Topic 1: Spin effects in high energy scattering
Description & objectives:
Quarks and gluons inside protons can be in various polarization states, which can give different contributions to scattering cross sections. Due to the confinement property of QCD this is not easily sorted out, rather it requires the measurement of complicated observables, typically azimuthal asymmetries, to disentangle the different spin contributions. One objective of my research is to find the simplest observables sensitive to the spin states and to predict their dependence on the energy and momentum of the particles involved.
Spin is the intrinsic angular momentum and like in any interacting theory there can be exchange between spin and orbital angular momentum. It turns out that in Quantum Field Theory, especially in the nonperturbative regime, the spin-orbit correlations are very hard to describe. Experiments have shown however that such effects are large. Once they are well-described theoretically (which is not the case yet), one can start using them as a tool. This is what my research on this topic is about: getting a handle on the spin states of quarks and gluons inside protons (which may itself be polarized or not) and try to apply the obtained knowledge. The ultimate goal is to reach the point where people view collisions with protons as the polarized quark/gluon collisions that they in essence are. This will eventually provide additional tools to study new physics beyond the Standard Model.
The possible non-trivial quark and gluon spin effects have been categorized and go by names like
the Sivers effect, the Collins effect, and one is also associated with my name: the
Boer-Mulders effect.
Funding:
Over the years my research in this topic has been received financial support from the Dutch foundation FOM and from the places where I had positions: NIKHEF, the RIKEN-BNL Research Center at Brookhaven National Laboratory, the VU University Amsterdam and the University of Groningen.
Highlights:
- Studies of linearly polarized gluons inside unpolarized hadrons, for instance to study possible CP violation in the Higgs sector.
- A new explanation of the Lambda polarization observed in unpolarized collisions, which could be tested with the high energy colliders LHC and RHIC.
- Together with Werner Vogelsang a new observable (asymmetric jet correlations) was suggested that allows to access the so-called Sivers effect, an asymmetric proton spin effect.
- The first quantitative studies of the effects of Sudakov factors in transverse momentum dependent azimuthal spin asymmetries.
- I put forward an explanation of anomalous Drell-Yan data in terms of a spin distribution first defined by Piet Mulders and me: the Boer-Mulders function.
- Rainer Jakob, Piet Mulders and I suggested a way to extract the Collins function from the electron-positron annihilation process. This method was used by the BELLE collaboration (KEK, Japan) and subsequently it allowed for the first extraction of the transversity spin distribution by Anselmino et al. in 2007.
Selected publications:
- “TMD evolution and the Higgs transverse momentum distribution”, by Daniel Boer, Wilco J. den Dunnen, published in Nuclear Physics B 886 (2014) 421–435.
- “Determining the Higgs spin and parity in the diphoton decay channel”, by Daniel Boer, Wilco J. den Dunnen, Cristian Pisano, Marc Schlegel, published in Physical Review Letters 111 (2013) 032002.
- “Linearly Polarized Gluons and the Higgs Transverse Momentum Distribution”, by Daniel Boer, Wilco J. den Dunnen, Cristian Pisano, Marc Schlegel, Werner Vogelsang, published in Physical Review Letters 108 (2012) 032002.
- “Bessel-Weighted Asymmetries in Semi Inclusive Deep Inelastic Scattering”, by Daniel Boer, Leonard Gamberg, Bernhard Musch, Alexei Prokudin, published in JHEP 1110 (2011) 021.
- “Direct Probes of Linearly Polarized Gluons inside Unpolarized Hadrons”, by Daniel Boer, Stanley J. Brodsky, Piet J. Mulders, Cristian Pisano, published in Physical Review Letters 106 (2011) 132001.
- “Bounding W-W' mixing with spin asymmetries at RHIC”, by Daniel Boer, Wilco J. den Dunnen, published in Physical Review Letters 105 (2010) 071801.
- “Angular dependences in inclusive two-hadron production at BELLE”, by Daniel Boer, published in Nuclear Physics B 806 (2009) 23-67.
- “Matches and mismatches in the descriptions of semi-inclusive processes at low and high transverse momentum”, by Alessandro Bacchetta, Daniël Boer, Markus Diehl and Piet J. Mulders, published in JHEP 0808 (2008) 023 (SPIRES TOPCITE = 100+)
- “Spin asymmetries in jet-hyperon production at LHC”, D. Boer, C.J. Bomhof , D.S. Hwang, P.J. Mulders, published in Physics Letters B659 (2008) 127-136.
- “Asymmetric jet correlations in p p↑scattering” by Daniël Boer and Werner Vogelsang, published in Physical Review D69 (2004) 094025 (10 pp.) (SPIRES TOPCITE = 50+)
- “Sudakov suppression in azimuthal spin asymmetries” by Daniël Boer, published in Nuclear Physics B603 (2001) 195-217 (SPIRES TOPCITE = 50+)
- “Investigating the origins of transverse spin asymmetries at RHIC” by Daniël Boer, published in Physical Review D60 (1999) 014012 (11 pp.) (SPIRES TOPCITE = 100+)
- “Time reversal odd distribution functions in leptoproduction” by Daniël Boer and P.J. Mulders, published in Physical Review D57 (1998) 5780-5786 (SPIRES TOPCITE = 500+).
- “Asymmetries in polarized hadron production in e+e- annihilation up to order 1/Q” by Daniël Boer, R. Jakob, P.J. Mulders, published in Nuclear Physics B504 (1997) 345-380 (SPIRES TOPCITE = 50+).