10 10 2 2 ' θ x Qe/ GeV Ee/ GeV e/ deg e 20 80 c) d) 10 events events events events 10 3 3 3 60 3 15 10 10 10 10 40 10 5 5 20 5 0 0 0 0 -5 -4 -3 -2 0 3 6 9 12 15 0 20406080 -40 -20 0 20 40 10 10 10 10 2 2 xΣ QΣ/ GeV E-pz/ GeV zvtx/ cm •Require a BST reconstructed vertex inside •Good understanding of detector of the interaction region, SpaCal cluster acceptance and control of the γp and BST track matching this cluster background 11 2 σr at very low Q r σ H1-0099 prel. 0.4 H1-97 H1-95 0.2 •New preliminary results extend H1 Q2 = 0.2 GeV2 Q2 = 0.25 GeV2 Q2 = 0.35 GeV2 0 measurements to low Q2 and high x by using of ISR events 0.5 Q2 = 0.5 GeV2 Q2 = 0.65 GeV2 Q2 = 0.85 GeV2 0 •Significant overlap between 1 H1-0099 prel. data and previously 0.5 published results Q2 = 1.2 GeV2 Q2 = 1.5 GeV2 Q2 = 2 GeV2 0 •New prel. data agree well with H1-97 1 and a bit lower than H1-95 0.5 (within normalization Q2 = 2.5 GeV2 Q2 = 3.5 GeV2 Q2 = 5 GeV2 0 uncertainty of 1995 data) 1 Q2 = 6.5 GeV2 Q2 = 8.5 GeV2 Q2 = 12 GeV2 0 -5 -3 -5 -3 -5 -3 12 10 10 10 10 10 10 x Rise of F2 towards low x 2 2 •F2 used to fit x-dependences •Around Q =1 GeV λ deviates in Q2 bins for x<0.01 and from log-dependence 2 -λ(Q2) W>12 GeV: F2=c(Q )•x ) 0.3 2 (Q H1 97-00 prel. λ 2 2 2 ZEUS BPT • λ~ln(Q /Λ ) and c(Q )~const. 0.25 for Q2>1 GeV2 0.2 λ C a) b) 0.15 0.2 0.2 0.15 0.15 0.1 0.1 0.1 0.05 0.05 0.05 λ fit 0 -1 from H1 10 1 10 0 0 Q2 /GeV2 1 5 1 5 Q2/GeV2 Q2/GeV2 13 2 F2 at very low Q 2 F H1 data prel. Fractal 0.4 Dipole GBW •Frises towards low x for all Dipole IIM 2 0.2 measured Q2 bins Q2 = 0.2 GeV2 Q2 = 0.25 GeV2 Q2 = 0.35 GeV2 0 • H1 prel. data agree with different 0.5 theoretical models: 9 Fractal fit – based on the concept Q2 = 0.5 GeV2 Q2 = 0.65 GeV2 Q2 = 0.85 GeV2 0 1 of self similarity 5 parameter model 9 Dipole 3 parameter fits – γ*p 0.5 scattering via γ* splitting into Q2 = 1.2 GeV2 Q2 = 1.5 GeV2 Q2 = 2 GeV2 0 dipole which scatters off the 1 proton. Two different dipole - 0.5 proton cross section models: GBW Q2 = 2.5 GeV2 Q2 = 3.5 GeV2 Q2 = 5 GeV2 0 (Golec-Biernat & Wusthoff) and 1 IIM (Iancu, Itakura & Munier) Q2 = 6.5 GeV2 Q2 = 8.5 GeV2 Q2 = 12 GeV2 0 -5 -3 -5 -3 -5 -3 •New precision of H1 prel. data:1.5% for 10 10 10 10 10 10 x Q2 > 5GeV2 14 The very low Q2 data b Fractal Fit μ 6 Dipole GBW Fit / 10 eff p * W=285GeV Dipole IIM Fit eff γ x4096 σ=* [ σ + 1f − ( y σ )] σ T L W=260GeV γ p x2048 W=190GeV x1024 5 2 2 W=150GeV 10 x512 (f ) y= /[ y 1 + ( 1 − y ) ] W=120GeV x256 W=95GeV 2 x128 eff π4 α 4 W=80GeV σ * = 2 σ r 10 x64 γ p Q( 1− x ) W=70GeV x32 W=50GeV eff x16 * for W* 200 GeV σγ p ≈ σγ p ≤ 3 W=40GeV 10 x8 W=30GeV x4 W=25GeV x2 W=16GeV 10 2 x1 H1 data prel. ZEUS’97 10 ZEUS BPT’97 -2 -1 10 10 1 10 Q2/ GeV2 e gap between published •H1 preliminary data cover th 15 ZEUS results and agree with them in the regions of overlap The very low Q2 data 2 F 0.5 H1 97-00 prel. NMC Fractal fit H1 QEDC 97 (DESY-04-083) ZEUS BPT97 (DESY-00-071) Dipole GBW H1 97 (DESY-01-104) Dipole IIM Q2 = 0.2 GeV2 Q2 = 0.25 GeV2 Q2 = 0.35 GeV2 •Data from H1, ZEUS and NMC 2 0 F 0.5 •Fits to H1 97-00 prel. data only Q2 = 0.5 GeV2 Q2 = 0.65 GeV2 Q2 = 0.85 GeV2 2 0 •HERA data are described by F phenomenological predictions 0.5 Q2 = 1.2 GeV2 Q2 = 1.5 GeV2 Q2 = 2 GeV2 2 0 F 1 Q2 = 2.5 GeV2 Q2 = 3.5 GeV2 Q2 = 5 GeV2 2 0 F 1 Q2 = 6.5 GeV2 Q2 = 8.5 GeV2 Q2 = 12 GeV2 0 -5 -3 -5 -3 -5 -3 16 10 10 10 10 10 10 x Conclusions • HERA analyses enter final stage • New precise low Q2 and high x preliminary results are covering the gap at Q2 ~1 GeV2 • They are consistent with other data in the regions of overlap •Precision of ~2−3 % achieved for σr • The HERA data is well described by Dipole and Fractal models 17.
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