PDF 4 LHC Comparison studies Feb 2008 A
PDF 4 LHC: Comparison studies Feb 2008 A M Cooper-Sarkar, Oxford • First change over time CTEQ 6. 1 to CTEQ 6. 5 • MRST 01 to MSTW 08 • Then CTEQ 6. 5 to MSTW 08 to ZEUS 2005 to H 12003 • All with asymmetric errors rather than • All with MRTS 04 as a common comparison line
CTEQ 6. 5 vs CTEQ 6. 1 Valence very similar light sea quarks larger (massive heavy quark treatment) gluon slightly different shape/larger errors As Q 2 increases these trends persist but are less dramatic
Valence, Total Sea and gluon CTEQ 6. 1 CTEQ 6. 5 Valence very similar, sea quarks larger (heavy quark treatment), gluon?
Valence, Total Sea and gluon CTEQ 6. 1 CTEQ 6. 5 Valence very similar, quarks larger (heavy quark treatment), gluon?
Valence, Total Sea and gluon CTEQ 6. 1 CTEQ 6. 5 AS Q 2 increases these trends persist but are less dramatic
Valence, Total Sea and gluon CTEQ 6. 1 CTEQ 6. 5 AS Q 2 increases these trends persist but are less dramatic
Light quarks u, d, ubar dbar CTEQ 6. 1 CTEQ 6. 5 Light sea quarks larger (heavy quark treatment)
u, d, ubar dbar CTEQ 6. 1 CTEQ 6. 5 AS Q 2 increases these trends persist but are less dramatic
also look at u/d and dbar-ubar CTEQ 6. 1 These have slightly different shapes Don’t change much with Q 2 CTEQ 6. 5
strange, charm, beauty CTEQ 6. 5 CTEQ 6. 1 For alternative strange PDFS see CTEQ 6 S or 6. 6 For alternative charm see CTEQ 6 C Strange a bit larger as for other light quarks Massive c and b treatment now
MSTW 08 vs MRST 01 MRST 04 was not much different from MRST 01 but MSTW 08 has Significantly asymmetric errors a different d-valence shape, smaller low-x sea very much larger low-x gluon errors Which feed to larger low-x sea errors as Q 2 increases More detailed treatment of strange sector
Valence, Total Sea and gluon MRST 01 MSTW 08 different d-valence shape, smaller low-x sea and very much larger low-x gluon errors
Valence, Total Sea and gluon MRST 01 MSTW 08 Let’s take a look at the gluon at slightly larger Q 2…. . it’s not as –ve as it used to be
Valence, Total Sea and gluon MRST 01 MSTW 08 And you can see the large low-x gluon errors feeding into large low-x sea errors
Valence, Total Sea and gluon MRST 01 MSTW 08
Valence, Total Sea and gluon MRST 01 MSTW 08 At large Q 2 the difference in low-x sea quark and gluon shapes is well within errors, but the larger uncertainty estimates remain
Light quarks u, d, ubar dbar MRST 01 MSTW 08 Light sea quarks slightly smaller, but within errors Large low-x uncertainties
Light quarks u, d, ubar dbar MRST 01 Same trends at higher Q 2 MSTW 08
also look at u/d and dbar-ubar MRST 01 MSTW 08 Similar shapes, slight differences at highest-x
strange, charm, beauty MSTW 08 MRST 01 Charm and beauty not very different though slightly less beauty and slightly more charm Strange treatment allows for a shape difference from other light quarksevident at high-x, and for s – sbar non zero
ZEUS 05 vs H 103 • • Both use restricted data sets H 1 PDF 2000 actually published 2003 H 1+BCDMS ZEUS only including JET data published 2005 Most obvious difference is in error estimates: ZEUS Offset/ H 1 Hessian with Δχ2=1 H 1 use of restricted valence parametrization also contributes to this. • Low-x gluon shape is also rather different • Shape differences wash out as Q 2 increases • Both have high-x gluons which are soft compared to MRST 04
Valence, Total Sea and gluon H 103 ZEUS 05 Most obvious difference is in error estimates: ZEUS Offset/ H 1 Hessian with Δχ2=1 H 1 use of restricted valence parametrization also contributes to this. gluon shape is also rather different
Valence, Total Sea and gluon ZEUS 05 H 103 gluon shape is rather different H 1 Sea quarks are somewhat smaller at x 10 -2 to 10 -1
Valence, Total Sea and gluon ZEUS 05 H 103 Even by Q 2=10 the difference in gluon shape is not so dramatic H 1 Sea quarks are somewhat smaller at x 10 -2 to 10 -1
Valence, Total Sea and gluon ZEUS 05 Differences wash out at high Q 2 H 103
Light quarks u, d, ubar dbar ZEUS 05 H 103 Tendency for ZEUS sea quarks to be larger at mid-x
ZEUS 05 Differences wash out as Q 2 increases H 103
also look at u/d and dbar-ubar ZEUS 05 H 103 Different high-x shape and errors for d/u Different uncertainty estimate for dbar-ubar: ZEUS imports information from E 866
strange, charm, beauty ZEUS 05 H 103 Implementation of H 1 beauty in LHAPDFv 5 cannot be right, was there any b-quark? Strange distributions not very different Charm not so different at Q 2=100, despite massive (ZEUS) vs massless (H 1) heavy quark treatment
CTEQ 6. 5 vs MSTW 08 • • • Previously uncertainties were generally larger for CTEQ, - but now look at low-x errors And differently asymmetric errors Valence: d-valence shape rather different Sea quarks smaller, gluon more negative for MSTW
Valence, Total Sea and gluon CTEQ 6. 5 MSTW 08 Sea errors larger for CTEQ, differently asymmetric errors Valence: d-valence shape rather different Quarks smaller, gluon more negative for MSTW- but look at low-x gluon errors.
