Cross section for quasi-real potoproduction of carged adrons wit ig p in μ + -d scattering DPG HK., Mainz Cristian Höppner (U Müncen on bealf of te Collaboration Marc st
Outline Introduction e experiment at CERN SPS Ingredients for Cross Section Luminosity Hadron yield Acceptance correction Results and comparison to NLO pqcd
Lepton-Nucleon Scattering in pqcd Lepton-nucleon scattering: probe te quark and gluon (spin-structure of te nucleon eory framework to interpret te data: perturbative QCD (pqcd Hig-p (ig transverse momentum adron production µ γ µ FF µ γ µ g FF g q q q PDF PDF N X N X Quasi-real potoproduction (low Q : Unpolarized cross section and double-spin asymmetry calculable up to NLO in pqcd (including resolved-poton processes [B. Jäger et al., EPJ C 44 (5 5] Applicability of NLO pqcd: Compare cross sections experiment vs. teory does NLO pqcd account for all significant contributions?
NLO pqcd vs. Experiment [C. Bourrely & J. Soffer, EPJ C 6 (4 7] Proton-proton scattering Works well at collider energies (RHIC Increasing underprediction wit decreasing center-of-mass energy Quasi-real potoproduction Works well at collider energies (HERA [S. Cekanov et al., PRD 76 (7 7] At energies?
Gluon Polarization in te Nucleon Once applicability of pqcd to te process is establised via cross section: Extract double-spin asymmetry of cross section for ig-p adrons at low Q Compare to NLO pqcd calculation of double-spin asymmetry wit different input Δg distributions. A, d LL.. [B. Jäger et al., EPJ C 44 (5 5] 'max. γ ' 'min. γ ' ' g = -g' ' g = ' 'std. g' -.. L = / fb ' g = g' input A, p p [GeV] 4 ' g = -g' LL
Experiment at CERN SPS polarized target 6 LiD in Helium bat 6 m [Abbon et al., NIM A 577 (7 455] optimized for spin asymmetry measurements no dedicated luminosity monitor 6 GeV/c μ + beam Intensity: 4 7 s - delivered in 4.8 s spills followed by s break
Definition of Cross Section Cross section in bin: p [p,i,,p,i, ] dσ i dp = p,i, p,i, L Ñi i Ingredients: Integrated luminosity: L Number of observed adrons in te bin: Ñ i Acceptance correction factors from MC: i = N rec i,mc N gen i,mc
Luminosity Selection of flat tops of good spills NMC 6 d Luminosity is determined via direct measurement of beam flux on target Correction of all dead times and inefficiencies / (F (F 5 4 =.75 (+5. x Bj =.5 (+4.5 x Bj =.75 (+4. x Bj =.5 (+.5 x Bj =.75 (+. x Bj =.45 (+.5 x Bj =.475 (+. x Bj Resulting luminosity, corrected for DAQ dead time: 4.4 pb - % (syst. Luminosity is cecked via structure function F comparison wit NMC : 6 GeV/c µ + beam - % of 4 arget composition: 4.% D, 4.5% Li, 5.% He 4 NMC parameterization: =.55 (+.5 x Bj =.575 (+. x Bj =.65 (+.5 x Bj =.675 (+. x Bj Q [M. Arneodo et al., PLB 64 (995 7] (GeV /c
Hadron Yield - (.5 GeV/c number of 6 5 4 - - - 4, µ + beam ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c, p "![,] mrad > GeV/c.5.5.5 4 p (GeV/c Q <. (GeV/c,(Q = q y [.,.8], (y = ν E z [.,.8], (z = E ν p > 5 GeV/c θ [, ] mrad, ( (p, q
Acceptance Correction + acceptance for.9.8.7.6.5.4. "![,] mrad + - - acceptance for.9.8.7.6.5.4. "![,] mrad... 4. 4.5.5.5 (GeV/c p.5.5.5 (GeV/c p Software cain: PYHIA6, GEAN, reconstruction Systematic error: 7% Possible background from secondary adrons Multidimensional acceptance
Cross Section - (pb (GeV/c d! dp " p % $[-.,.8] - - 4 µ d # µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty % stat. error syst. error &!!. -..5.5.5 p (GeV/c
Cross Section - (pb (GeV/c d! dp " p &!! - -. -. NLO pqcd curves by W. Vogelsang ( (DSS FF, CEQ6M5 µ=p / µ=p µ=p 4 µ d # µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty % % $[-.,.8] stat. error syst. error.5.5.5 p (GeV/c Underprediction by NLO pqcd for p >.75 GeV/c by factor -4 Spectral sape is predicted well Analogy to proton-proton scattering: Underprediction by a factor of -5 at fixed-target energies All-order resummation of tresold logaritms (soft gluon radiation reconcile discrepancy [D. de Florian & W. Vogelsang, PRD 7 (6 5]
Cross Section - (pb (GeV/c d! dp " p &!! - -. -. NLO pqcd curves by W. Vogelsang ( (DSS FF, CEQ6M5 µ=p / µ=p µ=p 4 µ d # µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty % % $[-.,.8] stat. error syst. error.5.5.5 p (GeV/c Underprediction by NLO pqcd for p >.75 GeV/c by factor -4 Spectral sape is predicted well Analogy to proton-proton scattering: Underprediction by a factor of -5 at fixed-target energies All-order resummation of tresold logaritms (soft gluon radiation reconcile discrepancy [D. de Florian & W. Vogelsang, PRD 7 (6 5]
