Experimental Tests of the BFKL Mechanism Zarah Casilum State University of New York at Stony Brook...
Transcript of Experimental Tests of the BFKL Mechanism Zarah Casilum State University of New York at Stony Brook...
Experimental Tests of the BFKL Mechanism
Zarah CasilumState University of New York at Stony
Brookfor the D0 Collaboration
1997 Joint April APS/AAPT MeetingApril 18-21, 1997Washington, DC
Title: d0logo.epsCreator: CLARIS EPSF Export Filter V1.0CreationDate: 2/24/97 5:03:44 p.m.
BFKL Dynamics at the Tevatron
• Inclusive dijet production at large rapidities
• Semi-hard region:
For large x:
• The BFKL formalism resums (s) to all orders in s (only leading logs) into the partonic cross section by using a multigluon amplitude
QCD Q s
ln
,s
Q2 1 2 1
p p J p J p X 1 1 1 2 2 2( , ) ( , )
dijet x P x Q x P x Q 1 1 12
2 2 22( , ) ( , )
p
J p1 1 1( ),
J p2 2 2( ),
p
X pi i i( ),
x1, kT1x2, kT2
xn, kTn
s x x s 1 2
• The BFKL resummation results in an exponential growth of the partonic cross section
• Contribution of real gluons leads to additional radiation between the two jets
Decorrelation of the dijets in the azimuth
Dijet decorrelation at large rapidities• Tevatron at a fixed cms energy (1.8 TeV)
-At large PDF’s control dijet cross section
-Difficult to see the growth of cross section
with -Look for evidence of additional radiation as
increases
,
BFKLsQ
e BFKL
1
2
1
BFKLS 1
12 2ln
• Measuring azimuthal decorrelation (cartoon analogy)
Qualitative: broadening 1/N dN/d as
Quantitative: falling off cos(as
Title: USR$ROOT1:[SYJUN.DPF96]BFKL_PREDICTION.EPS;1Creator: HIGZ Version 1.22/09CreationDate: 06/08/96 21.49
LO pt1
pt2
pt1
pt2
Higher Order
The DO Detector
Title: iplot9118.psCreator: I-DEASCreationDate:
• Hermetic coverage over large rapidity (|)• Fine transverse segmentation (0.1 x 0.1 in x )• Good jet energy response and resolution
Side view of the DO Detector
Event topology and Analysis variables
• Jets: ET sums in 0.7 cone in x space
• Single jet triggers: Inclusive: ET>12 Gev
Forward: ET>12 GeV and |
• Multiple pp interactions and fake jets removed
• Offline defines jets with ET>20 GeV , and |
• Rapidity ordering and tagging jets at extreme rapidities: (),()
• Require rapidity boost
• Analysis variables: 12 and
1 2 i
X(Ji)
Tagging Jet2
Tagging Jet1
J1
J2
1 2
20 5.
<cos(-)> vs.
1/N dN/d vs. Title: NU01_1:[TMP321.SYJUN.DPF]DELTA_PHI_DPF96_COLOR.EPS;Creator: HIGZ Version 1.22/09CreationDate: 04/08/96 01.28
Data Results:
Title: NU01_1:[TMP321.SYJUN.DPF]COS_GLB_DPF96_V2_COLOR.EPSCreator: HIGZ Version 1.22/09CreationDate: 09/08/96 02.52
LLA
1800/630 GeV Dijet Cross Section Ratio at large
• Mueller and Navelet suggested a method to explore BFKL dynamics by describing s dependence (Nucl. Phys. B282 (1987) 727)
• Fix x1, x2, Q2 and take the ratio of the cross sections at two different center of mass energies, sA and sB
– Cancellation of the parton distribution functions, hence removing large source of theoretical error
• By measuring R(1800,630) at the Tevatron, we can probe the perturbative BFKL dynamics and extract the effective coupling of the BFKL pomeron, BFKL=1+12sln2/ (using s(Q2)=0.16)
R s sx x Q s
x x Q s
eA B
A
B
s s
A B
BFKL A B
( , )( , , , )
( , , , ) /
( ) ln( / )
1 2
2
1 22
1
LO HERWIG BFKL
R 1.0 ~1.4 ~1.7
dijetS
x P x Q x P x QQ
BFKLe~ ( , ) ( , )( )
1 1 12
2 2 22
2
11
Q2 and x
• Data set– 1800 GeV: integrated Lum = 1.5 nb-1 – 630 GeV: integrated Lum = 34 nb-1
• Offline cuts: similar cuts as the decorrelation analysis, except that ||>2.0
• Q2 and x values:
Q E ET T2
1 2
xE
seT
1 21 22
,, cosh
Title: NU01_1:[TMP321.SYJUN.RESUM.RATIO]SMALLX_X1X2_NOYBAR.EPS;1Creator: HIGZ Version 1.22/09CreationDate: 07/08/96 14.48
630 GeV1800 GeV
1 bin: 400-1000GeV2
several bins: 0.06-0.25
Summary and Outlook
• Decorrelation study -Qualitatively, data show trends consistent with
BFKL
-However, quantitative results do not agree with
LLA BFKL but agree well with Herwig(V5.8,
parton shower model, including ISR,FSR,
interference terms)
-LLA BFKL with improved kinematics will be
available soon and NLL BFKL calculations are in
progress
• Dijet cross section ratio study -study under way
-Very promising measurement;directly sensitive
to BFKL dynamics
Title: smallx_q2.epsCreator: HIGZ Version 1.22/09CreationDate: 96/09/25 11.13
Q2 Distribution
630 GeV1800 GeV