Structure Functions and Low-x Working Group Summary Convenors A. - PowerPoint PPT Presentation

Structure Functions and Low-x Working Group Summary Convenors A. Glazov S. Moch K. Nagano Sven-Olaf.Moch@desy.de DESY Zeuthen ————————————————————————————————————– – XV International Workshop on Deep-Inelastic Scattering and Related Subjects, Munich, Apr 20, 2007 – S. Moch Structure Functions and Low-x – p.1

Plan Longitudinal structure function F L measurement of high- y cross sections, low energy run of HERA News on Parton density functions updates of global fits structure functions measurements (HERA) hard scattering cross sections (Tevatron) Forward jets and low- x HERA measurements and theory models Theory outlook S. Moch Structure Functions and Low-x – p.2

Structure function F L S. Moch Structure Functions and Low-x – p.3

Cross Section vargas Vargas Data fill the transition region at Q² ~1 GeV² Combined preliminary H1 data in agreement with ZEUS H1 low- Q 2 analysis final measurement for HERA-I at low Q 2 (long time effort) improved precision for extraction of F L Andrea Vargas Treviño DIS 2007, München S. Moch Structure Functions and Low-x – p.4

raicevic ���������� 2 2 d σ 2π Y α Q 2 / GeV 2 2 σ + Y 1 (1 y) = = + − r + 2 4 dxdQ Q x 10 4 H1 HERA-I 2 y H1 HERA-II high y 2 2 σ F (x, Q ) F (x, Q ) 0 F F ≤ ≤ = − r 2 L L 2 NMC Y + 10 3 BCDMS F L gives�sizable�contribution�only�at�high�y ' E 2 x Q /sy = 2 y 1 e sin (θ /2) = − 10 2 e E e � This�analysis:�high�y,�low�and�medium�Q 2� � as�low�as�possible�low�E’ e required 10 y = 1 y = 0.6 xg(x)�~F L� (at�low�x) � From ����� xg(x)�– gluon�density�function 1 -5 -4 -3 -2 -1 10 10 10 10 10 1 x � Experimental�challenges�of�this�analysis�are�similar�to�the�ones�for�analysis�of�� low�energy�run. direct measurement of F L in high- y region ����������� ��������������������������� � Raicevic (very difficult) S. Moch Structure Functions and Low-x – p.5

������������� raicevic large backgrounds H1 Preliminary 10 3 events 10 3 events Data HERA-II 20 MC+BG 30 BG (data) 15 20 10 photo-production 10 5 low- Q 2 electron 0 0 4 6 8 10 150 155 160 165 170 (wrong charge lepton) Θ e /deg E e /GeV 10 3 events 10 3 events 20 initial state radiation 20 large QED bkgd 15 (cut beam energy) 10 10 5 0 0 -40 -20 0 20 40 0 20 40 60 80 Z v /cm Total E-p z /GeV E�p z =�(E�– p z ) HFS +�(E�– p z ) e’ =�2P(measured�beam�energy) ����������� ��������������������������� / Raicevic S. Moch Structure Functions and Low-x – p.6

6m tagged sample ZEUS: background control by e − -tagging at low Q 2 shimizu Shimizu � 6m tagger located downstream of electron beam. different technologies as H1 (cross check) � Direct detection of PHP events with good acceptance. x pos on Energy in 6mT 6mT e + e + CAL energy � e of misidentified electron � Not perfect, but reasonable description of distribution shape by PHP MC. + data Normalized by Nevents – PHP MC 9 S. Moch Structure Functions and Low-x – p.7

Reduced cross section shimizu Shimizu � Measured reduced cross sections ZEUS are compared to SM predictions 2 2 2 2 2 2 2 2 2 Q = 27 GeV Q = 35 GeV Q = 45 GeV Q = 60 GeV with σ ~ 1 – CTEQ5D – ZEUS-Jets PDF 0 2 2 2 2 2 2 2 2 2 Q = 70 GeV Q = 90 GeV Q = 120 GeV Q = 150 GeV � They are well described by the 1 predictions. 0 2 2 2 2 2 2 2 2 2 Q = 200 GeV Q = 250 GeV Q = 350 GeV Q = 450 GeV � Systematics 1 • Electron energy scale 2% • PHP norm. factor 10% 0 2 2 2 2 2 2 2 Q = 650 GeV Q = 800 GeV Q = 1200 GeV ZEUS (prel.) • Electron finding inefficiency 10% -1 06e+p (29pb ) 1 • E-pz threshold 2GeV CTEQ5d ZEUS-Jets 0 0 0.5 1 0 0.5 1 0 0.5 1 y 14 S. Moch Structure Functions and Low-x – p.8