y-differential Cross Section d!/dy (pb 4 p "[.5,.75] GeV/c p "[.75,.65] GeV/c p "[.65,.875] GeV/c p "[.875,.5] GeV/c p "[.5,.75] GeV/c p "[.75,.65] GeV/c p "[.65,.875] GeV/c p "[.875,.5] GeV/c 4 µ d # µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty %...4.5.6.7.8...4.5.6.7.8...4.5.6.7.8 y
y-differential Cross Section - NLO pqcd / d! NLO pqcd d! 8 6 4 p "[.5,.75] GeV/c p "[.75,.65] GeV/c p "[.65,.875] GeV/c 8 6 4 p "[.875,.5] GeV/c p "[.5,.75] GeV/c p "[.75,.65] GeV/c Underprediction by NLO pqcd clearly increases wit decreasing poton energy 8 6 4 p "[.65,.875] GeV/c p "[.875,.5] GeV/c NLO pqcd cross section by W. Vogelsang ( (DSS FF, CEQ6M5 scale µ = p 4 µ d # µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty %...4.5.6.7.8...4.5.6.7.8...4.5.6.7.8 y
Carge Ratio of Cross Sections + ( d! dp / - ( d! dp.8.6.4..8.6.4 4 µ d " µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c $ #[-.,.8] Experiment: ratio < because of QCD Compton? N µ γ µ X q g..5.5.5 (GeV/c p eory: ratio > because of Fragmentation Functios?
Carge Ratio of Cross Sections + ( d! dp / - ( d! dp.8.6.4..8.6.4 4 µ d " µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c $ #[-.,.8] NLO pqcd curves by W. Vogelsang ( (DSS FF, CEQ6M5 µ=p / µ=p µ=p Experiment: ratio < because of QCD Compton? N µ γ µ X q g..5.5.5 p (GeV/c eory: ratio > because of Fragmentation Functios?
Conclusion and Outlook Measurements of single-inclusive particle production cross sections provide an important bencmark for pqcd metods (especially at fixed-target energies Unpolarized cross section for quasi-real poto-production of ig-p carged adrons at as been measured Less negative adrons tan positive adrons, ratio almost independent of p Comparison to NLO pqcd: s = 7.4GeV Cross section is underpredicted by factor - 4 ( -> resummations? Spectral sape described well (over full rapidity range Underprediction increases clearly wit decreasing poton energy p dependence of carge ratio from pqcd not confirmed (-> fragmentation functions? Once applicability of pqcd can be establised: Potential to constrain gluon polarization via double-spin asymmetry of cross section for ig-p adron production at low Q
Extra Slides
Kinematics!!! number of 5 4 number of 5 5 number of 5 5 5-4 4, µ + beam ( s = 7.4 GeV - p > 5 GeV/c, p - > GeV/c - Q (GeV /c 5 4, µ + beam ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c, p > GeV/c....4.5.6.7.8.9 y 5 4, µ + beam ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c, p > GeV/c 6 8 4 6 8 W (GeV/c
Kinematics! " number of 5 5 number of 5 4 5 4, µ + beam ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c, p > GeV/c....4.5.6.7.8.9 z 4, µ + beam ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c, p > GeV/c..4.6.8...4.6! (mrad
Cross Section in Rapidity Bins $ #[.69,.8] $ #[.8,.69] $ #[.,.8] $ #[-.,.] - (pb (GeV/c d! dp " p - - stat. error syst. error 4 µ d & µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty % %!!. -..5.5.5.5.5.5.5 p (GeV/c
Cross Section in Rapidity Bins - (pb (GeV/c d! dp " p %!! $ - -. -. #[.69,.8] - (pb (GeV/c dp d! " p %!! - -. -. $ #[.8,.69] - (pb (GeV/c dp d! " p.5 %!! - -. -. $ stat. error syst. error #[.,.8] - (pb (GeV/c d! dp " p.5.5 %!! - -. -. $ #[-.,.] NLO pqcd curves by W. Vogelsang ( (DSS FF, CEQ6M5 µ=p / µ=p µ=p 4 µ d & µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c normalization uncertainty %.5.5.5.5.5.5.5.5.5.5 p (GeV/c Underprediction consistent over rapidity range Spectral sape reproduced well over rapidity range
pqcd Calculation Calculation of cross section in pqcd: µ ( P γl µ µ ( P γl γ µ a = γ ( ˆσ c D c ( ˆσ a ( f γ a c D c b X b X N N ( f N b (a Direct-poton contribution. ( f N b (b Resolved-poton contribution.
Fragmentation Functions D c z c.7.6.5.4.. DSS NLO, µ - d "! u "! + = 4 (GeV/c + ( d! dp / - ( d! dp.8.6.4..8.6 4 µ d " µ' X ( s = 7.4 GeV Q <. (GeV/c, p > 5 GeV/c $ #[-.,.8] NLO pqcd curves by W. Vogelsang ( (DSS FF, CEQ6M5 µ=p / µ=p µ=p..4....4.5.6.7.8 z c µ.5.5.5 (GeV/c µ p γ q g N X