Valence, Total Sea and gluon CTEQ 6. 5 MSTW 08 Sea errors larger for CTEQ, differently asymmetric errors Valence: d-valence shape rather different Quarks smaller, gluon more negative for MSTW- but look at low-x gluon errors.
Valence, Total Sea and gluon CTEQ 6. 5 MSTW 08 AS Q 2 increases these trends persist but are less dramatic Note that large low-x uncertainty on gluon has fed into large low-x uncertainty of sea quarks for MSTW. . much larger than for CTEQ
Light quarks u, d, ubar dbar CTEQ 6. 5 MSTW 08 low-x quarks and gluon somewhat smaller for MSTW and low-x uncertainty on gluon has fed into large low-x uncertainty of sea quarks
Light quarks u, d, ubar dbar CTEQ 6. 5 MSTW 08 Even at high Q 2 low-x quarks and gluon somewhat smaller for MSTW and low-x uncertainty on gluon has fed into large low-x uncertainty of Sea quarks
also look at u/d and dbar-ubar CTEQ 6. 5 MSTW 08 Rather different shapes for dbar-ubar, difference in high-x error estimate for d/u
strange, charm, beauty CTEQ 6. 5 Most obvious difference is in low-x error estimate Strange shape is not so different – a bit smaller at low-x for MSTW Charm/beauty also are preferentially smaller at low-x for MSTW
ZEUS 05 vs CTEQ 65 • Comparison of a fit to restricted data sets (ZEUS) to a global fit (CTEQ) • Comparison of a fit using Offset method (ZEUS) to a fit using Hessian method Δχ2=100 (CTEQ) • At Q 2=1, slightly different u, d-valence shapes, • less low-x sea for ZEUS, • different gluon shapes but. . • PDFs pretty much compatible at Q 2 > 10, and even uncertainty estimates are similar
Valence, Total Sea and gluon ZEUS 05 CTEQ 6. 5 Slightly different u, d-valence shapes, less low-x sea for ZEUS, different gluon shapes but. .
Valence, Total Sea and gluon Difference in sea quarks already less pronounced, some difference in gluon persists
Valence, Total Sea and gluon CTEQ 6. 5 Pretty much compatible at high Q 2, even uncertainty estimates similar (and hence smaller than MSTW 08 at low-x) ZEUS Offset/ CTEQ Hessian Δχ2=100
Light quarks u, d, ubar dbar ZEUS 05 CTEQ 6. 5 Light quarks pretty much compatible even at Q 2=10
Light quarks u, d, ubar dbar ZEUS 05 CTEQ 6. 5
also look at u/d and dbar-ubar ZEUS 05 CTEQ 6. 5 d/u compatible, dbar-ubar more realistic error estimate from CTEQ
strange, charm, beauty ZEUS 05 Heavy quarks pretty much compatible CTEQ 6. 5
No conclusions Hard to summarize- purpose of meeting §Latest CTEQ, MSTW are significantly different from previous §All difference wash out as Q 2 increases BUT §MSTW low-x uncertainties remain much larger than those of other groups - beware §PDFs from HERA alone are suprisingly compatible with global PDFS over large parts of phase space, but beware high-x gluon
- Slides: 46