������������������(���)*+,-.�������������� raicevic 0�1��!!������� 23��& �4 σ red H1 Preliminary Y=0.825 1.4 1.3 cross section at 1.2 high y (preliminary) 1.1 H1 HERA-II prelim. (W=289 GeV) H1 1997 (W=273 GeV) 1 10 15 20 25 Q 2 /GeV 2 • The�precision�of�the�new�measurements�is�about�factor�of�2�better�than�in�the�� published�results�based�on�HERA�I�data. • Systematic�cross�section�uncertainty�2�3%. ����������� ��������������������������� �' Raicevic S. Moch Structure Functions and Low-x – p.9

� � � � Low Energy Running shimizu Shimizu � HERA has finished ‘usual’ operation on 21/Mar/2007 � Since then, HERA started to deliver luminosity with lowered proton beam energy (LER) successfully. Congratulations to HERA! 26/Mar � 2/Jul: 3 months of LER operation. � Main issue in LER: F L y ~ 2 F ( x , Q ) F ( x , Q ) 2 2 Y 2 L Cross sections with same (x,Q 2 ) but different y, i.e. Different centre of mass energy � Direct separation of F L from F 2 . w/o theory assumption � F L at low-x : legacy of HERA direct F L at HERA: unique measurement 17 S. Moch Structure Functions and Low-x – p.10

klein Luminosity collected by April 16th enlarged satelites increase of L and � with t Klein Max Klein low energy run 17.4.2007 DIS07 S. Moch Structure Functions and Low-x – p.11

Perturbative corrections for F L S.M., Vermaseren, Vogt ‘05 α ( n ) c ( n − 1) b a,i ( N ) ( N ) a,i large higher order corrections = (4 π ) 2 c ( n ) a,i ( N ) 0.8 1 ∧ 2,ns (N) x(c L,q q S ) α ⊗ 0.8 0.6 NLO LO 0.6 N 2 LO 0.4 NLO N 3 LO 0.4 NNLO 0.2 0.2 0 0 -5 -4 -3 -2 -1 5 10 15 10 10 10 10 10 1 4 ∧ L,ns (N) x(c L,g g) α ⊗ 0.4 3 α S = 0.2, n f = 4 NLO 0.3 2 N 2 LO 0.2 1 0.1 N f = 4 0 0 -5 -4 -3 -2 -1 5 10 15 10 10 10 10 10 1 x N S. Moch Structure Functions and Low-x – p.12

News on global fits S. Moch Structure Functions and Low-x – p.13

Obtain NNLO partons with uncertainties due to experimental errors for the first partons go NNLO with errors thorne 1.5 time. Reported last year. Same procedure as before – 15 eigenvector sets of partons and ∆ χ 2 = 50 for 90% confidence limit. 1 xu(x,Q 2 =20) First time we have full NNLO with no major approximations. (Heavy flavours a major issue.) In general size of uncertainties similar 0.5 (perhaps a little smaller) to at NLO. Change from NLO to NNLO greater than uncertainty in each. NNLO fit consistently better than NLO. 0 -4 -3 -2 -1 NNLO resolves more features of theory e.g. 10 10 10 10 q s , q v , q − all evolve with different kernels Thorne DIS07 MRST(MSTW) 3 S. Moch Structure Functions and Low-x – p.14

�$-�"������������ �������=��"���������� tung ?�'�#�(�*-�"�-!�"-��4 �#"-��"���������� ���@�8� Tung �A���> �#-��*�%-#"-������ �������= heavy flavor scheme with general mass implemented (charm) changes in PDF updates larger than previous error estimates � � S. Moch Structure Functions and Low-x – p.15

CDF k T robson Measured in 5 bins of y jet Forward jet - asymmetric interaction DonÕt expect new physics in high y jet region High- x gluon from inclusive jets Robson Aidan Robson Glasgow University 17/22 S. Moch Structure Functions and Low-x – p.16

Z Rapidity toole Submitted to PRD � Main contributions to syst's: eff's, backgrounds. At high y: eff's, PDFs � Theory and data in good agreement Toole � Measurement is currently statistics limited * Curves made with code from Anastasiou, et. al., PRD69, 094008 (2004). April 17, 2007 DIS 2007 6 S. Moch Structure Functions and Low-x – p.17

W Charge Asymmetry with muons toole ∫ L dt = 230 pb -1 � Curves produced with Resbos-A constrain u/d ratio � Main systematic uncertainty is from efficiencies ε ± � Measurement currently statistics limited Toole April 17, 2007 DIS 2007 9 S. Moch Structure Functions and Low-x – p.18